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Copyright (C) 1995-2002, Free Software Foundation

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU Free Documentation License", with the
Front-Cover Texts being "GNAT User's Guide for OpenVMS Alpha", and with
no Back-Cover Texts.  A copy of the license is included in the section
entitled "GNU Free Documentation License".

File: gnat_ug_vms.info,  Node: Top,  Next: About This Guide,  Prev: (dir),  Up: (dir)

GNAT User's Guide
*****************

   GNAT User's Guide for OpenVMS Alpha

   GNAT, The GNU Ada 95 Compiler

   GNAT Version for GCC 3.3.1

   Ada Core Technologies, Inc.

Copyright (C) 1995-2002, Free Software Foundation

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU Free Documentation License", with the
Front-Cover Texts being "GNAT User's Guide for OpenVMS Alpha", and with
no Back-Cover Texts.  A copy of the license is included in the section
entitled "GNU Free Documentation License".
* Menu:

* About This Guide::
* Getting Started with GNAT::
* The GNAT Compilation Model::
* Compiling Using GNAT COMPILE::
* Binding Using GNAT BIND::
* Linking Using GNAT LINK::
* The GNAT Make Program GNAT MAKE::
* Renaming Files Using GNAT CHOP::
* Configuration Pragmas::
* Handling Arbitrary File Naming Conventions Using gnatname::
* GNAT Project Manager::
* Elaboration Order Handling in GNAT::
* The Cross-Referencing Tools GNAT XREF and GNAT FIND::
* File Name Krunching Using GNAT KRUNCH::
* Preprocessing Using GNAT PREPROCESS::
* The GNAT Run-Time Library Builder GNAT LIBRARY::
* The GNAT Library Browser GNAT LIST::
* Finding Memory Problems with GNAT Debug Pool::
* Creating Sample Bodies Using GNAT STUB::
* Reducing the Size of Ada Executables with GNAT ELIM::
* Other Utility Programs::
* Compatibility with DEC Ada::
* Running and Debugging Ada Programs::
* Inline Assembler::
* Performance Considerations::
* GNU Free Documentation License::
* Index::

 --- The Detailed Node Listing ---

About This Guide

* What This Guide Contains::
* What You Should Know before Reading This Guide::
* Related Information::
* Conventions::


Getting Started with GNAT

* Running GNAT::
* Running a Simple Ada Program::
* Running a Program with Multiple Units::
* Using the GNAT MAKE Utility::
* Editing with EMACS::

The GNAT Compilation Model

* Source Representation::
* Foreign Language Representation::
* File Naming Rules::
* Using Other File Names::
* Alternative File Naming Schemes::
* Generating Object Files::
* Source Dependencies::
* The Ada Library Information Files::
* Binding an Ada Program::
* Mixed Language Programming::
* Building Mixed Ada & C++ Programs::
* Comparison between GNAT and C/C++ Compilation Models::
* Comparison between GNAT and Conventional Ada Library Models::

Foreign Language Representation

* Latin-1::
* Other 8-Bit Codes::
* Wide Character Encodings::

Compiling Ada Programs With GNAT COMPILE

* Compiling Programs::
* Qualifiers for GNAT COMPILE::
* Search Paths and the Run-Time Library (RTL)::
* Order of Compilation Issues::
* Examples::

Qualifiers for GNAT COMPILE

* Output and Error Message Control::
* Debugging and Assertion Control::
* Run-Time Checks::
* Stack Overflow Checking::
* Run-Time Control::
* Validity Checking::
* Style Checking::
* Using GNAT COMPILE for Syntax Checking::
* Using GNAT COMPILE for Semantic Checking::
* Compiling Ada 83 Programs::
* Character Set Control::
* File Naming Control::
* Subprogram Inlining Control::
* Auxiliary Output Control::
* Debugging Control::
* Units to Sources Mapping Files::

Binding Ada Programs With GNAT BIND

* Running GNAT BIND::
* Generating the Binder Program in C::
* Consistency-Checking Modes::
* Binder Error Message Control::
* Elaboration Control::
* Output Control::
* Binding with Non-Ada Main Programs::
* Binding Programs with No Main Subprogram::
* Summary of Binder Qualifiers::
* Command-Line Access::
* Search Paths for GNAT BIND::
* Examples of GNAT BIND Usage::

Linking Using GNAT LINK

* Running GNAT LINK::
* Qualifiers for GNAT LINK::
* Setting Stack Size from GNAT LINK::
* Setting Heap Size from GNAT LINK::

The GNAT Make Program GNAT MAKE

* Running GNAT MAKE::
* Qualifiers for GNAT MAKE::
* Mode Qualifiers for GNAT MAKE::
* Notes on the Command Line::
* How GNAT MAKE Works::
* Examples of GNAT MAKE Usage::

Renaming Files Using GNAT CHOP

* Handling Files with Multiple Units::
* Operating GNAT CHOP in Compilation Mode::
* Command Line for GNAT CHOP::
* Qualifiers for GNAT CHOP::
* Examples of GNAT CHOP Usage::

Configuration Pragmas

* Handling of Configuration Pragmas::
* The Configuration Pragmas Files::

Handling Arbitrary File Naming Conventions Using gnatname

* Arbitrary File Naming Conventions::
* Running gnatname::
* Qualifiers for gnatname::
* Examples of gnatname Usage::

GNAT Project Manager

* Introduction::
* Examples of Project Files::
* Project File Syntax::
* Objects and Sources in Project Files::
* Importing Projects::
* Project Extension::
* External References in Project Files::
* Packages in Project Files::
* Variables from Imported Projects::
* Naming Schemes::
* Library Projects::
* Qualifiers Related to Project Files::
* Tools Supporting Project Files::
* An Extended Example::
* Project File Complete Syntax::

Elaboration Order Handling in GNAT

* Elaboration Code in Ada 95::
* Checking the Elaboration Order in Ada 95::
* Controlling the Elaboration Order in Ada 95::
* Controlling Elaboration in GNAT - Internal Calls::
* Controlling Elaboration in GNAT - External Calls::
* Default Behavior in GNAT - Ensuring Safety::
* Elaboration Issues for Library Tasks::
* Mixing Elaboration Models::
* What to Do If the Default Elaboration Behavior Fails::
* Elaboration for Access-to-Subprogram Values::
* Summary of Procedures for Elaboration Control::
* Other Elaboration Order Considerations::

The Cross-Referencing Tools GNAT XREF and GNAT FIND

* GNAT XREF Qualifiers::
* GNAT FIND Qualifiers::
* Project Files for GNAT XREF and GNAT FIND::
* Regular Expressions in GNAT FIND and GNAT XREF::
* Examples of GNAT XREF Usage::
* Examples of GNAT FIND Usage::

File Name Krunching Using GNAT KRUNCH

* About GNAT KRUNCH::
* Using GNAT KRUNCH::
* Krunching Method::
* Examples of GNAT KRUNCH Usage::

Preprocessing Using GNAT PREPROCESS

* Using GNAT PREPROCESS::
* Qualifiers for GNAT PREPROCESS::
* Form of Definitions File::
* Form of Input Text for GNAT PREPROCESS::

The GNAT Run-Time Library Builder GNAT LIBRARY

* Running GNAT LIBRARY::
* Qualifiers for GNAT LIBRARY::
* Examples of GNAT LIBRARY Usage::

The GNAT Library Browser GNAT LIST

* Running GNAT LIST::
* Qualifiers for GNAT LIST::
* Examples of GNAT LIST Usage::


Finding Memory Problems with GNAT Debug Pool

Creating Sample Bodies Using GNAT STUB

* Running GNAT STUB::
* Qualifiers for GNAT STUB::

Reducing the Size of Ada Executables with GNAT ELIM

* About GNAT ELIM::
* Eliminate Pragma::
* Tree Files::
* Preparing Tree and Bind Files for GNAT ELIM::
* Running GNAT ELIM::
* Correcting the List of Eliminate Pragmas::
* Making Your Executables Smaller::
* Summary of the GNAT ELIM Usage Cycle::

Other Utility Programs

* Using Other Utility Programs with GNAT::
* The GNAT STANDARD Utility Program::
* The External Symbol Naming Scheme of GNAT::
* Ada Mode for Glide::
* Converting Ada Files to html with gnathtml::
* LSE::

Compatibility with DEC Ada

* Ada 95 Compatibility::
* Differences in the Definition of Package System::
* Language-Related Features::
* The Package STANDARD::
* The Package SYSTEM::
* Tasking and Task-Related Features::
* Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems::
* Pragmas and Pragma-Related Features::
* Library of Predefined Units::
* Bindings::
* Main Program Definition::
* Implementation-Defined Attributes::
* Compiler and Run-Time Interfacing::
* Program Compilation and Library Management::
* Input-Output::
* Implementation Limits::
* Tools::

Language-Related Features

* Integer Types and Representations::
* Floating-Point Types and Representations::
* Pragmas Float_Representation and Long_Float::
* Fixed-Point Types and Representations::
* Record and Array Component Alignment::
* Address Clauses::
* Other Representation Clauses::

Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

* Assigning Task IDs::
* Task IDs and Delays::
* Task-Related Pragmas::
* Scheduling and Task Priority::
* The Task Stack::
* External Interrupts::

Pragmas and Pragma-Related Features

* Restrictions on the Pragma INLINE::
* Restrictions on the Pragma INTERFACE::
* Restrictions on the Pragma SYSTEM_NAME::

Library of Predefined Units

* Changes to DECLIB::

Bindings

* Shared Libraries and Options Files::
* Interfaces to C::

Running and Debugging Ada Programs

* The GNAT Debugger GDB::
* Running GDB::
* Introduction to GDB Commands::
* Using Ada Expressions::
* Calling User-Defined Subprograms::
* Using the Next Command in a Function::
* Ada Exceptions::
* Ada Tasks::
* Debugging Generic Units::
* GNAT Abnormal Termination or Failure to Terminate::
* Naming Conventions for GNAT Source Files::
* Getting Internal Debugging Information::
* Stack Traceback::

Inline Assembler

* Basic Assembler Syntax::
* A Simple Example of Inline Assembler::
* Output Variables in Inline Assembler::
* Input Variables in Inline Assembler::
* Inlining Inline Assembler Code::
* Other Asm Functionality::
* A Complete Example::



Performance Considerations

* Controlling Run-Time Checks::
* Optimization Levels::
* Debugging Optimized Code::
* Inlining of Subprograms::
* Coverage Analysis::

* Index::


File: gnat_ug_vms.info,  Node: About This Guide,  Next: Getting Started with GNAT,  Prev: Top,  Up: Top

About This Guide
****************

This guide describes the use of of GNAT, a full language compiler for
the Ada 95 programming language, implemented on DIGITAL OpenVMS Alpha
Systems.  It describes the features of the compiler and tools, and
details how to use them to build Ada 95 applications.

* Menu:

* What This Guide Contains::
* What You Should Know before Reading This Guide::
* Related Information::
* Conventions::


File: gnat_ug_vms.info,  Node: What This Guide Contains,  Next: What You Should Know before Reading This Guide,  Up: About This Guide

What This Guide Contains
========================

This guide contains the following chapters:
   * *Note Getting Started with GNAT::, describes how to get started
     compiling and running Ada programs with the GNAT Ada programming
     environment.

   * *Note The GNAT Compilation Model::, describes the compilation
     model used by GNAT.

   * *Note Compiling Using GNAT COMPILE::, describes how to compile Ada
     programs with `GNAT COMPILE', the Ada compiler.

   * *Note Binding Using GNAT BIND::, describes how to perform binding
     of Ada programs with `GNAT BIND', the GNAT binding utility.

   * *Note Linking Using GNAT LINK::, describes `GNAT LINK', a program
     that provides for linking using the GNAT run-time library to
     construct a program. `GNAT LINK' can also incorporate foreign
     language object units into the executable.

   * *Note The GNAT Make Program GNAT MAKE::, describes `GNAT MAKE', a
     utility that automatically determines the set of sources needed by
     an Ada compilation unit, and executes the necessary compilations
     binding and link.

   * *Note Renaming Files Using GNAT CHOP::, describes `GNAT CHOP', a
     utility that allows you to preprocess a file that contains Ada
     source code, and split it into one or more new files, one for each
     compilation unit.

   * *Note Configuration Pragmas::, describes the configuration pragmas
     handled by GNAT.

   * *Note Handling Arbitrary File Naming Conventions Using gnatname::,
     shows how to override the default GNAT file naming conventions,
     either for an individual unit or globally.

   * *Note GNAT Project Manager::, describes how to use project files
     to organize large projects.

   * *Note Elaboration Order Handling in GNAT::, describes how GNAT
     helps you deal with elaboration order issues.

   * *Note The Cross-Referencing Tools GNAT XREF and GNAT FIND::,
     discusses `GNAT XREF' and `GNAT FIND', two tools that provide an
     easy way to navigate through sources.

   * *Note File Name Krunching Using GNAT KRUNCH::, describes the `GNAT
     KRUNCH' file name krunching utility, used to handle shortened file
     names on operating systems with a limit on the length of names.

   * *Note Preprocessing Using GNAT PREPROCESS::, describes `GNAT
     PREPROCESS', a preprocessor utility that allows a single source
     file to be used to generate multiple or parameterized source
     files, by means of macro substitution.

   * *Note The GNAT Library Browser GNAT LIST::, describes `GNAT LIST',
     a utility that displays information about compiled units,
     including dependences on the corresponding sources files, and
     consistency of compilations.

   * *Note Finding Memory Problems with GNAT Debug Pool::, describes
     how to use the GNAT-specific Debug Pool in order to detect as
     early as possible the use of incorrect memory references.

   * *Note Creating Sample Bodies Using GNAT STUB::, discusses `GNAT
     STUB', a utility that generates empty but compilable bodies for
     library units.

   * *Note Reducing the Size of Ada Executables with GNAT ELIM::,
     describes `GNAT ELIM', a tool which detects unused subprograms and
     helps the compiler to create a smaller executable for the program.

   * *Note Other Utility Programs::, discusses several other GNAT
     utilities, including `GNAT STANDARD'.

   * *Note Running and Debugging Ada Programs::, describes how to run
     and debug Ada programs.

   * *Note Inline Assembler::, shows how to use the inline assembly
     facility in an Ada program.

   * *Note Performance Considerations::, reviews the trade offs between
     using defaults or options in program development.

   * *Note Compatibility with DEC Ada::, details the compatibility of
     GNAT with DEC Ada 83 for OpenVMS Alpha.


File: gnat_ug_vms.info,  Node: What You Should Know before Reading This Guide,  Next: Related Information,  Prev: What This Guide Contains,  Up: About This Guide

What You Should Know before Reading This Guide
==============================================

This user's guide assumes that you are familiar with Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, Jan
1995.


File: gnat_ug_vms.info,  Node: Related Information,  Next: Conventions,  Prev: What You Should Know before Reading This Guide,  Up: About This Guide

Related Information
===================

For further information about related tools, refer to the following
documents:

   * `GNAT Reference Manual', which contains all reference material for
     the GNAT implementation of Ada 95.

   * `Ada 95 Language Reference Manual', which contains all reference
     material for the Ada 95 programming language.

   * `Debugging with GDB' , located in the GNU:[DOCS] directory,
     contains all details on the use of the GNU source-level debugger.

   * `GNU EMACS Manual' , located in the GNU:[DOCS] directory if the
     EMACS kit is installed, contains full information on the
     extensible editor and programming environment EMACS.



File: gnat_ug_vms.info,  Node: Conventions,  Prev: Related Information,  Up: About This Guide

Conventions
===========

Following are examples of the typographical and graphic conventions used
in this guide:

   * `Functions', `utility program names', `standard names', and
     `classes'.

   * `Option flags'

   * `File Names', `button names', and `field names'.

   * VARIABLES.

   * _Emphasis_.

   * [optional information or parameters]

   * Examples are described by text
          and then shown this way.

Commands that are entered by the user are preceded in this manual by the
characters "`$ '" (dollar sign followed by space). If your system uses
this sequence as a prompt, then the commands will appear exactly as you
see them in the manual. If your system uses some other prompt, then the
command will appear with the `$' replaced by whatever prompt character
you are using.


File: gnat_ug_vms.info,  Node: Getting Started with GNAT,  Next: The GNAT Compilation Model,  Prev: About This Guide,  Up: Top

Getting Started with GNAT
*************************

This chapter describes some simple ways of using GNAT to build
executable Ada programs.

* Menu:

* Running GNAT::
* Running a Simple Ada Program::

* Running a Program with Multiple Units::

* Using the GNAT MAKE Utility::
* Editing with EMACS::


File: gnat_ug_vms.info,  Node: Running GNAT,  Next: Running a Simple Ada Program,  Up: Getting Started with GNAT

Running GNAT
============

Three steps are needed to create an executable file from an Ada source
file:

  1. The source file(s) must be compiled.

  2. The file(s) must be bound using the GNAT binder.

  3. All appropriate object files must be linked to produce an
     executable.

All three steps are most commonly handled by using the `GNAT MAKE'
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.


File: gnat_ug_vms.info,  Node: Running a Simple Ada Program,  Next: Running a Program with Multiple Units,  Prev: Running GNAT,  Up: Getting Started with GNAT

Running a Simple Ada Program
============================

Any text editor may be used to prepare an Ada program. If `Glide' is
used, the optional Ada mode may be helpful in laying out the program.
The program text is a normal text file. We will suppose in our initial
example that you have used your editor to prepare the following
standard format text file:

     with Ada.Text_IO; use Ada.Text_IO;
     procedure Hello is
     begin
        Put_Line ("Hello WORLD!");
     end Hello;

This file should be named `HELLO.ADB'.  With the normal default file
naming conventions, GNAT requires that each file contain a single
compilation unit whose file name is the unit name, with periods
replaced by hyphens; the extension is `ads' for a spec and `adb' for a
body.  You can override this default file naming convention by use of
the special pragma `Source_File_Name' (*note Using Other File Names::).
Alternatively, if you want to rename your files according to this
default convention, which is probably more convenient if you will be
using GNAT for all your compilations, then the `GNAT CHOP' utility can
be used to generate correctly-named source files (*note Renaming Files
Using GNAT CHOP::).

   You can compile the program using the following command (`$' is used
as the command prompt in the examples in this document):

     $ GNAT COMPILE HELLO.ADB

`GNAT COMPILE' is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada 95 and
C. It assumes that you have given it an Ada program if the file
extension is either `.ADS' or `.ADB', and it will then call the GNAT
compiler to compile the specified file.

   This compile command generates a file `HELLO.OBJ', which is the
object file corresponding to your Ada program. It also generates an
"Ada Library Information" file `HELLO.ALI', which contains additional
information used to check that an Ada program is consistent.  To build
an executable file, use `GNAT BIND' to bind the program and `GNAT LINK'
to link it. The argument to both `GNAT BIND' and `GNAT LINK' is the
name of the `ali' file, but the default extension of `.ALI' can be
omitted. This means that in the most common case, the argument is
simply the name of the main program:

     $ GNAT BIND hello
     $ GNAT LINK hello

A simpler method of carrying out these steps is to use `GNAT MAKE', a
master program that invokes all the required compilation, binding and
linking tools in the correct order. In particular, `GNAT MAKE'
automatically recompiles any sources that have been modified since they
were last compiled, or sources that depend on such modified sources, so
that "version skew" is avoided.

     $ GNAT MAKE HELLO.ADB

The result is an executable program called `hello', which can be run by
entering:

     $ hello

assuming that the current directory is on the search path for
executable programs.

and, if all has gone well, you will see

     Hello WORLD!

appear in response to this command.


File: gnat_ug_vms.info,  Node: Running a Program with Multiple Units,  Next: Using the GNAT MAKE Utility,  Prev: Running a Simple Ada Program,  Up: Getting Started with GNAT

Running a Program with Multiple Units
=====================================

Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:

     package Greetings is
        procedure Hello;
        procedure Goodbye;
     end Greetings;
     
     with Ada.Text_IO; use Ada.Text_IO;
     package body Greetings is
        procedure Hello is
        begin
           Put_Line ("Hello WORLD!");
        end Hello;
     
        procedure Goodbye is
        begin
           Put_Line ("Goodbye WORLD!");
        end Goodbye;
     end Greetings;

     with Greetings;
     procedure Gmain is
     begin
        Greetings.Hello;
        Greetings.Goodbye;
     end Gmain;

Following the one-unit-per-file rule, place this program in the
following three separate files:

`GREETINGS.ADS'
     spec of package `Greetings'

`GREETINGS.ADB'
     body of package `Greetings'

`GMAIN.ADB'
     body of main program

To build an executable version of this program, we could use four
separate steps to compile, bind, and link the program, as follows:

     $ GNAT COMPILE GMAIN.ADB
     $ GNAT COMPILE GREETINGS.ADB
     $ GNAT BIND gmain
     $ GNAT LINK gmain

Note that there is no required order of compilation when using GNAT.
In particular it is perfectly fine to compile the main program first.
Also, it is not necessary to compile package specs in the case where
there is an accompanying body; you only need to compile the body. If
you want to submit these files to the compiler for semantic checking
and not code generation, then use the `/NOLOAD' qualifier:

        $ GNAT COMPILE GREETINGS.ADS /NOLOAD

Although the compilation can be done in separate steps as in the above
example, in practice it is almost always more convenient to use the
`GNAT MAKE' tool. All you need to know in this case is the name of the
main program's source file. The effect of the above four commands can
be achieved with a single one:

     $ GNAT MAKE GMAIN.ADB

In the next section we discuss the advantages of using `GNAT MAKE' in
more detail.


File: gnat_ug_vms.info,  Node: Using the GNAT MAKE Utility,  Next: Editing with EMACS,  Prev: Running a Program with Multiple Units,  Up: Getting Started with GNAT

Using the `GNAT MAKE' Utility
=============================

If you work on a program by compiling single components at a time using
`GNAT COMPILE', you typically keep track of the units you modify. In
order to build a consistent system, you compile not only these units,
but also any units that depend on the units you have modified.  For
example, in the preceding case, if you edit `GMAIN.ADB', you only need
to recompile that file. But if you edit `GREETINGS.ADS', you must
recompile both `GREETINGS.ADB' and `GMAIN.ADB', because both files
contain units that depend on `GREETINGS.ADS'.

   `GNAT BIND' will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.  One approach to
handle the dependency-bookkeeping is to use a makefile. However,
makefiles present maintenance problems of their own: if the
dependencies change as you change the program, you must make sure that
the makefile is kept up-to-date manually, which is also an error-prone
process.

   The `GNAT MAKE' utility takes care of these details automatically.
Invoke it using either one of the following forms:

     $ GNAT MAKE GMAIN.ADB
     $ GNAT MAKE GMAIN

The argument is the name of the file containing the main program; you
may omit the extension. `GNAT MAKE' examines the environment,
automatically recompiles any files that need recompiling, and binds and
links the resulting set of object files, generating the executable
file, `GMAIN.EXE'.  In a large program, it can be extremely helpful to
use `GNAT MAKE', because working out by hand what needs to be
recompiled can be difficult.

   Note that `GNAT MAKE' takes into account all the Ada 95 rules that
establish dependencies among units. These include dependencies that
result from inlining subprogram bodies, and from generic instantiation.
Unlike some other Ada make tools, `GNAT MAKE' does not rely on the
dependencies that were found by the compiler on a previous compilation,
which may possibly be wrong when sources change. `GNAT MAKE' determines
the exact set of dependencies from scratch each time it is run.


File: gnat_ug_vms.info,  Node: Editing with EMACS,  Prev: Using the GNAT MAKE Utility,  Up: Getting Started with GNAT

Editing with EMACS
==================

EMACS is an extensible self-documenting text editor that is available
in a separate VMSINSTAL kit.

   Invoke EMACS by typing "EMACS" at the command prompt. To get started,
click on the EMACS Help menu and run the EMACS Tutorial.  In a
character cell terminal, EMACS help is invoked with "Ctrl-h" (also
written as "C-h"), and the tutorial by "C-h t".

   Documentation on EMACS and other tools is available in EMACS under
the pull-down menu button: Help - Info. After selecting Info, use the
middle mouse button to select a topic (e.g. EMACS).

   In a character cell terminal, do "C-h i" to invoke info, and then "m"
(stands for menu) followed by the menu item desired, as in "m EMACS",
to get to the EMACS manual.  Help on EMACS is also available by typing
"HELP EMACS" at the DCL command prompt.

   The tutorial is highly recommended in order to learn the intricacies
of EMACS, which is sufficiently extensible to provide for a complete
programming environment and shell for the sophisticated user.


File: gnat_ug_vms.info,  Node: The GNAT Compilation Model,  Next: Compiling Using GNAT COMPILE,  Prev: Getting Started with GNAT,  Up: Top

The GNAT Compilation Model
**************************

* Menu:

* Source Representation::
* Foreign Language Representation::
* File Naming Rules::
* Using Other File Names::
* Alternative File Naming Schemes::
* Generating Object Files::
* Source Dependencies::
* The Ada Library Information Files::
* Binding an Ada Program::
* Mixed Language Programming::
* Building Mixed Ada & C++ Programs::
* Comparison between GNAT and C/C++ Compilation Models::
* Comparison between GNAT and Conventional Ada Library Models::

This chapter describes the compilation model used by GNAT. Although
similar to that used by other languages, such as C and C++, this model
is substantially different from the traditional Ada compilation models,
which are based on a library. The model is initially described without
reference to the library-based model. If you have not previously used an
Ada compiler, you need only read the first part of this chapter. The
last section describes and discusses the differences between the GNAT
model and the traditional Ada compiler models. If you have used other
Ada compilers, this section will help you to understand those
differences, and the advantages of the GNAT model.


File: gnat_ug_vms.info,  Node: Source Representation,  Next: Foreign Language Representation,  Up: The GNAT Compilation Model

Source Representation
=====================

Ada source programs are represented in standard text files, using
Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar
7-bit ASCII set, plus additional characters used for representing
foreign languages (*note Foreign Language Representation:: for support
of non-USA character sets). The format effector characters are
represented using their standard ASCII encodings, as follows:

`VT'
     Vertical tab, `16#0B#'

`HT'
     Horizontal tab, `16#09#'

`CR'
     Carriage return, `16#0D#'

`LF'
     Line feed, `16#0A#'

`FF'
     Form feed, `16#0C#'

Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of physical
physical lines is marked by any of the following sequences: `LF', `CR',
`CR-LF', or `LF-CR'. This is useful in accommodating files that are
imported from other operating systems.

   The end of a source file is normally represented by the physical end
of file. However, the control character `16#1A#' (`SUB') is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this code
is used to represent the end of file.

   Each file contains a single Ada compilation unit, including any
pragmas associated with the unit. For example, this means you must
place a package declaration (a package "spec") and the corresponding
body in separate files. An Ada "compilation" (which is a sequence of
compilation units) is represented using a sequence of files. Similarly,
you will place each subunit or child unit in a separate file.


File: gnat_ug_vms.info,  Node: Foreign Language Representation,  Next: File Naming Rules,  Prev: Source Representation,  Up: The GNAT Compilation Model

Foreign Language Representation
===============================

GNAT supports the standard character sets defined in Ada 95 as well as
several other non-standard character sets for use in localized versions
of the compiler (*note Character Set Control::).

* Menu:

* Latin-1::
* Other 8-Bit Codes::
* Wide Character Encodings::


File: gnat_ug_vms.info,  Node: Latin-1,  Next: Other 8-Bit Codes,  Up: Foreign Language Representation

Latin-1
-------

The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes `16#00#' ...
`16#7F#)' is identical to standard ASCII coding, but the upper half is
used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with
umlauts used in German, and the extra letter A-ring used in Swedish.

   For a complete list of Latin-1 codes and their encodings, see the
source file of library unit `Ada.Characters.Latin_1' in file
`A-CHLAT1.ADS'.  You may use any of these extended characters freely in
character or string literals. In addition, the extended characters that
represent letters can be used in identifiers.


File: gnat_ug_vms.info,  Node: Other 8-Bit Codes,  Next: Wide Character Encodings,  Prev: Latin-1,  Up: Foreign Language Representation

Other 8-Bit Codes
-----------------

GNAT also supports several other 8-bit coding schemes:

Latin-2
     Latin-2 letters allowed in identifiers, with uppercase and
     lowercase equivalence.

Latin-3
     Latin-3 letters allowed in identifiers, with uppercase and
     lowercase equivalence.

Latin-4
     Latin-4 letters allowed in identifiers, with uppercase and
     lowercase equivalence.

Latin-5
     Latin-4 letters (Cyrillic) allowed in identifiers, with uppercase
     and lowercase equivalence.

IBM PC (code page 437)
     This code page is the normal default for PCs in the U.S. It
     corresponds to the original IBM PC character set. This set has
     some, but not all, of the extended Latin-1 letters, but these
     letters do not have the same encoding as Latin-1. In this mode,
     these letters are allowed in identifiers with uppercase and
     lowercase equivalence.

IBM PC (code page 850)
     This code page is a modification of 437 extended to include all the
     Latin-1 letters, but still not with the usual Latin-1 encoding. In
     this mode, all these letters are allowed in identifiers with
     uppercase and lowercase equivalence.

Full Upper 8-bit
     Any character in the range 80-FF allowed in identifiers, and all
     are considered distinct. In other words, there are no uppercase
     and lowercase equivalences in this range. This is useful in
     conjunction with certain encoding schemes used for some foreign
     character sets (e.g.  the typical method of representing Chinese
     characters on the PC).

No Upper-Half
     No upper-half characters in the range 80-FF are allowed in
     identifiers.  This gives Ada 83 compatibility for identifier names.

For precise data on the encodings permitted, and the uppercase and
lowercase equivalences that are recognized, see the file `CSETS.ADB' in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.


File: gnat_ug_vms.info,  Node: Wide Character Encodings,  Prev: Other 8-Bit Codes,  Up: Foreign Language Representation

Wide Character Encodings
------------------------

GNAT allows wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:

Hex Coding
     In this encoding, a wide character is represented by the following
     five character sequence:

          ESC a b c d

     Where `a', `b', `c', `d' are the four hexadecimal characters
     (using uppercase letters) of the wide character code. For example,
     ESC A345 is used to represent the wide character with code
     `16#A345#'.  This scheme is compatible with use of the full
     Wide_Character set.

Upper-Half Coding
     The wide character with encoding `16#abcd#' where the upper bit is
     on (in other words, "a" is in the range 8-F) is represented as two
     bytes, `16#ab#' and `16#cd#'. The second byte cannot be a format
     control character, but is not required to be in the upper half.
     This method can be also used for shift-JIS or EUC, where the
     internal coding matches the external coding.

Shift JIS Coding
     A wide character is represented by a two-character sequence,
     `16#ab#' and `16#cd#', with the restrictions described for
     upper-half encoding as described above. The internal character
     code is the corresponding JIS character according to the standard
     algorithm for Shift-JIS conversion. Only characters defined in the
     JIS code set table can be used with this encoding method.

EUC Coding
     A wide character is represented by a two-character sequence
     `16#ab#' and `16#cd#', with both characters being in the upper
     half. The internal character code is the corresponding JIS
     character according to the EUC encoding algorithm. Only characters
     defined in the JIS code set table can be used with this encoding
     method.

UTF-8 Coding
     A wide character is represented using UCS Transformation Format 8
     (UTF-8) as defined in Annex R of ISO 10646-1/Am.2. Depending on
     the character value, the representation is a one, two, or three
     byte sequence:
          16#0000#-16#007f#: 2#0xxxxxxx#
          16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
          16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#

     where the xxx bits correspond to the left-padded bits of the
     16-bit character value. Note that all lower half ASCII characters
     are represented as ASCII bytes and all upper half characters and
     other wide characters are represented as sequences of upper-half
     (The full UTF-8 scheme allows for encoding 31-bit characters as
     6-byte sequences, but in this implementation, all UTF-8 sequences
     of four or more bytes length will be treated as illegal).

Brackets Coding
     In this encoding, a wide character is represented by the following
     eight character sequence:

          [ " a b c d " ]

     Where `a', `b', `c', `d' are the four hexadecimal characters
     (using uppercase letters) of the wide character code. For example,
     ["A345"] is used to represent the wide character with code
     `16#A345#'. It is also possible (though not required) to use the
     Brackets coding for upper half characters. For example, the code
     `16#A3#' can be represented as `["A3"]'.

     This scheme is compatible with use of the full Wide_Character set,
     and is also the method used for wide character encoding in the
     standard ACVC (Ada Compiler Validation Capability) test suite
     distributions.


Note: Some of these coding schemes do not permit the full use of the
Ada 95 character set. For example, neither Shift JIS, nor EUC allow the
use of the upper half of the Latin-1 set.


File: gnat_ug_vms.info,  Node: File Naming Rules,  Next: Using Other File Names,  Prev: Foreign Language Representation,  Up: The GNAT Compilation Model

File Naming Rules
=================

The default file name is determined by the name of the unit that the
file contains. The name is formed by taking the full expanded name of
the unit and replacing the separating dots with hyphens and using
uppercase for all letters.

   An exception arises if the file name generated by the above rules
starts with one of the characters A,G,I, or S, and the second character
is a minus. In this case, the character dollar sign is used in place of
the minus. The reason for this special rule is to avoid clashes with
the standard names for child units of the packages System, Ada,
Interfaces, and GNAT, which use the prefixes S- A- I- and G-
respectively.

   The file extension is `.ADS' for a spec and `.ADB' for a body. The
following list shows some examples of these rules.

`MAIN.ADS'
     Main (spec)

`MAIN.ADB'
     Main (body)

`ARITH_FUNCTIONS.ADS'
     Arith_Functions (package spec)

`ARITH_FUNCTIONS.ADB'
     Arith_Functions (package body)

`FUNC-SPEC.ADS'
     Func.Spec (child package spec)

`FUNC-SPEC.ADB'
     Func.Spec (child package body)

`MAIN-SUB.ADB'
     Sub (subunit of Main)

`A$BAD.ADB'
     A.Bad (child package body)

Following these rules can result in excessively long file names if
corresponding unit names are long (for example, if child units or
subunits are heavily nested). An option is available to shorten such
long file names (called file name "krunching"). This may be
particularly useful when programs being developed with GNAT are to be
used on operating systems with limited file name lengths. *Note Using
GNAT KRUNCH::.

   Of course, no file shortening algorithm can guarantee uniqueness over
all possible unit names; if file name krunching is used, it is your
responsibility to ensure no name clashes occur. Alternatively you can
specify the exact file names that you want used, as described in the
next section. Finally, if your Ada programs are migrating from a
compiler with a different naming convention, you can use the GNAT CHOP
utility to produce source files that follow the GNAT naming conventions.
(For details *note Renaming Files Using GNAT CHOP::.)


File: gnat_ug_vms.info,  Node: Using Other File Names,  Next: Alternative File Naming Schemes,  Prev: File Naming Rules,  Up: The GNAT Compilation Model

Using Other File Names
======================

In the previous section, we have described the default rules used by
GNAT to determine the file name in which a given unit resides. It is
often convenient to follow these default rules, and if you follow them,
the compiler knows without being explicitly told where to find all the
files it needs.

   However, in some cases, particularly when a program is imported from
another Ada compiler environment, it may be more convenient for the
programmer to specify which file names contain which units. GNAT allows
arbitrary file names to be used by means of the Source_File_Name pragma.
The form of this pragma is as shown in the following examples:

     pragma Source_File_Name (My_Utilities.Stacks,
       Spec_File_Name => "MYUTILST_A.ADA");
     pragma Source_File_name (My_Utilities.Stacks,
       Body_File_Name => "MYUTILST.ADA");

As shown in this example, the first argument for the pragma is the unit
name (in this example a child unit). The second argument has the form
of a named association. The identifier indicates whether the file name
is for a spec or a body; the file name itself is given by a string
literal.

   The source file name pragma is a configuration pragma, which means
that normally it will be placed in the `GNAT.ADC' file used to hold
configuration pragmas that apply to a complete compilation environment.
For more details on how the `GNAT.ADC' file is created and used *note
Handling of Configuration Pragmas::

`GNAT MAKE' handles non-standard file names in the usual manner (the
non-standard file name for the main program is simply used as the
argument to GNAT MAKE). Note that if the extension is also non-standard,
then it must be included in the GNAT MAKE command, it may not be
omitted.


File: gnat_ug_vms.info,  Node: Alternative File Naming Schemes,  Next: Generating Object Files,  Prev: Using Other File Names,  Up: The GNAT Compilation Model

Alternative File Naming Schemes
===============================

   In the previous section, we described the use of the
`Source_File_Name' pragma to allow arbitrary names to be assigned to
individual source files.  However, this approach requires one pragma
for each file, and especially in large systems can result in very long
`GNAT.ADC' files, and also create a maintenance problem.

   GNAT also provides a facility for specifying systematic file naming
schemes other than the standard default naming scheme previously
described. An alternative scheme for naming is specified by the use of
`Source_File_Name' pragmas having the following format:

     pragma Source_File_Name (
        Spec_File_Name  => FILE_NAME_PATTERN
      [,Casing          => CASING_SPEC]
      [,Dot_Replacement => STRING_LITERAL]);
     
     pragma Source_File_Name (
        Body_File_Name  => FILE_NAME_PATTERN
      [,Casing          => CASING_SPEC]
      [,Dot_Replacement => STRING_LITERAL]);
     
     pragma Source_File_Name (
        Subunit_File_Name  => FILE_NAME_PATTERN
      [,Casing             => CASING_SPEC]
      [,Dot_Replacement    => STRING_LITERAL]);
     
     FILE_NAME_PATTERN ::= STRING_LITERAL
     CASING_SPEC ::= Lowercase | Uppercase | Mixedcase

The `FILE_NAME_PATTERN' string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is
substituted systematically for this asterisk. The optional parameter
`Casing' indicates whether the unit name is to be all upper-case
letters, all lower-case letters, or mixed-case. If no `Casing'
parameter is used, then the default is all upper-case.

   The optional `Dot_Replacement' string is used to replace any periods
that occur in subunit or child unit names. If no `Dot_Replacement'
argument is used then separating dots appear unchanged in the resulting
file name.  Although the above syntax indicates that the `Casing'
argument must appear before the `Dot_Replacement' argument, but it is
also permissible to write these arguments in the opposite order.

   As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give a
separate `Subunit_File_Name' rule, and in this case the
`Body_File_name' rule is used for subunits as well.

   The separate rule for subunits can also be used to implement the
rather unusual case of a compilation environment (e.g. a single
directory) which contains a subunit and a child unit with the same unit
name. Although both units cannot appear in the same partition, the Ada
Reference Manual allows (but does not require) the possibility of the
two units coexisting in the same environment.

   The file name translation works in the following steps:

   * If there is a specific `Source_File_Name' pragma for the given
     unit, then this is always used, and any general pattern rules are
     ignored.

   * If there is a pattern type `Source_File_Name' pragma that applies
     to the unit, then the resulting file name will be used if the file
     exists. If more than one pattern matches, the latest one will be
     tried first, and the first attempt resulting in a reference to a
     file that exists will be used.

   * If no pattern type `Source_File_Name' pragma that applies to the
     unit for which the corresponding file exists, then the standard
     GNAT default naming rules are used.


As an example of the use of this mechanism, consider a commonly used
scheme in which file names are all lower case, with separating periods
copied unchanged to the resulting file name, and specs end with
".1.ADA", and bodies end with ".2.ADA". GNAT will follow this scheme if
the following two pragmas appear:

     pragma Source_File_Name
       (Spec_File_Name => "*.1.ADA");
     pragma Source_File_Name
       (Body_File_Name => "*.2.ADA");

The default GNAT scheme is actually implemented by providing the
following default pragmas internally:

     pragma Source_File_Name
       (Spec_File_Name => "*.ADS", Dot_Replacement => "-");
     pragma Source_File_Name
       (Body_File_Name => "*.ADB", Dot_Replacement => "-");

Our final example implements a scheme typically used with one of the
Ada 83 compilers, where the separator character for subunits was "__"
(two underscores), specs were identified by adding `_.ADA', bodies by
adding `.ADA', and subunits by adding `.SEP'. All file names were upper
case. Child units were not present of course since this was an Ada 83
compiler, but it seems reasonable to extend this scheme to use the same
double underscore separator for child units.

     pragma Source_File_Name
       (Spec_File_Name => "*_.ADA",
        Dot_Replacement => "__",
        Casing = Uppercase);
     pragma Source_File_Name
       (Body_File_Name => "*.ADA",
        Dot_Replacement => "__",
        Casing = Uppercase);
     pragma Source_File_Name
       (Subunit_File_Name => "*.SEP",
        Dot_Replacement => "__",
        Casing = Uppercase);


File: gnat_ug_vms.info,  Node: Generating Object Files,  Next: Source Dependencies,  Prev: Alternative File Naming Schemes,  Up: The GNAT Compilation Model

Generating Object Files
=======================

An Ada program consists of a set of source files, and the first step in
compiling the program is to generate the corresponding object files.
These are generated by compiling a subset of these source files.  The
files you need to compile are the following:

   * If a package spec has no body, compile the package spec to produce
     the object file for the package.

   * If a package has both a spec and a body, compile the body to
     produce the object file for the package. The source file for the
     package spec need not be compiled in this case because there is
     only one object file, which contains the code for both the spec
     and body of the package.

   * For a subprogram, compile the subprogram body to produce the
     object file for the subprogram. The spec, if one is present, is as
     usual in a separate file, and need not be compiled.

   * In the case of subunits, only compile the parent unit. A single
     object file is generated for the entire subunit tree, which
     includes all the subunits.

   * Compile child units independently of their parent units (though,
     of course, the spec of all the ancestor unit must be present in
     order to compile a child unit).

   * Compile generic units in the same manner as any other units. The
     object files in this case are small dummy files that contain at
     most the flag used for elaboration checking. This is because GNAT
     always handles generic instantiation by means of macro expansion.
     However, it is still necessary to compile generic units, for
     dependency checking and elaboration purposes.

The preceding rules describe the set of files that must be compiled to
generate the object files for a program. Each object file has the same
name as the corresponding source file, except that the extension is
`.OBJ' as usual.

   You may wish to compile other files for the purpose of checking their
syntactic and semantic correctness. For example, in the case where a
package has a separate spec and body, you would not normally compile the
spec. However, it is convenient in practice to compile the spec to make
sure it is error-free before compiling clients of this spec, because
such compilations will fail if there is an error in the spec.

   GNAT provides an option for compiling such files purely for the
purposes of checking correctness; such compilations are not required as
part of the process of building a program. To compile a file in this
checking mode, use the `/NOLOAD' qualifier.


File: gnat_ug_vms.info,  Node: Source Dependencies,  Next: The Ada Library Information Files,  Prev: Generating Object Files,  Up: The GNAT Compilation Model

Source Dependencies
===================

A given object file clearly depends on the source file which is compiled
to produce it. Here we are using "depends" in the sense of a typical
`make' utility; in other words, an object file depends on a source file
if changes to the source file require the object file to be recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:

   * If a file being compiled `with''s a unit X, the object file
     depends on the file containing the spec of unit X. This includes
     files that are `with''ed implicitly either because they are parents
     of `with''ed child units or they are run-time units required by the
     language constructs used in a particular unit.

   * If a file being compiled instantiates a library level generic
     unit, the object file depends on both the spec and body files for
     this generic unit.

   * If a file being compiled instantiates a generic unit defined
     within a package, the object file depends on the body file for the
     package as well as the spec file.

   * If a file being compiled contains a call to a subprogram for which
     pragma `Inline' applies and inlining is activated with the
     `/INLINE=PRAGMA' qualifier, the object file depends on the file
     containing the body of this subprogram as well as on the file
     containing the spec. Note that for inlining to actually occur as a
     result of the use of this qualifier, it is necessary to compile in
     optimizing mode.

     The use of `-gnatN' activates a more extensive inlining
     optimization that is performed by the front end of the compiler.
     This inlining does not require that the code generation be
     optimized. Like `/INLINE=PRAGMA', the use of this qualifier
     generates additional dependencies.

   * If an object file O  depends on the proper body of a subunit
     through inlining or instantiation, it depends on the parent unit
     of the subunit. This means that any modification of the parent
     unit or one of its subunits affects the compilation of O.

   * The object file for a parent unit depends on all its subunit body
     files.

   * The previous two rules meant that for purposes of computing
     dependencies and recompilation, a body and all its subunits are
     treated as an indivisible whole.

     These rules are applied transitively: if unit `A' `with''s unit
     `B', whose elaboration calls an inlined procedure in package `C',
     the object file for unit `A' will depend on the body of `C', in
     file `C.ADB'.

     The set of dependent files described by these rules includes all
     the files on which the unit is semantically dependent, as
     described in the Ada 95 Language Reference Manual. However, it is
     a superset of what the ARM describes, because it includes generic,
     inline, and subunit dependencies.

     An object file must be recreated by recompiling the corresponding
     source file if any of the source files on which it depends are
     modified. For example, if the `make' utility is used to control
     compilation, the rule for an Ada object file must mention all the
     source files on which the object file depends, according to the
     above definition.  The determination of the necessary
     recompilations is done automatically when one uses `GNAT MAKE'.


File: gnat_ug_vms.info,  Node: The Ada Library Information Files,  Next: Binding an Ada Program,  Prev: Source Dependencies,  Up: The GNAT Compilation Model

The Ada Library Information Files
=================================

Each compilation actually generates two output files. The first of these
is the normal object file that has a `.OBJ' extension. The second is a
text file containing full dependency information. It has the same name
as the source file, but an `.ALI' extension.  This file is known as the
Ada Library Information (`ali') file.  The following information is
contained in the `ali' file.

   * Version information (indicates which version of GNAT was used to
     compile the unit(s) in question)

   * Main program information (including priority and time slice
     settings, as well as the wide character encoding used during
     compilation).

   * List of arguments used in the `GNAT COMPILE' command for the
     compilation

   * Attributes of the unit, including configuration pragmas used, an
     indication of whether the compilation was successful, exception
     model used etc.

   * A list of relevant restrictions applying to the unit (used for
     consistency) checking.

   * Categorization information (e.g. use of pragma `Pure').

   * Information on all `with''ed units, including presence of
     `Elaborate' or `Elaborate_All' pragmas.

   * Information from any `Linker_Options' pragmas used in the unit

   * Information on the use of `Body_Version' or `Version' attributes
     in the unit.

   * Dependency information. This is a list of files, together with
     time stamp and checksum information. These are files on which the
     unit depends in the sense that recompilation is required if any of
     these units are modified.

   * Cross-reference data. Contains information on all entities
     referenced in the unit. Used by tools like `GNAT XREF' and `GNAT
     FIND' to provide cross-reference information.


For a full detailed description of the format of the `ali' file, see
the source of the body of unit `Lib.Writ', contained in file
`LIB-WRIT.ADB' in the GNAT compiler sources.


File: gnat_ug_vms.info,  Node: Binding an Ada Program,  Next: Mixed Language Programming,  Prev: The Ada Library Information Files,  Up: The GNAT Compilation Model

Binding an Ada Program
======================

When using languages such as C and C++, once the source files have been
compiled the only remaining step in building an executable program is
linking the object modules together. This means that it is possible to
link an inconsistent version of a program, in which two units have
included different versions of the same header.

   The rules of Ada do not permit such an inconsistent program to be
built.  For example, if two clients have different versions of the same
package, it is illegal to build a program containing these two clients.
These rules are enforced by the GNAT binder, which also determines an
elaboration order consistent with the Ada rules.

   The GNAT binder is run after all the object files for a program have
been created. It is given the name of the main program unit, and from
this it determines the set of units required by the program, by reading
the corresponding ALI files. It generates error messages if the program
is inconsistent or if no valid order of elaboration exists.

   If no errors are detected, the binder produces a main program, in
Ada by default, that contains calls to the elaboration procedures of
those compilation unit that require them, followed by a call to the
main program. This Ada program is compiled to generate the object file
for the main program. The name of the Ada file is `B$XXX.ADB' (with the
corresponding spec `B$XXX.ADS') where XXX is the name of the main
program unit.

   Finally, the linker is used to build the resulting executable
program, using the object from the main program from the bind step as
well as the object files for the Ada units of the program.


File: gnat_ug_vms.info,  Node: Mixed Language Programming,  Next: Building Mixed Ada & C++ Programs,  Prev: Binding an Ada Program,  Up: The GNAT Compilation Model

Mixed Language Programming
==========================

* Menu:

* Interfacing to C::
* Calling Conventions::


File: gnat_ug_vms.info,  Node: Interfacing to C,  Next: Calling Conventions,  Up: Mixed Language Programming

Interfacing to C
----------------

There are two ways to build a program that contains some Ada files and
some other language files depending on whether the main program is in
Ada or not.  If the main program is in Ada, you should proceed as
follows:

  1. Compile the other language files to generate object files. For
     instance:
          GNAT COMPILE FILE1.C
          GNAT COMPILE FILE2.C

  2. Compile the Ada units to produce a set of object files and ALI
     files. For instance:
          GNAT MAKE /ACTIONS=COMPILE MY_MAIN.ADB

  3. Run the Ada binder on the Ada main program. For instance:
          GNAT BIND MY_MAIN.ALI

  4. Link the Ada main program, the Ada objects and the other language
     objects. For instance:
          GNAT LINK MY_MAIN.ALI FILE1.OBJ FILE2.OBJ

   The three last steps can be grouped in a single command:
     GNAT MAKE MY_MAIN.ADB /LINKER_QUALIFIERS FILE1.OBJ FILE2.OBJ

If the main program is in some language other than Ada, Then you may
have more than one entry point in the Ada subsystem. You must use a
special option of the binder to generate callable routines to initialize
and finalize the Ada units (*note Binding with Non-Ada Main Programs::).
Calls to the initialization and finalization routines must be inserted
in the main program, or some other appropriate point in the code. The
call to initialize the Ada units must occur before the first Ada
subprogram is called, and the call to finalize the Ada units must occur
after the last Ada subprogram returns. You use the same procedure for
building the program as described previously. In this case, however,
the binder only places the initialization and finalization subprograms
into file `B$XXX.ADB' instead of the main program.  So, if the main
program is not in Ada, you should proceed as follows:

  1. Compile the other language files to generate object files. For
     instance:
          GNAT COMPILE FILE1.C
          GNAT COMPILE FILE2.C

  2. Compile the Ada units to produce a set of object files and ALI
     files. For instance:
          GNAT MAKE /ACTIONS=COMPILE ENTRY_POINT1.ADB
          GNAT MAKE /ACTIONS=COMPILE ENTRY_POINT2.ADB

  3. Run the Ada binder on the Ada main program. For instance:
          GNAT BIND /NOMAIN ENTRY_POINT1.ALI ENTRY_POINT2.ALI

  4. Link the Ada main program, the Ada objects and the other language
     objects. You only need to give the last entry point here. For
     instance:
          GNAT LINK ENTRY_POINT2.ALI FILE1.OBJ FILE2.OBJ


File: gnat_ug_vms.info,  Node: Calling Conventions,  Prev: Interfacing to C,  Up: Mixed Language Programming

Calling Conventions
-------------------

   GNAT follows standard calling sequence conventions and will thus
interface to any other language that also follows these conventions.
The following Convention identifiers are recognized by GNAT:

   * Ada. This indicates that the standard Ada calling sequence will be
     used and all Ada data items may be passed without any limitations
     in the case where GNAT is used to generate both the caller and
     callee. It is also possible to mix GNAT generated code and code
     generated by another Ada compiler. In this case, the data types
     should be restricted to simple cases, including primitive types.
     Whether complex data types can be passed depends on the situation.
     Probably it is safe to pass simple arrays, such as arrays of
     integers or floats. Records may or may not work, depending on
     whether both compilers lay them out identically. Complex structures
     involving variant records, access parameters, tasks, or protected
     types, are unlikely to be able to be passed.

     Note that in the case of GNAT running on a platform that supports
     DEC Ada 83, a higher degree of compatibility can be guaranteed,
     and in particular records are layed out in an identical manner in
     the two compilers. Note also that if output from two different
     compilers is mixed, the program is responsible for dealing with
     elaboration issues. Probably the safest approach is to write the
     main program in the version of Ada other than GNAT, so that it
     takes care of its own elaboration requirements, and then call the
     GNAT-generated adainit procedure to ensure elaboration of the GNAT
     components. Consult the documentation of the other Ada compiler
     for further details on elaboration.

     However, it is not possible to mix the tasking run time of GNAT and
     DEC Ada 83, All the tasking operations must either be entirely
     within GNAT compiled sections of the program, or entirely within
     DEC Ada 83 compiled sections of the program.

   * Assembler. Specifies assembler as the convention. In practice this
     has the same effect as convention Ada (but is not equivalent in
     the sense of being considered the same convention).

   * Asm. Equivalent to Assembler.

   * Asm. Equivalent to Assembly.

   * COBOL. Data will be passed according to the conventions described
     in section B.4 of the Ada 95 Reference Manual.

   * C. Data will be passed according to the conventions described in
     section B.3 of the Ada 95 Reference Manual.

   * Default. Equivalent to C.

   * External. Equivalent to C.

   * CPP. This stands for C++. For most purposes this is identical to C.
     See the separate description of the specialized GNAT pragmas
     relating to C++ interfacing for further details.

   * Fortran. Data will be passed according to the conventions described
     in section B.5 of the Ada 95 Reference Manual.

   * Intrinsic. This applies to an intrinsic operation, as defined in
     the Ada 95 Reference Manual. If a a pragma Import (Intrinsic)
     applies to a subprogram, this means that the body of the
     subprogram is provided by the compiler itself, usually by means of
     an efficient code sequence, and that the user does not supply an
     explicit body for it. In an application program, the pragma can
     only be applied to the following two sets of names, which the GNAT
     compiler recognizes.
        * Rotate_Left, Rotate_Right, Shift_Left, Shift_Right,
          Shift_Right_- Arithmetic.  The corresponding subprogram
          declaration must have two formal parameters. The first one
          must be a signed integer type or a modular type with a binary
          modulus, and the second parameter must be of type Natural.
          The return type must be the same as the type of the first
          argument. The size of this type can only be 8, 16, 32, or 64.

        * binary arithmetic operators: "+", "-", "*", "/" The
          corresponding operator declaration must have parameters and
          result type that have the same root numeric type (for
          example, all three are long_float types). This simplifies the
          definition of operations that use type checking to perform
          dimensional checks:
               type Distance is new Long_Float;
               type Time     is new Long_Float;
               type Velocity is new Long_Float;
               function "/" (D : Distance; T : Time)
                 return Velocity;
               pragma Import (Intrinsic, "/");

          This common idiom is often programmed with a generic
          definition and an explicit body. The pragma makes it simpler
          to introduce such declarations. It incurs no overhead in
          compilation time or code size, because it is implemented as a
          single machine instruction.

   * Stdcall. This is relevant only to NT/Win95 implementations of GNAT,
     and specifies that the Stdcall calling sequence will be used, as
     defined by the NT API.

   * DLL. This is equivalent to Stdcall.

   * Win32. This is equivalent to Stdcall.

   * Stubbed. This is a special convention that indicates that the
     compiler should provide a stub body that raises `Program_Error'.

GNAT additionally provides a useful pragma `Convention_Identifier' that
can be used to parametrize conventions and allow additional synonyms to
be specified. For example if you have legacy code in which the
convention identifier Fortran77 was used for Fortran, you can use the
configuration pragma:

        pragma Convention_Identifier (Fortran77, Fortran);

And from now on the identifier Fortran77 may be used as a convention
identifier (for example in an `Import' pragma) with the same meaning as
Fortran.


File: gnat_ug_vms.info,  Node: Building Mixed Ada & C++ Programs,  Next: Comparison between GNAT and C/C++ Compilation Models,  Prev: Mixed Language Programming,  Up: The GNAT Compilation Model

Building Mixed Ada & C++ Programs
=================================

Building a mixed application containing both Ada and C++ code may be a
challenge for the unaware programmer. As a matter of fact, this
interfacing has not been standardized in the Ada 95 reference manual due
to the immaturity and lack of standard of C++ at the time. This section
gives a few hints that should make this task easier. In particular the
first section addresses the differences with interfacing with C. The
second section looks into the delicate problem of linking the complete
application from its Ada and C++ parts. The last section give some
hints on how the GNAT run time can be adapted in order to allow
inter-language dispatching with a new C++ compiler.

* Menu:

* Interfacing to C++::
* Linking a Mixed C++ & Ada Program::
* A Simple Example::
* Adapting the Run Time to a New C++ Compiler::


File: gnat_ug_vms.info,  Node: Interfacing to C++,  Next: Linking a Mixed C++ & Ada Program,  Up: Building Mixed Ada & C++ Programs

Interfacing to C++
------------------

GNAT supports interfacing with C++ compilers generating code that is
compatible with the standard Application Binary Interface of the given
platform.

Interfacing can be done at 3 levels: simple data, subprograms and
classes. In the first 2 cases, GNAT offer a specific CONVENTION CPP
that behaves exactly like CONVENTION C. Usually C++ mangle names of
subprograms and currently GNAT does not provide any help to solve the
demangling problem. This problem can be addressed in 2 ways:
   * by modifying the C++ code in order to force a C convention using
     the EXTERN "C" syntax.

   * by figuring out the mangled name and use it as the Link_Name
     argument of the pragma import.

Interfacing at the class level can be achieved by using the GNAT
specific pragmas such as `CPP_Class' and `CPP_Virtual'. See the GNAT
Reference Manual for additional information.


File: gnat_ug_vms.info,  Node: Linking a Mixed C++ & Ada Program,  Next: A Simple Example,  Prev: Interfacing to C++,  Up: Building Mixed Ada & C++ Programs

Linking a Mixed C++ & Ada Program
---------------------------------

Usually the linker of the C++ development system must be used to link
mixed applications because most C++ systems will resolve elaboration
issues (such as calling constructors on global class instances)
transparently during the link phase. GNAT has been adapted to ease the
use of a foreign linker for the last phase. Three cases can be
considered:
  1. Using GNAT and G++ (GNU C++ compiler) from the same GCC
     installation. The c++ linker can simply be called by using the c++
     specific driver called `c++'. Note that this setup is not very
     common because it may request recompiling the whole GCC tree from
     sources and it does not allow to upgrade easily to a new version
     of one compiler for one of the two languages without taking the
     risk of destabilizing the other.

          $ c++ -c file1.C
          $ c++ -c file2.C
          $ GNAT MAKE ada_unit /LINKER_QUALIFIERS FILE1.OBJ FILE2.OBJ --LINK=c++

  2. Using GNAT and G++ from 2 different GCC installations. If both
     compilers are on the PATH, the same method can be used. It is
     important to be aware that environment variables such as
     C_INCLUDE_PATH, GCC_EXEC_PREFIX, BINUTILS_ROOT or GCC_ROOT will
     affect both compilers at the same time and thus may make one of
     the 2 compilers operate improperly if they are set for the other.
     In particular it is important that the link command has access to
     the proper GNAT COMPILE library `libgcc.a', that is to say the one
     that is part of the C++ compiler installation. The implicit link
     command as suggested in the GNAT MAKE command from the former
     example can be replaced by an explicit link command with full
     verbosity in order to verify which library is used:
          $ GNAT BIND ada_unit
          $ GNAT LINK -v -v ada_unit FILE1.OBJ FILE2.OBJ --LINK=c++
     If there is a problem due to interfering environment variables, it
     can be workaround by using an intermediate script. The following
     example shows the proper script to use when GNAT has not been
     installed at its default location and g++ has been installed at
     its default location:

          $ GNAT LINK -v -v ada_unit FILE1.OBJ FILE2.OBJ --LINK=./my_script
          $ cat ./my_script
          #!/bin/sh
          unset BINUTILS_ROOT
          unset GCC_ROOT
          c++ $*

  3. Using a non GNU C++ compiler. The same set of command as previously
     described can be used to insure that the c++ linker is used.
     Nonetheless, you need to add the path to libgcc explicitely, since
     some libraries needed by GNAT are located in this directory:


          $ GNAT LINK ada_unit FILE1.OBJ FILE2.OBJ --LINK=./my_script
          $ cat ./my_script
          #!/bin/sh
          CC $* `GNAT COMPILE -print-libgcc-file-name`

     Where CC is the name of the non GNU C++ compiler.



File: gnat_ug_vms.info,  Node: A Simple Example,  Next: Adapting the Run Time to a New C++ Compiler,  Prev: Linking a Mixed C++ & Ada Program,  Up: Building Mixed Ada & C++ Programs

A Simple Example
----------------

The following example, provided as part of the GNAT examples, show how
to achieve procedural interfacing between Ada and C++ in both
directions. The C++ class A has 2 methods. The first method is exported
to Ada by the means of an extern C wrapper function. The second method
calls an Ada subprogram. On the Ada side, The C++ calls is modelized by
a limited record with a layout comparable to the C++ class. The Ada
subprogram, in turn, calls the c++ method. So from the C++ main program
the code goes back and forth between the 2 languages.

Here are the compilation commands for native configurations:
     $ GNAT MAKE -c simple_cpp_interface
     $ c++ -c cpp_main.C
     $ c++ -c ex7.C
     $ GNAT BIND -n simple_cpp_interface
     $ GNAT LINK simple_cpp_interface -o cpp_main --LINK=$(CPLUSPLUS)
           -lstdc++ EX7.OBJ CPP_MAIN.OBJ

Here are the corresponding sources:

     //cpp_main.C
     
     #include "ex7.h"
     
     extern "C" {
       void adainit (void);
       void adafinal (void);
       void method1 (A *t);
     }
     
     void method1 (A *t)
     {
       t->method1 ();
     }
     
     int main ()
     {
       A obj;
       adainit ();
       obj.method2 (3030);
       adafinal ();
     }
     
     //ex7.h
     
     class Origin {
      public:
       int o_value;
     };
     class A : public Origin {
      public:
       void method1 (void);
       virtual void method2 (int v);
       A();
       int   a_value;
     };
     
     //ex7.C
     
     #include "ex7.h"
     #include <stdio.h>
     
     extern "C" { void ada_method2 (A *t, int v);}
     
     void A::method1 (void)
     {
       a_value = 2020;
       printf ("in A::method1, a_value = %d \n",a_value);
     
     }
     
     void A::method2 (int v)
     {
        ada_method2 (this, v);
        printf ("in A::method2, a_value = %d \n",a_value);
     
     }
     
     A::A(void)
     {
        a_value = 1010;
       printf ("in A::A, a_value = %d \n",a_value);
     }
     
     -- Ada sources
     package body Simple_Cpp_Interface is
     
        procedure Ada_Method2 (This : in out A; V : Integer) is
        begin
           Method1 (This);
           This.A_Value := V;
        end Ada_Method2;
     
     end Simple_Cpp_Interface;
     
     package Simple_Cpp_Interface is
        type A is limited
           record
              O_Value : Integer;
              A_Value : Integer;
           end record;
        pragma Convention (C, A);
     
        procedure Method1 (This : in out A);
        pragma Import (C, Method1);
     
        procedure Ada_Method2 (This : in out A; V : Integer);
        pragma Export (C, Ada_Method2);
     
     end Simple_Cpp_Interface;


File: gnat_ug_vms.info,  Node: Adapting the Run Time to a New C++ Compiler,  Prev: A Simple Example,  Up: Building Mixed Ada & C++ Programs

Adapting the Run Time to a New C++ Compiler
-------------------------------------------

GNAT offers the capability to derive Ada 95 tagged types directly from
preexisting C++ classes and . See "Interfacing with C++" in the GNAT
reference manual. The mechanism used by GNAT for achieving such a goal
has been made user configurable through a GNAT library unit
`Interfaces.CPP'. The default version of this file is adapted to the
GNU c++ compiler. Internal knowledge of the virtual table layout used
by the new C++ compiler is needed to configure properly this unit. The
Interface of this unit is known by the compiler and cannot be changed
except for the value of the constants defining the characteristics of
the virtual table: CPP_DT_Prologue_Size, CPP_DT_Entry_Size,
CPP_TSD_Prologue_Size, CPP_TSD_Entry_Size. Read comments in the source
of this unit for more details.


File: gnat_ug_vms.info,  Node: Comparison between GNAT and C/C++ Compilation Models,  Next: Comparison between GNAT and Conventional Ada Library Models,  Prev: Building Mixed Ada & C++ Programs,  Up: The GNAT Compilation Model

Comparison between GNAT and C/C++ Compilation Models
====================================================

The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don't need to compile specs; they are compiled when they are used. The
Ada `with' is similar in effect to the `#include' of a C header.

   One notable difference is that, in Ada, you may compile specs
separately to check them for semantic and syntactic accuracy. This is
not always possible with C headers because they are fragments of
programs that have less specific syntactic or semantic rules.

   The other major difference is the requirement for running the binder,
which performs two important functions. First, it checks for
consistency. In C or C++, the only defense against assembling
inconsistent programs lies outside the compiler, in a makefile, for
example. The binder satisfies the Ada requirement that it be impossible
to construct an inconsistent program when the compiler is used in normal
mode.

   The other important function of the binder is to deal with
elaboration issues. There are also elaboration issues in C++ that are
handled automatically. This automatic handling has the advantage of
being simpler to use, but the C++ programmer has no control over
elaboration.  Where `GNAT BIND' might complain there was no valid order
of elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.


File: gnat_ug_vms.info,  Node: Comparison between GNAT and Conventional Ada Library Models,  Prev: Comparison between GNAT and C/C++ Compilation Models,  Up: The GNAT Compilation Model

Comparison between GNAT and Conventional Ada Library Models
===========================================================

This section is intended to be useful to Ada programmers who have
previously used an Ada compiler implementing the traditional Ada library
model, as described in the Ada 95 Language Reference Manual. If you
have not used such a system, please go on to the next section.

   In GNAT, there is no "library" in the normal sense. Instead, the set
of source files themselves acts as the library. Compiling Ada programs
does not generate any centralized information, but rather an object
file and a ALI file, which are of interest only to the binder and
linker.  In a traditional system, the compiler reads information not
only from the source file being compiled, but also from the centralized
library.  This means that the effect of a compilation depends on what
has been previously compiled. In particular:

   * When a unit is `with''ed, the unit seen by the compiler corresponds
     to the version of the unit most recently compiled into the library.

   * Inlining is effective only if the necessary body has already been
     compiled into the library.

   * Compiling a unit may obsolete other units in the library.

In GNAT, compiling one unit never affects the compilation of any other
units because the compiler reads only source files. Only changes to
source files can affect the results of a compilation. In particular:

   * When a unit is `with''ed, the unit seen by the compiler corresponds
     to the source version of the unit that is currently accessible to
     the compiler.

   * Inlining requires the appropriate source files for the package or
     subprogram bodies to be available to the compiler. Inlining is
     always effective, independent of the order in which units are
     complied.

   * Compiling a unit never affects any other compilations. The editing
     of sources may cause previous compilations to be out of date if
     they depended on the source file being modified.

The most important result of these differences is that order of
compilation is never significant in GNAT. There is no situation in
which one is required to do one compilation before another. What shows
up as order of compilation requirements in the traditional Ada library
becomes, in GNAT, simple source dependencies; in other words, there is
only a set of rules saying what source files must be present when a
file is compiled.


File: gnat_ug_vms.info,  Node: Compiling Using GNAT COMPILE,  Next: Binding Using GNAT BIND,  Prev: The GNAT Compilation Model,  Up: Top

Compiling Using `GNAT COMPILE'
******************************

This chapter discusses how to compile Ada programs using the `GNAT
COMPILE' command. It also describes the set of qualifiers that can be
used to control the behavior of the compiler.

* Menu:

* Compiling Programs::
* Qualifiers for GNAT COMPILE::
* Search Paths and the Run-Time Library (RTL)::
* Order of Compilation Issues::
* Examples::


File: gnat_ug_vms.info,  Node: Compiling Programs,  Next: Qualifiers for GNAT COMPILE,  Up: Compiling Using GNAT COMPILE

Compiling Programs
==================

The first step in creating an executable program is to compile the units
of the program using the `GNAT COMPILE' command. You must compile the
following files:

   * the body file (`.ADB') for a library level subprogram or generic
     subprogram

   * the spec file (`.ADS') for a library level package or generic
     package that has no body

   * the body file (`.ADB') for a library level package or generic
     package that has a body


You need _not_ compile the following files

   * the spec of a library unit which has a body

   * subunits

because they are compiled as part of compiling related units. GNAT
package specs when the corresponding body is compiled, and subunits
when the parent is compiled.  If you attempt to compile any of these
files, you will get one of the following error messages (where fff is
the name of the file you compiled):

     No code generated for file FFF (PACKAGE SPEC)
     No code generated for file FFF (SUBUNIT)

The basic command for compiling a file containing an Ada unit is

     $ GNAT COMPILE [QUALIFIERS] `file name'

where FILE NAME is the name of the Ada file (usually having an extension
`.ADS' for a spec or `.ADB' for a body).  The result of a successful
compilation is an object file, which has the same name as the source
file but an extension of `.OBJ' and an Ada Library Information (ALI)
file, which also has the same name as the source file, but with `.ALI'
as the extension. GNAT creates these two output files in the current
directory, but you may specify a source file in any directory using an
absolute or relative path specification containing the directory
information.

   `GNAT COMPILE' is actually a driver program that looks at the
extensions of the file arguments and loads the appropriate compiler.
For example, the GNU C compiler is `CC1', and the Ada compiler is
`GNAT1'.  These programs are in directories known to the driver program
(in some configurations via environment variables you set), but need
not be in your path. The `GNAT COMPILE' driver also calls the assembler
and any other utilities needed to complete the generation of the
required object files.

   It is possible to supply several file names on the same `GNAT
COMPILE' command. This causes `GNAT COMPILE' to call the appropriate
compiler for each file. For example, the following command lists three
separate files to be compiled:

     $ GNAT COMPILE X.ADB Y.ADB Z.C

calls `GNAT1' (the Ada compiler) twice to compile `X.ADB' and `Y.ADB',
and `CC1' (the C compiler) once to compile `Z.C'.  The compiler
generates three object files `X.OBJ', `Y.OBJ' and `Z.OBJ' and the two
ALI files `X.ALI' and `Y.ALI' from the Ada compilations. Any qualifiers
apply to all the files listed.


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT COMPILE,  Next: Search Paths and the Run-Time Library (RTL),  Prev: Compiling Programs,  Up: Compiling Using GNAT COMPILE

Qualifiers for `GNAT COMPILE'
=============================

The `GNAT COMPILE' command accepts qualifiers that control the
compilation process. These qualifiers are fully described in this
section.  First we briefly list all the qualifiers, in alphabetical
order, then we describe the qualifiers in more detail in functionally
grouped sections.

* Menu:

* Output and Error Message Control::
* Debugging and Assertion Control::
* Run-Time Checks::
* Stack Overflow Checking::
* Run-Time Control::
* Validity Checking::
* Style Checking::
* Using GNAT COMPILE for Syntax Checking::
* Using GNAT COMPILE for Semantic Checking::
* Compiling Ada 83 Programs::
* Character Set Control::
* File Naming Control::
* Subprogram Inlining Control::
* Auxiliary Output Control::
* Debugging Control::
* Units to Sources Mapping Files::

`/DEBUG'
     Generate debugging information. This information is stored in the
     object file and copied from there to the final executable file by
     the linker, where it can be read by the debugger. You must use the
     `/DEBUG' qualifier if you plan on using the debugger.

`/SEARCH=DIR'
     Direct GNAT to search the DIR directory for source files needed by
     the current compilation (*note Search Paths and the Run-Time
     Library (RTL)::).

`/NOCURRENT_DIRECTORY'
     Except for the source file named in the command line, do not look
     for source files in the directory containing the source file named
     in the command line (*note Search Paths and the Run-Time Library
     (RTL)::).

`/NOOPTIMIZE (default)'
`/OPTIMIZE[=(keyword[,...])]'
     Selects the level of optimization for your program. The supported
     keywords are as follows:
    `ALL (default)'
          Perform most optimizations, including those that be expensive.

    `NONE'
          Do not do any optimizations. Same as `/NOOPTIMIZE'.

    `SOME'
          Perform some optimizations, but omit ones that are costly.

    `DEVELOPMENT'
          Same as `SOME'.

    `INLINING'
          Full optimization, and also attempt automatic inlining of
          small subprograms within a unit (*note Inlining of
          Subprograms::).

    `UNROLL_LOOPS'
          Try to unroll loops. This keyword may be specified together
          with any keyword above other than `NONE'. Loop unrolling
          usually, but not always, improves the performance of programs.

`/RUNTIME_SYSTEM=RTS-PATH'
     Specifies the default location of the runtime library. Same
     meaning as the equivalent `GNAT MAKE' flag (see *Note Qualifiers
     for GNAT MAKE::).

`/ASM'
     Used to cause the assembler source file to be generated, using
     `.S' as the extension, instead of the object file.  This may be
     useful if you need to examine the generated assembly code.

`/VERBOSE'
     Show commands generated by the `GNAT COMPILE' driver. Normally
     used only for debugging purposes or if you need to be sure what
     version of the compiler you are executing.

`/CHECKS=ASSERTIONS'
     Assertions enabled. `Pragma Assert' and `pragma Debug' to be
     activated.

`-gnatA'
     Avoid processing `GNAT.ADC'. If a GNAT.ADC file is present, it
     will be ignored.

`/WARNINGS=BRIEF'
     Generate brief messages to `SYS$ERROR' even if verbose mode set.

`/NOLOAD'
     Check syntax and semantics only (no code generation attempted).

`/COMPRESS_NAMES'
     Compress debug information and external symbol name table entries.

`/XDEBUG'
     Output expanded source files for source level debugging. This
     qualifier also suppress generation of cross-reference information
     (see /XREF=SUPPRESS).

`-gnatecPATH'
     Specify a configuration pragma file. (see *Note The Configuration
     Pragmas Files::)

`-gnatemPATH'
     Specify a mapping file. (see *Note Units to Sources Mapping
     Files::)

`/CHECKS=ELABORATION'
     Full dynamic elaboration checks.

`/REPORT_ERRORS=FULL'
     Full errors. Multiple errors per line, all undefined references.

`/UPPERCASE_EXTERNALS'
     Externals names are folded to all uppercase.

`/STYLE=GNAT'
     Internal GNAT implementation mode. This should not be used for
     applications programs, it is intended only for use by the compiler
     and its run-time library. For documentation, see the GNAT sources.

`/EXPAND_SOURCE'
     List generated expanded code in source form.

`/IDENTIFIER_CHARACTER_SET=C'
     Identifier character set For details of the possible selections
     for C, see *Note Character Set Control::.

`/HELP'
     Output usage information. The output is written to `SYS$OUTPUT'.

`/FILE_NAME_MAX_LENGTH=N'
     Limit file names to N (1-999) characters .

`/LIST'
     Output full source listing with embedded error messages.

`/ERROR_LIMIT=N'
     Limit number of detected errors to N (1-999).

`/INLINE=PRAGMA'
     Activate inlining across unit boundaries for subprograms for which
     pragma `inline' is specified.

`-gnatN'
     Activate front end inlining.

`/INLINE=SUPPRESS'
     Suppresses all inlining, even if other optimization or inlining
     qualifiers are set.

`/CHECKS=OVERFLOW'
     Enable numeric overflow checking (which is not normally enabled by
     default). Not that division by zero is a separate check that is not
     controlled by this qualifier (division by zero checking is on by
     default).

`/CHECKS=SUPPRESS_ALL'
     Suppress all checks.

`/TRY_SEMANTICS'
     Don't quit; try semantics, even if parse errors.

`/FORCE_ALI'
     Don't quit; generate `ali' and tree files even if illegalities.

`/POLLING_ENABLE'
     Enable polling. This is required on some systems (notably Windows
     NT) to obtain asynchronous abort and asynchronous transfer of
     control capability.  See the description of pragma Polling in the
     GNAT Reference Manual for full details.

`/REPRESENTATION_INFO[0/1/2/3][s]'
     Output representation information for declared types and objects.

`/SYNTAX_ONLY'
     Syntax check only.

`/TREE_OUTPUT'
     Tree output file to be generated.

`-gnatT nnn'
     Set time slice to specified number of microseconds

`/UNITS_LIST'
     List units for this compilation.

`/UNIQUE_ERROR_TAG'
     Tag all error messages with the unique string "error:"

`/REPORT_ERRORS=VERBOSE'
     Verbose mode. Full error output with source lines to `SYS$OUTPUT'.

`/VALIDITY_CHECKING'
     Control level of validity checking. See separate section describing
     this feature.

`/WARNINGS=XXX'
     Warning mode where XXX is a string of options describing the exact
     warnings that are enabled or disabled. See separate section on
     warning control.

`/WIDE_CHARACTER_ENCODING=E'
     Wide character encoding method (E=`BRACKETS, NONE, HEX, UPPER,
     SHIFT_JIS, EUC, UTF8')

`/XREF=SUPPRESS'
     Suppress generation of cross-reference information.

`/STYLE_CHECKS=(option,option..)'
     Enable built-in style checks. See separate section describing this
     feature.

`/DISTRIBUTION_STUBS=M'
     Distribution stub generation and compilation (M=`RECEIVER' or
     `CALLER' to specify the type of stubs to be generated and
     compiled).

`/83'
     Enforce Ada 83 restrictions.


The following restrictions apply to the combination of qualifiers in
this manner:

   * The qualifier `/NOLOAD' if combined with other qualifiers must come
     first in the string.

   * The qualifier `/SYNTAX_ONLY' if combined with other qualifiers
     must come first in the string.

   * Once a "y" appears in the string (that is a use of the `/STYLE='
     qualifier), then all further characters in the qualifier are
     interpreted as style modifiers (see description of `/STYLE=').

   * Once a "d" appears in the string (that is a use of the `-gnatd'
     qualifier), then all further characters in the qualifier are
     interpreted as debug flags (see description of `-gnatd').

   * Once a "w" appears in the string (that is a use of the `-gnatw'
     qualifier), then all further characters in the qualifier are
     interpreted as warning mode modifiers (see description of
     `-gnatw').

   * Once a "V" appears in the string (that is a use of the
     `/VALIDITY_CHECKING' qualifier), then all further characters in
     the qualifier are interpreted as validity checking options (see
     description of `/VALIDITY_CHECKING').



File: gnat_ug_vms.info,  Node: Output and Error Message Control,  Next: Debugging and Assertion Control,  Up: Qualifiers for GNAT COMPILE

Output and Error Message Control
--------------------------------

The standard default format for error messages is called "brief format."
Brief format messages are written to `SYS$ERROR' (the standard error
file) and have the following form:

     E.ADB:3:04: Incorrect spelling of keyword "function"
     E.ADB:4:20: ";" should be "is"

The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.  `glide'
can parse the error messages and point to the referenced character.
The following qualifiers provide control over the error message format:

`/REPORT_ERRORS=VERBOSE'
     The effect of this setting is to write long-format error messages
     to `SYS$OUTPUT' (the standard output file.  The same program
     compiled with the `/REPORT_ERRORS=VERBOSE' qualifier would
     generate:

          3. funcion X (Q : Integer)
             |
          >>> Incorrect spelling of keyword "function"
          4. return Integer;
                           |
          >>> ";" should be "is"

     The vertical bar indicates the location of the error, and the `>>>'
     prefix can be used to search for error messages. When this
     qualifier is used the only source lines output are those with
     errors.

`/LIST'
     This qualifier causes a full listing of the file to be generated.
     The output might look as follows:

           1. procedure E is
           2.    V : Integer;
           3.    funcion X (Q : Integer)
                 |
              >>> Incorrect spelling of keyword "function"
           4.     return Integer;
                                |
              >>> ";" should be "is"
           5.    begin
           6.       return Q + Q;
           7.    end;
           8. begin
           9.    V := X + X;
          10.end E;

     When you specify the `/REPORT_ERRORS=VERBOSE' or `/LIST'
     qualifiers and standard output is redirected, a brief summary is
     written to `SYS$ERROR' (standard error) giving the number of error
     messages and warning messages generated.

`/UNIQUE_ERROR_TAG'
     This qualifier forces all error messages to be preceded by the
     unique string "error:". This means that error messages take a few
     more characters in space, but allows easy searching for and
     identification of error messages.

`/WARNINGS=BRIEF'
     This qualifier causes GNAT to generate the brief format error
     messages to `SYS$ERROR' (the standard error file) as well as the
     verbose format message or full listing (which as usual is written
     to `SYS$OUTPUT' (the standard output file).

`/ERROR_LIMIT=N'
     N is a decimal integer in the range of 1 to 999 and limits the
     number of error messages to be generated. For example, using
     `/ERROR_LIMIT=2' might yield

          E.ADB:3:04: Incorrect spelling of keyword "function"
          E.ADB:5:35: missing ".."
          fatal error: maximum errors reached
          compilation abandoned

`/REPORT_ERRORS=FULL'
     Normally, the compiler suppresses error messages that are likely
     to be redundant. This qualifier causes all error messages to be
     generated. In particular, in the case of references to undefined
     variables. If a given variable is referenced several times, the
     normal format of messages is
          E.ADB:7:07: "V" is undefined (more references follow)

     where the parenthetical comment warns that there are additional
     references to the variable `V'. Compiling the same program with the
     `/REPORT_ERRORS=FULL' qualifier yields

          E.ADB:7:07: "V" is undefined
          E.ADB:8:07: "V" is undefined
          E.ADB:8:12: "V" is undefined
          E.ADB:8:16: "V" is undefined
          E.ADB:9:07: "V" is undefined
          E.ADB:9:12: "V" is undefined

`/TRY_SEMANTICS'
     In normal operation mode, the compiler first parses the program and
     determines if there are any syntax errors. If there are,
     appropriate error messages are generated and compilation is
     immediately terminated.  This qualifier tells GNAT to continue
     with semantic analysis even if syntax errors have been found. This
     may enable the detection of more errors in a single run. On the
     other hand, the semantic analyzer is more likely to encounter some
     internal fatal error when given a syntactically invalid tree.

`/FORCE_ALI'
     In normal operation mode, the `ali' file is not generated if any
     illegalities are detected in the program. The use of `/FORCE_ALI'
     forces generation of the `ali' file. This file is marked as being
     in error, so it cannot be used for binding purposes, but it does
     contain reasonably complete cross-reference information, and thus
     may be useful for use by tools (e.g. semantic browsing tools or
     integrated development environments) that are driven from the
     `ali' file.

     In addition, if `/TREE_OUTPUT' is also specified, then the tree
     file is generated even if there are illegalities. It may be useful
     in this case to also specify `/TRY_SEMANTICS' to ensure that full
     semantic processing occurs. The resulting tree file can be
     processed by ASIS, for the purpose of providing partial
     information about illegal units, but if the error causes the tree
     to be badly malformed, then ASIS may crash during the analysis.


In addition to error messages, which correspond to illegalities as
defined in the Ada 95 Reference Manual, the compiler detects two kinds
of warning situations.

   First, the compiler considers some constructs suspicious and
generates a warning message to alert you to a possible error. Second,
if the compiler detects a situation that is sure to raise an exception
at run time, it generates a warning message. The following shows an
example of warning messages:
     E.ADB:4:24: warning: creation of object may raise Storage_Error
     E.ADB:10:17: warning: static value out of range
     E.ADB:10:17: warning: "Constraint_Error" will be raised at run time

GNAT considers a large number of situations as appropriate for the
generation of warning messages. As always, warnings are not definite
indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
`Constraint_Error' exception, then the warning that may be issued does
not indicate an error. Some of the situations for which GNAT issues
warnings (at least some of the time) are given in the following list,
which is not necessarily complete.

   * Possible infinitely recursive calls

   * Out-of-range values being assigned

   * Possible order of elaboration problems

   * Unreachable code

   * Fixed-point type declarations with a null range

   * Variables that are never assigned a value

   * Variables that are referenced before being initialized

   * Task entries with no corresponding accept statement

   * Duplicate accepts for the same task entry in a select

   * Objects that take too much storage

   * Unchecked conversion between types of differing sizes

   * Missing return statements along some execution paths in a function

   * Incorrect (unrecognized) pragmas

   * Incorrect external names

   * Allocation from empty storage pool

   * Potentially blocking operations in protected types

   * Suspicious parenthesization of expressions

   * Mismatching bounds in an aggregate

   * Attempt to return local value by reference

   * Unrecognized pragmas

   * Premature instantiation of a generic body

   * Attempt to pack aliased components

   * Out of bounds array subscripts

   * Wrong length on string assignment

   * Violations of style rules if style checking is enabled

   * Unused with clauses

   * Bit_Order usage that does not have any effect

   * Compile time biased rounding of floating-point constant

   * Standard.Duration used to resolve universal fixed expression

   * Dereference of possibly null value

   * Declaration that is likely to cause storage error

   * Internal GNAT unit with'ed by application unit

   * Values known to be out of range at compile time

   * Unreferenced labels and variables

   * Address overlays that could clobber memory

   * Unexpected initialization when address clause present

   * Bad alignment for address clause

   * Useless type conversions

   * Redundant assignment statements

   * Accidental hiding of name by child unit

   * Unreachable code

   * Access before elaboration detected at compile time

   * A range in a `for' loop that is known to be null or might be null


The following qualifiers are available to control the handling of
warning messages:

`/WARNINGS=OPTIONAL (activate all optional errors)'
     This qualifier activates most optional warning messages, see
     remaining list in this section for details on optional warning
     messages that can be individually controlled. The warnings that
     are not turned on by this qualifier are
     `/WARNINGS=BIASED_ROUNDING' (biased rounding),
     `/WARNINGS=IMPLICIT_DEREFERENCE' (implicit dereferencing), and
     `/WARNINGS=HIDING' (hiding). All other optional warnings are
     turned on.

`/WARNINGS=NOOPTIONAL (suppress all optional errors)'
     This qualifier suppresses all optional warning messages, see
     remaining list in this section for details on optional warning
     messages that can be individually controlled.

`/WARNINGS=BIASED_ROUNDING (activate warnings on biased rounding)'
     If a static floating-point expression has a value that is exactly
     half way between two adjacent machine numbers, then the rules of
     Ada (Ada Reference Manual, section 4.9(38)) require that this
     rounding be done away from zero, even if the normal unbiased
     rounding rules at run time would require rounding towards zero.
     This warning message alerts you to such instances where
     compile-time rounding and run-time rounding are not equivalent. If
     it is important to get proper run-time rounding, then you can
     force this by making one of the operands into a variable. The
     default is that such warnings are not generated.  Note that
     `/WARNINGS=OPTIONAL' does not affect the setting of this warning
     option.

`/WARNINGS=NOBIASED_ROUNDING (suppress warnings on biased rounding)'
     This qualifier disables warnings on biased rounding.

`/WARNINGS=CONDITIONALS (activate warnings on conditionals)'
     This qualifier activates warnings for conditional expressions used
     in tests that are known to be True or False at compile time. The
     default is that such warnings are not generated.  This warning can
     also be turned on using `/WARNINGS=OPTIONAL'.

`/WARNINGS=NOCONDITIONALS (suppress warnings on conditionals)'
     This qualifier suppresses warnings for conditional expressions
     used in tests that are known to be True or False at compile time.

`/WARNINGS=IMPLICIT_DEREFERENCE (activate warnings on implicit dereferencing)'
     If this qualifier is set, then the use of a prefix of an access
     type in an indexed component, slice, or selected component without
     an explicit `.all' will generate a warning. With this warning
     enabled, access checks occur only at points where an explicit
     `.all' appears in the source code (assuming no warnings are
     generated as a result of this qualifier). The default is that such
     warnings are not generated.  Note that `/WARNINGS=OPTIONAL' does
     not affect the setting of this warning option.

`/WARNINGS=NOIMPLICIT_DEREFERENCE (suppress warnings on implicit dereferencing)'
     This qualifier suppresses warnings for implicit deferences in
     indexed components, slices, and selected components.

`/WARNINGS=ERROR (treat warnings as errors)'
     This qualifier causes warning messages to be treated as errors.
     The warning string still appears, but the warning messages are
     counted as errors, and prevent the generation of an object file.

`/WARNINGS=UNREFERENCED_FORMALS (activate warnings on unreferenced formals)'
     This qualifier causes a warning to be generated if a formal
     parameter is not referenced in the body of the subprogram. This
     warning can also be turned on using `/WARNINGS=OPTIONAL' or
     `/WARNINGS=UNUSED'.

`/WARNINGS=NOUNREFERENCED_FORMALS (suppress warnings on unreferenced formals)'
     This qualifier suppresses warnings for unreferenced formal
     parameters. Note that the combination `/WARNINGS=UNUSED' followed
     by `/WARNINGS=NOUNREFERENCED_FORMALS' has the effect of warning on
     unreferenced entities other than subprogram formals.

`/WARNINGS=HIDING (activate warnings on hiding)'
     This qualifier activates warnings on hiding declarations.  A
     declaration is considered hiding if it is for a non-overloadable
     entity, and it declares an entity with the same name as some other
     entity that is directly or use-visible. The default is that such
     warnings are not generated.  Note that `/WARNINGS=OPTIONAL' does
     not affect the setting of this warning option.

`/WARNINGS=NOHIDING (suppress warnings on hiding)'
     This qualifier suppresses warnings on hiding declarations.

`/WARNINGS=IMPLEMENTATION (activate warnings on implementation units).'
     This qualifier activates warnings for a `with' of an internal GNAT
     implementation unit, defined as any unit from the `Ada',
     `Interfaces', `GNAT', `DEC', or `System' hierarchies that is not
     documented in either the Ada Reference Manual or the GNAT
     Programmer's Reference Manual. Such units are intended only for
     internal implementation purposes and should not be `with''ed by
     user programs. The default is that such warnings are generated
     This warning can also be turned on using `/WARNINGS=OPTIONAL'.

`/WARNINGS=NOIMPLEMENTATION (disable warnings on implementation units).'
     This qualifier disables warnings for a `with' of an internal GNAT
     implementation unit.

`/WARNINGS=ELABORATION (activate warnings on elaboration pragmas)'
     This qualifier activates warnings on missing pragma Elaborate_All
     statements.  See the section in this guide on elaboration checking
     for details on when such pragma should be used. The default is
     that such warnings are not generated.  This warning can also be
     turned on using `/WARNINGS=OPTIONAL'.

`/WARNINGS=NOELABORATION (suppress warnings on elaboration pragmas)'
     This qualifier suppresses warnings on missing pragma Elaborate_All
     statements.  See the section in this guide on elaboration checking
     for details on when such pragma should be used.

`/WARNINGS=OVERLAYS (activate warnings on address clause overlays)'
     This qualifier activates warnings for possibly unintended
     initialization effects of defining address clauses that cause one
     variable to overlap another. The default is that such warnings are
     generated.  This warning can also be turned on using
     `/WARNINGS=OPTIONAL'.

`/WARNINGS=NOOVERLAYS (suppress warnings on address clause overlays)'
     This qualifier suppresses warnings on possibly unintended
     initialization effects of defining address clauses that cause one
     variable to overlap another.

`-gnatwp (activate warnings on ineffective pragma Inlines)'
     This qualifier activates warnings for failure of front end inlining
     (activated by `-gnatN') to inline a particular call. There are
     many reasons for not being able to inline a call, including most
     commonly that the call is too complex to inline.  This warning can
     also be turned on using `/WARNINGS=OPTIONAL'.

`-gnatwP (suppress warnings on ineffective pragma Inlines)'
     This qualifier suppresses warnings on ineffective pragma Inlines.
     If the inlining mechanism cannot inline a call, it will simply
     ignore the request silently.

`/WARNINGS=REDUNDANT (activate warnings on redundant constructs)'
     This qualifier activates warnings for redundant constructs. The
     following is the current list of constructs regarded as redundant:
     This warning can also be turned on using `/WARNINGS=OPTIONAL'.

        * Assignment of an item to itself.

        * Type conversion that converts an expression to its own type.

        * Use of the attribute `Base' where `typ'Base' is the same as
          `typ'.

        * Use of pragma `Pack' when all components are placed by a
          record representation clause.

`/WARNINGS=NOREDUNDANT (suppress warnings on redundant constructs)'
     This qualifier suppresses warnings for redundant constructs.

`/WARNINGS=SUPPRESS (suppress all warnings)'
     This qualifier completely suppresses the output of all warning
     messages from the GNAT front end.  Note that it does not suppress
     warnings from the `GNAT COMPILE' back end.  To suppress these back
     end warnings as well, use the qualifier `-w' in addition to
     `/WARNINGS=SUPPRESS'.

`/WARNINGS=UNUSED (activate warnings on unused entities)'
     This qualifier activates warnings to be generated for entities that
     are defined but not referenced, and for units that are `with''ed
     and not referenced. In the case of packages, a warning is also
     generated if no entities in the package are referenced. This means
     that if the package is referenced but the only references are in
     `use' clauses or `renames' declarations, a warning is still
     generated. A warning is also generated for a generic package that
     is `with''ed but never instantiated.  In the case where a package
     or subprogram body is compiled, and there is a `with' on the
     corresponding spec that is only referenced in the body, a warning
     is also generated, noting that the `with' can be moved to the
     body. The default is that such warnings are not generated.  This
     qualifier also activates warnings on unreferenced formals (it is
     includes the effect of `/WARNINGS=UNREFERENCED_FORMALS').  This
     warning can also be turned on using `/WARNINGS=OPTIONAL'.

`/WARNINGS=NOUNUSED (suppress warnings on unused entities)'
     This qualifier suppresses warnings for unused entities and
     packages.  It also turns off warnings on unreferenced formals (and
     thus includes the effect of `/WARNINGS=NOUNREFERENCED_FORMALS').

     A string of warning parameters can be used in the same parameter.
     For example:

          -gnatwaLe

     Would turn on all optional warnings except for elaboration pragma
     warnings, and also specify that warnings should be treated as
     errors.

`-w'
     This qualifier suppresses warnings from the `GNAT COMPILE'
     backend. It may be used in conjunction with `/WARNINGS=SUPPRESS'
     to ensure that all warnings are suppressed during the entire
     compilation process.



File: gnat_ug_vms.info,  Node: Debugging and Assertion Control,  Next: Run-Time Checks,  Prev: Output and Error Message Control,  Up: Qualifiers for GNAT COMPILE

Debugging and Assertion Control
-------------------------------

`/CHECKS=ASSERTIONS'
     The pragmas `Assert' and `Debug' normally have no effect and are
     ignored. This qualifier, where `a' stands for assert, causes
     `Assert' and `Debug' pragmas to be activated.

     The pragmas have the form:

             pragma Assert (BOOLEAN-EXPRESSION [,
                                STATIC-STRING-EXPRESSION])
             pragma Debug (PROCEDURE CALL)

     The `Assert' pragma causes BOOLEAN-EXPRESSION to be tested.  If
     the result is `True', the pragma has no effect (other than
     possible side effects from evaluating the expression). If the
     result is `False', the exception `Assert_Failure' declared in the
     package `System.Assertions' is raised (passing
     STATIC-STRING-EXPRESSION, if present, as the message associated
     with the exception). If no string expression is given the default
     is a string giving the file name and line number of the pragma.

     The `Debug' pragma causes PROCEDURE to be called. Note that
     `pragma Debug' may appear within a declaration sequence, allowing
     debugging procedures to be called between declarations.

`/DEBUG[=debug-level]'
`/NODEBUG'
     Specifies how much debugging information is to be included in the
     resulting object file where 'debug-level' is one of the following:
    `TRACEBACK (default)'
          Include both debugger symbol records and traceback the object
          file.

    `ALL'
          Include both debugger symbol records and traceback in object
          file.

    `NONE'
          Excludes both debugger symbol records and traceback the
          object file. Same as /NODEBUG.

    `SYMBOLS'
          Includes only debugger symbol records in the object file.
          Note that this doesn't include traceback information.


File: gnat_ug_vms.info,  Node: Validity Checking,  Next: Style Checking,  Prev: Run-Time Control,  Up: Qualifiers for GNAT COMPILE

Validity Checking
-----------------

The Ada 95 Reference Manual has specific requirements for checking for
invalid values. In particular, RM 13.9.1 requires that the evaluation
of invalid values (for example from unchecked conversions), not result
in erroneous execution. In GNAT, the result of such an evaluation in
normal default mode is to either use the value unmodified, or to raise
Constraint_Error in those cases where use of the unmodified value would
cause erroneous execution. The cases where unmodified values might lead
to erroneous execution are case statements (where a wild jump might
result from an invalid value), and subscripts on the left hand side
(where memory corruption could occur as a result of an invalid value).

   The `-gnatVx' qualifier allows more control over the validity
checking mode. The `x' argument here is a string of letters which
control which validity checks are performed in addition to the default
checks described above.

   * `-gnatVc' Validity checks for copies

     The right hand side of assignments, and the initializing values of
     object declarations are validity checked.

   * `/VALIDITY_CHECKING=RM' Default (RM) validity checks

     Some validity checks are done by default following normal Ada
     semantics (RM 13.9.1 (9-11)).  A check is done in case statements
     that the expression is within the range of the subtype. If it is
     not, Constraint_Error is raised.  For assignments to array
     components, a check is done that the expression used as index is
     within the range. If it is not, Constraint_Error is raised.  Both
     these validity checks may be turned off using qualifier `-gnatVD'.
     They are turned on by default. If `-gnatVD' is specified, a
     subsequent qualifier `/VALIDITY_CHECKING=RM' will leave the checks
     turned on.  Qualifier `-gnatVD' should be used only if you are
     sure that all such expressions have valid values. If you use this
     qualifier and invalid values are present, then the program is
     erroneous, and wild jumps or memory overwriting may occur.

   * `-gnatVi' Validity checks for `in' mode parameters

     Arguments for parameters of mode `in' are validity checked in
     function and procedure calls at the point of call.

   * `-gnatVm' Validity checks for `in out' mode parameters

     Arguments for parameters of mode `in out' are validity checked in
     procedure calls at the point of call. The `'m'' here stands for
     modify, since this concerns parameters that can be modified by the
     call.  Note that there is no specific option to test `out'
     parameters, but any reference within the subprogram will be tested
     in the usual manner, and if an invalid value is copied back, any
     reference to it will be subject to validity checking.

   * `-gnatVo' Validity checks for operator and attribute operands

     Arguments for predefined operators and attributes are validity
     checked.  This includes all operators in package `Standard', the
     shift operators defined as intrinsic in package `Interfaces' and
     operands for attributes such as `Pos'.

   * `-gnatVr' Validity checks for function returns

     The expression in `return' statements in functions is validity
     checked.

   * `-gnatVs' Validity checks for subscripts

     All subscripts expressions are checked for validity, whether they
     appear on the right side or left side (in default mode only left
     side subscripts are validity checked).

   * `-gnatVt' Validity checks for tests

     Expressions used as conditions in `if', `while' or `exit'
     statements are checked, as well as guard expressions in entry
     calls.

   * `/VALIDITY_CHECKING=FULL' Validity checks for floating-point values

     In the absence of this qualifier, validity checking occurs only
     for discrete values. If `/VALIDITY_CHECKING=FULL' is specified,
     then validity checking also applies for floating-point values, and
     NaN's and infinities are considered invalid, as well as out of
     range values for constrained types. Note that this means that
     standard `IEEE' infinity mode is not allowed. The exact contexts
     in which floating-point values are checked depends on the setting
     of other options. For example `-gnatVif' or `-gnatVfi' (the order
     does not matter) specifies that floating-point parameters of mode
     `in' should be validity checked.

   * `-gnatVa' All validity checks

     All the above validity checks are turned on. That is `-gnatVa' is
     equivalent to `gnatVcdfimorst'.

   * `-gnatVn' No validity checks

     This qualifier turns off all validity checking, including the
     default checking for case statements and left hand side
     subscripts. Note that the use of the qualifier
     `/CHECKS=SUPPRESS_ALL' supresses all run-time checks, including
     validity checks, and thus implies `-gnatVn'.


   The `/VALIDITY_CHECKING' qualifier may be followed by a string of
letters to turn on a series of validity checking options. For example,
`-gnatVcr' specifies that in addition to the default validity checking,
copies and function return expressions be validity checked. In order to
make it easier to specify a set of options, the upper case letters
`CDFIMORST' may be used to turn off the corresponding lower case
option, so for example `-gnatVaM' turns on all validity checking
options except for checking of `in out' procedure arguments.

   The specification of additional validity checking generates extra
code (and in the case of `-gnatva' the code expansion can be
substantial. However, these additional checks can be very useful in
smoking out cases of uninitialized variables, incorrect use of
unchecked conversion, and other errors leading to invalid values. The
use of pragma `Initialize_Scalars' is useful in conjunction with the
extra validity checking, since this ensures that wherever possible
uninitialized variables have invalid values.

   See also the pragma `Validity_Checks' which allows modification of
the validity checking mode at the program source level, and also allows
for temporary disabling of validity checks.


File: gnat_ug_vms.info,  Node: Style Checking,  Next: Using GNAT COMPILE for Syntax Checking,  Prev: Validity Checking,  Up: Qualifiers for GNAT COMPILE

Style Checking
--------------

The /STYLE=(OPTION,OPTION,..) qualifier causes the compiler to enforce
specified style rules. A limited set of style rules has been used in
writing the GNAT sources themselves. This qualifier allows user programs
to activate all or some of these checks. If the source program fails a
specified style check, an appropriate warning message is given,
preceded by the character sequence "(style)".  (OPTION,OPTION,..) is a
sequence of keywords indicating the particular style checks to be
performed. The following checks are defined:

`1-9 (specify indentation level)'
     If a digit from 1-9 appears in the string after `/STYLE=' then
     proper indentation is checked, with the digit indicating the
     indentation level required. The general style of required
     indentation is as specified by the examples in the Ada Reference
     Manual. Full line comments must be aligned with the `--' starting
     on a column that is a multiple of the alignment level.

`ATTRIBUTE (check attribute casing)'
     If the word ATTRIBUTE appears in the string after `/STYLE=' then
     attribute names, including the case of keywords such as `digits'
     used as attributes names, must be written in mixed case, that is,
     the initial letter and any letter following an underscore must be
     uppercase.  All other letters must be lowercase.

`BLANKS (blanks not allowed at statement end)'
     If the word BLANKS appears in the string after `/STYLE=' then
     trailing blanks are not allowed at the end of statements. The
     purpose of this rule, together with h (no horizontal tabs), is to
     enforce a canonical format for the use of blanks to separate
     source tokens.

`COMMENTS (check comments)'
     If the word COMMENTS appears in the string after `/STYLE=' then
     comments must meet the following set of rules:

        * The "-" that starts the column must either start in column
          one, or else at least one blank must precede this sequence.

        * Comments that follow other tokens on a line must have at
          least one blank following the "-" at the start of the comment.

        * Full line comments must have two blanks following the "-"
          that starts the comment, with the following exceptions.

        * A line consisting only of the "-" characters, possibly
          preceded by blanks is permitted.

        * A comment starting with "-x" where x is a special character
          is permitted.  This alows proper processing of the output
          generated by specialized tools including `GNAT PREPROCESS'
          (where -! is used) and the SPARK annnotation language (where
          -# is used). For the purposes of this rule, a special
          character is defined as being in one of the ASCII ranges
          16#21#..16#2F# or 16#3A#..16#3F#.

        * A line consisting entirely of minus signs, possibly preceded
          by blanks, is permitted. This allows the construction of box
          comments where lines of minus signs are used to form the top
          and bottom of the box.

        * If a comment starts and ends with "-" is permitted as long as
          at least one blank follows the initial "-". Together with the
          preceding rule, this allows the construction of box comments,
          as shown in the following example:
               ---------------------------
               -- This is a box comment --
               -- with two text lines.  --
               ---------------------------

`END (check end/exit labels)'
     If the word END appears in the string after `/STYLE=' then
     optional labels on `end' statements ending subprograms and on
     `exit' statements exiting named loops, are required to be present.

`VTABS (no form feeds or vertical tabs)'
     If the word VTABS appears in the string after `/STYLE=' then
     neither form feeds nor vertical tab characters are not permitted
     in the source text.

`HTABS (no horizontal tabs)'
     If the word HTABS appears in the string after `/STYLE=' then
     horizontal tab characters are not permitted in the source text.
     Together with the b (no blanks at end of line) check, this
     enforces a canonical form for the use of blanks to separate source
     tokens.

`IF_THEN (check if-then layout)'
     If the word IF_THEN appears in the string after `/STYLE=', then
     the keyword `then' must appear either on the same line as
     corresponding `if', or on a line on its own, lined up under the
     `if' with at least one non-blank line in between containing all or
     part of the condition to be tested.

`KEYWORD (check keyword casing)'
     If the word KEYWORD appears in the string after `/STYLE=' then all
     keywords must be in lower case (with the exception of keywords
     such as `digits' used as attribute names to which this check does
     not apply).

`LAYOUT (check layout)'
     If the word LAYOUT appears in the string after `/STYLE=' then
     layout of statement and declaration constructs must follow the
     recommendations in the Ada Reference Manual, as indicated by the
     form of the syntax rules. For example an `else' keyword must be
     lined up with the corresponding `if' keyword.

     There are two respects in which the style rule enforced by this
     check option are more liberal than those in the Ada Reference
     Manual. First in the case of record declarations, it is
     permissible to put the `record' keyword on the same line as the
     `type' keyword, and then the `end' in `end record' must line up
     under `type'.  For example, either of the following two layouts is
     acceptable:

          type q is record
             a : integer;
             b : integer;
          end record;
          
          type q is
             record
                a : integer;
                b : integer;
             end record;

     Second, in the case of a block statement, a permitted alternative
     is to put the block label on the same line as the `declare' or
     `begin' keyword, and then line the `end' keyword up under the
     block label. For example both the following are permitted:

          Block : declare
             A : Integer := 3;
          begin
             Proc (A, A);
          end Block;
          
          Block :
             declare
                A : Integer := 3;
             begin
                Proc (A, A);
             end Block;

     The same alternative format is allowed for loops. For example,
     both of the following are permitted:

          Clear : while J < 10 loop
             A (J) := 0;
          end loop Clear;
          
          Clear :
             while J < 10 loop
                A (J) := 0;
             end loop Clear;

`LINE_LENGTH (check maximum line length)'
     If the word LINE_LENGTH appears in the string after `/STYLE=' then
     the length of source lines must not exceed 79 characters, including
     any trailing blanks. The value of 79 allows convenient display on
     an 80 character wide device or window, allowing for possible
     special treatment of 80 character lines.

`MAX_LENGTH=nnn (set maximum line length)'
     If the sequence MAX_LENGTH=nnn, where nnn is a decimal number,
     appears in the string after `/STYLE=' then the length of lines
     must not exceed the given value.

`STANDARD_CASING (check casing of entities in Standard)'
     If the word STANDARD_CASING appears in the string after `/STYLE='
     then any identifier from Standard must be cased to match the
     presentation in the Ada Reference Manual (for example, `Integer'
     and `ASCII.NUL').

`ORDERED_SUBPROGRAMS (check order of subprogram bodies)'
     If the word ORDERED_SUBPROGRAMS appears in the string after
     `/STYLE=' then all subprogram bodies in a given scope (e.g. a
     package body) must be in alphabetical order. The ordering rule
     uses normal Ada rules for comparing strings, ignoring casing of
     letters, except that if there is a trailing numeric suffix, then
     the value of this suffix is used in the ordering (e.g. Junk2 comes
     before Junk10).

`PRAGMA (check pragma casing)'
     If the word PRAGMA appears in the string after `/STYLE=' then
     pragma names must be written in mixed case, that is, the initial
     letter and any letter following an underscore must be uppercase.
     All other letters must be lowercase.

`REFERENCES (check references)'
     If the word REFERENCES appears in the string after `/STYLE=' then
     all identifier references must be cased in the same way as the
     corresponding declaration. No specific casing style is imposed on
     identifiers. The only requirement is for consistency of references
     with declarations.

`SPECS (check separate specs)'
     If the word SPECS appears in the string after `/STYLE=' then
     separate declarations ("specs") are required for subprograms (a
     body is not allowed to serve as its own declaration). The only
     exception is that parameterless library level procedures are not
     required to have a separate declaration. This exception covers the
     most frequent form of main program procedures.

`TOKEN (check token spacing)'
     If the word TOKEN appears in the string after `/STYLE=' then the
     following token spacing rules are enforced:

        * The keywords `abs' and `not' must be followed by a space.

        * The token `=>' must be surrounded by spaces.

        * The token `<>' must be preceded by a space or a left
          parenthesis.

        * Binary operators other than `**' must be surrounded by spaces.
          There is no restriction on the layout of the `**' binary
          operator.

        * Colon must be surrounded by spaces.

        * Colon-equal (assignment) must be surrounded by spaces.

        * Comma must be the first non-blank character on the line, or be
          immediately preceded by a non-blank character, and must be
          followed by a space.

        * If the token preceding a left paren ends with a letter or
          digit, then a space must separate the two tokens.

        * A right parenthesis must either be the first non-blank
          character on a line, or it must be preceded by a non-blank
          character.

        * A semicolon must not be preceded by a space, and must not be
          followed by a non-blank character.

        * A unary plus or minus may not be followed by a space.

        * A vertical bar must be surrounded by spaces.

     In the above rules, appearing in column one is always permitted,
     that is, counts as meeting either a requirement for a required
     preceding space, or as meeting a requirement for no preceding
     space.

     Appearing at the end of a line is also always permitted, that is,
     counts as meeting either a requirement for a following space, or
     as meeting a requirement for no following space.


If any of these style rules is violated, a message is generated giving
details on the violation. The initial characters of such messages are
always "(style)". Note that these messages are treated as warning
messages, so they normally do not prevent the generation of an object
file. The `/WARNINGS=ERROR' qualifier can be used to treat warning
messages, including style messages, as fatal errors.

The qualifier /STYLE_CHECKS=ALL_BUILTIN is equivalent to  all checking
options  enabled with the exception of ORDERED_SUBPROGRAMS, with an
indentation level of 3. This is the standard checking option that is
used for the GNAT sources.


File: gnat_ug_vms.info,  Node: Run-Time Checks,  Next: Stack Overflow Checking,  Prev: Debugging and Assertion Control,  Up: Qualifiers for GNAT COMPILE

Run-Time Checks
---------------

If you compile with the default options, GNAT will insert many run-time
checks into the compiled code, including code that performs range
checking against constraints, but not arithmetic overflow checking for
integer operations (including division by zero) or checks for access
before elaboration on subprogram calls. All other run-time checks, as
required by the Ada 95 Reference Manual, are generated by default.  The
following `GNAT COMPILE' qualifiers refine this default behavior:

`/CHECKS=SUPPRESS_ALL'
     Suppress all run-time checks as though `pragma Suppress
     (all_checks') had been present in the source. Validity checks are
     also suppressed (in other words `/CHECKS=SUPPRESS_ALL' also
     implies `-gnatVn'.  Use this qualifier to improve the performance
     of the code at the expense of safety in the presence of invalid
     data or program bugs.

`/CHECKS=OVERFLOW'
     Enables overflow checking for integer operations.  This causes
     GNAT to generate slower and larger executable programs by adding
     code to check for overflow (resulting in raising
     `Constraint_Error' as required by standard Ada semantics). These
     overflow checks correspond to situations in which the true value
     of the result of an operation may be outside the base range of the
     result type. The following example shows the distinction:

          X1 : Integer := Integer'Last;
          X2 : Integer range 1 .. 5 := 5;
          ...
          X1 := X1 + 1;   -- `/CHECKS=OVERFLOW' required to catch the Constraint_Error
          X2 := X2 + 1;   -- range check, `/CHECKS=OVERFLOW' has no effect here

     Here the first addition results in a value that is outside the
     base range of Integer, and hence requires an overflow check for
     detection of the constraint error. The second increment operation
     results in a violation of the explicit range constraint, and such
     range checks are always performed. Basically the compiler can
     assume that in the absence of the `/CHECKS=OVERFLOW' qualifier
     that any value of type `xxx' is in range of the base type of `xxx'.

     Note that the `/CHECKS=OVERFLOW' qualifier does not affect the
     code generated for any floating-point operations; it applies only
     to integer semantics).  For floating-point, GNAT has the
     `Machine_Overflows' attribute set to `False' and the normal mode
     of operation is to generate IEEE NaN and infinite values on
     overflow or invalid operations (such as dividing 0.0 by 0.0).

     The reason that we distinguish overflow checking from other kinds
     of range constraint checking is that a failure of an overflow
     check can generate an incorrect value, but cannot cause erroneous
     behavior. This is unlike the situation with a constraint check on
     an array subscript, where failure to perform the check can result
     in random memory description, or the range check on a case
     statement, where failure to perform the check can cause a wild
     jump.

     Note again that `/CHECKS=OVERFLOW' is off by default, so overflow
     checking is not performed in default mode. This means that out of
     the box, with the default settings, GNAT does not do all the
     checks expected from the language description in the Ada Reference
     Manual. If you want all constraint checks to be performed, as
     described in this Manual, then you must explicitly use the
     /CHECKS=OVERFLOW qualifier either on the `GNAT MAKE' or `GNAT
     COMPILE' command.

`/CHECKS=ELABORATION'
     Enables dynamic checks for access-before-elaboration on subprogram
     calls and generic instantiations.  For full details of the effect
     and use of this qualifier, *Note Compiling Using GNAT COMPILE::.

The setting of these qualifiers only controls the default setting of the
checks. You may modify them using either `Suppress' (to remove checks)
or `Unsuppress' (to add back suppressed checks) pragmas in the program
source.


File: gnat_ug_vms.info,  Node: Stack Overflow Checking,  Next: Run-Time Control,  Prev: Run-Time Checks,  Up: Qualifiers for GNAT COMPILE

Stack Overflow Checking
-----------------------

For most operating systems, `GNAT COMPILE' does not perform stack
overflow checking by default. This means that if the main environment
task or some other task exceeds the available stack space, then
unpredictable behavior will occur.

   To activate stack checking, compile all units with the GNAT COMPILE
option `-fstack-check'. For example:

     GNAT COMPILE -fstack-check PACKAGE1.ADB

Units compiled with this option will generate extra instructions to
check that any use of the stack (for procedure calls or for declaring
local variables in declare blocks) do not exceed the available stack
space.  If the space is exceeded, then a `Storage_Error' exception is
raised.

   For declared tasks, the stack size is always controlled by the size
given in an applicable `Storage_Size' pragma (or is set to the default
size if no pragma is used.

   For the environment task, the stack size depends on system defaults
and is unknown to the compiler. The stack may even dynamically grow on
some systems, precluding the normal Ada semantics for stack overflow.
In the worst case, unbounded stack usage, causes unbounded stack
expansion resulting in the system running out of virtual memory.

   The stack checking may still work correctly if a fixed size stack is
allocated, but this cannot be guaranteed.  To ensure that a clean
exception is signalled for stack overflow, set the environment variable
`GNAT_STACK_LIMIT' to indicate the maximum stack area that can be used,
as in:

     SET GNAT_STACK_LIMIT 1600

The limit is given in kilobytes, so the above declaration would set the
stack limit of the environment task to 1.6 megabytes.  Note that the
only purpose of this usage is to limit the amount of stack used by the
environment task. If it is necessary to increase the amount of stack
for the environment task, then this is an operating systems issue, and
must be addressed with the appropriate operating systems commands.


File: gnat_ug_vms.info,  Node: Run-Time Control,  Next: Validity Checking,  Prev: Stack Overflow Checking,  Up: Qualifiers for GNAT COMPILE

Run-Time Control
----------------

`-gnatT nnn'
     The `gnatT' qualifier can be used to specify the time-slicing value
     to be used for task switching between equal priority tasks. The
     value `nnn' is given in microseconds as a decimal integer.

     Setting the time-slicing value is only effective if the underlying
     thread control system can accommodate time slicing. Check the
     documentation of your operating system for details. Note that the
     time-slicing value can also be set by use of pragma `Time_Slice'
     or by use of the `t' qualifier in the GNAT BIND step. The pragma
     overrides a command line argument if both are present, and the `t'
     qualifier for GNAT BIND overrides both the pragma and the `GNAT
     COMPILE' command line qualifier.


File: gnat_ug_vms.info,  Node: Using GNAT COMPILE for Syntax Checking,  Next: Using GNAT COMPILE for Semantic Checking,  Prev: Style Checking,  Up: Qualifiers for GNAT COMPILE

Using `GNAT COMPILE' for Syntax Checking
----------------------------------------

`/SYNTAX_ONLY'
     Run GNAT in syntax checking only mode. For example, the command

          $ GNAT COMPILE /SYNTAX_ONLY X.ADB

     compiles file `X.ADB' in syntax-check-only mode. You can check a
     series of files in a single command .

     You may use other qualifiers in conjunction with `/SYNTAX_ONLY'. In
     particular, `/LIST' and `/REPORT_ERRORS=VERBOSE' are useful to
     control the format of any generated error messages.

     The output is simply the error messages, if any. No object file or
     ALI file is generated by a syntax-only compilation. Also, no units
     other than the one specified are accessed. For example, if a unit
     `X' `with''s a unit `Y', compiling unit `X' in syntax check only
     mode does not access the source file containing unit `Y'.

     Normally, GNAT allows only a single unit in a source file.
     However, this restriction does not apply in syntax-check-only
     mode, and it is possible to check a file containing multiple
     compilation units concatenated together. This is primarily used by
     the `GNAT CHOP' utility (*note Renaming Files Using GNAT CHOP::).


File: gnat_ug_vms.info,  Node: Using GNAT COMPILE for Semantic Checking,  Next: Compiling Ada 83 Programs,  Prev: Using GNAT COMPILE for Syntax Checking,  Up: Qualifiers for GNAT COMPILE

Using `GNAT COMPILE' for Semantic Checking
------------------------------------------

`/NOLOAD'
     Causes the compiler to operate in semantic check mode, with full
     checking for all illegalities specified in the Ada 95 Reference
     Manual, but without generation of any object code (no object file
     is generated).

     Because dependent files must be accessed, you must follow the GNAT
     semantic restrictions on file structuring to operate in this mode:

        * The needed source files must be accessible (*note Search
          Paths and the Run-Time Library (RTL)::).

        * Each file must contain only one compilation unit.

        * The file name and unit name must match (*note File Naming
          Rules::).

     The output consists of error messages as appropriate. No object
     file is generated. An `ALI' file is generated for use in the
     context of cross-reference tools, but this file is marked as not
     being suitable for binding (since no object file is generated).
     The checking corresponds exactly to the notion of legality in the
     Ada 95 Reference Manual.

     Any unit can be compiled in semantics-checking-only mode, including
     units that would not normally be compiled (subunits, and
     specifications where a separate body is present).


File: gnat_ug_vms.info,  Node: Compiling Ada 83 Programs,  Next: Character Set Control,  Prev: Using GNAT COMPILE for Semantic Checking,  Up: Qualifiers for GNAT COMPILE

Compiling Ada 83 Programs
-------------------------

`/83'
     Although GNAT is primarily an Ada 95 compiler, it accepts this
     qualifier to specify that an Ada 83 program is to be compiled in
     Ada83 mode. If you specify this qualifier, GNAT rejects most Ada
     95 extensions and applies Ada 83 semantics where this can be done
     easily.  It is not possible to guarantee this qualifier does a
     perfect job; for example, some subtle tests, such as are found in
     earlier ACVC tests (that have been removed from the ACVC suite for
     Ada 95), may not compile correctly. However, for most purposes,
     using this qualifier should help to ensure that programs that
     compile correctly under the `/83' qualifier can be ported easily
     to an Ada 83 compiler. This is the main use of the qualifier.

     With few exceptions (most notably the need to use `<>' on
     unconstrained generic formal parameters, the use of the new Ada 95
     keywords, and the use of packages with optional bodies), it is not
     necessary to use the `/83' qualifier when compiling Ada 83
     programs, because, with rare exceptions, Ada 95 is upwardly
     compatible with Ada 83. This means that a correct Ada 83 program
     is usually also a correct Ada 95 program.



File: gnat_ug_vms.info,  Node: Character Set Control,  Next: File Naming Control,  Prev: Compiling Ada 83 Programs,  Up: Qualifiers for GNAT COMPILE

Character Set Control
---------------------

`/IDENTIFIER_CHARACTER_SET=C'
     Normally GNAT recognizes the Latin-1 character set in source
     program identifiers, as described in the Ada 95 Reference Manual.
     This qualifier causes GNAT to recognize alternate character sets
     in identifiers. C is a single character or word indicating the
     character set, as follows:

    `1'
          Latin-1 identifiers

    `2'
          Latin-2 letters allowed in identifiers

    `3'
          Latin-3 letters allowed in identifiers

    `4'
          Latin-4 letters allowed in identifiers

    `5'
          Latin-5 (Cyrillic) letters allowed in identifiers

    `9'
          Latin-9 letters allowed in identifiers

    `PC'
          IBM PC letters (code page 437) allowed in identifiers

    `PC850'
          IBM PC letters (code page 850) allowed in identifiers

    `FULL_UPPER'
          Full upper-half codes allowed in identifiers

    `NO_UPPER'
          No upper-half codes allowed in identifiers

    `WIDE'
          Wide-character codes (that is, codes greater than 255)
          allowed in identifiers

     *Note Foreign Language Representation::, for full details on the
     implementation of these character sets.

`/WIDE_CHARACTER_ENCODING=E'
     Specify the method of encoding for wide characters.  E is one of
     the following:

    `HEX'
          Hex encoding (brackets coding also recognized)

    `UPPER'
          Upper half encoding (brackets encoding also recognized)

    `SHIFT_JIS'
          Shift/JIS encoding (brackets encoding also recognized)

    `EUC'
          EUC encoding (brackets encoding also recognized)

    `UTF8'
          UTF-8 encoding (brackets encoding also recognized)

    `BRACKETS'
          Brackets encoding only (default value)
     For full details on the these encoding methods see *Note Wide
     Character Encodings::.  Note that brackets coding is always
     accepted, even if one of the other options is specified, so for
     example `/WIDE_CHARACTER_ENCODING=UTF8' specifies that both
     brackets and `UTF-8' encodings will be recognized. The units that
     are with'ed directly or indirectly will be scanned using the
     specified representation scheme, and so if one of the non-brackets
     scheme is used, it must be used consistently throughout the
     program. However, since brackets encoding is always recognized, it
     may be conveniently used in standard libraries, allowing these
     libraries to be used with any of the available coding schemes.
     scheme. If no `/WIDE_CHARACTER_ENCODING=?' parameter is present,
     then the default representation is Brackets encoding only.

     Note that the wide character representation that is specified
     (explicitly or by default) for the main program also acts as the
     default encoding used for Wide_Text_IO files if not specifically
     overridden by a WCEM form parameter.



File: gnat_ug_vms.info,  Node: File Naming Control,  Next: Subprogram Inlining Control,  Prev: Character Set Control,  Up: Qualifiers for GNAT COMPILE

File Naming Control
-------------------

`/FILE_NAME_MAX_LENGTH=N'
     Activates file name "krunching". N, a decimal integer in the range
     1-999, indicates the maximum allowable length of a file name (not
     including the `.ADS' or `.ADB' extension). The default is not to
     enable file name krunching.

     For the source file naming rules, *Note File Naming Rules::.


File: gnat_ug_vms.info,  Node: Subprogram Inlining Control,  Next: Auxiliary Output Control,  Prev: File Naming Control,  Up: Qualifiers for GNAT COMPILE

Subprogram Inlining Control
---------------------------

`/INLINE=PRAGMA'
     GNAT recognizes and processes `Inline' pragmas. However, for the
     inlining to actually occur, optimization must be enabled. To enable
     inlining across unit boundaries, this is, inlining a call in one
     unit of a subprogram declared in a `with''ed unit, you must also
     specify this qualifier.  In the absence of this qualifier, GNAT
     does not attempt inlining across units and does not need to access
     the bodies of subprograms for which `pragma Inline' is specified
     if they are not in the current unit.

     If you specify this qualifier the compiler will access these
     bodies, creating an extra source dependency for the resulting
     object file, and where possible, the call will be inlined.  For
     further details on when inlining is possible see *Note Inlining of
     Subprograms::.

`-gnatN'
     The front end inlining activated by this qualifier is generally
     more extensive, and quite often more effective than the standard
     `/INLINE=PRAGMA' inlining mode.  It will also generate additional
     dependencies.



File: gnat_ug_vms.info,  Node: Auxiliary Output Control,  Next: Debugging Control,  Prev: Subprogram Inlining Control,  Up: Qualifiers for GNAT COMPILE

Auxiliary Output Control
------------------------

`/TREE_OUTPUT'
     Causes GNAT to write the internal tree for a unit to a file (with
     the extension `.adt'.  This not normally required, but is used by
     separate analysis tools.  Typically these tools do the necessary
     compilations automatically, so you should not have to specify this
     qualifier in normal operation.

`/UNITS_LIST'
     Print a list of units required by this compilation on `SYS$OUTPUT'.
     The listing includes all units on which the unit being compiled
     depends either directly or indirectly.



File: gnat_ug_vms.info,  Node: Debugging Control,  Next: Units to Sources Mapping Files,  Prev: Auxiliary Output Control,  Up: Qualifiers for GNAT COMPILE

Debugging Control
-----------------

`/EXPAND_SOURCE'
     This qualifier causes the compiler to generate auxiliary output
     containing a pseudo-source listing of the generated expanded code.
     Like most Ada compilers, GNAT works by first transforming the high
     level Ada code into lower level constructs. For example, tasking
     operations are transformed into calls to the tasking run-time
     routines. A unique capability of GNAT is to list this expanded
     code in a form very close to normal Ada source.  This is very
     useful in understanding the implications of various Ada usage on
     the efficiency of the generated code. There are many cases in Ada
     (e.g. the use of controlled types), where simple Ada statements can
     generate a lot of run-time code. By using `/EXPAND_SOURCE' you can
     identify these cases, and consider whether it may be desirable to
     modify the coding approach to improve efficiency.

     The format of the output is very similar to standard Ada source,
     and is easily understood by an Ada programmer. The following
     special syntactic additions correspond to low level features used
     in the generated code that do not have any exact analogies in pure
     Ada source form. The following is a partial list of these special
     constructions. See the specification of package `Sprint' in file
     `SPRINT.ADS' for a full list.

    `new XXX [storage_pool = YYY]'
          Shows the storage pool being used for an allocator.

    `at end PROCEDURE-NAME;'
          Shows the finalization (cleanup) procedure for a scope.

    `(if EXPR then EXPR else EXPR)'
          Conditional expression equivalent to the `x?y:z' construction
          in C.

    `TARGET^(SOURCE)'
          A conversion with floating-point truncation instead of
          rounding.

    `TARGET?(SOURCE)'
          A conversion that bypasses normal Ada semantic checking. In
          particular enumeration types and fixed-point types are
          treated simply as integers.

    `TARGET?^(SOURCE)'
          Combines the above two cases.

    `X #/ Y'
    `X #mod Y'
    `X #* Y'
    `X #rem Y'
          A division or multiplication of fixed-point values which are
          treated as integers without any kind of scaling.

    `free EXPR [storage_pool = XXX]'
          Shows the storage pool associated with a `free' statement.

    `freeze TYPENAME [ACTIONS]'
          Shows the point at which TYPENAME is frozen, with possible
          associated actions to be performed at the freeze point.

    `reference ITYPE'
          Reference (and hence definition) to internal type ITYPE.

    `FUNCTION-NAME! (ARG, ARG, ARG)'
          Intrinsic function call.

    `LABELNAME : label'
          Declaration of label LABELNAME.

    `EXPR && EXPR && EXPR ... && EXPR'
          A multiple concatenation (same effect as EXPR & EXPR & EXPR,
          but handled more efficiently).

    `[constraint_error]'
          Raise the `Constraint_Error' exception.

    `EXPRESSION'reference'
          A pointer to the result of evaluating EXPRESSION.

    `TARGET-TYPE!(SOURCE-EXPRESSION)'
          An unchecked conversion of SOURCE-EXPRESSION to TARGET-TYPE.

    `[NUMERATOR/DENOMINATOR]'
          Used to represent internal real literals (that) have no exact
          representation in base 2-16 (for example, the result of
          compile time evaluation of the expression 1.0/27.0).

    `/XDEBUG'
          This qualifier is used in conjunction with `/EXPAND_SOURCE'
          to cause the expanded source, as described above to be
          written to files with names `XXX_DG', where `xxx' is the
          normal file name, for example, if the source file name is
          `HELLO.ADB', then a file `HELLO.ADB_DG' will be written.  The
          debugging information generated by the `GNAT COMPILE'
          `/DEBUG' qualifier will refer to the generated `XXX_DG' file.
          This allows you to do source level debugging using the
          generated code which is sometimes useful for complex code,
          for example to find out exactly which part of a complex
          construction raised an exception. This qualifier also
          suppress generation of cross-reference information (see
          /XREF=SUPPRESS).

    `/COMPRESS_NAMES'
          In the generated debugging information, and also in the case
          of long external names, the compiler uses a compression
          mechanism if the name is very long.  This compression method
          uses a checksum, and avoids trouble on some operating systems
          which have difficulty with very long names. The
          `/COMPRESS_NAMES' qualifier forces this compression approach
          to be used on all external names and names in the debugging
          information tables. This reduces the size of the generated
          executable, at the expense of making the naming scheme more
          complex. The compression only affects the qualification of
          the name. Thus a name in the source:

               Very_Long_Package.Very_Long_Inner_Package.Var

          would normally appear in these tables as:

               very_long_package__very_long_inner_package__var

          but if the `/COMPRESS_NAMES' qualifier is used, then the name
          appears as

               XCb7e0c705__var

          Here b7e0c705 is a compressed encoding of the qualification
          prefix.  The GNAT Ada aware version of GDB understands these
          encoded prefixes, so if this debugger is used, the encoding
          is largely hidden from the user of the compiler.


`/REPRESENTATION_INFO[0|1|2|3][s]'
     This qualifier controls output from the compiler of a listing
     showing representation information for declared types and objects.
     For `/REPRESENTATION_INFO=NONE', no information is output
     (equivalent to omitting the `/REPRESENTATION_INFO' qualifier). For
     `/REPRESENTATION_INFO=ARRAYS' (which is the default, so
     `/REPRESENTATION_INFO' with no parameter has the same effect),
     size and alignment information is listed for declared array and
     record types. For `/REPRESENTATION_INFO=OBJECTS', size and
     alignment information is listed for all expression information for
     values that are computed at run time for variant records. These
     symbolic expressions have a mostly obvious format with #n being
     used to represent the value of the n'th discriminant. See source
     files `REPINFO.ADS/adb' in the `GNAT' sources for full detalis on
     the format of `/REPRESENTATION_INFO=SYMBOLIC' output. If the
     qualifier is followed by an s (e.g. `-gnatR2s'), then the output
     is to a file with the name `file_REP' where file is the name of
     the corresponding source file.

`/XREF=SUPPRESS'
     Normally the compiler generates full cross-referencing information
     in the `ALI' file. This information is used by a number of tools,
     including `GNAT FIND' and `GNAT XREF'. The /XREF=SUPPRESS qualifier
     suppresses this information. This saves some space and may slightly
     speed up compilation, but means that these tools cannot be used.


File: gnat_ug_vms.info,  Node: Units to Sources Mapping Files,  Prev: Debugging Control,  Up: Qualifiers for GNAT COMPILE

Units to Sources Mapping Files
------------------------------

`-gnatemPATH'
     A mapping file is a way to communicate to the compiler two
     mappings: from unit names to file names (without any directory
     information) and from file names to path names (with full
     directory information). These mappings are used by the compiler to
     short-circuit the path search.

     A mapping file is a sequence of sets of three lines. In each set,
     the first line is the unit name, in lower case, with "%s" appended
     for specifications and "%b" appended for bodies; the second line
     is the file name; and the third line is the path name.

     Example:
             main%b
             main.2.ADA
             /gnat/project1/sources/main.2.ADA

     When the qualifier `-gnatem' is specified, the compiler will create
     in memory the two mappings from the specified file. If there is
     any problem (non existent file, truncated file or duplicate
     entries), no mapping will be created.

     Several `-gnatem' qualifiers may be specified; however, only the
     last one on the command line will be taken into account.

     When using a project file, `GNAT MAKE' create a temporary mapping
     file and communicates it to the compiler using this qualifier.



File: gnat_ug_vms.info,  Node: Search Paths and the Run-Time Library (RTL),  Next: Order of Compilation Issues,  Prev: Qualifiers for GNAT COMPILE,  Up: Compiling Using GNAT COMPILE

Search Paths and the Run-Time Library (RTL)
===========================================

With the GNAT source-based library system, the compiler must be able to
find source files for units that are needed by the unit being compiled.
Search paths are used to guide this process.

   The compiler compiles one source file whose name must be given
explicitly on the command line. In other words, no searching is done
for this file. To find all other source files that are needed (the most
common being the specs of units), the compiler examines the following
directories, in the following order:

  1. The directory containing the source file of the main unit being
     compiled (the file name on the command line).

  2. Each directory named by an `/SOURCE_SEARCH' qualifier given on the
     `GNAT COMPILE' command line, in the order given.

  3. Each of the directories listed in the value of the
     `ADA_INCLUDE_PATH' logical name.  Normally, define this value as a
     logical name containing a comma separated list of directory names.

     This variable can also be defined by means of an environment string
     (an argument to the DEC C exec* set of functions).

     Logical Name:
          DEFINE ANOTHER_PATH FOO:[BAG]
          DEFINE ADA_INCLUDE_PATH ANOTHER_PATH,FOO:[BAM],FOO:[BAR]

     By default, the path includes GNU:[LIB.OPENVMS7_x.2_8_x.DECLIB]
     first, followed by the standard Ada 95 libraries in
     GNU:[LIB.OPENVMS7_x.2_8_x.ADAINCLUDE].  If this is not redefined,
     the user will obtain the DEC Ada83 IO packages (Text_IO,
     Sequential_IO, etc) instead of the Ada95 packages. Thus, in order
     to get the Ada 95 packages by default, ADA_INCLUDE_PATH must be
     redefined.

  4. The content of the "ada_source_path" file which is part of the GNAT
     installation tree and is used to store standard libraries such as
     the GNAT Run Time Library (RTL) source files.

Specifying the qualifier `/NOCURRENT_DIRECTORY' inhibits the use of the
directory containing the source file named in the command line. You can
still have this directory on your search path, but in this case it must
be explicitly requested with a `/SOURCE_SEARCH' qualifier.

   Specifying the qualifier `/NOSTD_INCLUDES' inhibits the search of
the default location for the GNAT Run Time Library (RTL) source files.

   The compiler outputs its object files and ALI files in the current
working directory.

   The packages `Ada', `System', and `Interfaces' and their children
make up the GNAT RTL, together with the simple `System.IO' package used
in the "Hello World" example. The sources for these units are needed by
the compiler and are kept together in one directory. Not all of the
bodies are needed, but all of the sources are kept together anyway. In
a normal installation, you need not specify these directory names when
compiling or binding. Either the environment variables or the built-in
defaults cause these files to be found.

   In addition to the language-defined hierarchies (System, Ada and
Interfaces), the GNAT distribution provides a fourth hierarchy,
consisting of child units of GNAT. This is a collection of generally
useful routines. See the GNAT Reference Manual for further details.

   Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.


File: gnat_ug_vms.info,  Node: Order of Compilation Issues,  Next: Examples,  Prev: Search Paths and the Run-Time Library (RTL),  Up: Compiling Using GNAT COMPILE

Order of Compilation Issues
===========================

If, in our earlier example, there was a spec for the `hello' procedure,
it would be contained in the file `HELLO.ADS'; yet this file would not
have to be explicitly compiled. This is the result of the model we
chose to implement library management. Some of the consequences of this
model are as follows:

   * There is no point in compiling specs (except for package specs
     with no bodies) because these are compiled as needed by clients. If
     you attempt a useless compilation, you will receive an error
     message.  It is also useless to compile subunits because they are
     compiled as needed by the parent.

   * There are no order of compilation requirements: performing a
     compilation never obsoletes anything. The only way you can obsolete
     something and require recompilations is to modify one of the
     source files on which it depends.

   * There is no library as such, apart from the ALI files (*note The
     Ada Library Information Files::, for information on the format of
     these files). For now we find it convenient to create separate ALI
     files, but eventually the information therein may be incorporated
     into the object file directly.

   * When you compile a unit, the source files for the specs of all
     units that it `with''s, all its subunits, and the bodies of any
     generics it instantiates must be available (reachable by the
     search-paths mechanism described above), or you will receive a
     fatal error message.


File: gnat_ug_vms.info,  Node: Examples,  Prev: Order of Compilation Issues,  Up: Compiling Using GNAT COMPILE

Examples
========

The following are some typical Ada compilation command line examples:

`$ GNAT COMPILE XYZ.ADB'
     Compile body in file `XYZ.ADB' with all default options.

`$ GNAT COMPILE /OPTIMIZE=ALL /CHECKS=ASSERTIONS XYZ-DEF.ADB'
     Compile the child unit package in file `XYZ-DEF.ADB' with extensive
     optimizations, and pragma `Assert'/`Debug' statements enabled.

`$ GNAT COMPILE /NOLOAD ABC-DEF.ADB'
     Compile the subunit in file `ABC-DEF.ADB' in semantic-checking-only
     mode.


File: gnat_ug_vms.info,  Node: Binding Using GNAT BIND,  Next: Linking Using GNAT LINK,  Prev: Compiling Using GNAT COMPILE,  Up: Top

Binding Using `GNAT BIND'
*************************

* Menu:

* Running GNAT BIND::
* Generating the Binder Program in C::
* Consistency-Checking Modes::
* Binder Error Message Control::
* Elaboration Control::
* Output Control::
* Binding with Non-Ada Main Programs::
* Binding Programs with No Main Subprogram::
* Summary of Binder Qualifiers::
* Command-Line Access::
* Search Paths for GNAT BIND::
* Examples of GNAT BIND Usage::

This chapter describes the GNAT binder, `GNAT BIND', which is used to
bind compiled GNAT objects. The `GNAT BIND' program performs four
separate functions:

  1. Checks that a program is consistent, in accordance with the rules
     in Chapter 10 of the Ada 95 Reference Manual. In particular, error
     messages are generated if a program uses inconsistent versions of a
     given unit.

  2. Checks that an acceptable order of elaboration exists for the
     program and issues an error message if it cannot find an order of
     elaboration that satisfies the rules in Chapter 10 of the Ada 95
     Language Manual.

  3. Generates a main program incorporating the given elaboration order.
     This program is a small Ada package (body and spec) that must be
     subsequently compiled using the GNAT compiler. The necessary
     compilation step is usually performed automatically by `GNAT
     LINK'. The two most important functions of this program are to
     call the elaboration routines of units in an appropriate order and
     to call the main program.

  4. Determines the set of object files required by the given main
     program.  This information is output in the forms of comments in
     the generated program, to be read by the `GNAT LINK' utility used
     to link the Ada application.


File: gnat_ug_vms.info,  Node: Running GNAT BIND,  Next: Generating the Binder Program in C,  Up: Binding Using GNAT BIND

Running `GNAT BIND'
===================

The form of the `GNAT BIND' command is

     $ GNAT BIND [QUALIFIERS] MAINPROG[.ALI] [QUALIFIERS]

where MAINPROG.ADB is the Ada file containing the main program unit
body. If no qualifiers are specified, `GNAT BIND' constructs an Ada
package in two files which names are `B$ADA_MAIN.ADS', and
`B$ADA_MAIN.ADB'.  For example, if given the parameter `HELLO.ALI', for
a main program contained in file `HELLO.ADB', the binder output files
would be `B~HELLO.ADS' and `B~HELLO.ADB'.

   When doing consistency checking, the binder takes into consideration
any source files it can locate. For example, if the binder determines
that the given main program requires the package `Pack', whose `.ALI'
file is `PACK.ALI' and whose corresponding source spec file is
`PACK.ADS', it attempts to locate the source file `PACK.ADS' (using the
same search path conventions as previously described for the `GNAT
COMPILE' command). If it can locate this source file, it checks that
the time stamps or source checksums of the source and its references to
in `ali' files match. In other words, any `ali' files that mentions
this spec must have resulted from compiling this version of the source
file (or in the case where the source checksums match, a version close
enough that the difference does not matter).

   The effect of this consistency checking, which includes source
files, is that the binder ensures that the program is consistent with
the latest version of the source files that can be located at bind
time. Editing a source file without compiling files that depend on the
source file cause error messages to be generated by the binder.

   For example, suppose you have a main program `HELLO.ADB' and a
package `P', from file `P.ADS' and you perform the following steps:

  1. Enter `GNAT COMPILE HELLO.ADB' to compile the main program.

  2. Enter `GNAT COMPILE P.ADS' to compile package `P'.

  3. Edit file `P.ADS'.

  4. Enter `GNAT BIND hello'.

   At this point, the file `P.ALI' contains an out-of-date time stamp
because the file `P.ADS' has been edited. The attempt at binding fails,
and the binder generates the following error messages:

     error: "HELLO.ADB" must be recompiled ("P.ADS" has been modified)
     error: "P.ADS" has been modified and must be recompiled

Now both files must be recompiled as indicated, and then the bind can
succeed, generating a main program. You need not normally be concerned
with the contents of this file, but it is similar to the following which
is the binder file generated for a simple "hello world" program.

     --  The package is called Ada_Main unless this name is actually used
     --  as a unit name in the partition, in which case some other unique
     --  name is used.
     
     with System;
     package ada_main is
     
        Elab_Final_Code : Integer;
        pragma Import (C, Elab_Final_Code, "__gnat_inside_elab_final_code");
     
        --  The main program saves the parameters (argument count,
        --  argument values, environment pointer) in global variables
        --  for later access by other units including
        --  Ada.Command_Line.
     
        gnat_argc : Integer;
        gnat_argv : System.Address;
        gnat_envp : System.Address;
     
        --  The actual variables are stored in a library routine. This
        --  is useful for some shared library situations, where there
        --  are problems if variables are not in the library.
     
        pragma Import (C, gnat_argc);
        pragma Import (C, gnat_argv);
        pragma Import (C, gnat_envp);
     
        --  The exit status is similarly an external location
     
        gnat_exit_status : Integer;
        pragma Import (C, gnat_exit_status);
     
        GNAT_Version : constant String :=
                         "GNAT Version: 3.15w (20010315)";
        pragma Export (C, GNAT_Version, "__gnat_version");
     
        --  This is the generated adafinal routine that performs
        --  finalization at the end of execution. In the case where
        --  Ada is the main program, this main program makes a call
        --  to adafinal at program termination.
     
        procedure adafinal;
        pragma Export (C, adafinal, "adafinal");
     
        --  This is the generated adainit routine that performs
        --  initialization at the start of execution. In the case
        --  where Ada is the main program, this main program makes
        --  a call to adainit at program startup.
     
        procedure adainit;
        pragma Export (C, adainit, "adainit");
     
        --  This routine is called at the start of execution. It is
        --  a dummy routine that is used by the debugger to breakpoint
        --  at the start of execution.
     
        procedure Break_Start;
        pragma Import (C, Break_Start, "__gnat_break_start");
     
        --  This is the actual generated main program (it would be
        --  suppressed if the no main program qualifier were used). As
        --  required by standard system conventions, this program has
        --  the external name main.
     
        function main
          (argc : Integer;
           argv : System.Address;
           envp : System.Address)
           return Integer;
        pragma Export (C, main, "main");
     
        --  The following set of constants give the version
        --  identification values for every unit in the bound
        --  partition. This identification is computed from all
        --  dependent semantic units, and corresponds to the
        --  string that would be returned by use of the
        --  Body_Version or Version attributes.
     
        type Version_32 is mod 2 ** 32;
        u00001 : constant Version_32 := 16#7880BEB3#;
        u00002 : constant Version_32 := 16#0D24CBD0#;
        u00003 : constant Version_32 := 16#3283DBEB#;
        u00004 : constant Version_32 := 16#2359F9ED#;
        u00005 : constant Version_32 := 16#664FB847#;
        u00006 : constant Version_32 := 16#68E803DF#;
        u00007 : constant Version_32 := 16#5572E604#;
        u00008 : constant Version_32 := 16#46B173D8#;
        u00009 : constant Version_32 := 16#156A40CF#;
        u00010 : constant Version_32 := 16#033DABE0#;
        u00011 : constant Version_32 := 16#6AB38FEA#;
        u00012 : constant Version_32 := 16#22B6217D#;
        u00013 : constant Version_32 := 16#68A22947#;
        u00014 : constant Version_32 := 16#18CC4A56#;
        u00015 : constant Version_32 := 16#08258E1B#;
        u00016 : constant Version_32 := 16#367D5222#;
        u00017 : constant Version_32 := 16#20C9ECA4#;
        u00018 : constant Version_32 := 16#50D32CB6#;
        u00019 : constant Version_32 := 16#39A8BB77#;
        u00020 : constant Version_32 := 16#5CF8FA2B#;
        u00021 : constant Version_32 := 16#2F1EB794#;
        u00022 : constant Version_32 := 16#31AB6444#;
        u00023 : constant Version_32 := 16#1574B6E9#;
        u00024 : constant Version_32 := 16#5109C189#;
        u00025 : constant Version_32 := 16#56D770CD#;
        u00026 : constant Version_32 := 16#02F9DE3D#;
        u00027 : constant Version_32 := 16#08AB6B2C#;
        u00028 : constant Version_32 := 16#3FA37670#;
        u00029 : constant Version_32 := 16#476457A0#;
        u00030 : constant Version_32 := 16#731E1B6E#;
        u00031 : constant Version_32 := 16#23C2E789#;
        u00032 : constant Version_32 := 16#0F1BD6A1#;
        u00033 : constant Version_32 := 16#7C25DE96#;
        u00034 : constant Version_32 := 16#39ADFFA2#;
        u00035 : constant Version_32 := 16#571DE3E7#;
        u00036 : constant Version_32 := 16#5EB646AB#;
        u00037 : constant Version_32 := 16#4249379B#;
        u00038 : constant Version_32 := 16#0357E00A#;
        u00039 : constant Version_32 := 16#3784FB72#;
        u00040 : constant Version_32 := 16#2E723019#;
        u00041 : constant Version_32 := 16#623358EA#;
        u00042 : constant Version_32 := 16#107F9465#;
        u00043 : constant Version_32 := 16#6843F68A#;
        u00044 : constant Version_32 := 16#63305874#;
        u00045 : constant Version_32 := 16#31E56CE1#;
        u00046 : constant Version_32 := 16#02917970#;
        u00047 : constant Version_32 := 16#6CCBA70E#;
        u00048 : constant Version_32 := 16#41CD4204#;
        u00049 : constant Version_32 := 16#572E3F58#;
        u00050 : constant Version_32 := 16#20729FF5#;
        u00051 : constant Version_32 := 16#1D4F93E8#;
        u00052 : constant Version_32 := 16#30B2EC3D#;
        u00053 : constant Version_32 := 16#34054F96#;
        u00054 : constant Version_32 := 16#5A199860#;
        u00055 : constant Version_32 := 16#0E7F912B#;
        u00056 : constant Version_32 := 16#5760634A#;
        u00057 : constant Version_32 := 16#5D851835#;
     
        --  The following Export pragmas export the version numbers
        --  with symbolic names ending in B (for body) or S
        --  (for spec) so that they can be located in a link. The
        --  information provided here is sufficient to track down
        --  the exact versions of units used in a given build.
     
        pragma Export (C, u00001, "helloB");
        pragma Export (C, u00002, "system__standard_libraryB");
        pragma Export (C, u00003, "system__standard_libraryS");
        pragma Export (C, u00004, "adaS");
        pragma Export (C, u00005, "ada__text_ioB");
        pragma Export (C, u00006, "ada__text_ioS");
        pragma Export (C, u00007, "ada__exceptionsB");
        pragma Export (C, u00008, "ada__exceptionsS");
        pragma Export (C, u00009, "gnatS");
        pragma Export (C, u00010, "gnat__heap_sort_aB");
        pragma Export (C, u00011, "gnat__heap_sort_aS");
        pragma Export (C, u00012, "systemS");
        pragma Export (C, u00013, "system__exception_tableB");
        pragma Export (C, u00014, "system__exception_tableS");
        pragma Export (C, u00015, "gnat__htableB");
        pragma Export (C, u00016, "gnat__htableS");
        pragma Export (C, u00017, "system__exceptionsS");
        pragma Export (C, u00018, "system__machine_state_operationsB");
        pragma Export (C, u00019, "system__machine_state_operationsS");
        pragma Export (C, u00020, "system__machine_codeS");
        pragma Export (C, u00021, "system__storage_elementsB");
        pragma Export (C, u00022, "system__storage_elementsS");
        pragma Export (C, u00023, "system__secondary_stackB");
        pragma Export (C, u00024, "system__secondary_stackS");
        pragma Export (C, u00025, "system__parametersB");
        pragma Export (C, u00026, "system__parametersS");
        pragma Export (C, u00027, "system__soft_linksB");
        pragma Export (C, u00028, "system__soft_linksS");
        pragma Export (C, u00029, "system__stack_checkingB");
        pragma Export (C, u00030, "system__stack_checkingS");
        pragma Export (C, u00031, "system__tracebackB");
        pragma Export (C, u00032, "system__tracebackS");
        pragma Export (C, u00033, "ada__streamsS");
        pragma Export (C, u00034, "ada__tagsB");
        pragma Export (C, u00035, "ada__tagsS");
        pragma Export (C, u00036, "system__string_opsB");
        pragma Export (C, u00037, "system__string_opsS");
        pragma Export (C, u00038, "interfacesS");
        pragma Export (C, u00039, "interfaces__c_streamsB");
        pragma Export (C, u00040, "interfaces__c_streamsS");
        pragma Export (C, u00041, "system__file_ioB");
        pragma Export (C, u00042, "system__file_ioS");
        pragma Export (C, u00043, "ada__finalizationB");
        pragma Export (C, u00044, "ada__finalizationS");
        pragma Export (C, u00045, "system__finalization_rootB");
        pragma Export (C, u00046, "system__finalization_rootS");
        pragma Export (C, u00047, "system__finalization_implementationB");
        pragma Export (C, u00048, "system__finalization_implementationS");
        pragma Export (C, u00049, "system__string_ops_concat_3B");
        pragma Export (C, u00050, "system__string_ops_concat_3S");
        pragma Export (C, u00051, "system__stream_attributesB");
        pragma Export (C, u00052, "system__stream_attributesS");
        pragma Export (C, u00053, "ada__io_exceptionsS");
        pragma Export (C, u00054, "system__unsigned_typesS");
        pragma Export (C, u00055, "system__file_control_blockS");
        pragma Export (C, u00056, "ada__finalization__list_controllerB");
        pragma Export (C, u00057, "ada__finalization__list_controllerS");
     
        -- BEGIN ELABORATION ORDER
        -- ada (spec)
        -- gnat (spec)
        -- gnat.heap_sort_a (spec)
        -- gnat.heap_sort_a (body)
        -- gnat.htable (spec)
        -- gnat.htable (body)
        -- interfaces (spec)
        -- system (spec)
        -- system.machine_code (spec)
        -- system.parameters (spec)
        -- system.parameters (body)
        -- interfaces.c_streams (spec)
        -- interfaces.c_streams (body)
        -- system.standard_library (spec)
        -- ada.exceptions (spec)
        -- system.exception_table (spec)
        -- system.exception_table (body)
        -- ada.io_exceptions (spec)
        -- system.exceptions (spec)
        -- system.storage_elements (spec)
        -- system.storage_elements (body)
        -- system.machine_state_operations (spec)
        -- system.machine_state_operations (body)
        -- system.secondary_stack (spec)
        -- system.stack_checking (spec)
        -- system.soft_links (spec)
        -- system.soft_links (body)
        -- system.stack_checking (body)
        -- system.secondary_stack (body)
        -- system.standard_library (body)
        -- system.string_ops (spec)
        -- system.string_ops (body)
        -- ada.tags (spec)
        -- ada.tags (body)
        -- ada.streams (spec)
        -- system.finalization_root (spec)
        -- system.finalization_root (body)
        -- system.string_ops_concat_3 (spec)
        -- system.string_ops_concat_3 (body)
        -- system.traceback (spec)
        -- system.traceback (body)
        -- ada.exceptions (body)
        -- system.unsigned_types (spec)
        -- system.stream_attributes (spec)
        -- system.stream_attributes (body)
        -- system.finalization_implementation (spec)
        -- system.finalization_implementation (body)
        -- ada.finalization (spec)
        -- ada.finalization (body)
        -- ada.finalization.list_controller (spec)
        -- ada.finalization.list_controller (body)
        -- system.file_control_block (spec)
        -- system.file_io (spec)
        -- system.file_io (body)
        -- ada.text_io (spec)
        -- ada.text_io (body)
        -- hello (body)
        -- END ELABORATION ORDER
     
     end ada_main;
     
     --  The following source file name pragmas allow the generated file
     --  names to be unique for different main programs. They are needed
     --  since the package name will always be Ada_Main.
     
     pragma Source_File_Name (ada_main, Spec_File_Name => "B~HELLO.ADS");
     pragma Source_File_Name (ada_main, Body_File_Name => "B~HELLO.ADB");
     
     --  Generated package body for Ada_Main starts here
     
     package body ada_main is
     
        --  The actual finalization is performed by calling the
        --  library routine in System.Standard_Library.Adafinal
     
        procedure Do_Finalize;
        pragma Import (C, Do_Finalize, "system__standard_library__adafinal");
     
        -------------
        -- adainit --
        -------------
     
        procedure adainit is
     
           --  These booleans are set to True once the associated unit has
           --  been elaborated. It is also used to avoid elaborating the
           --  same unit twice.
     
           E040 : Boolean; pragma Import (Ada, E040, "interfaces__c_streams_E");
           E008 : Boolean; pragma Import (Ada, E008, "ada__exceptions_E");
           E014 : Boolean; pragma Import (Ada, E014, "system__exception_table_E");
           E053 : Boolean; pragma Import (Ada, E053, "ada__io_exceptions_E");
           E017 : Boolean; pragma Import (Ada, E017, "system__exceptions_E");
           E024 : Boolean; pragma Import (Ada, E024, "system__secondary_stack_E");
           E030 : Boolean; pragma Import (Ada, E030, "system__stack_checking_E");
           E028 : Boolean; pragma Import (Ada, E028, "system__soft_links_E");
           E035 : Boolean; pragma Import (Ada, E035, "ada__tags_E");
           E033 : Boolean; pragma Import (Ada, E033, "ada__streams_E");
           E046 : Boolean; pragma Import (Ada, E046, "system__finalization_root_E");
           E048 : Boolean; pragma Import (Ada, E048, "system__finalization_implementation_E");
           E044 : Boolean; pragma Import (Ada, E044, "ada__finalization_E");
           E057 : Boolean; pragma Import (Ada, E057, "ada__finalization__list_controller_E");
           E055 : Boolean; pragma Import (Ada, E055, "system__file_control_block_E");
           E042 : Boolean; pragma Import (Ada, E042, "system__file_io_E");
           E006 : Boolean; pragma Import (Ada, E006, "ada__text_io_E");
     
           --  Set_Globals is a library routine that stores away the
           --  value of the indicated set of global values in global
           --  variables within the library.
     
           procedure Set_Globals
             (Main_Priority            : Integer;
              Time_Slice_Value         : Integer;
              WC_Encoding              : Character;
              Locking_Policy           : Character;
              Queuing_Policy           : Character;
              Task_Dispatching_Policy  : Character;
              Adafinal                 : System.Address;
              Unreserve_All_Interrupts : Integer;
              Exception_Tracebacks     : Integer);
           pragma Import (C, Set_Globals, "__gnat_set_globals");
     
           --  SDP_Table_Build is a library routine used to build the
           --  exception tables. See unit Ada.Exceptions in files
           --  A-EXCEPT.ADS/adb for full details of how zero cost
           --  exception handling works. This procedure, the call to
           --  it, and the two following tables are all omitted if the
           --  build is in longjmp/setjump exception mode.
     
           procedure SDP_Table_Build
             (SDP_Addresses   : System.Address;
              SDP_Count       : Natural;
              Elab_Addresses  : System.Address;
              Elab_Addr_Count : Natural);
           pragma Import (C, SDP_Table_Build, "__gnat_SDP_Table_Build");
     
           --  Table of Unit_Exception_Table addresses. Used for zero
           --  cost exception handling to build the top level table.
     
           ST : aliased constant array (1 .. 23) of System.Address := (
             Hello'UET_Address,
             Ada.Text_Io'UET_Address,
             Ada.Exceptions'UET_Address,
             Gnat.Heap_Sort_A'UET_Address,
             System.Exception_Table'UET_Address,
             System.Machine_State_Operations'UET_Address,
             System.Secondary_Stack'UET_Address,
             System.Parameters'UET_Address,
             System.Soft_Links'UET_Address,
             System.Stack_Checking'UET_Address,
             System.Traceback'UET_Address,
             Ada.Streams'UET_Address,
             Ada.Tags'UET_Address,
             System.String_Ops'UET_Address,
             Interfaces.C_Streams'UET_Address,
             System.File_Io'UET_Address,
             Ada.Finalization'UET_Address,
             System.Finalization_Root'UET_Address,
             System.Finalization_Implementation'UET_Address,
             System.String_Ops_Concat_3'UET_Address,
             System.Stream_Attributes'UET_Address,
             System.File_Control_Block'UET_Address,
             Ada.Finalization.List_Controller'UET_Address);
     
           --  Table of addresses of elaboration routines. Used for
           --  zero cost exception handling to make sure these
           --  addresses are included in the top level procedure
           --  address table.
     
           EA : aliased constant array (1 .. 23) of System.Address := (
             adainit'Code_Address,
             Do_Finalize'Code_Address,
             Ada.Exceptions'Elab_Spec'Address,
             System.Exceptions'Elab_Spec'Address,
             Interfaces.C_Streams'Elab_Spec'Address,
             System.Exception_Table'Elab_Body'Address,
             Ada.Io_Exceptions'Elab_Spec'Address,
             System.Stack_Checking'Elab_Spec'Address,
             System.Soft_Links'Elab_Body'Address,
             System.Secondary_Stack'Elab_Body'Address,
             Ada.Tags'Elab_Spec'Address,
             Ada.Tags'Elab_Body'Address,
             Ada.Streams'Elab_Spec'Address,
             System.Finalization_Root'Elab_Spec'Address,
             Ada.Exceptions'Elab_Body'Address,
             System.Finalization_Implementation'Elab_Spec'Address,
             System.Finalization_Implementation'Elab_Body'Address,
             Ada.Finalization'Elab_Spec'Address,
             Ada.Finalization.List_Controller'Elab_Spec'Address,
             System.File_Control_Block'Elab_Spec'Address,
             System.File_Io'Elab_Body'Address,
             Ada.Text_Io'Elab_Spec'Address,
             Ada.Text_Io'Elab_Body'Address);
     
        --  Start of processing for adainit
     
        begin
     
           --  Call SDP_Table_Build to build the top level procedure
           --  table for zero cost exception handling (omitted in
           --  longjmp/setjump mode).
     
           SDP_Table_Build (ST'Address, 23, EA'Address, 23);
     
           --  Call Set_Globals to record various information for
           --  this partition.  The values are derived by the binder
           --  from information stored in the ali files by the compiler.
     
           Set_Globals
             (Main_Priority            => -1,
              --  Priority of main program, -1 if no pragma Priority used
     
              Time_Slice_Value         => -1,
              --  Time slice from Time_Slice pragma, -1 if none used
     
              WC_Encoding              => 'b',
              --  Wide_Character encoding used, default is brackets
     
              Locking_Policy           => ' ',
              --  Locking_Policy used, default of space means not
              --  specified, otherwise it is the first character of
              --  the policy name.
     
              Queuing_Policy           => ' ',
              --  Queuing_Policy used, default of space means not
              --  specified, otherwise it is the first character of
              --  the policy name.
     
              Task_Dispatching_Policy  => ' ',
              --  Task_Dispatching_Policy used, default of space means
              --  not specified, otherwise first character of the
              --  policy name.
     
              Adafinal                 => System.Null_Address,
              --  Address of Adafinal routine, not used anymore
     
              Unreserve_All_Interrupts => 0,
              --  Set true if pragma Unreserve_All_Interrupts was used
     
              Exception_Tracebacks     => 0);
              --  Indicates if exception tracebacks are enabled
     
           Elab_Final_Code := 1;
     
           --  Now we have the elaboration calls for all units in the partition.
           --  The Elab_Spec and Elab_Body attributes generate references to the
           --  implicit elaboration procedures generated by the compiler for
           --  each unit that requires elaboration.
     
           if not E040 then
              Interfaces.C_Streams'Elab_Spec;
           end if;
           E040 := True;
           if not E008 then
              Ada.Exceptions'Elab_Spec;
           end if;
           if not E014 then
              System.Exception_Table'Elab_Body;
              E014 := True;
           end if;
           if not E053 then
              Ada.Io_Exceptions'Elab_Spec;
              E053 := True;
           end if;
           if not E017 then
              System.Exceptions'Elab_Spec;
              E017 := True;
           end if;
           if not E030 then
              System.Stack_Checking'Elab_Spec;
           end if;
           if not E028 then
              System.Soft_Links'Elab_Body;
              E028 := True;
           end if;
           E030 := True;
           if not E024 then
              System.Secondary_Stack'Elab_Body;
              E024 := True;
           end if;
           if not E035 then
              Ada.Tags'Elab_Spec;
           end if;
           if not E035 then
              Ada.Tags'Elab_Body;
              E035 := True;
           end if;
           if not E033 then
              Ada.Streams'Elab_Spec;
              E033 := True;
           end if;
           if not E046 then
              System.Finalization_Root'Elab_Spec;
           end if;
           E046 := True;
           if not E008 then
              Ada.Exceptions'Elab_Body;
              E008 := True;
           end if;
           if not E048 then
              System.Finalization_Implementation'Elab_Spec;
           end if;
           if not E048 then
              System.Finalization_Implementation'Elab_Body;
              E048 := True;
           end if;
           if not E044 then
              Ada.Finalization'Elab_Spec;
           end if;
           E044 := True;
           if not E057 then
              Ada.Finalization.List_Controller'Elab_Spec;
           end if;
           E057 := True;
           if not E055 then
              System.File_Control_Block'Elab_Spec;
              E055 := True;
           end if;
           if not E042 then
              System.File_Io'Elab_Body;
              E042 := True;
           end if;
           if not E006 then
              Ada.Text_Io'Elab_Spec;
           end if;
           if not E006 then
              Ada.Text_Io'Elab_Body;
              E006 := True;
           end if;
     
           Elab_Final_Code := 0;
        end adainit;
     
        --------------
        -- adafinal --
        --------------
     
        procedure adafinal is
        begin
           Do_Finalize;
        end adafinal;
     
        ----------
        -- main --
        ----------
     
        --  main is actually a function, as in the ANSI C standard,
        --  defined to return the exit status. The three parameters
        --  are the argument count, argument values and environment
        --  pointer.
     
        function main
          (argc : Integer;
           argv : System.Address;
           envp : System.Address)
           return Integer
        is
           --  The initialize routine performs low level system
           --  initialization using a standard library routine which
           --  sets up signal handling and performs any other
           --  required setup. The routine can be found in file
           --  A-INIT.C.
     
           procedure initialize;
           pragma Import (C, initialize, "__gnat_initialize");
     
           --  The finalize routine performs low level system
           --  finalization using a standard library routine. The
           --  routine is found in file A-FINAL.C and in the standard
           --  distribution is a dummy routine that does nothing, so
           --  really this is a hook for special user finalization.
     
           procedure finalize;
           pragma Import (C, finalize, "__gnat_finalize");
     
           --  We get to the main program of the partition by using
           --  pragma Import because if we try to with the unit and
           --  call it Ada style, then not only do we waste time
           --  recompiling it, but also, we don't really know the right
           --  qualifiers (e.g. identifier character set) to be used
           --  to compile it.
     
           procedure Ada_Main_Program;
           pragma Import (Ada, Ada_Main_Program, "_ada_hello");
     
        --  Start of processing for main
     
        begin
           --  Save global variables
     
           gnat_argc := argc;
           gnat_argv := argv;
           gnat_envp := envp;
     
           --  Call low level system initialization
     
           Initialize;
     
           --  Call our generated Ada initialization routine
     
           adainit;
     
           --  This is the point at which we want the debugger to get
           --  control
     
           Break_Start;
     
           --  Now we call the main program of the partition
     
           Ada_Main_Program;
     
           --  Perform Ada finalization
     
           adafinal;
     
           --  Perform low level system finalization
     
           Finalize;
     
           --  Return the proper exit status
           return (gnat_exit_status);
        end;
     
     --  This section is entirely comments, so it has no effect on the
     --  compilation of the Ada_Main package. It provides the list of
     --  object files and linker options, as well as some standard
     --  libraries needed for the link. The GNAT LINK utility parses
     --  this B~HELLO.ADB file to read these comment lines to generate
     --  the appropriate command line arguments for the call to the
     --  system linker. The BEGIN/END lines are used for sentinels for
     --  this parsing operation.
     
     --  The exact file names will of course depend on the environment,
     --  host/target and location of files on the host system.
     
     -- BEGIN Object file/option list
        --   ./HELLO.OBJ
        --   -L./
        --   -L/usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/
        --   /usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/libgnat.a
     -- END Object file/option list
     
     end ada_main;

The Ada code in the above example is exactly what is generated by the
binder. We have added comments to more clearly indicate the function of
each part of the generated `Ada_Main' package.

   The code is standard Ada in all respects, and can be processed by any
tools that handle Ada. In particular, it is possible to use the debugger
in Ada mode to debug the generated Ada_Main package. For example,
suppose that for reasons that you do not understand, your program is
blowing up during elaboration of the body of `Ada.Text_IO'. To chase
this bug down, you can place a breakpoint on the call:

     Ada.Text_Io'Elab_Body;

and trace the elaboration routine for this package to find out where
the problem might be (more usually of course you would be debugging
elaboration code in your own application).


File: gnat_ug_vms.info,  Node: Generating the Binder Program in C,  Next: Consistency-Checking Modes,  Prev: Running GNAT BIND,  Up: Binding Using GNAT BIND

Generating the Binder Program in C
==================================

In most normal usage, the default mode of `GNAT BIND' which is to
generate the main package in Ada, as described in the previous section.
In particular, this means that any Ada programmer can read and
understand the generated main program. It can also be debugged just
like any other Ada code provided the `-g' qualifier is used for `GNAT
BIND' and `GNAT LINK'.

   However for some purposes it may be convenient to generate the main
program in C rather than Ada. This may for example be helpful when you
are generating a mixed language program with the main program in C. The
GNAT compiler itself is an example. The use of the `-C' qualifier for
both `GNAT BIND' and `GNAT LINK' will cause the program to be generated
in C (and compiled using the gnu C compiler). The following shows the C
code generated for the same "Hello World" program:


     #ifdef __STDC__
     #define PARAMS(paramlist) paramlist
     #else
     #define PARAMS(paramlist) ()
     #endif
     
     extern void __gnat_set_globals
      PARAMS ((int, int, int, int, int, int,
               void (*) PARAMS ((void)), int, int));
     extern void adafinal PARAMS ((void));
     extern void adainit PARAMS ((void));
     extern void system__standard_library__adafinal PARAMS ((void));
     extern int main PARAMS ((int, char **, char **));
     extern void exit PARAMS ((int));
     extern void __gnat_break_start PARAMS ((void));
     extern void _ada_hello PARAMS ((void));
     extern void __gnat_initialize PARAMS ((void));
     extern void __gnat_finalize PARAMS ((void));
     
     extern void ada__exceptions___elabs PARAMS ((void));
     extern void system__exceptions___elabs PARAMS ((void));
     extern void interfaces__c_streams___elabs PARAMS ((void));
     extern void system__exception_table___elabb PARAMS ((void));
     extern void ada__io_exceptions___elabs PARAMS ((void));
     extern void system__stack_checking___elabs PARAMS ((void));
     extern void system__soft_links___elabb PARAMS ((void));
     extern void system__secondary_stack___elabb PARAMS ((void));
     extern void ada__tags___elabs PARAMS ((void));
     extern void ada__tags___elabb PARAMS ((void));
     extern void ada__streams___elabs PARAMS ((void));
     extern void system__finalization_root___elabs PARAMS ((void));
     extern void ada__exceptions___elabb PARAMS ((void));
     extern void system__finalization_implementation___elabs PARAMS ((void));
     extern void system__finalization_implementation___elabb PARAMS ((void));
     extern void ada__finalization___elabs PARAMS ((void));
     extern void ada__finalization__list_controller___elabs PARAMS ((void));
     extern void system__file_control_block___elabs PARAMS ((void));
     extern void system__file_io___elabb PARAMS ((void));
     extern void ada__text_io___elabs PARAMS ((void));
     extern void ada__text_io___elabb PARAMS ((void));
     
     extern int __gnat_inside_elab_final_code;
     
     extern int gnat_argc;
     extern char **gnat_argv;
     extern char **gnat_envp;
     extern int gnat_exit_status;
     
     char __gnat_version[] = "GNAT Version: 3.15w (20010315)";
     void adafinal () {
        system__standard_library__adafinal ();
     }
     
     void adainit ()
     {
        extern char ada__exceptions_E;
        extern char system__exceptions_E;
        extern char interfaces__c_streams_E;
        extern char system__exception_table_E;
        extern char ada__io_exceptions_E;
        extern char system__secondary_stack_E;
        extern char system__stack_checking_E;
        extern char system__soft_links_E;
        extern char ada__tags_E;
        extern char ada__streams_E;
        extern char system__finalization_root_E;
        extern char system__finalization_implementation_E;
        extern char ada__finalization_E;
        extern char ada__finalization__list_controller_E;
        extern char system__file_control_block_E;
        extern char system__file_io_E;
        extern char ada__text_io_E;
     
        extern void *__gnat_hello__SDP;
        extern void *__gnat_ada__text_io__SDP;
        extern void *__gnat_ada__exceptions__SDP;
        extern void *__gnat_gnat__heap_sort_a__SDP;
        extern void *__gnat_system__exception_table__SDP;
        extern void *__gnat_system__machine_state_operations__SDP;
        extern void *__gnat_system__secondary_stack__SDP;
        extern void *__gnat_system__parameters__SDP;
        extern void *__gnat_system__soft_links__SDP;
        extern void *__gnat_system__stack_checking__SDP;
        extern void *__gnat_system__traceback__SDP;
        extern void *__gnat_ada__streams__SDP;
        extern void *__gnat_ada__tags__SDP;
        extern void *__gnat_system__string_ops__SDP;
        extern void *__gnat_interfaces__c_streams__SDP;
        extern void *__gnat_system__file_io__SDP;
        extern void *__gnat_ada__finalization__SDP;
        extern void *__gnat_system__finalization_root__SDP;
        extern void *__gnat_system__finalization_implementation__SDP;
        extern void *__gnat_system__string_ops_concat_3__SDP;
        extern void *__gnat_system__stream_attributes__SDP;
        extern void *__gnat_system__file_control_block__SDP;
        extern void *__gnat_ada__finalization__list_controller__SDP;
     
        void **st[23] = {
          &__gnat_hello__SDP,
          &__gnat_ada__text_io__SDP,
          &__gnat_ada__exceptions__SDP,
          &__gnat_gnat__heap_sort_a__SDP,
          &__gnat_system__exception_table__SDP,
          &__gnat_system__machine_state_operations__SDP,
          &__gnat_system__secondary_stack__SDP,
          &__gnat_system__parameters__SDP,
          &__gnat_system__soft_links__SDP,
          &__gnat_system__stack_checking__SDP,
          &__gnat_system__traceback__SDP,
          &__gnat_ada__streams__SDP,
          &__gnat_ada__tags__SDP,
          &__gnat_system__string_ops__SDP,
          &__gnat_interfaces__c_streams__SDP,
          &__gnat_system__file_io__SDP,
          &__gnat_ada__finalization__SDP,
          &__gnat_system__finalization_root__SDP,
          &__gnat_system__finalization_implementation__SDP,
          &__gnat_system__string_ops_concat_3__SDP,
          &__gnat_system__stream_attributes__SDP,
          &__gnat_system__file_control_block__SDP,
          &__gnat_ada__finalization__list_controller__SDP};
     
        extern void ada__exceptions___elabs ();
        extern void system__exceptions___elabs ();
        extern void interfaces__c_streams___elabs ();
        extern void system__exception_table___elabb ();
        extern void ada__io_exceptions___elabs ();
        extern void system__stack_checking___elabs ();
        extern void system__soft_links___elabb ();
        extern void system__secondary_stack___elabb ();
        extern void ada__tags___elabs ();
        extern void ada__tags___elabb ();
        extern void ada__streams___elabs ();
        extern void system__finalization_root___elabs ();
        extern void ada__exceptions___elabb ();
        extern void system__finalization_implementation___elabs ();
        extern void system__finalization_implementation___elabb ();
        extern void ada__finalization___elabs ();
        extern void ada__finalization__list_controller___elabs ();
        extern void system__file_control_block___elabs ();
        extern void system__file_io___elabb ();
        extern void ada__text_io___elabs ();
        extern void ada__text_io___elabb ();
     
        void (*ea[23]) () = {
          adainit,
          system__standard_library__adafinal,
          ada__exceptions___elabs,
          system__exceptions___elabs,
          interfaces__c_streams___elabs,
          system__exception_table___elabb,
          ada__io_exceptions___elabs,
          system__stack_checking___elabs,
          system__soft_links___elabb,
          system__secondary_stack___elabb,
          ada__tags___elabs,
          ada__tags___elabb,
          ada__streams___elabs,
          system__finalization_root___elabs,
          ada__exceptions___elabb,
          system__finalization_implementation___elabs,
          system__finalization_implementation___elabb,
          ada__finalization___elabs,
          ada__finalization__list_controller___elabs,
          system__file_control_block___elabs,
          system__file_io___elabb,
          ada__text_io___elabs,
          ada__text_io___elabb};
     
        __gnat_SDP_Table_Build (&st, 23, ea, 23);
        __gnat_set_globals (
           -1,      /* Main_Priority              */
           -1,      /* Time_Slice_Value           */
           'b',     /* WC_Encoding                */
           ' ',     /* Locking_Policy             */
           ' ',     /* Queuing_Policy             */
           ' ',     /* Tasking_Dispatching_Policy */
           0,       /* Finalization routine address, not used anymore */
           0,       /* Unreserve_All_Interrupts */
           0);      /* Exception_Tracebacks */
     
        __gnat_inside_elab_final_code = 1;
     
        if (ada__exceptions_E == 0) {
           ada__exceptions___elabs ();
        }
        if (system__exceptions_E == 0) {
           system__exceptions___elabs ();
           system__exceptions_E++;
        }
        if (interfaces__c_streams_E == 0) {
           interfaces__c_streams___elabs ();
        }
        interfaces__c_streams_E = 1;
        if (system__exception_table_E == 0) {
           system__exception_table___elabb ();
           system__exception_table_E++;
        }
        if (ada__io_exceptions_E == 0) {
           ada__io_exceptions___elabs ();
           ada__io_exceptions_E++;
        }
        if (system__stack_checking_E == 0) {
           system__stack_checking___elabs ();
        }
        if (system__soft_links_E == 0) {
           system__soft_links___elabb ();
           system__soft_links_E++;
        }
        system__stack_checking_E = 1;
        if (system__secondary_stack_E == 0) {
           system__secondary_stack___elabb ();
           system__secondary_stack_E++;
        }
        if (ada__tags_E == 0) {
           ada__tags___elabs ();
        }
        if (ada__tags_E == 0) {
           ada__tags___elabb ();
           ada__tags_E++;
        }
        if (ada__streams_E == 0) {
           ada__streams___elabs ();
           ada__streams_E++;
        }
        if (system__finalization_root_E == 0) {
           system__finalization_root___elabs ();
        }
        system__finalization_root_E = 1;
        if (ada__exceptions_E == 0) {
           ada__exceptions___elabb ();
           ada__exceptions_E++;
        }
        if (system__finalization_implementation_E == 0) {
           system__finalization_implementation___elabs ();
        }
        if (system__finalization_implementation_E == 0) {
           system__finalization_implementation___elabb ();
           system__finalization_implementation_E++;
        }
        if (ada__finalization_E == 0) {
           ada__finalization___elabs ();
        }
        ada__finalization_E = 1;
        if (ada__finalization__list_controller_E == 0) {
           ada__finalization__list_controller___elabs ();
        }
        ada__finalization__list_controller_E = 1;
        if (system__file_control_block_E == 0) {
           system__file_control_block___elabs ();
           system__file_control_block_E++;
        }
        if (system__file_io_E == 0) {
           system__file_io___elabb ();
           system__file_io_E++;
        }
        if (ada__text_io_E == 0) {
           ada__text_io___elabs ();
        }
        if (ada__text_io_E == 0) {
           ada__text_io___elabb ();
           ada__text_io_E++;
        }
     
        __gnat_inside_elab_final_code = 0;
     }
     int main (argc, argv, envp)
         int argc;
         char **argv;
         char **envp;
     {
        gnat_argc = argc;
        gnat_argv = argv;
        gnat_envp = envp;
     
        __gnat_initialize ();
        adainit ();
        __gnat_break_start ();
     
        _ada_hello ();
     
        system__standard_library__adafinal ();
        __gnat_finalize ();
        exit (gnat_exit_status);
     }
     unsigned helloB = 0x7880BEB3;
     unsigned system__standard_libraryB = 0x0D24CBD0;
     unsigned system__standard_libraryS = 0x3283DBEB;
     unsigned adaS = 0x2359F9ED;
     unsigned ada__text_ioB = 0x47C85FC4;
     unsigned ada__text_ioS = 0x496FE45C;
     unsigned ada__exceptionsB = 0x74F50187;
     unsigned ada__exceptionsS = 0x6736945B;
     unsigned gnatS = 0x156A40CF;
     unsigned gnat__heap_sort_aB = 0x033DABE0;
     unsigned gnat__heap_sort_aS = 0x6AB38FEA;
     unsigned systemS = 0x0331C6FE;
     unsigned system__exceptionsS = 0x20C9ECA4;
     unsigned system__exception_tableB = 0x68A22947;
     unsigned system__exception_tableS = 0x394BADD5;
     unsigned gnat__htableB = 0x08258E1B;
     unsigned gnat__htableS = 0x367D5222;
     unsigned system__machine_state_operationsB = 0x4F3B7492;
     unsigned system__machine_state_operationsS = 0x182F5CF4;
     unsigned system__storage_elementsB = 0x2F1EB794;
     unsigned system__storage_elementsS = 0x102C83C7;
     unsigned system__secondary_stackB = 0x1574B6E9;
     unsigned system__secondary_stackS = 0x708E260A;
     unsigned system__parametersB = 0x56D770CD;
     unsigned system__parametersS = 0x237E39BE;
     unsigned system__soft_linksB = 0x08AB6B2C;
     unsigned system__soft_linksS = 0x1E2491F3;
     unsigned system__stack_checkingB = 0x476457A0;
     unsigned system__stack_checkingS = 0x5299FCED;
     unsigned system__tracebackB = 0x2971EBDE;
     unsigned system__tracebackS = 0x2E9C3122;
     unsigned ada__streamsS = 0x7C25DE96;
     unsigned ada__tagsB = 0x39ADFFA2;
     unsigned ada__tagsS = 0x769A0464;
     unsigned system__string_opsB = 0x5EB646AB;
     unsigned system__string_opsS = 0x63CED018;
     unsigned interfacesS = 0x0357E00A;
     unsigned interfaces__c_streamsB = 0x3784FB72;
     unsigned interfaces__c_streamsS = 0x2E723019;
     unsigned system__file_ioB = 0x623358EA;
     unsigned system__file_ioS = 0x31F873E6;
     unsigned ada__finalizationB = 0x6843F68A;
     unsigned ada__finalizationS = 0x63305874;
     unsigned system__finalization_rootB = 0x31E56CE1;
     unsigned system__finalization_rootS = 0x23169EF3;
     unsigned system__finalization_implementationB = 0x6CCBA70E;
     unsigned system__finalization_implementationS = 0x604AA587;
     unsigned system__string_ops_concat_3B = 0x572E3F58;
     unsigned system__string_ops_concat_3S = 0x01F57876;
     unsigned system__stream_attributesB = 0x1D4F93E8;
     unsigned system__stream_attributesS = 0x30B2EC3D;
     unsigned ada__io_exceptionsS = 0x34054F96;
     unsigned system__unsigned_typesS = 0x7B9E7FE3;
     unsigned system__file_control_blockS = 0x2FF876A8;
     unsigned ada__finalization__list_controllerB = 0x5760634A;
     unsigned ada__finalization__list_controllerS = 0x5D851835;
     
     /* BEGIN ELABORATION ORDER
     ada (spec)
     gnat (spec)
     gnat.heap_sort_a (spec)
     gnat.htable (spec)
     gnat.htable (body)
     interfaces (spec)
     system (spec)
     system.parameters (spec)
     system.standard_library (spec)
     ada.exceptions (spec)
     system.exceptions (spec)
     system.parameters (body)
     gnat.heap_sort_a (body)
     interfaces.c_streams (spec)
     interfaces.c_streams (body)
     system.exception_table (spec)
     system.exception_table (body)
     ada.io_exceptions (spec)
     system.storage_elements (spec)
     system.storage_elements (body)
     system.machine_state_operations (spec)
     system.machine_state_operations (body)
     system.secondary_stack (spec)
     system.stack_checking (spec)
     system.soft_links (spec)
     system.soft_links (body)
     system.stack_checking (body)
     system.secondary_stack (body)
     system.standard_library (body)
     system.string_ops (spec)
     system.string_ops (body)
     ada.tags (spec)
     ada.tags (body)
     ada.streams (spec)
     system.finalization_root (spec)
     system.finalization_root (body)
     system.string_ops_concat_3 (spec)
     system.string_ops_concat_3 (body)
     system.traceback (spec)
     system.traceback (body)
     ada.exceptions (body)
     system.unsigned_types (spec)
     system.stream_attributes (spec)
     system.stream_attributes (body)
     system.finalization_implementation (spec)
     system.finalization_implementation (body)
     ada.finalization (spec)
     ada.finalization (body)
     ada.finalization.list_controller (spec)
     ada.finalization.list_controller (body)
     system.file_control_block (spec)
     system.file_io (spec)
     system.file_io (body)
     ada.text_io (spec)
     ada.text_io (body)
     hello (body)
        END ELABORATION ORDER */
     
     /* BEGIN Object file/option list
     ./HELLO.OBJ
     -L./
     -L/usr/local/gnat/lib/gcc-lib/alpha-dec-osf5.1/2.8.1/adalib/
     /usr/local/gnat/lib/gcc-lib/alpha-dec-osf5.1/2.8.1/adalib/libgnat.a
     -lexc
        END Object file/option list */

Here again, the C code is exactly what is generated by the binder. The
functions of the various parts of this code correspond in an obvious
manner with the commented Ada code shown in the example in the previous
section.


File: gnat_ug_vms.info,  Node: Consistency-Checking Modes,  Next: Binder Error Message Control,  Prev: Generating the Binder Program in C,  Up: Binding Using GNAT BIND

Consistency-Checking Modes
==========================

As described in the previous section, by default `GNAT BIND' checks
that object files are consistent with one another and are consistent
with any source files it can locate. The following qualifiers control
binder access to sources.

`/READ_SOURCES=ALL'
     Require source files to be present. In this mode, the binder must
     be able to locate all source files that are referenced, in order
     to check their consistency. In normal mode, if a source file
     cannot be located it is simply ignored. If you specify this
     qualifier, a missing source file is an error.

`/READ_SOURCES=NONE'
     Exclude source files. In this mode, the binder only checks that ALI
     files are consistent with one another. Source files are not
     accessed.  The binder runs faster in this mode, and there is still
     a guarantee that the resulting program is self-consistent.  If a
     source file has been edited since it was last compiled, and you
     specify this qualifier, the binder will not detect that the object
     file is out of date with respect to the source file. Note that
     this is the mode that is automatically used by `GNAT MAKE' because
     in this case the checking against sources has already been
     performed by `GNAT MAKE' in the course of compilation (i.e. before
     binding).

`/READ_SOURCES=AVAILABLE'
     This is the default mode in which source files are checked if they
     are available, and ignored if they are not available.


File: gnat_ug_vms.info,  Node: Binder Error Message Control,  Next: Elaboration Control,  Prev: Consistency-Checking Modes,  Up: Binding Using GNAT BIND

Binder Error Message Control
============================

The following qualifiers provide control over the generation of error
messages from the binder:

`/REPORT_ERRORS=VERBOSE'
     Verbose mode. In the normal mode, brief error messages are
     generated to `SYS$ERROR'. If this qualifier is present, a header
     is written to `SYS$OUTPUT' and any error messages are directed to
     `SYS$OUTPUT'.  All that is written to `SYS$ERROR' is a brief
     summary message.

`/REPORT_ERRORS=BRIEF'
     Generate brief error messages to `SYS$ERROR' even if verbose mode
     is specified. This is relevant only when used with the
     `/REPORT_ERRORS=VERBOSE' qualifier.

`/WARNINGS=SUPPRESS'
     Suppress all warning messages.

`/WARNINGS=ERROR'
     Treat any warning messages as fatal errors.

`/WARNINGS=NORMAL'
     Standard mode with warnings generated, but warnings do not get
     treated as errors.

`/NOTIME_STAMP_CHECK'
     The binder performs a number of consistency checks including:

        * Check that time stamps of a given source unit are consistent

        * Check that checksums of a given source unit are consistent

        * Check that consistent versions of `GNAT' were used for
          compilation

        * Check consistency of configuration pragmas as required

     Normally failure of such checks, in accordance with the consistency
     requirements of the Ada Reference Manual, causes error messages to
     be generated which abort the binder and prevent the output of a
     binder file and subsequent link to obtain an executable.

     The `/NOTIME_STAMP_CHECK' qualifier converts these error messages
     into warnings, so that binding and linking can continue to
     completion even in the presence of such errors. The result may be
     a failed link (due to missing symbols), or a non-functional
     executable which has undefined semantics.  _This means that
     `/NOTIME_STAMP_CHECK' should be used only in unusual situations,
     with extreme care._


File: gnat_ug_vms.info,  Node: Elaboration Control,  Next: Output Control,  Prev: Binder Error Message Control,  Up: Binding Using GNAT BIND

Elaboration Control
===================

The following qualifiers provide additional control over the elaboration
order. For full details see *Note Elaboration Order Handling in GNAT::.

`/PESSIMISTIC_ELABORATION'
     Normally the binder attempts to choose an elaboration order that is
     likely to minimize the likelihood of an elaboration order error
     resulting in raising a `Program_Error' exception. This qualifier
     reverses the action of the binder, and requests that it
     deliberately choose an order that is likely to maximize the
     likelihood of an elaboration error.  This is useful in ensuring
     portability and avoiding dependence on accidental fortuitous
     elaboration ordering.

     Normally it only makes sense to use the `-p' qualifier if dynamic
     elaboration checking is used (`/CHECKS=ELABORATION' qualifier used
     for compilation).  This is because in the default static
     elaboration mode, all necessary `Elaborate_All' pragmas are
     implicitly inserted. These implicit pragmas are still respected by
     the binder in `-p' mode, so a safe elaboration order is assured.


File: gnat_ug_vms.info,  Node: Output Control,  Next: Binding with Non-Ada Main Programs,  Prev: Elaboration Control,  Up: Binding Using GNAT BIND

Output Control
==============

The following qualifiers allow additional control over the output
generated by the binder.

`/BIND_FILE=ADA'
     Generate binder program in Ada (default). The binder program is
     named `B$MAINPROG.ADB' by default. This can be changed with `-o'
     `GNAT BIND' option.

`/NOOUTPUT'
     Check only. Do not generate the binder output file. In this mode
     the binder performs all error checks but does not generate an
     output file.

`/BIND_FILE=C'
     Generate binder program in C. The binder program is named
     `B_MAINPROG.C'. This can be changed with `-o' `GNAT BIND' option.

`/ELABORATION_DEPENDENCIES'
     Output complete list of elaboration-order dependencies, showing the
     reason for each dependency. This output can be rather extensive
     but may be useful in diagnosing problems with elaboration order.
     The output is written to `SYS$OUTPUT'.

`/HELP'
     Output usage information. The output is written to `SYS$OUTPUT'.

`/LINKER_OPTION_LIST'
     Output linker options to `SYS$OUTPUT'. Includes library search
     paths, contents of pragmas Ident and Linker_Options, and libraries
     added by `GNAT BIND'.

`/ORDER_OF_ELABORATION'
     Output chosen elaboration order. The output is written to
     `SYS$OUTPUT'.

`/OBJECT_LIST'
     Output full names of all the object files that must be linked to
     provide the Ada component of the program. The output is written to
     `SYS$OUTPUT'.  This list includes the files explicitly supplied
     and referenced by the user as well as implicitly referenced
     run-time unit files. The latter are omitted if the corresponding
     units reside in shared libraries. The directory names for the
     run-time units depend on the system configuration.

`/OUTPUT=FILE'
     Set name of output file to FILE instead of the normal
     `B$MAINPROG.ADB' default. Note that FILE denote the Ada binder
     generated body filename. In C mode you would normally give FILE an
     extension of `.C' because it will be a C source program.  Note
     that if this option is used, then linking must be done manually.
     It is not possible to use GNAT LINK in this case, since it cannot
     locate the binder file.

`/RESTRICTION_LIST'
     Generate list of `pragma Rerstrictions' that could be applied to
     the current unit. This is useful for code audit purposes, and also
     may be used to improve code generation in some cases.



File: gnat_ug_vms.info,  Node: Binding with Non-Ada Main Programs,  Next: Binding Programs with No Main Subprogram,  Prev: Output Control,  Up: Binding Using GNAT BIND

Binding with Non-Ada Main Programs
==================================

In our description so far we have assumed that the main program is in
Ada, and that the task of the binder is to generate a corresponding
function `main' that invokes this Ada main program. GNAT also supports
the building of executable programs where the main program is not in
Ada, but some of the called routines are written in Ada and compiled
using GNAT (*note Mixed Language Programming::).  The following
qualifier is used in this situation:

`/NOMAIN'
     No main program. The main program is not in Ada.

In this case, most of the functions of the binder are still required,
but instead of generating a main program, the binder generates a file
containing the following callable routines:

`adainit'
     You must call this routine to initialize the Ada part of the
     program by calling the necessary elaboration routines. A call to
     `adainit' is required before the first call to an Ada subprogram.

     Note that it is assumed that the basic execution environment must
     be setup to be appropriate for Ada execution at the point where
     the first Ada subprogram is called. In particular, if the Ada code
     will do any floating-point operations, then the FPU must be setup
     in an appropriate manner. For the case of the x86, for example,
     full precision mode is required. The procedure
     GNAT.Float_Control.Reset may be used to ensure that the FPU is in
     the right state.

`adafinal'
     You must call this routine to perform any library-level
     finalization required by the Ada subprograms. A call to `adafinal'
     is required after the last call to an Ada subprogram, and before
     the program terminates.

If the `/NOMAIN' qualifier is given, more than one ALI file may appear
on the command line for `GNAT BIND'. The normal "closure" calculation
is performed for each of the specified units. Calculating the closure
means finding out the set of units involved by tracing `with'
references. The reason it is necessary to be able to specify more than
one ALI file is that a given program may invoke two or more quite
separate groups of Ada units.

   The binder takes the name of its output file from the last specified
ALI file, unless overridden by the use of the `/OUTPUT=file'.  The
output is an Ada unit in source form that can be compiled with GNAT
unless the -C qualifier is used in which case the output is a C source
file, which must be compiled using the C compiler.  This compilation
occurs automatically as part of the `GNAT LINK' processing.

   Currently the GNAT run time requires a FPU using 80 bits mode
precision. Under targets where this is not the default it is required to
call GNAT.Float_Control.Reset before using floating point numbers (this
include float computation, float input and output) in the Ada code. A
side effect is that this could be the wrong mode for the foreign code
where floating point computation could be broken after this call.


File: gnat_ug_vms.info,  Node: Binding Programs with No Main Subprogram,  Next: Summary of Binder Qualifiers,  Prev: Binding with Non-Ada Main Programs,  Up: Binding Using GNAT BIND

Binding Programs with No Main Subprogram
========================================

It is possible to have an Ada program which does not have a main
subprogram. This program will call the elaboration routines of all the
packages, then the finalization routines.

   The following qualifier is used to bind programs organized in this
manner:

`/ZERO_MAIN'
     Normally the binder checks that the unit name given on the command
     line corresponds to a suitable main subprogram. When this
     qualifier is used, a list of ALI files can be given, and the
     execution of the program consists of elaboration of these units in
     an appropriate order.


File: gnat_ug_vms.info,  Node: Summary of Binder Qualifiers,  Next: Command-Line Access,  Prev: Binding Programs with No Main Subprogram,  Up: Binding Using GNAT BIND

Summary of Binder Qualifiers
============================

The following are the qualifiers available with `GNAT BIND':

`/OBJECT_SEARCH'
     Specify directory to be searched for ALI files.

`/SOURCE_SEARCH'
     Specify directory to be searched for source file.

`/BIND_FILE=ADA'
     Generate binder program in Ada (default)

`/REPORT_ERRORS=BRIEF'
     Generate brief messages to `SYS$ERROR' even if verbose mode set.

`/NOOUTPUT'
     Check only, no generation of binder output file.

`/BIND_FILE=C'
     Generate binder program in C

`/ELABORATION_DEPENDENCIES'
     Output complete list of elaboration-order dependencies.

`-E'
     Store tracebacks in exception occurrences when the target supports
     it.  This is the default with the zero cost exception mechanism.
     This option is currently supported on the following targets: all
     x86 ports, Solaris, Windows, HP-UX, AIX, PowerPC VxWorks and Alpha
     VxWorks.  See also the packages `GNAT.Traceback' and
     `GNAT.Traceback.Symbolic' for more information.  Note that on x86
     ports, you must not use `-fomit-frame-pointer' `GNAT COMPILE'
     option.

`-h'
     Output usage (help) information

`/SEARCH'
     Specify directory to be searched for source and ALI files.

`/NOCURRENT_DIRECTORY'
     Do not look for sources in the current directory where `GNAT BIND'
     was invoked, and do not look for ALI files in the directory
     containing the ALI file named in the `GNAT BIND' command line.

`/ORDER_OF_ELABORATION'
     Output chosen elaboration order.

`-Lxxx'
     Binds the units for library building. In this case the adainit and
     adafinal procedures (See *note Binding with Non-Ada Main
     Programs::) are renamed to xxxinit and xxxfinal. Implies -n.

`-Mxyz'
     Rename generated main program from main to xyz

`/ERROR_LIMIT=N'
     Limit number of detected errors to N (1-999).

`/NOMAIN'
     No main program.

`/NOSTD_INCLUDES'
     Do not look for sources in the system default directory.

`/NOSTD_LIBRARIES'
     Do not look for library files in the system default directory.

`/RUNTIME_SYSTEM=RTS-PATH'
     Specifies the default location of the runtime library. Same
     meaning as the equivalent `GNAT MAKE' flag (see *Note Qualifiers
     for GNAT MAKE::).

`/OUTPUT=FILE'
     Name the output file FILE (default is `B$XXX.ADB').  Note that if
     this option is used, then linking must be done manually, GNAT LINK
     cannot be used.

`/OBJECT_LIST'
     Output object list.

`-p'
     Pessimistic (worst-case) elaboration order

`/READ_SOURCES=ALL'
     Require all source files to be present.

`/NOTIME_STAMP_CHECK'
     Tolerate time stamp and other consistency errors

`-TN'
     Set the time slice value to n microseconds. A value of zero means
     no time slicing and also indicates to the tasking run time to
     match as close as possible to the annex D requirements of the RM.

`/REPORT_ERRORS=VERBOSE'
     Verbose mode. Write error messages, header, summary output to
     `SYS$OUTPUT'.

`/WARNINGS=NORMAL'
     Normal warnings mode. Warnings are issued but ignored

`/WARNINGS=SUPPRESS'
     All warning messages are suppressed

`/WARNINGS=ERROR'
     Warning messages are treated as fatal errors

`/READ_SOURCES=NONE'
     Exclude source files (check object consistency only).

`/READ_SOURCES=AVAILABLE'
     Default mode, in which sources are checked for consistency only if
     they are available.

`/ZERO_MAIN'
     No main subprogram.



File: gnat_ug_vms.info,  Node: Command-Line Access,  Next: Search Paths for GNAT BIND,  Prev: Summary of Binder Qualifiers,  Up: Binding Using GNAT BIND

Command-Line Access
===================

The package `Ada.Command_Line' provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables

     int gnat_argc;
     char **gnat_argv;

are declared in one of the GNAT library routines. These variables must
be set from the actual `argc' and `argv' values passed to the main
program. With no `/NOMAIN' present, `GNAT BIND' generates the C main
program to automatically set these variables.  If the `/NOMAIN'
qualifier is used, there is no automatic way to set these variables. If
they are not set, the procedures in `Ada.Command_Line' will not be
available, and any attempt to use them will raise `Constraint_Error'.
If command line access is required, your main program must set
`gnat_argc' and `gnat_argv' from the `argc' and `argv' values passed to
it.


File: gnat_ug_vms.info,  Node: Search Paths for GNAT BIND,  Next: Examples of GNAT BIND Usage,  Prev: Command-Line Access,  Up: Binding Using GNAT BIND

Search Paths for `GNAT BIND'
============================

The binder takes the name of an ALI file as its argument and needs to
locate source files as well as other ALI files to verify object
consistency.

   For source files, it follows exactly the same search rules as `GNAT
COMPILE' (*note Search Paths and the Run-Time Library (RTL)::). For ALI
files the directories searched are:

  1. The directory containing the ALI file named in the command line,
     unless the qualifier `/NOCURRENT_DIRECTORY' is specified.

  2. All directories specified by `/SEARCH' qualifiers on the `GNAT
     BIND' command line, in the order given.

  3. Each of the directories listed in the value of the
     `ADA_OBJECTS_PATH' logical name.  Normally, define this value as a
     logical name containing a comma separated list of directory names.

     This variable can also be defined by means of an environment string
     (an argument to the DEC C exec* set of functions).

     Logical Name:
          DEFINE ANOTHER_PATH FOO:[BAG]
          DEFINE ADA_OBJECTS_PATH ANOTHER_PATH,FOO:[BAM],FOO:[BAR]

     By default, the path includes GNU:[LIB.OPENVMS7_x.2_8_x.DECLIB]
     first, followed by the standard Ada 95 libraries in
     GNU:[LIB.OPENVMS7_x.2_8_x.ADALIB].  If this is not redefined, the
     user will obtain the DEC Ada83 IO packages (Text_IO,
     Sequential_IO, etc) instead of the Ada95 packages. Thus, in order
     to get the Ada 95 packages by default, ADA_OBJECTS_PATH must be
     redefined.

  4. The content of the "ada_object_path" file which is part of the GNAT
     installation tree and is used to store standard libraries such as
     the GNAT Run Time Library (RTL) unless the qualifier
     `/NOSTD_LIBRARIES' is specified.

In the binder the qualifier `/SEARCH' is used to specify both source and
library file paths. Use `/SOURCE_SEARCH' instead if you want to specify
source paths only, and `/LIBRARY_SEARCH' if you want to specify library
paths only. This means that for the binder `/SEARCH='DIR is equivalent
to `/SOURCE_SEARCH='DIR `/OBJECT_SEARCH='DIR.  The binder generates the
bind file (a C language source file) in the current working directory.

   The packages `Ada', `System', and `Interfaces' and their children
make up the GNAT Run-Time Library, together with the package GNAT and
its children, which contain a set of useful additional library
functions provided by GNAT. The sources for these units are needed by
the compiler and are kept together in one directory. The ALI files and
object files generated by compiling the RTL are needed by the binder
and the linker and are kept together in one directory, typically
different from the directory containing the sources. In a normal
installation, you need not specify these directory names when compiling
or binding. Either the environment variables or the built-in defaults
cause these files to be found.

   Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.


File: gnat_ug_vms.info,  Node: Examples of GNAT BIND Usage,  Prev: Search Paths for GNAT BIND,  Up: Binding Using GNAT BIND

Examples of `GNAT BIND' Usage
=============================

This section contains a number of examples of using the GNAT binding
utility `GNAT BIND'.

`GNAT BIND hello'
     The main program `Hello' (source program in `HELLO.ADB') is bound
     using the standard qualifier settings. The generated main program
     is `B~HELLO.ADB'. This is the normal, default use of the binder.

`GNAT BIND HELLO.ALI /OUTPUT=Mainprog.ADB'
     The main program `Hello' (source program in `HELLO.ADB') is bound
     using the standard qualifier settings. The generated main program
     is `MAINPROG.ADB' with the associated spec in `MAINPROG.ADS'. Note
     that you must specify the body here not the spec, in the case
     where the output is in Ada. Note that if this option is used, then
     linking must be done manually, since GNAT LINK will not be able to
     find the generated file.

`GNAT BIND MAIN.ALI /BIND_FILE=C /OUTPUT=Mainprog.C /READ_SOURCES=NONE'
     The main program `Main' (source program in `MAIN.ADB') is bound,
     excluding source files from the consistency checking, generating
     the file `MAINPROG.C'.

`GNAT BIND /NOMAIN math dbase /BIND_FILE=C /OUTPUT=ADA-CONTROL.C'
     The main program is in a language other than Ada, but calls to
     subprograms in packages `Math' and `Dbase' appear. This call to
     `GNAT BIND' generates the file `ADA-CONTROL.C' containing the
     `adainit' and `adafinal' routines to be called before and after
     accessing the Ada units.


File: gnat_ug_vms.info,  Node: Linking Using GNAT LINK,  Next: The GNAT Make Program GNAT MAKE,  Prev: Binding Using GNAT BIND,  Up: Top

Linking Using `GNAT LINK'
*************************

This chapter discusses `GNAT LINK', a utility program used to link Ada
programs and build an executable file. This is a simple program that
invokes the Unix linker (via the `GNAT COMPILE' command) with a correct
list of object files and library references.  `GNAT LINK' automatically
determines the list of files and references for the Ada part of a
program. It uses the binder file generated by the binder to determine
this list.

* Menu:

* Running GNAT LINK::
* Qualifiers for GNAT LINK::
* Setting Stack Size from GNAT LINK::
* Setting Heap Size from GNAT LINK::


File: gnat_ug_vms.info,  Node: Running GNAT LINK,  Next: Qualifiers for GNAT LINK,  Up: Linking Using GNAT LINK

Running `GNAT LINK'
===================

The form of the `GNAT LINK' command is

     $ GNAT LINK [QUALIFIERS] MAINPROG[.ALI] [NON-ADA OBJECTS]
           [LINKER OPTIONS]

`MAINPROG.ALI' references the ALI file of the main program.  The `.ALI'
extension of this file can be omitted. From this reference, `GNAT LINK'
locates the corresponding binder file `B$MAINPROG.ADB' and, using the
information in this file along with the list of non-Ada objects and
linker options, constructs a Unix linker command file to create the
executable.

   The arguments following `MAINPROG.ALI' are passed to the linker
uninterpreted. They typically include the names of object files for
units written in other languages than Ada and any library references
required to resolve references in any of these foreign language units,
or in `pragma Import' statements in any Ada units.

   LINKER OPTIONS is an optional list of linker specific qualifiers.
The default linker called by GNAT LINK is GNAT COMPILE which in turn
calls the appropriate system linker usually called LD. Standard options
for the linker such as `-lmy_lib' or `-Ldir' can be added as is. For
options that are not recognized by GNAT COMPILE as linker options, the
GNAT COMPILE qualifiers `-Xlinker' or `-Wl,' shall be used. Refer to
the GCC documentation for details. Here is an example showing how to
generate a linker map assuming that the underlying linker is GNU ld:

     $ GNAT LINK my_prog -Wl,-Map,MAPFILE

   Using LINKER OPTIONS it is possible to set the program stack and
heap size. See *note Setting Stack Size from GNAT LINK:: and *note
Setting Heap Size from GNAT LINK::.

   `GNAT LINK' determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
`GNAT LINK' also gathers any arguments set by the use of `pragma
Linker_Options' and adds them to the list of arguments presented to the
linker.

   `GNAT LINK' accepts the following types of extra files on the command
line: objects (.OBJ), libraries (.OLB), shareable images (.EXE), and
options files (.OPT). These are recognized and handled according to
their extension.


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT LINK,  Next: Setting Stack Size from GNAT LINK,  Prev: Running GNAT LINK,  Up: Linking Using GNAT LINK

Qualifiers for `GNAT LINK'
==========================

The following qualifiers are available with the `GNAT LINK' utility:

`/BIND_FILE=ADA'
     The binder has generated code in Ada. This is the default.

`/BIND_FILE=C'
     If instead of generating a file in Ada, the binder has generated
     one in C, then the linker needs to know about it. Use this
     qualifier to signal to `GNAT LINK' that the binder has generated C
     code rather than Ada code.

`-f'
     On some targets, the command line length is limited, and `GNAT
     LINK' will generate a separate file for the linker if the list of
     object files is too long. The `-f' flag forces this file to be
     generated even if the limit is not exceeded. This is useful in
     some cases to deal with special situations where the command line
     length is exceeded.

`/DEBUG'
     The option to include debugging information causes the Ada bind
     file (in other words, `B$MAINPROG.ADB') to be compiled with
     `/DEBUG'.  In addition, the binder does not delete the
     `B$MAINPROG.ADB', `B$MAINPROG.OBJ' and `B$MAINPROG.ALI' files.
     Without `/DEBUG', the binder removes these files by default. The
     same procedure apply if a C bind file was generated using
     `/BIND_FILE=C' `GNAT BIND' option, in this case the filenames are
     `B_MAINPROG.C' and `B_MAINPROG.OBJ'.

`/VERBOSE'
     Causes additional information to be output, including a full list
     of the included object files. This qualifier option is most useful
     when you want to see what set of object files are being used in
     the link step.

`/EXECUTABLE=EXEC-NAME'
     EXEC-NAME specifies an alternate name for the generated executable
     program. If this qualifier is omitted, the executable has the same
     name as the main unit. For example, `GNAT LINK TRY.ALI' creates an
     executable called `TRY.EXE'.

`/DEBUG=TRACEBACK'
     This qualifier causes sufficient information to be included in the
     executable file to allow a traceback, but does not include the full
     symbol information needed by the debugger.

`/IDENTIFICATION="<string>"'
     "<string>" specifies the string to be stored in the image file
     identification field in the image header. It overrides any pragma
     Ident specified string.

`/NOINHIBIT-EXEC'
     Generate the executable file even if there are linker warnings.

`/NOSTART_FILES'
     Don't link in the object file containing the "main" transfer
     address.  Used when linking with a foreign language main program
     compiled with a Digital compiler.

`/STATIC'
     Prefer linking with object libraries over shareable images, even
     without /DEBUG.



File: gnat_ug_vms.info,  Node: Setting Stack Size from GNAT LINK,  Next: Setting Heap Size from GNAT LINK,  Prev: Qualifiers for GNAT LINK,  Up: Linking Using GNAT LINK

Setting Stack Size from `GNAT LINK'
===================================

It is possible to specify the program stack size from `GNAT LINK'.
Assuming that the underlying linker is GNU ld there is two ways to do
so:

   * using `-Xlinker' linker option

          $ GNAT LINK hello -Xlinker --stack=0x10000,0x1000

     This set the stack reserve size to 0x10000 bytes and the stack
     commit size to 0x1000 bytes.

   * using `-Wl' linker option

          $ GNAT LINK hello -Wl,--stack=0x1000000

     This set the stack reserve size to 0x1000000 bytes. Note that with
     `-Wl' option it is not possible to set the stack commit size
     because the coma is a separator for this option.



File: gnat_ug_vms.info,  Node: Setting Heap Size from GNAT LINK,  Prev: Setting Stack Size from GNAT LINK,  Up: Linking Using GNAT LINK

Setting Heap Size from `GNAT LINK'
==================================

It is possible to specify the program heap size from `GNAT LINK'.
Assuming that the underlying linker is GNU ld there is two ways to do
so:

   * using `-Xlinker' linker option

          $ GNAT LINK hello -Xlinker --heap=0x10000,0x1000

     This set the heap reserve size to 0x10000 bytes and the heap commit
     size to 0x1000 bytes.

   * using `-Wl' linker option

          $ GNAT LINK hello -Wl,--heap=0x1000000

     This set the heap reserve size to 0x1000000 bytes. Note that with
     `-Wl' option it is not possible to set the heap commit size
     because the coma is a separator for this option.



File: gnat_ug_vms.info,  Node: The GNAT Make Program GNAT MAKE,  Next: Renaming Files Using GNAT CHOP,  Prev: Linking Using GNAT LINK,  Up: Top

The GNAT Make Program `GNAT MAKE'
*********************************

* Menu:

* Running GNAT MAKE::
* Qualifiers for GNAT MAKE::
* Mode Qualifiers for GNAT MAKE::
* Notes on the Command Line::
* How GNAT MAKE Works::
* Examples of GNAT MAKE Usage::

A typical development cycle when working on an Ada program consists of
the following steps:

  1. Edit some sources to fix bugs.

  2. Add enhancements.

  3. Compile all sources affected.

  4. Rebind and relink.

  5. Test.

The third step can be tricky, because not only do the modified files
have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, `use' clauses, generics and inlined
subprograms.

   `GNAT MAKE' automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.

   Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by `GNAT
MAKE'.


File: gnat_ug_vms.info,  Node: Running GNAT MAKE,  Next: Qualifiers for GNAT MAKE,  Up: The GNAT Make Program GNAT MAKE

Running `GNAT MAKE'
===================

The usual form of the `GNAT MAKE' command is

     $ GNAT MAKE [QUALIFIERS] FILE_NAME [FILE_NAMES] [MODE_QUALIFIERS]

The only required argument is one FILE_NAME, which specifies a
compilation unit that is a main program. Several FILE_NAMES can be
specified: this will result in several executables being built.  If
`qualifiers' are present, they can be placed before the first
FILE_NAME, between FILE_NAMES or after the last FILE_NAME.  If
MODE_QUALIFIERS are present, they must always be placed after the last
FILE_NAME and all `qualifiers'.

   If you are using standard file extensions (.ADB and .ADS), then the
extension may be omitted from the FILE_NAME arguments. However, if you
are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a FILE_NAME, in which case, the input source file will be
searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where `GNAT MAKE'
was invoked and if it is not found, it will be search on the source
path of the compiler as described in *Note Search Paths and the
Run-Time Library (RTL)::.

   When several FILE_NAMES are specified, if an executable needs to be
rebuilt and relinked, all subsequent executables will be rebuilt and
relinked, even if this would not be absolutely necessary.

   All `GNAT MAKE' output (except when you specify
`/DEPENDENCIES_LIST') is to `SYS$ERROR'. The output produced by the
`/DEPENDENCIES_LIST' qualifier is send to `SYS$OUTPUT'.


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT MAKE,  Next: Mode Qualifiers for GNAT MAKE,  Prev: Running GNAT MAKE,  Up: The GNAT Make Program GNAT MAKE

Qualifiers for `GNAT MAKE'
==========================

You may specify any of the following qualifiers to `GNAT MAKE':

`/ALL_FILES'
     Consider all files in the make process, even the GNAT internal
     system files (for example, the predefined Ada library files), as
     well as any locked files. Locked files are files whose ALI file is
     write-protected.  By default, `GNAT MAKE' does not check these
     files, because the assumption is that the GNAT internal files are
     properly up to date, and also that any write protected ALI files
     have been properly installed. Note that if there is an
     installation problem, such that one of these files is not up to
     date, it will be properly caught by the binder.  You may have to
     specify this qualifier if you are working on GNAT itself.
     `/ALL_FILES' is also useful in conjunction with `/FORCE_COMPILE'
     if you need to recompile an entire application, including run-time
     files, using special configuration pragma settings, such as a
     non-standard `Float_Representation' pragma.  By default `GNAT MAKE
     /ALL_FILES' compiles all GNAT internal files with the
     `/CHECKS=SUPPRESS_ALL /STYLE_CHECKS=GNAT' qualifier.

`/ACTIONS=BIND'
     Bind only. Can be combined with `/ACTIONS=COMPILE' to do
     compilation and binding, but no link. Can be combined with
     `/ACTIONS=LINK' to do binding and linking. When not combined with
     `/ACTIONS=COMPILE' all the units in the closure of the main
     program must have been previously compiled and must be up to date.
     The root unit specified by FILE_NAME may be given without
     extension, with the source extension or, if no GNAT Project File
     is specified, with the ALI file extension.

`/ACTIONS=COMPILE'
     Compile only. Do not perform binding, except when `/ACTIONS=BIND'
     is also specified. Do not perform linking, except if both
     `/ACTIONS=BIND' and  `/ACTIONS=LINK' are also specified.  If the
     root unit specified by FILE_NAME is not a main unit, this is the
     default. Otherwise `GNAT MAKE' will attempt binding and linking
     unless all objects are up to date and the executable is more
     recent than the objects.

`/MAPPING'
     Use a mapping file. A mapping file is a way to communicate to the
     compiler two mappings: from unit names to file names (without any
     directory information) and from file names to path names (with
     full directory information).  These mappings are used by the
     compiler to short-circuit the path search.  When `GNAT MAKE' is
     invoked with this qualifier, it will create a mapping file,
     initially populated by the project manager, if `-P' is used,
     otherwise initially empty. Each invocation of the compiler will
     add the newly accessed sources to the mapping file. This will
     improve the source search during the next invocation of the
     compiler.

`/FORCE_COMPILE'
     Force recompilations. Recompile all sources, even though some
     object files may be up to date, but don't recompile predefined or
     GNAT internal files or locked files (files with a write-protected
     ALI file), unless the `/ALL_FILES' qualifier is also specified.

`'

`/IN_PLACE'
     In normal mode, `GNAT MAKE' compiles all object files and ALI files
     into the current directory. If the `/IN_PLACE' qualifier is used,
     then instead object files and ALI files that already exist are
     overwritten in place. This means that once a large project is
     organized into separate directories in the desired manner, then
     `GNAT MAKE' will automatically maintain and update this
     organization. If no ALI files are found on the Ada object path
     (*Note Search Paths and the Run-Time Library (RTL)::), the new
     object and ALI files are created in the directory containing the
     source being compiled. If another organization is desired, where
     objects and sources are kept in different directories, a useful
     technique is to create dummy ALI files in the desired directories.
     When detecting such a dummy file, `GNAT MAKE' will be forced to
     recompile the corresponding source file, and it will be put the
     resulting object and ALI files in the directory where it found the
     dummy file.

`/PROCESSES=N'
     Use N processes to carry out the (re)compilations. On a
     multiprocessor machine compilations will occur in parallel. In the
     event of compilation errors, messages from various compilations
     might get interspersed (but `GNAT MAKE' will give you the full
     ordered list of failing compiles at the end). If this is
     problematic, rerun the make process with n set to 1 to get a clean
     list of messages.

`/CONTINUE_ON_ERROR'
     Keep going. Continue as much as possible after a compilation
     error. To ease the programmer's task in case of compilation
     errors, the list of sources for which the compile fails is given
     when `GNAT MAKE' terminates.

     If `GNAT MAKE' is invoked with several `file_names' and with this
     qualifier, if there are compilation errors when building an
     executable, `GNAT MAKE' will not attempt to build the following
     executables.

`/ACTIONS=LINK'
     Link only. Can be combined with `/ACTIONS=BIND' to binding and
     linking. Linking will not be performed if combined with
     `/ACTIONS=COMPILE' but not with `/ACTIONS=BIND'.  When not
     combined with `/ACTIONS=BIND' all the units in the closure of the
     main program must have been previously compiled and must be up to
     date, and the main program need to have been bound.  The root unit
     specified by FILE_NAME may be given without extension, with the
     source extension or, if no GNAT Project File is specified, with
     the ALI file extension.

`/MINIMAL_RECOMPILATION'
     Specifies that the minimum necessary amount of recompilations be
     performed. In this mode `GNAT MAKE' ignores time stamp differences
     when the only modifications to a source file consist in
     adding/removing comments, empty lines, spaces or tabs. This means
     that if you have changed the comments in a source file or have
     simply reformatted it, using this qualifier will tell GNAT MAKE
     not to recompile files that depend on it (provided other sources
     on which these files depend have undergone no semantic
     modifications). Note that the debugging information may be out of
     date with respect to the sources if the `-m' qualifier causes a
     compilation to be switched, so the use of this qualifier
     represents a trade-off between compilation time and accurate
     debugging information.

`/DEPENDENCIES_LIST'
     Check if all objects are up to date. If they are, output the object
     dependences to `SYS$OUTPUT' in a form that can be directly
     exploited in a `Makefile'. By default, each source file is
     prefixed with its (relative or absolute) directory name. This name
     is whatever you specified in the various `/SOURCE_SEARCH' and
     `/SEARCH' qualifiers. If you use `GNAT MAKE /DEPENDENCIES_LIST'
     `/QUIET' (see below), only the source file names, without relative
     paths, are output. If you just specify the `/DEPENDENCIES_LIST'
     qualifier, dependencies of the GNAT internal system files are
     omitted. This is typically what you want. If you also specify the
     `/ALL_FILES' qualifier, dependencies of the GNAT internal files
     are also listed. Note that dependencies of the objects in external
     Ada libraries (see qualifier `/SKIP_MISSING='DIR in the following
     list) are never reported.

`/DO_OBJECT_CHECK'
     Don't compile, bind, or link. Checks if all objects are up to date.
     If they are not, the full name of the first file that needs to be
     recompiled is printed.  Repeated use of this option, followed by
     compiling the indicated source file, will eventually result in
     recompiling all required units.

`/EXECUTABLE=EXEC_NAME'
     Output executable name. The name of the final executable program
     will be EXEC_NAME. If the `/EXECUTABLE' qualifier is omitted the
     default name for the executable will be the name of the input file
     in appropriate form for an executable file on the host system.

     This qualifier cannot be used when invoking `GNAT MAKE' with
     several `file_names'.

`/QUIET'
     Quiet. When this flag is not set, the commands carried out by
     `GNAT MAKE' are displayed.

`/SWITCH_CHECK/'
     Recompile if compiler qualifiers have changed since last
     compilation.  All compiler qualifiers but -I and -o are taken into
     account in the following way: orders between different "first
     letter" qualifiers are ignored, but orders between same qualifiers
     are taken into account. For example, `-O /OPTIMIZE=ALL' is
     different than `/OPTIMIZE=ALL -O', but `-g -O' is equivalent to
     `-O -g'.

`/UNIQUE'
     Unique. Recompile at most the main file. It implies -c. Combined
     with -f, it is equivalent to calling the compiler directly.

`/REASONS'
     Verbose. Displays the reason for all recompilations `GNAT MAKE'
     decides are necessary.

`/NOMAIN'
     No main subprogram. Bind and link the program even if the unit name
     given on the command line is a package name. The resulting
     executable will execute the elaboration routines of the package
     and its closure, then the finalization routines.

``GNAT COMPILE' qualifiers'
     Any qualifier that cannot be recognized as a qualifier for `GNAT
     MAKE' but is recognizable as a valid qualifier for `GNAT COMPILE'
     is automatically treated as a compiler qualifier, and passed on to
     all compilations that are carried out.

Source and library search path qualifiers:

`/SOURCE_SEARCH=DIR'
     When looking for source files also look in directory DIR.  The
     order in which source files search is undertaken is described in
     *Note Search Paths and the Run-Time Library (RTL)::.

`/SKIP_MISSING=DIR'
     Consider DIR as being an externally provided Ada library.
     Instructs `GNAT MAKE' to skip compilation units whose `.ALI' files
     have been located in directory DIR. This allows you to have
     missing bodies for the units in DIR and to ignore out of date
     bodies for the same units. You still need to specify the location
     of the specs for these units by using the qualifiers
     `/SOURCE_SEARCH=DIR' or `/SEARCH=DIR'.  Note: this qualifier is
     provided for compatibility with previous versions of `GNAT MAKE'.
     The easier method of causing standard libraries to be excluded
     from consideration is to write-protect the corresponding ALI files.

`/OBJECT_SEARCH=DIR'
     When searching for library and object files, look in directory
     DIR. The order in which library files are searched is described in
     *Note Search Paths for GNAT BIND::.

`/CONDITIONAL_SOURCE_SEARCH=DIR'
     Equivalent to `/SKIP_MISSING=DIR /SOURCE_SEARCH=DIR'.

`/SEARCH=DIR'
     Equivalent to `/OBJECT_SEARCH=DIR /SOURCE_SEARCH=DIR'.

`/NOCURRENT_DIRECTORY'
     Do not look for source files in the directory containing the source
     file named in the command line.  Do not look for ALI or object
     files in the directory where `GNAT MAKE' was invoked.

`/LIBRARY_SEARCH=DIR'
     Add directory DIR to the list of directories in which the linker
     will search for libraries. This is equivalent to
     `/LINKER_QUALIFIERS /LIBRARY_SEARCH='DIR.

`/NOSTD_INCLUDES'
     Do not look for source files in the system default directory.

`/NOSTD_LIBRARIES'
     Do not look for library files in the system default directory.

`/RUNTIME_SYSTEM=RTS-PATH'
     Specifies the default location of the runtime library. We look for
     the runtime in the following directories, and stop as soon as a
     valid runtime is found ("adainclude" or "ada_source_path", and
     "adalib" or "ada_object_path" present):

        * <current directory>/$rts_path

        * <default-search-dir>/$rts_path

        * <default-search-dir>/rts-$rts_path

     The selected path is handled like a normal RTS path.



File: gnat_ug_vms.info,  Node: Mode Qualifiers for GNAT MAKE,  Next: Notes on the Command Line,  Prev: Qualifiers for GNAT MAKE,  Up: The GNAT Make Program GNAT MAKE

Mode Qualifiers for `GNAT MAKE'
===============================

The mode qualifiers (referred to as `mode_qualifiers') allow the
inclusion of qualifiers that are to be passed to the compiler itself,
the binder or the linker. The effect of a mode qualifier is to cause all
subsequent qualifiers up to the end of the qualifier list, or up to the
next mode qualifier, to be interpreted as qualifiers to be passed on to
the designated component of GNAT.

`/COMPILER_QUALIFIERS QUALIFIERS'
     Compiler qualifiers. Here QUALIFIERS is a list of qualifiers that
     are valid qualifiers for `GNAT COMPILE'. They will be passed on to
     all compile steps performed by `GNAT MAKE'.

`/BINDER_QUALIFIERS QUALIFIERS'
     Binder qualifiers. Here QUALIFIERS is a list of qualifiers that
     are valid qualifiers for `GNAT COMPILE'. They will be passed on to
     all bind steps performed by `GNAT MAKE'.

`/LINKER_QUALIFIERS QUALIFIERS'
     Linker qualifiers. Here QUALIFIERS is a list of qualifiers that
     are valid qualifiers for `GNAT COMPILE'. They will be passed on to
     all link steps performed by `GNAT MAKE'.


File: gnat_ug_vms.info,  Node: Notes on the Command Line,  Next: How GNAT MAKE Works,  Prev: Mode Qualifiers for GNAT MAKE,  Up: The GNAT Make Program GNAT MAKE

Notes on the Command Line
=========================

This section contains some additional useful notes on the operation of
the `GNAT MAKE' command.

   * If `GNAT MAKE' finds no ALI files, it recompiles the main program
     and all other units required by the main program.  This means that
     `GNAT MAKE' can be used for the initial compile, as well as during
     subsequent steps of the development cycle.

   * If you enter `GNAT MAKE FILE.ADB', where `FILE.ADB' is a subunit
     or body of a generic unit, `GNAT MAKE' recompiles `FILE.ADB'
     (because it finds no ALI) and stops, issuing a warning.

   * In `GNAT MAKE' the qualifier `/SEARCH' is used to specify both
     source and library file paths. Use `/SOURCE_SEARCH' instead if you
     just want to specify source paths only and `/OBJECT_SEARCH' if you
     want to specify library paths only.

   * `GNAT MAKE' examines both an ALI file and its corresponding object
     file for consistency. If an ALI is more recent than its
     corresponding object, or if the object file is missing, the
     corresponding source will be recompiled.  Note that `GNAT MAKE'
     expects an ALI and the corresponding object file to be in the same
     directory.

   * `GNAT MAKE' will ignore any files whose ALI file is
     write-protected.  This may conveniently be used to exclude
     standard libraries from consideration and in particular it means
     that the use of the `/FORCE_COMPILE' qualifier will not recompile
     these files unless `/ALL_FILES' is also specified.

   * `GNAT MAKE' has been designed to make the use of Ada libraries
     particularly convenient. Assume you have an Ada library organized
     as follows: [OBJ_DIR] contains the objects and ALI files for of
     your Ada compilation units, whereas [INCLUDE_DIR] contains the
     specs of these units, but no bodies. Then to compile a unit stored
     in `MAIN.ADB', which uses this Ada library you would just type

          $ GNAT MAKE /SOURCE_SEARCH=[INCLUDE_DIR]
                     /SKIP_MISSING=[OBJ_DIR] main

   * Using `GNAT MAKE' along with the `/MINIMAL_RECOMPILATION'
     qualifier provides a mechanism for avoiding unnecessary
     rcompilations. Using this qualifier, you can update the
     comments/format of your source files without having to recompile
     everything. Note, however, that adding or deleting lines in a
     source files may render its debugging info obsolete. If the file
     in question is a spec, the impact is rather limited, as that
     debugging info will only be useful during the elaboration phase of
     your program. For bodies the impact can be more significant. In
     all events, your debugger will warn you if a source file is more
     recent than the corresponding object, and alert you to the fact
     that the debugging information may be out of date.


File: gnat_ug_vms.info,  Node: How GNAT MAKE Works,  Next: Examples of GNAT MAKE Usage,  Prev: Notes on the Command Line,  Up: The GNAT Make Program GNAT MAKE

How `GNAT MAKE' Works
=====================

Generally `GNAT MAKE' automatically performs all necessary
recompilations and you don't need to worry about how it works. However,
it may be useful to have some basic understanding of the `GNAT MAKE'
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.

   First a definition: an object file is considered "up to date" if the
corresponding ALI file exists and its time stamp predates that of the
object file and if all the source files listed in the dependency
section of this ALI file have time stamps matching those in the ALI
file. This means that neither the source file itself nor any files that
it depends on have been modified, and hence there is no need to
recompile this file.

   `GNAT MAKE' works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit. If not,
`GNAT MAKE' compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and `GNAT MAKE' recursively applies the above procedure on all these
files.

   This process ensures that `GNAT MAKE' only trusts the dependencies
in an existing ALI file if they are known to be correct. Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled "upside down" from
what may be more familiar as the required order of compilation in some
other Ada systems. In particular, clients are compiled before the units
on which they depend. The ability of GNAT to compile in any order is
critical in allowing an order of compilation to be chosen that
guarantees that `GNAT MAKE' will recompute a correct set of new
dependencies if necessary.

   When invoking `GNAT MAKE' with several FILE_NAMES, if a unit is
imported by several of the executables, it will be recompiled at most
once.


File: gnat_ug_vms.info,  Node: Examples of GNAT MAKE Usage,  Prev: How GNAT MAKE Works,  Up: The GNAT Make Program GNAT MAKE

Examples of `GNAT MAKE' Usage
=============================

`GNAT MAKE HELLO.ADB'
     Compile all files necessary to bind and link the main program
     `HELLO.ADB' (containing unit `Hello') and bind and link the
     resulting object files to generate an executable file `HELLO.EXE'.

`GNAT MAKE main1 main2 main3'
     Compile all files necessary to bind and link the main programs
     `MAIN1.ADB' (containing unit `Main1'), `MAIN2.ADB' (containing
     unit `Main2') and `MAIN3.ADB' (containing unit `Main3') and bind
     and link the resulting object files to generate three executable
     files `MAIN1.EXE', `MAIN2.EXE' and `MAIN3.EXE'.

`GNAT MAKE Main_Unit /QUIET /COMPILER_QUALIFIERS /OPTIMIZE=ALL /BINDER_QUALIFIERS /ORDER_OF_ELABORATION'
     Compile all files necessary to bind and link the main program unit
     `Main_Unit' (from file `MAIN_UNIT.ADB'). All compilations will be
     done with optimization level 2 and the order of elaboration will be
     listed by the binder. `GNAT MAKE' will operate in quiet mode, not
     displaying commands it is executing.


File: gnat_ug_vms.info,  Node: Renaming Files Using GNAT CHOP,  Next: Configuration Pragmas,  Prev: The GNAT Make Program GNAT MAKE,  Up: Top

Renaming Files Using `GNAT CHOP'
********************************

This chapter discusses how to handle files with multiple units by using
the `GNAT CHOP' utility. This utility is also useful in renaming files
to meet the standard GNAT default file naming conventions.

* Menu:

* Handling Files with Multiple Units::
* Operating GNAT CHOP in Compilation Mode::
* Command Line for GNAT CHOP::
* Qualifiers for GNAT CHOP::
* Examples of GNAT CHOP Usage::


File: gnat_ug_vms.info,  Node: Handling Files with Multiple Units,  Next: Operating GNAT CHOP in Compilation Mode,  Up: Renaming Files Using GNAT CHOP

Handling Files with Multiple Units
==================================

The basic compilation model of GNAT requires that a file submitted to
the compiler have only one unit and there be a strict correspondence
between the file name and the unit name.

   The `GNAT CHOP' utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. `GNAT CHOP' reads the specified
file and generates one or more output files, containing one unit per
file. The unit and the file name correspond, as required by GNAT.

   If you want to permanently restructure a set of "foreign" files so
that they match the GNAT rules, and do the remaining development using
the GNAT structure, you can simply use `GNAT CHOP' once, generate the
new set of files and work with them from that point on.

   Alternatively, if you want to keep your files in the "foreign"
format, perhaps to maintain compatibility with some other Ada
compilation system, you can set up a procedure where you use `GNAT
CHOP' each time you compile, regarding the source files that it writes
as temporary files that you throw away.


File: gnat_ug_vms.info,  Node: Operating GNAT CHOP in Compilation Mode,  Next: Command Line for GNAT CHOP,  Prev: Handling Files with Multiple Units,  Up: Renaming Files Using GNAT CHOP

Operating GNAT CHOP in Compilation Mode
=======================================

The basic function of `GNAT CHOP' is to take a file with multiple units
and split it into separate files. The boundary between files is
reasonably clear, except for the issue of comments and pragmas. In
default mode, the rule is that any pragmas between units belong to the
previous unit, except that configuration pragmas always belong to the
following unit. Any comments belong to the following unit. These rules
almost always result in the right choice of the split point without
needing to mark it explicitly and most users will find this default to
be what they want. In this default mode it is incorrect to submit a
file containing only configuration pragmas, or one that ends in
configuration pragmas, to `GNAT CHOP'.

   However, using a special option to activate "compilation mode",
`GNAT CHOP' can perform another function, which is to provide exactly
the semantics required by the RM for handling of configuration pragmas
in a compilation.  In the absence of configuration pragmas (at the main
file level), this option has no effect, but it causes such
configuration pragmas to be handled in a quite different manner.

   First, in compilation mode, if `GNAT CHOP' is given a file that
consists of only configuration pragmas, then this file is appended to
the `GNAT.ADC' file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
`GNAT.ADC' file is the representation of a compilation environment. For
more information on the `GNAT.ADC' file, see the section on handling of
configuration pragmas *note Handling of Configuration Pragmas::.

   Second, in compilation mode, if `GNAT CHOP' is given a file that
starts with configuration pragmas, and contains one or more units, then
these configuration pragmas are prepended to each of the chopped files.
This behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.

   Finally, if configuration pragmas appear between units, they are
appended to the previous unit. This results in the previous unit being
illegal, since the compiler does not accept configuration pragmas that
follow a unit. This provides the required RM behavior that forbids
configuration pragmas other than those preceding the first compilation
unit of a compilation.

   For most purposes, `GNAT CHOP' will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files that
contain multiple units and configuration pragmas. In this circumstance
the use of `GNAT CHOP' with the compilation mode qualifier provides the
required behavior, and is for example the mode in which GNAT processes
the ACVC tests.


File: gnat_ug_vms.info,  Node: Command Line for GNAT CHOP,  Next: Qualifiers for GNAT CHOP,  Prev: Operating GNAT CHOP in Compilation Mode,  Up: Renaming Files Using GNAT CHOP

Command Line for `GNAT CHOP'
============================

The `GNAT CHOP' command has the form:

     $ GNAT CHOP qualifiers FILE NAME [FILE NAME FILE NAME ...]
           [DIRECTORY]

The only required argument is the file name of the file to be chopped.
There are no restrictions on the form of this file name. The file itself
contains one or more Ada units, in normal GNAT format, concatenated
together. As shown, more than one file may be presented to be chopped.

   When run in default mode, `GNAT CHOP' generates one output file in
the current directory for each unit in each of the files.

   DIRECTORY, if specified, gives the name of the directory to which
the output files will be written. If it is not specified, all files are
written to the current directory.

   For example, given a file called `hellofiles' containing

     procedure hello;
     
     with Text_IO; use Text_IO;
     procedure hello is
     begin
        Put_Line ("Hello");
     end hello;

the command

     $ GNAT CHOP HELLOFILES.

generates two files in the current directory, one called `HELLO.ADS'
containing the single line that is the procedure spec, and the other
called `HELLO.ADB' containing the remaining text. The original file is
not affected. The generated files can be compiled in the normal manner.


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT CHOP,  Next: Examples of GNAT CHOP Usage,  Prev: Command Line for GNAT CHOP,  Up: Renaming Files Using GNAT CHOP

Qualifiers for `GNAT CHOP'
==========================

`GNAT CHOP' recognizes the following qualifiers:

`/COMPILATION'
     Causes `GNAT CHOP' to operate in compilation mode, in which
     configuration pragmas are handled according to strict RM rules. See
     previous section for a full description of this mode.

`/HELP'
     Causes `GNAT CHOP' to generate a brief help summary to the standard
     output file showing usage information.

`/FILE_NAME_MAX_LENGTH=MM'
     Limit generated file names to the specified number `mm' of
     characters.  This is useful if the resulting set of files is
     required to be interoperable with systems which limit the length
     of file names.  If no value is given, or if no
     `/FILE_NAME_MAX_LENGTH' qualifier is given, a default of 39,
     suitable for OpenVMS Alpha Systems, is assumed

`/PRESERVE'
     Causes the file creation time stamp of the input file to be
     preserved and used for the time stamp of the output file(s). This
     may be useful for preserving coherency of time stamps in an
     enviroment where `GNAT CHOP' is used as part of a standard build
     process.

`/QUIET'
     Causes output of informational messages indicating the set of
     generated files to be suppressed. Warnings and error messages are
     unaffected.

`/REFERENCE'
     Generate `Source_Reference' pragmas. Use this qualifier if the
     output files are regarded as temporary and development is to be
     done in terms of the original unchopped file. This qualifier causes
     `Source_Reference' pragmas to be inserted into each of the
     generated files to refers back to the original file name and line
     number.  The result is that all error messages refer back to the
     original unchopped file.  In addition, the debugging information
     placed into the object file (when the `/DEBUG' qualifier of `GNAT
     COMPILE' or `GNAT MAKE' is specified) also refers back to this
     original file so that tools like profilers and debuggers will give
     information in terms of the original unchopped file.

     If the original file to be chopped itself contains a
     `Source_Reference' pragma referencing a third file, then GNAT CHOP
     respects this pragma, and the generated `Source_Reference' pragmas
     in the chopped file refer to the original file, with appropriate
     line numbers. This is particularly useful when `GNAT CHOP' is used
     in conjunction with `GNAT PREPROCESS' to compile files that
     contain preprocessing statements and multiple units.

`/VERBOSE'
     Causes `GNAT CHOP' to operate in verbose mode. The version number
     and copyright notice are output, as well as exact copies of the
     GNAT1 commands spawned to obtain the chop control information.

`/OVERWRITE'
     Overwrite existing file names. Normally `GNAT CHOP' regards it as a
     fatal error if there is already a file with the same name as a
     file it would otherwise output, in other words if the files to be
     chopped contain duplicated units. This qualifier bypasses this
     check, and causes all but the last instance of such duplicated
     units to be skipped.



File: gnat_ug_vms.info,  Node: Examples of GNAT CHOP Usage,  Prev: Qualifiers for GNAT CHOP,  Up: Renaming Files Using GNAT CHOP

Examples of `GNAT CHOP' Usage
=============================

`GNAT CHOP /OVERWRITE HELLO_S.ADA [ICHBIAH.FILES]'
     Chops the source file `HELLO_S.ADA'. The output files will be
     placed in the directory `[ICHBIAH.FILES]', overwriting any files
     with matching names in that directory (no files in the current
     directory are modified).

`GNAT CHOP ARCHIVE.'
     Chops the source file `ARCHIVE.' into the current directory. One
     useful application of `GNAT CHOP' is in sending sets of sources
     around, for example in email messages. The required sources are
     simply concatenated (for example, using a VMS `APPEND/NEW'
     command), and then `GNAT CHOP' is used at the other end to
     reconstitute the original file names.

`GNAT CHOP file1 file2 file3 direc'
     Chops all units in files `file1', `file2', `file3', placing the
     resulting files in the directory `direc'. Note that if any units
     occur more than once anywhere within this set of files, an error
     message is generated, and no files are written. To override this
     check, use the `/OVERWRITE' qualifier, in which case the last
     occurrence in the last file will be the one that is output, and
     earlier duplicate occurrences for a given unit will be skipped.


File: gnat_ug_vms.info,  Node: Configuration Pragmas,  Next: Handling Arbitrary File Naming Conventions Using gnatname,  Prev: Renaming Files Using GNAT CHOP,  Up: Top

Configuration Pragmas
*********************

In Ada 95, configuration pragmas include those pragmas described as
such in the Ada 95 Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas. See the
individual descriptions of pragmas in the GNAT Reference Manual for
details on these additional GNAT-specific configuration pragmas. Most
notably, the pragma `Source_File_Name', which allows specifying
non-default names for source files, is a configuration pragma. The
following is a complete list of configuration pragmas recognized by
`GNAT':

        Ada_83
        Ada_95
        C_Pass_By_Copy
        Component_Alignment
        Discard_Names
        Elaboration_Checks
        Eliminate
        Extend_System
        Extensions_Allowed
        External_Name_Casing
        Float_Representation
        Initialize_Scalars
        License
        Locking_Policy
        Long_Float
        No_Run_Time
        Normalize_Scalars
        Polling
        Propagate_Exceptions
        Queuing_Policy
        Ravenscar
        Restricted_Run_Time
        Restrictions
        Reviewable
        Source_File_Name
        Style_Checks
        Suppress
        Task_Dispatching_Policy
        Unsuppress
        Use_VADS_Size
        Warnings
        Validity_Checks

* Menu:

* Handling of Configuration Pragmas::
* The Configuration Pragmas Files::


File: gnat_ug_vms.info,  Node: Handling of Configuration Pragmas,  Next: The Configuration Pragmas Files,  Up: Configuration Pragmas

Handling of Configuration Pragmas
=================================

   Configuration pragmas may either appear at the start of a compilation
unit, in which case they apply only to that unit, or they may apply to
all compilations performed in a given compilation environment.

   GNAT also provides the `GNAT CHOP' utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See section *note Operating GNAT CHOP in Compilation Mode:: for details.
However, for most purposes, it will be more convenient to edit the
`GNAT.ADC' file that contains configuration pragmas directly, as
described in the following section.


File: gnat_ug_vms.info,  Node: The Configuration Pragmas Files,  Prev: Handling of Configuration Pragmas,  Up: Configuration Pragmas

The Configuration Pragmas Files
===============================

In GNAT a compilation environment is defined by the current directory
at the time that a compile command is given. This current directory is
searched for a file whose name is `GNAT.ADC'. If this file is present,
it is expected to contain one or more configuration pragmas that will
be applied to the current compilation.  However, if the qualifier
`-gnatA' is used, `GNAT.ADC' is not considered.

   Configuration pragmas may be entered into the `GNAT.ADC' file either
by running `GNAT CHOP' on a source file that consists only of
configuration pragmas, or more conveniently  by direct editing of the
`GNAT.ADC' file, which is a standard format source file.

   In addition to `GNAT.ADC', one additional file containing
configuration pragmas may be applied to the current compilation using
the qualifier `-gnatec'PATH. PATH must designate an existing file that
contains only configuration pragmas. These configuration pragmas are in
addition to those found in `GNAT.ADC' (provided `GNAT.ADC' is present
and qualifier `-gnatA' is not used).

   It is allowed to specify several qualifiers `-gnatec', however only
the last one on the command line will be taken into account.

   Of special interest to GNAT OpenVMS Alpha is the following
configuration pragma:

     pragma Extend_System (Aux_DEC);

In the presence of this pragma, GNAT adds to the definition of the
predefined package SYSTEM all the additional types and subprograms that
are defined in DEC Ada. See *note Compatibility with DEC Ada:: for
details.


File: gnat_ug_vms.info,  Node: Handling Arbitrary File Naming Conventions Using gnatname,  Next: GNAT Project Manager,  Prev: Configuration Pragmas,  Up: Top

Handling Arbitrary File Naming Conventions Using `gnatname'
***********************************************************

* Menu:

* Arbitrary File Naming Conventions::
* Running gnatname::
* Qualifiers for gnatname::
* Examples of gnatname Usage::


File: gnat_ug_vms.info,  Node: Arbitrary File Naming Conventions,  Next: Running gnatname,  Up: Handling Arbitrary File Naming Conventions Using gnatname

Arbitrary File Naming Conventions
=================================

The GNAT compiler must be able to know the source file name of a
compilation unit.  When using the standard GNAT default file naming
conventions (`.ADS' for specs, `.ADB' for bodies), the GNAT compiler
does not need additional information.

When the source file names do not follow the standard GNAT default file
naming conventions, the GNAT compiler must be given additional
information through a configuration pragmas file (see *Note
Configuration Pragmas::) or a project file.  When the non standard file
naming conventions are well-defined, a small number of pragmas
`Source_File_Name' specifying a naming pattern (see *Note Alternative
File Naming Schemes::) may be sufficient. However, if the file naming
conventions are irregular or arbitrary, a number of pragma
`Source_File_Name' for individual compilation units must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler, GNAT provides a tool `gnatname'
to generate the required pragmas for a set of files.


File: gnat_ug_vms.info,  Node: Running gnatname,  Next: Qualifiers for gnatname,  Prev: Arbitrary File Naming Conventions,  Up: Handling Arbitrary File Naming Conventions Using gnatname

Running `gnatname'
==================

The usual form of the `gnatname' command is

     $ gnatname [QUALIFIERS] NAMING_PATTERN [NAMING_PATTERNS]

All of the arguments are optional. If invoked without any argument,
`gnatname' will display its usage.

When used with at least one naming pattern, `gnatname' will attempt to
find all the compilation units in files that follow at least one of the
naming patterns. To find these compilation units, `gnatname' will use
the GNAT compiler in syntax-check-only mode on all regular files.

One or several Naming Patterns may be given as arguments to `gnatname'.
Each Naming Pattern is enclosed between double quotes.  A Naming
Pattern is a regular expression similar to the wildcard patterns used
in file names by the Unix shells or the DOS prompt.

Examples of Naming Patterns are

        "*.[12].ADA"
        "*.ad[sb]*"
        "body_*"    "spec_*"

For a more complete description of the syntax of Naming Patterns, see
the second kind of regular expressions described in `G-REGEXP.ADS' (the
"Glob" regular expressions).

When invoked with no qualifiers, `gnatname' will create a configuration
pragmas file `GNAT.ADC' in the current working directory, with pragmas
`Source_File_Name' for each file that contains a valid Ada unit.


File: gnat_ug_vms.info,  Node: Qualifiers for gnatname,  Next: Examples of gnatname Usage,  Prev: Running gnatname,  Up: Handling Arbitrary File Naming Conventions Using gnatname

Qualifiers for `gnatname'
=========================

Qualifiers for `gnatname' must precede any specified Naming Pattern.

You may specify any of the following qualifiers to `gnatname':

`-c`file''
     Create a configuration pragmas file `file' (instead of the default
     `GNAT.ADC'). There may be zero, one or more space between `-c' and
     `file'. `file' may include directory information. `file' must be
     writeable. There may be only one qualifier `-c'. When a qualifier
     `-c' is specified, no qualifier `-P' may be specified (see below).

`-d`dir''
     Look for source files in directory `dir'. There may be zero, one
     or more spaces between `-d' and `dir'. When a qualifier `-d' is
     specified, the current working directory will not be searched for
     source files, unless it is explictly specified with a `-d' or `-D'
     qualifier. Several qualifiers `-d' may be specified. If `dir' is a
     relative path, it is relative to the directory of the
     configuration pragmas file specified with qualifier `-c', or to
     the directory of the project file specified with qualifier `-P'
     or, if neither qualifier `-c' nor qualifier `-P' are specified, it
     is relative to the current working directory. The directory
     specified with qualifier `-c' must exist and be readable.

`-D`file''
     Look for source files in all directories listed in text file
     `file'. There may be zero, one or more spaces between `-d' and
     `dir'. `file' must be an existing, readable text file. Each non
     empty line in `file' must be a directory. Specifying qualifier
     `-D' is equivalent to specifying as many qualifiers `-d' as there
     are non empty lines in `file'.

`-h'
     Output usage (help) information. The output is written to
     `SYS$OUTPUT'.

`-P`proj''
     Create or update project file `proj'. There may be zero, one or
     more space between `-P' and `proj'. `proj' may include directory
     information.  `proj' must be writeable. There may be only one
     qualifier `-P'.  When a qualifier `-P' is specified, no qualifier
     `-c' may be specified.

`-v'
     Verbose mode. Output detailed explanation of behavior to
     `SYS$OUTPUT'. This includes name of the file written, the name of
     the directories to search and, for each file in those directories
     whose name matches at least one of the Naming Patterns, an
     indication of whether the file contains a unit, and if so the name
     of the unit.

`-v -v'
     Very Verbose mode. In addition to the output produced in verbose
     mode, for each file in the searched directories whose name matches
     none of the Naming Patterns, an indication is given that there is
     no match.

`-x`pattern''
     Excluded patterns. Using this qualifier, it is possible to exclude
     some files that would match the name patterns. For example,
     `"gnatname -x "*_NT.ADA" "*.ADA"' will look for Ada units in all
     files with the `.ADA' extension, except those whose names end with
     `_NT.ADA'.



File: gnat_ug_vms.info,  Node: Examples of gnatname Usage,  Prev: Qualifiers for gnatname,  Up: Handling Arbitrary File Naming Conventions Using gnatname

Examples of `gnatname' Usage
============================

     $ gnatname -c /home/me/NAMES.ADC -d sources "[a-z]*.ADA*"

   In this example, the directory `/home/me' must already exist and be
writeable. In addition, the directory `/home/me/sources' (specified by
`-d sources') must exist and be readable. Note the optional spaces after
`-c' and `-d'.

     $ gnatname -P/home/me/proj -x "*_NT_BODY.ADA" -dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"

   Note that several qualifiers `-d' may be used, even in conjunction
with one or several qualifiers `-D'. Several Naming Patterns and one
excluded pattern are used in this example.


File: gnat_ug_vms.info,  Node: GNAT Project Manager,  Next: Elaboration Order Handling in GNAT,  Prev: Handling Arbitrary File Naming Conventions Using gnatname,  Up: Top

GNAT Project Manager
********************

* Menu:

* Introduction::
* Examples of Project Files::
* Project File Syntax::
* Objects and Sources in Project Files::
* Importing Projects::
* Project Extension::
* External References in Project Files::
* Packages in Project Files::
* Variables from Imported Projects::
* Naming Schemes::
* Library Projects::
* Qualifiers Related to Project Files::
* Tools Supporting Project Files::
* An Extended Example::
* Project File Complete Syntax::


File: gnat_ug_vms.info,  Node: Introduction,  Next: Examples of Project Files,  Up: GNAT Project Manager

Introduction
============

This chapter describes GNAT's _Project Manager_, a facility that lets
you configure various properties for a collection of source files.  In
particular, you can specify:
   * The directory or set of directories containing the source files,
     and/or the names of the specific source files themselves

   * The directory in which the compiler's output (`ALI' files, object
     files, tree files) will be placed

   * The directory in which the executable programs will be placed

   * Qualifier settings for any of the project-enabled tools (`GNAT
     MAKE', compiler, binder, linker, `GNAT LIST', `GNAT XREF', `GNAT
     FIND'); you can apply these settings either globally or to
     individual units

   * The source files containing the main subprogram(s) to be built

   * The source programming language(s) (currently Ada and/or C)

   * Source file naming conventions; you can specify these either
     globally or for individual units

* Menu:

* Project Files::


File: gnat_ug_vms.info,  Node: Project Files,  Up: Introduction

Project Files
-------------

A "project" is a specific set of values for these properties.  You can
define a project's settings in a "project file", a text file with an
Ada-like syntax; a property value is either a string or a list of
strings.  Properties that are not explicitly set receive default
values.  A project file may interrogate the values of "external
variables" (user-defined command-line qualifiers or environment
variables), and it may specify property settings conditionally, based
on the value of such variables.

   In simple cases, a project's source files depend only on other
source files in the same project, or on the predefined libraries.
("Dependence" is in the technical sense; for example, one Ada unit
"with"ing another.)  However, the Project Manager also allows much more
sophisticated arrangements, with the source files in one project
depending on source files in other projects:
   * One project can _import_ other projects containing needed source
     files.

   * You can organize GNAT projects in a hierarchy: a _child_ project
     can extend a _parent_ project, inheriting the parent's source
     files and optionally overriding any of them with alternative
     versions

More generally, the Project Manager lets you structure large development
efforts into hierarchical subsystems, with build decisions deferred to
the subsystem level and thus different compilation environments
(qualifier settings) used for different subsystems.

   The Project Manager is invoked through the `-P_projectfile_'
qualifier to `GNAT MAKE' or to the `gnat' front driver.  If you want to
define (on the command line) an external variable that is queried by
the project file, additionally use the `-X_vbl_=_value_' qualifier.
The Project Manager parses and interprets the project file, and drives
the invoked tool based on the project settings.

   The Project Manager supports a wide range of development strategies,
for systems of all sizes.  Some typical practices that are easily
handled:
   * Using a common set of source files, but generating object files in
     different directories via different qualifier settings

   * Using a mostly-shared set of source files, but with different
     versions of some unit or units

The destination of an executable can be controlled inside a project file
using the `-o' qualifier. In the absence of such a qualifier either
inside the project file or on the command line, any executable files
generated by `GNAT MAKE' will be placed in the directory `Exec_Dir'
specified in the project file. If no `Exec_Dir' is specified, they will
be placed in the object directory of the project.

   You can use project files to achieve some of the effects of a source
versioning system (for example, defining separate projects for the
different sets of sources that comprise different releases) but the
Project Manager is independent of any source configuration management
tools that might be used by the developers.

   The next section introduces the main features of GNAT's project
facility through a sequence of examples; subsequent sections will
present the syntax and semantics in more detail.


File: gnat_ug_vms.info,  Node: Examples of Project Files,  Next: Project File Syntax,  Prev: Introduction,  Up: GNAT Project Manager

Examples of Project Files
=========================

This section illustrates some of the typical uses of project files and
explains their basic structure and behavior.

* Menu:

* Common Sources with Different Qualifiers and Different Output Directories::
* Using External Variables::
* Importing Other Projects::
* Extending a Project::


File: gnat_ug_vms.info,  Node: Common Sources with Different Qualifiers and Different Output Directories,  Next: Using External Variables,  Up: Examples of Project Files

Common Sources with Different Qualifiers and Different Output Directories
-------------------------------------------------------------------------

* Menu:

* Source Files::
* Specifying the Object Directory::
* Specifying the Exec Directory::
* Project File Packages::
* Specifying Qualifier Settings::
* Main Subprograms::
* Source File Naming Conventions::
* Source Language(s)::

Assume that the Ada source files `PACK.ADS', `PACK.ADB', and `PROC.ADB'
are in the `/common' directory.  The file `PROC.ADB' contains an Ada
main subprogram `Proc' that "with"s package `Pack'.  We want to compile
these source files under two sets of qualifiers:
   * When debugging, we want to pass the `-g' qualifier to `GNAT MAKE',
     and the `/CHECKS=ASSERTIONS', `/CHECKS=OVERFLOW', and
     `/CHECKS=ELABORATION' qualifiers to the compiler; the compiler's
     output is to appear in `/common/debug'

   * When preparing a release version, we want to pass the
     `/OPTIMIZE=ALL' qualifier to the compiler; the compiler's output
     is to appear in `/common/release'

The GNAT project files shown below, respectively `debug.gpr' and
`release.gpr' in the `/common' directory, achieve these effects.

   Diagrammatically:
     /common
       debug.gpr
       release.gpr
       PACK.ADS
       PACK.ADB
       PROC.ADB
     /common/debug {-g, /CHECKS=ASSERTIONS, /CHECKS=OVERFLOW, /CHECKS=ELABORATION}
       PROC.ALI, PROC.OBJ
       PACK.ALI, PACK.OBJ
     /common/release {/OPTIMIZE=ALL}
       PROC.ALI, PROC.OBJ
       PACK.ALI, PACK.OBJ
Here are the project files:
     project Debug is
       for Object_Dir use "debug";
       for Main use ("proc");
     
       package Builder is
         for Default_Qualifiers ("Ada") use ("-g");
       end Builder;
     
       package Compiler is
         for Default_Qualifiers ("Ada")
            use ("-fstack-check", "/CHECKS=ASSERTIONS", "/CHECKS=OVERFLOW", "/CHECKS=ELABORATION");
       end Compiler;
     end Debug;

     project Release is
       for Object_Dir use "release";
       for Exec_Dir use ".";
       for Main use ("proc");
     
       package Compiler is
         for Default_Qualifiers ("Ada") use ("/OPTIMIZE=ALL");
       end Compiler;
     end Release;

The name of the project defined by `debug.gpr' is `"Debug"' (case
insensitive), and analogously the project defined by `release.gpr' is
`"Release"'.  For consistency the file should have the same name as the
project, and the project file's extension should be `"gpr"'. These
conventions are not required, but a warning is issued if they are not
followed.

   If the current directory is `/temp', then the command
     GNAT MAKE -P/common/debug.gpr

generates object and ALI files in `/common/debug', and the `proc'
executable also in `/common/debug', using the qualifier settings
defined in the project file.

   Likewise, the command
     GNAT MAKE -P/common/release.gpr

generates object and ALI files in `/common/release', and the `proc'
executable in `/common', using the qualifier settings from the project
file.


File: gnat_ug_vms.info,  Node: Source Files,  Next: Specifying the Object Directory,  Up: Common Sources with Different Qualifiers and Different Output Directories

Source Files
............

If a project file does not explicitly specify a set of source
directories or a set of source files, then by default the project's
source files are the Ada source files in the project file directory.
Thus `PACK.ADS', `PACK.ADB', and `PROC.ADB' are the source files for
both projects.


File: gnat_ug_vms.info,  Node: Specifying the Object Directory,  Next: Specifying the Exec Directory,  Prev: Source Files,  Up: Common Sources with Different Qualifiers and Different Output Directories

Specifying the Object Directory
...............................

Several project properties are modeled by Ada-style _attributes_; you
define the property by supplying the equivalent of an Ada attribute
definition clause in the project file.  A project's object directory is
such a property; the corresponding attribute is `Object_Dir', and its
value is a string expression.  A directory may be specified either as
absolute or as relative; in the latter case, it is relative to the
project file directory.  Thus the compiler's output is directed to
`/common/debug' (for the `Debug' project) and to `/common/release' (for
the `Release' project).  If `Object_Dir' is not specified, then the
default is the project file directory.


File: gnat_ug_vms.info,  Node: Specifying the Exec Directory,  Next: Project File Packages,  Prev: Specifying the Object Directory,  Up: Common Sources with Different Qualifiers and Different Output Directories

Specifying the Exec Directory
.............................

A project's exec directory is another property; the corresponding
attribute is `Exec_Dir', and its value is also a string expression,
either specified as relative or absolute. If `Exec_Dir' is not
specified, then the default is the object directory (which may also be
the project file directory if attribute `Object_Dir' is not specified).
Thus the executable is placed in `/common/debug' for the `Debug'
project (attribute `Exec_Dir' not specified) and in `/common' for the
`Release' project.


File: gnat_ug_vms.info,  Node: Project File Packages,  Next: Specifying Qualifier Settings,  Prev: Specifying the Exec Directory,  Up: Common Sources with Different Qualifiers and Different Output Directories

Project File Packages
.....................

A GNAT tool integrated with the Project Manager is modeled by a
corresponding package in the project file.  The `Debug' project defines
the packages `Builder' (for `GNAT MAKE') and `Compiler'; the `Release'
project defines only the `Compiler' package.

   The Ada package syntax is not to be taken literally.  Although
packages in project files bear a surface resemblance to packages in Ada
source code, the notation is simply a way to convey a grouping of
properties for a named entity.  Indeed, the package names permitted in
project files are restricted to a predefined set, corresponding to the
project-aware tools, and the contents of packages are limited to a
small set of constructs.  The packages in the example above contain
attribute definitions.


File: gnat_ug_vms.info,  Node: Specifying Qualifier Settings,  Next: Main Subprograms,  Prev: Project File Packages,  Up: Common Sources with Different Qualifiers and Different Output Directories

Specifying Qualifier Settings
.............................

Qualifier settings for a project-aware tool can be specified through
attributes in the package corresponding to the tool.  The example above
illustrates one of the relevant attributes, `Default_Qualifiers',
defined in the packages in both project files.  Unlike simple
attributes like `Source_Dirs', `Default_Qualifiers' is known as an
_associative array_.  When you define this attribute, you must supply
an "index" (a literal string), and the effect of the attribute
definition is to set the value of the "array" at the specified "index".
For the `Default_Qualifiers' attribute, the index is a programming
language (in our case, Ada) , and the value specified (after `use')
must be a list of string expressions.

   The attributes permitted in project files are restricted to a
predefined set.  Some may appear at project level, others in packages.
For any attribute that is an associate array, the index must always be a
literal string, but the restrictions on this string (e.g., a file name
or a language name) depend on the individual attribute.  Also depending
on the attribute, its specified value will need to be either a string
or a string list.

   In the `Debug' project, we set the qualifiers for two tools, `GNAT
MAKE' and the compiler, and thus we include corresponding packages,
with each package defining the `Default_Qualifiers' attribute with
index `"Ada"'.  Note that the package corresponding to `GNAT MAKE' is
named `Builder'.  The `Release' project is similar, but with just the
`Compiler' package.

   In project `Debug' above the qualifiers starting with `-gnat' that
are specified in package `Compiler' could have been placed in package
`Builder', since `GNAT MAKE' transmits all such qualifiers to the
compiler.


File: gnat_ug_vms.info,  Node: Main Subprograms,  Next: Source File Naming Conventions,  Prev: Specifying Qualifier Settings,  Up: Common Sources with Different Qualifiers and Different Output Directories

Main Subprograms
................

One of the properties of a project is its list of main subprograms
(actually a list of names of source files containing main subprograms,
with the file extension optional.  This property is captured in the
`Main' attribute, whose value is a list of strings.  If a project
defines the `Main' attribute, then you do not need to identify the main
subprogram(s) when invoking `GNAT MAKE' (see *Note GNAT MAKE and
Project Files::).


File: gnat_ug_vms.info,  Node: Source File Naming Conventions,  Next: Source Language(s),  Prev: Main Subprograms,  Up: Common Sources with Different Qualifiers and Different Output Directories

Source File Naming Conventions
..............................

Since the project files do not specify any source file naming
conventions, the GNAT defaults are used.  The mechanism for defining
source file naming conventions - a package named `Naming' - will be
described below (*note Naming Schemes::).


File: gnat_ug_vms.info,  Node: Source Language(s),  Prev: Source File Naming Conventions,  Up: Common Sources with Different Qualifiers and Different Output Directories

Source Language(s)
..................

Since the project files do not specify a `Languages' attribute, by
default the GNAT tools assume that the language of the project file is
Ada.  More generally, a project can comprise source files in Ada, C,
and/or other languages.


File: gnat_ug_vms.info,  Node: Using External Variables,  Next: Importing Other Projects,  Prev: Common Sources with Different Qualifiers and Different Output Directories,  Up: Examples of Project Files

Using External Variables
------------------------

Instead of supplying different project files for debug and release, we
can define a single project file that queries an external variable (set
either on the command line or via an environment variable) in order to
conditionally define the appropriate settings.  Again, assume that the
source files `PACK.ADS', `PACK.ADB', and `PROC.ADB' are located in
directory `/common'.  The following project file, `build.gpr', queries
the external variable named `STYLE' and defines an object directory and
qualifier settings based on whether the value is `"deb"' (debug) or
`"rel"' (release), where the default is `"deb"'.

     project Build is
       for Main use ("proc");
     
       type Style_Type is ("deb", "rel");
       Style : Style_Type := external ("STYLE", "deb");
     
       case Style is
         when "deb" =>
           for Object_Dir use "debug";
     
         when "rel" =>
           for Object_Dir use "release";
           for Exec_Dir use ".";
       end case;
     
       package Builder is
     
         case Style is
           when "deb" =>
             for Default_Qualifiers ("Ada") use ("-g");
         end case;
     
       end Builder;
     
       package Compiler is
     
         case Style is
           when "deb" =>
             for Default_Qualifiers ("Ada") use ("/CHECKS=ASSERTIONS", "/CHECKS=OVERFLOW", "/CHECKS=ELABORATION");
     
           when "rel" =>
             for Default_Qualifiers ("Ada") use ("/OPTIMIZE=ALL");
         end case;
     
       end Compiler;
     
     end Build;

`Style_Type' is an example of a _string type_, which is the project
file analog of an Ada enumeration type but containing string literals
rather than identifiers.  `Style' is declared as a variable of this
type.

   The form `external("STYLE", "deb")' is known as an _external
reference_; its first argument is the name of an _external variable_,
and the second argument is a default value to be used if the external
variable doesn't exist.  You can define an external variable on the
command line via the `-X' qualifier, or you can use an environment
variable as an external variable.

   Each `case' construct is expanded by the Project Manager based on the
value of `Style'. Thus the command
     GNAT MAKE -P/common/build.gpr -XSTYLE=deb

is equivalent to the `GNAT MAKE' invocation using the project file
`debug.gpr' in the earlier example.  So is the command
     GNAT MAKE -P/common/build.gpr

since `"deb"' is the default for `STYLE'.

   Analogously,
     GNAT MAKE -P/common/build.gpr -XSTYLE=rel

is equivalent to the `GNAT MAKE' invocation using the project file
`release.gpr' in the earlier example.


File: gnat_ug_vms.info,  Node: Importing Other Projects,  Next: Extending a Project,  Prev: Using External Variables,  Up: Examples of Project Files

Importing Other Projects
------------------------

A compilation unit in a source file in one project may depend on
compilation units in source files in other projects.  To obtain this
behavior, the dependent project must _import_ the projects containing
the needed source files.  This effect is embodied in syntax similar to
an Ada `with' clause, but the "with"ed entities are strings denoting
project files.

   As an example, suppose that the two projects `GUI_Proj' and
`Comm_Proj' are defined in the project files `gui_proj.gpr' and
`comm_proj.gpr' in directories `/gui' and `/comm', respectively.
Assume that the source files for `GUI_Proj' are `GUI.ADS' and
`GUI.ADB', and that the source files for `Comm_Proj' are `COMM.ADS' and
`COMM.ADB', with each set of files located in its respective project
file directory.  Diagrammatically:

     /gui
       gui_proj.gpr
       GUI.ADS
       GUI.ADB
     
     /comm
       comm_proj.gpr
       COMM.ADS
       COMM.ADB

We want to develop an application in directory `/app' that "with"s the
packages `GUI' and `Comm', using the properties of the corresponding
project files (e.g. the qualifier settings and object directory).
Skeletal code for a main procedure might be something like the
following:

     with GUI, Comm;
     procedure App_Main is
        ...
     begin
        ...
     end App_Main;

Here is a project file, `app_proj.gpr', that achieves the desired
effect:

     with "/gui/gui_proj", "/comm/comm_proj";
     project App_Proj is
        for Main use ("app_main");
     end App_Proj;

Building an executable is achieved through the command:
     GNAT MAKE -P/app/app_proj

which will generate the `app_main' executable in the directory where
`app_proj.gpr' resides.

   If an imported project file uses the standard extension (`gpr') then
(as illustrated above) the `with' clause can omit the extension.

   Our example specified an absolute path for each imported project
file.  Alternatively, you can omit the directory if either
   * The imported project file is in the same directory as the
     importing project file, or

   * You have defined an environment variable `ADA_PROJECT_PATH' that
     includes the directory containing the needed project file.

Thus, if we define `ADA_PROJECT_PATH' to include `/gui' and `/comm',
then our project file `app_proj.gpr' could be written as follows:

     with "gui_proj", "comm_proj";
     project App_Proj is
        for Main use ("app_main");
     end App_Proj;

Importing other projects raises the possibility of ambiguities.  For
example, the same unit might be present in different imported projects,
or it might be present in both the importing project and an imported
project.  Both of these conditions are errors.  Note that in the
current version of the Project Manager, it is illegal to have an
ambiguous unit even if the unit is never referenced by the importing
project.  This restriction may be relaxed in a future release.


File: gnat_ug_vms.info,  Node: Extending a Project,  Prev: Importing Other Projects,  Up: Examples of Project Files

Extending a Project
-------------------

A common situation in large software systems is to have multiple
implementations for a common interface; in Ada terms, multiple versions
of a package body for the same specification.  For example, one
implementation might be safe for use in tasking programs, while another
might only be used in sequential applications.  This can be modeled in
GNAT using the concept of _project extension_.  If one project (the
"child") _extends_ another project (the "parent") then by default all
source files of the parent project are inherited by the child, but the
child project can override any of the parent's source files with new
versions, and can also add new files.  This facility is the project
analog of extension in Object-Oriented Programming.  Project
hierarchies are permitted (a child project may be the parent of yet
another project), and a project that inherits one project can also
import other projects.

   As an example, suppose that directory `/seq' contains the project
file `seq_proj.gpr' and the source files `PACK.ADS', `PACK.ADB', and
`PROC.ADB':

     /seq
       PACK.ADS
       PACK.ADB
       PROC.ADB
       seq_proj.gpr

Note that the project file can simply be empty (that is, no attribute or
package is defined):

     project Seq_Proj is
     end Seq_Proj;

implying that its source files are all the Ada source files in the
project directory.

   Suppose we want to supply an alternate version of `PACK.ADB', in
directory `/tasking', but use the existing versions of `PACK.ADS' and
`PROC.ADB'.  We can define a project `Tasking_Proj' that inherits
`Seq_Proj':

     /tasking
       PACK.ADB
       tasking_proj.gpr
     
     project Tasking_Proj extends "/seq/seq_proj" is
     end Tasking_Proj;

The version of `PACK.ADB' used in a build depends on which project file
is specified.

   Note that we could have designed this using project import rather
than project inheritance; a `base' project would contain the sources for
`PACK.ADS' and `PROC.ADB', a sequential project would import `base' and
add `PACK.ADB', and likewise a tasking project would import `base' and
add a different version of `PACK.ADB'.  The choice depends on whether
other sources in the original project need to be overridden.  If they
do, then project extension is necessary, otherwise, importing is
sufficient.


File: gnat_ug_vms.info,  Node: Project File Syntax,  Next: Objects and Sources in Project Files,  Prev: Examples of Project Files,  Up: GNAT Project Manager

Project File Syntax
===================

* Menu:

* Basic Syntax::
* Packages::
* Expressions::
* String Types::
* Variables::
* Attributes::
* Associative Array Attributes::
* case Constructions::

This section describes the structure of project files.

   A project may be an _independent project_, entirely defined by a
single project file. Any Ada source file in an independent project
depends only on the predefined library and other Ada source files in
the same project.

A project may also "depend on" other projects, in either or both of the
following ways:
   * It may import any number of projects

   * It may extend at most one other project

The dependence relation is a directed acyclic graph (the subgraph
reflecting the "extends" relation is a tree).

   A project's "immediate sources" are the source files directly
defined by that project, either implicitly by residing in the project
file's directory, or explicitly through any of the source-related
attributes described below.  More generally, a project PROJ's "sources"
are the immediate sources of PROJ together with the immediate sources
(unless overridden) of any project on which PROJ depends (either
directly or indirectly).


File: gnat_ug_vms.info,  Node: Basic Syntax,  Next: Packages,  Up: Project File Syntax

Basic Syntax
------------

As seen in the earlier examples, project files have an Ada-like syntax.
The minimal project file is:
     project Empty is
     
     end Empty;

The identifier `Empty' is the name of the project.  This project name
must be present after the reserved word `end' at the end of the project
file, followed by a semi-colon.

   Any name in a project file, such as the project name or a variable
name, has the same syntax as an Ada identifier.

   The reserved words of project files are the Ada reserved words plus
`extends', `external', and `project'.  Note that the only Ada reserved
words currently used in project file syntax are:

   * `case'

   * `end'

   * `for'

   * `is'

   * `others'

   * `package'

   * `renames'

   * `type'

   * `use'

   * `when'

   * `with'

Comments in project files have the same syntax as in Ada, two
consecutives hyphens through the end of the line.


File: gnat_ug_vms.info,  Node: Packages,  Next: Expressions,  Prev: Basic Syntax,  Up: Project File Syntax

Packages
--------

A project file may contain _packages_. The name of a package must be one
of the identifiers (case insensitive) from a predefined list, and a
package with a given name may only appear once in a project file. The
predefined list includes the following packages:

   * `Naming'

   * `Builder'

   * `Compiler'

   * `Binder'

   * `Linker'

   * `Finder'

   * `Cross_Reference'

   * `GNAT LIST'

(The complete list of the package names and their attributes can be
found in file `PRJ-ATTR.ADB').

In its simplest form, a package may be empty:

     project Simple is
       package Builder is
       end Builder;
     end Simple;

A package may contain _attribute declarations_, _variable declarations_
and _case constructions_, as will be described below.

   When there is ambiguity between a project name and a package name,
the name always designates the project. To avoid possible confusion, it
is always a good idea to avoid naming a project with one of the names
allowed for packages or any name that starts with `gnat'.


File: gnat_ug_vms.info,  Node: Expressions,  Next: String Types,  Prev: Packages,  Up: Project File Syntax

Expressions
-----------

An _expression_ is either a _string expression_ or a _string list
expression_.

   A _string expression_ is either a _simple string expression_ or a
_compound string expression_.

   A _simple string expression_ is one of the following:
   * A literal string; e.g.`"comm/my_proj.gpr"'

   * A string-valued variable reference (see *Note Variables::)

   * A string-valued attribute reference (see *Note Attributes::)

   * An external reference (see *Note External References in Project
     Files::)

A _compound string expression_ is a concatenation of string expressions,
using `"&"'
            Path & "/" & File_Name & ".ADS"

A _string list expression_ is either a _simple string list expression_
or a _compound string list expression_.

   A _simple string list expression_ is one of the following:
   * A parenthesized list of zero or more string expressions, separated
     by commas
             File_Names := (File_Name, "GNAT.ADC", File_Name & ".orig");
             Empty_List := ();

   * A string list-valued variable reference

   * A string list-valued attribute reference

A _compound string list expression_ is the concatenation (using `"&"')
of a simple string list expression and an expression.  Note that each
term in a compound string list expression, except the first, may be
either a string expression or a string list expression.

        File_Name_List := () & File_Name; --  One string in this list
        Extended_File_Name_List := File_Name_List & (File_Name & ".orig");
        --  Two strings
        Big_List := File_Name_List & Extended_File_Name_List;
        --  Concatenation of two string lists: three strings
        Illegal_List := "GNAT.ADC" & Extended_File_Name_List;
        --  Illegal: must start with a string list


File: gnat_ug_vms.info,  Node: String Types,  Next: Variables,  Prev: Expressions,  Up: Project File Syntax

String Types
------------

The value of a variable may be restricted to a list of string literals.
The restricted list of string literals is given in a _string type
declaration_.

   Here is an example of a string type declaration:

        type OS is ("NT, "nt", "Unix", "Linux", "other OS");

Variables of a string type are called _typed variables_; all other
variables are called _untyped variables_. Typed variables are
particularly useful in `case' constructions (see *Note case
Constructions::).

   A string type declaration starts with the reserved word `type',
followed by the name of the string type (case-insensitive), followed by
the reserved word `is', followed by a parenthesized list of one or more
string literals separated by commas, followed by a semicolon.

   The string literals in the list are case sensitive and must all be
different.  They may include any graphic characters allowed in Ada,
including spaces.

   A string type may only be declared at the project level, not inside
a package.

   A string type may be referenced by its name if it has been declared
in the same project file, or by its project name, followed by a dot,
followed by the string type name.


File: gnat_ug_vms.info,  Node: Variables,  Next: Attributes,  Prev: String Types,  Up: Project File Syntax

Variables
---------

A variable may be declared at the project file level, or in a package.
Here are some examples of variable declarations:

        This_OS : OS := external ("OS"); --  a typed variable declaration
        That_OS := "Linux";              --  an untyped variable declaration

A _typed variable declaration_ includes the variable name, followed by
a colon, followed by the name of a string type, followed by `:=',
followed by a simple string expression.

   An _untyped variable declaration_ includes the variable name,
followed by `:=', followed by an expression.  Note that, despite the
terminology, this form of "declaration" resembles more an assignment
than a declaration in Ada.  It is a declaration in several senses:
   * The variable name does not need to be defined previously

   * The declaration establishes the _kind_ (string versus string list)
     of the variable, and later declarations of the same variable need
     to be consistent with this

A string variable declaration (typed or untyped) declares a variable
whose value is a string. This variable may be used as a string
expression.
        File_Name       := "readme.txt";
        Saved_File_Name := File_Name & ".saved";

A string list variable declaration declares a variable whose value is a
list of strings. The list may contain any number (zero or more) of
strings.

        Empty_List := ();
        List_With_One_Element := ("/STYLE=");
        List_With_Two_Elements := List_With_One_Element & "/STYLE=GNAT";
        Long_List := ("MAIN.ADA", "PACK1_.ADA", "PACK1.ADA", "PACK2_.ADA"
                      "PACK2.ADA", "UTIL_.ADA", "UTIL.ADA");

The same typed variable may not be declared more than once at project
level, and it may not be declared more than once in any package; it is
in effect a constant or a readonly variable.

   The same untyped variable may be declared several times.  In this
case, the new value replaces the old one, and any subsequent reference
to the variable uses the new value.  However, as noted above, if a
variable has been declared as a string, all subsequent declarations
must give it a string value. Similarly, if a variable has been declared
as a string list, all subsequent declarations must give it a string
list value.

   A _variable reference_ may take several forms:

   * The simple variable name, for a variable in the current package
     (if any) or in the current project

   * A context name, followed by a dot, followed by the variable name.

A _context_ may be one of the following:

   * The name of an existing package in the current project

   * The name of an imported project of the current project

   * The name of an ancestor project (i.e., a project extended by the
     current project, either directly or indirectly)

   * An imported/parent project name, followed by a dot, followed by a
     package name

A variable reference may be used in an expression.


File: gnat_ug_vms.info,  Node: Attributes,  Next: Associative Array Attributes,  Prev: Variables,  Up: Project File Syntax

Attributes
----------

A project (and its packages) may have _attributes_ that define the
project's properties.  Some attributes have values that are strings;
others have values that are string lists.

   There are two categories of attributes: _simple attributes_ and
_associative arrays_ (see *Note Associative Array Attributes::).

   The names of the attributes are restricted; there is a list of
project attributes, and a list of package attributes for each package.
The names are not case sensitive.

   The project attributes are as follows (all are simple attributes):

_Attribute Name_              _Value_
`Source_Files'                string list
`Source_Dirs'                 string list
`Source_List_File'            string
`Object_Dir'                  string
`Exec_Dir'                    string
`Main'                        string list
`Languages'                   string list
`Library_Dir'                 string
`Library_Name'                string
`Library_Kind'                string
`Library_Elaboration'         string
`Library_Version'             string

The attributes for package `Naming' are as follows (see *Note Naming
Schemes::):

Attribute Name                Category       Index          Value
`Specification_Suffix'        associative    language name  string
                              array                         
`Implementation_Suffix'       associative    language name  string
                              array                         
`Separate_Suffix'             simple         n/a            string
                              attribute                     
`Casing'                      simple         n/a            string
                              attribute                     
`Dot_Replacement'             simple         n/a            string
                              attribute                     
`Specification'               associative    Ada unit name  string
                              array                         
`Implementation'              associative    Ada unit name  string
                              array                         
`Specification_Exceptions'    associative    language name  string list
                              array                         
`Implementation_Exceptions'   associative    language name  string list
                              array                         

The attributes for package `Builder', `Compiler', `Binder', `Linker',
`Cross_Reference', and `Finder' are as follows (see *Note Qualifiers
and Project Files::).

Attribute Name                Category       Index          Value
`Default_Qualifiers'          associative    language name  string list
                              array                         
`Qualifiers'                  associative    file name      string list
                              array                         

In addition, package `Builder' has a single string attribute
`Local_Configuration_Pragmas' and package `Builder' has a single string
attribute `Global_Configuration_Pragmas'.

The attribute for package `Glide' are not documented: they are for
internal use only.

Each simple attribute has a default value: the empty string (for
string-valued attributes) and the empty list (for string list-valued
attributes).

   Similar to variable declarations, an attribute declaration defines a
new value for an attribute.

   Examples of simple attribute declarations:

        for Object_Dir use "objects";
        for Source_Dirs use ("units", "test/drivers");

A "simple attribute declaration" starts with the reserved word `for',
followed by the name of the attribute, followed by the reserved word
`use', followed by an expression (whose kind depends on the attribute),
followed by a semicolon.

   Attributes may be referenced in expressions.  The general form for
such a reference is `<entity>'<attribute>': the entity for which the
attribute is defined, followed by an apostrophe, followed by the name
of the attribute.  For associative array attributes, a litteral string
between parentheses need to be supplied as index.

   Examples are:

       project'Object_Dir
       Naming'Dot_Replacement
       Imported_Project'Source_Dirs
       Imported_Project.Naming'Casing
       Builder'Default_Qualifiers("Ada")

The entity may be:
   * `project' for an attribute of the current project

   * The name of an existing package of the current project

   * The name of an imported project

   * The name of a parent project (extended by the current project)

   * An imported/parent project name, followed by a dot,       followed
     by a package name

Example:
        project Prj is
          for Source_Dirs use project'Source_Dirs & "units";
          for Source_Dirs use project'Source_Dirs & "test/drivers"
        end Prj;

In the first attribute declaration, initially the attribute
`Source_Dirs' has the default value: an empty string list. After this
declaration, `Source_Dirs' is a string list of one element: "units".
After the second attribute declaration `Source_Dirs' is a string list of
two elements: "units" and "test/drivers".

   Note: this example is for illustration only. In practice, the
project file would contain only one attribute declaration:

        for Source_Dirs use ("units", "test/drivers");


File: gnat_ug_vms.info,  Node: Associative Array Attributes,  Next: case Constructions,  Prev: Attributes,  Up: Project File Syntax

Associative Array Attributes
----------------------------

Some attributes are defined as _associative arrays_. An associative
array may be regarded as a function that takes a string as a parameter
and delivers a string or string list value as its result.

   Here are some examples of associative array attribute declarations:

        for Implementation ("main") use "MAIN.ADA";
        for Qualifiers ("MAIN.ADA") use ("-v", "/REPORT_ERRORS=VERBOSE");
        for Qualifiers ("MAIN.ADA") use Builder'Qualifiers ("MAIN.ADA") & "-g";

Like untyped variables and simple attributes, associative array
attributes may be declared several times. Each declaration supplies a
new value for the attribute, replacing the previous setting.


File: gnat_ug_vms.info,  Node: case Constructions,  Prev: Associative Array Attributes,  Up: Project File Syntax

`case' Constructions
--------------------

A `case' construction is used in a project file to effect conditional
behavior.  Here is a typical example:

     project MyProj is
        type OS_Type is ("Linux", "Unix", "NT", "VMS");
     
        OS : OS_Type := external ("OS", "Linux");
     
        package Compiler is
          case OS is
            when "Linux" | "Unix" =>
              for Default_Qualifiers ("Ada") use ("-gnath");
            when "NT" =>
              for Default_Qualifiers ("Ada") use ("/POLLING_ENABLE");
            when others =>
          end case;
        end Compiler;
     end MyProj;

The syntax of a `case' construction is based on the Ada case statement
(although there is no `null' construction for empty alternatives).

   Following the reserved word `case' there is the case variable (a
typed string variable), the reserved word `is', and then a sequence of
one or more alternatives.  Each alternative comprises the reserved word
`when', either a list of literal strings separated by the `"|"'
character or the reserved word `others',  and the `"=>"' token.  Each
literal string must belong to the string type that is the type of the
case variable.  An `others' alternative, if present, must occur last.
The `end case;' sequence terminates the case construction.

   After each `=>', there are zero or more constructions.  The only
constructions allowed in a case construction are other case
constructions and attribute declarations. String type declarations,
variable declarations and package declarations are not allowed.

   The value of the case variable is often given by an external
reference (see *Note External References in Project Files::).


File: gnat_ug_vms.info,  Node: Objects and Sources in Project Files,  Next: Importing Projects,  Prev: Project File Syntax,  Up: GNAT Project Manager

Objects and Sources in Project Files
====================================

* Menu:

* Object Directory::
* Exec Directory::
* Source Directories::
* Source File Names::

Each project has exactly one object directory and one or more source
directories. The source directories must contain at least one source
file, unless  the project file explicitly specifies that no source
files are present (see *Note Source File Names::).


File: gnat_ug_vms.info,  Node: Object Directory,  Next: Exec Directory,  Up: Objects and Sources in Project Files

Object Directory
----------------

The object directory for a project is the directory containing the
compiler's output (such as `ALI' files and object files) for the
project's immediate sources. Note that for inherited sources (when
extending a parent project) the parent project's object directory is
used.

   The object directory is given by the value of the attribute
`Object_Dir' in the project file.

        for Object_Dir use "objects";

The attribute OBJECT_DIR has a string value, the path name of the object
directory. The path name may be absolute or relative to the directory
of the project file. This directory must already exist, and be readable
and writable.

   By default, when the attribute `Object_Dir' is not given an explicit
value or when its value is the empty string, the object directory is
the same as the directory containing the project file.


File: gnat_ug_vms.info,  Node: Exec Directory,  Next: Source Directories,  Prev: Object Directory,  Up: Objects and Sources in Project Files

Exec Directory
--------------

The exec directory for a project is the directory containing the
executables for the project's main subprograms.

   The exec directory is given by the value of the attribute `Exec_Dir'
in the project file.

        for Exec_Dir use "executables";

The attribute EXEC_DIR has a string value, the path name of the exec
directory. The path name may be absolute or relative to the directory
of the project file. This directory must already exist, and be writable.

   By default, when the attribute `Exec_Dir' is not given an explicit
value or when its value is the empty string, the exec directory is the
same as the object directory of the project file.


File: gnat_ug_vms.info,  Node: Source Directories,  Next: Source File Names,  Prev: Exec Directory,  Up: Objects and Sources in Project Files

Source Directories
------------------

The source directories of a project are specified by the project file
attribute `Source_Dirs'.

   This attribute's value is a string list. If the attribute is not
given an explicit value, then there is only one source directory, the
one where the project file resides.

   A `Source_Dirs' attribute that is explicitly defined to be the empty
list, as in

         for Source_Dirs use ();

indicates that the project contains no source files.

   Otherwise, each string in the string list designates one or more
source directories.

        for Source_Dirs use ("sources", "test/drivers");

If a string in the list ends with `"/**"',  then the directory whose
path name precedes the two asterisks, as well as all its subdirectories
(recursively), are source directories.

        for Source_Dirs use ("/system/sources/**");

Here the directory `/system/sources' and all of its subdirectories
(recursively) are source directories.

   To specify that the source directories are the directory of the
project file and all of its subdirectories, you can declare
`Source_Dirs' as follows:
        for Source_Dirs use ("./**");

Each of the source directories must exist and be readable.


File: gnat_ug_vms.info,  Node: Source File Names,  Prev: Source Directories,  Up: Objects and Sources in Project Files

Source File Names
-----------------

In a project that contains source files, their names may be specified
by the attributes `Source_Files' (a string list) or `Source_List_File'
(a string). Source file names never include any directory information.

   If the attribute `Source_Files' is given an explicit value, then each
element of the list is a source file name.

        for Source_Files use ("MAIN.ADB");
        for Source_Files use ("MAIN.ADB", "PACK1.ADS", "PACK2.ADB");

If the attribute `Source_Files' is not given an explicit value, but the
attribute `Source_List_File' is given a string value, then the source
file names are contained in the text file whose path name (absolute or
relative to the directory of the project file) is the value of the
attribute `Source_List_File'.

   Each line in the file that is not empty or is not a comment contains
a source file name. A comment line starts with two hyphens.

        for Source_List_File use "source_list.txt";

By default, if neither the attribute `Source_Files' nor the attribute
`Source_List_File' is given an explicit value, then each file in the
source directories that conforms to the project's naming scheme (see
*Note Naming Schemes::) is an immediate source of the project.

   A warning is issued if both attributes `Source_Files' and
`Source_List_File' are given explicit values. In this case, the
attribute `Source_Files' prevails.

   Each source file name must be the name of one and only one existing
source file in one of the source directories.

   A `Source_Files' attribute defined with an empty list as its value
indicates that there are no source files in the project.

   Except for projects that are clearly specified as containing no Ada
source files (`Source_Dirs' or `Source_Files' specified as an empty
list, or `Languages' specified without `"Ada"' in the list)
        for Source_Dirs use ();
        for Source_Files use ();
        for Languages use ("C", "C++");

a project must contain at least one immediate source.

   Projects with no source files are useful as template packages (see
*Note Packages in Project Files::) for other projects; in particular to
define a package `Naming' (see *Note Naming Schemes::).


File: gnat_ug_vms.info,  Node: Importing Projects,  Next: Project Extension,  Prev: Objects and Sources in Project Files,  Up: GNAT Project Manager

Importing Projects
==================

An immediate source of a project P may depend on source files that are
neither immediate sources of P nor in the predefined library.  To get
this effect, P must _import_ the projects that contain the needed
source files.

       with "project1", "utilities.gpr";
       with "/namings/apex.gpr";
       project Main is
         ...

As can be seen in this example, the syntax for importing projects is
similar to the syntax for importing compilation units in Ada. However,
project files use literal strings instead of names, and the `with'
clause identifies project files rather than packages.

   Each literal string is the file name or path name (absolute or
relative) of a project file. If a string is simply a file name, with no
path, then its location is determined by the _project path_:

   * If the environment variable `ADA_PROJECT_PATH' exists, then the
     project path includes all the directories in this environment
     variable, plus the directory of the project file.

   * If the environment variable `ADA_PROJECT_PATH' does not exist,
     then the project path contains only one directory, namely the one
     where the project file is located.

If a relative pathname is used as in

       with "tests/proj";

then the path is relative to the directory where the importing project
file is located. Any symbolic link will be fully resolved in the
directory of the importing project file before the imported project
file is looked up.

   When the `with''ed project file name does not have an extension, the
default is `.gpr'. If a file with this extension is not found, then the
file name as specified in the `with' clause (no extension) will be
used. In the above example, if a file `project1.gpr' is found, then it
will be used; otherwise, if a file `project1' exists then it will be
used; if neither file exists, this is an error.

   A warning is issued if the name of the project file does not match
the name of the project; this check is case insensitive.

   Any source file that is an immediate source of the imported project
can be used by the immediate sources of the importing project, and
recursively. Thus if `A' imports `B', and `B' imports `C', the immediate
sources of `A' may depend on the immediate sources of `C', even if `A'
does not import `C' explicitly. However, this is not recommended,
because if and when `B' ceases to import `C', some sources in `A' will
no longer compile.

   A side effect of this capability is that cyclic dependences are not
permitted: if `A' imports `B' (directly or indirectly) then `B' is not
allowed to import `A'.


File: gnat_ug_vms.info,  Node: Project Extension,  Next: External References in Project Files,  Prev: Importing Projects,  Up: GNAT Project Manager

Project Extension
=================

During development of a large system, it is sometimes necessary to use
modified versions of some of the source files without changing the
original sources. This can be achieved through a facility known as
_project extension_.

        project Modified_Utilities extends "/baseline/utilities.gpr" is ...

The project file for the project being extended (the _parent_) is
identified by the literal string that follows the reserved word
`extends', which itself follows the name of the extending project (the
_child_).

   By default, a child project inherits all the sources of its parent.
However, inherited sources can be overridden: a unit with the same name
as one in the parent will hide the original unit.  Inherited sources
are considered to be sources (but not immediate sources) of the child
project; see *Note Project File Syntax::.

   An inherited source file retains any qualifiers specified in the
parent project.

   For example if the project `Utilities' contains the specification
and the body of an Ada package `Util_IO', then the project
`Modified_Utilities' can contain a new body for package `Util_IO'.  The
original body of `Util_IO' will not be considered in program builds.
However, the package specification will still be found in the project
`Utilities'.

   A child project can have only one parent but it may import any
number of other projects.

   A project is not allowed to import directly or indirectly at the
same time a child project and any of its ancestors.


File: gnat_ug_vms.info,  Node: External References in Project Files,  Next: Packages in Project Files,  Prev: Project Extension,  Up: GNAT Project Manager

External References in Project Files
====================================

A project file may contain references to external variables; such
references are called _external references_.

   An external variable is either defined as part of the environment (an
environment variable in Unix, for example) or else specified on the
command line via the `-X_vbl_=_value_' qualifier. If both, then the
command line value is used.

   An external reference is denoted by the built-in function
`external', which returns a string value.  This function has two forms:
   * `external (external_variable_name)'

   * `external (external_variable_name, default_value)'

Each parameter must be a string literal.  For example:

        external ("USER")
        external ("OS", "Linux")

In the form with one parameter, the function returns the value of the
external variable given as parameter. If this name is not present in the
environment, then the returned value is an empty string.

   In the form with two string parameters, the second parameter is the
value returned when the variable given as the first parameter is not
present in the environment. In the example above, if `"OS"' is not the
name of an environment variable and is not passed on the command line,
then the returned value will be `"Linux"'.

   An external reference may be part of a string expression or of a
string list expression, to define variables or attributes.

        type Mode_Type is ("Debug", "Release");
        Mode : Mode_Type := external ("MODE");
        case Mode is
          when "Debug" =>
             ...


File: gnat_ug_vms.info,  Node: Packages in Project Files,  Next: Variables from Imported Projects,  Prev: External References in Project Files,  Up: GNAT Project Manager

Packages in Project Files
=========================

The _package_ is the project file feature that defines the settings for
project-aware tools.  For each such tool you can declare a
corresponding package; the names for these packages are preset (see
*Note Packages::) but are not case sensitive.  A package may contain
variable declarations, attribute declarations, and case constructions.

        project Proj is
           package Builder is  -- used by GNAT MAKE
              for Default_Qualifiers ("Ada") use ("-v", "-g");
           end Builder;
        end Proj;

A package declaration starts with the reserved word `package', followed
by the package name (case insensitive), followed by the reserved word
`is'. It ends with the reserved word `end', followed by the package
name, finally followed by a semi-colon.

   Most of the packages have an attribute `Default_Qualifiers'.  This
attribute is an associative array, and its value is a string list.  The
index of the associative array is the name of a programming language
(case insensitive). This attribute indicates the qualifier or
qualifiers to be used with the corresponding tool.

   Some packages also have another attribute, `Qualifiers', an
associative array whose value is a string list. The index is the name
of a source file.  This attribute indicates the qualifier or qualifiers
to be used by the corresponding tool when dealing with this specific
file.

   Further information on these qualifier-related attributes is found in
*Note Qualifiers and Project Files::.

   A package may be declared as a _renaming_ of another package; e.g.,
from the project file for an imported project.

       with "/global/apex.gpr";
       project Example is
         package Naming renames Apex.Naming;
         ...
       end Example;

Packages that are renamed in other project files often come from
project files that have no sources: they are just used as templates.
Any modification in the template will be reflected automatically in all
the project files that rename a package from the template.

   In addition to the tool-oriented packages, you can also declare a
package named `Naming' to establish specialized source file naming
conventions (see *Note Naming Schemes::).


File: gnat_ug_vms.info,  Node: Variables from Imported Projects,  Next: Naming Schemes,  Prev: Packages in Project Files,  Up: GNAT Project Manager

Variables from Imported Projects
================================

An attribute or variable defined in an imported or parent project can
be used in expressions in the importing / extending project.  Such an
attribute or variable is prefixed with the name of the project and (if
relevant) the name of package where it is defined.

       with "imported";
       project Main extends "base" is
          Var1 := Imported.Var;
          Var2 := Base.Var & ".new";
     
          package Builder is
             for Default_Qualifiers ("Ada") use Imported.Builder.Ada_Qualifiers &
                              "/STYLE=GNAT" & "-v";
          end Builder;
     
          package Compiler is
             for Default_Qualifiers ("Ada") use Base.Compiler.Ada_Qualifiers;
          end Compiler;
       end Main;

In this example:

   * `Var1' is a copy of the variable `Var' defined in the project file
     `"imported.gpr"'

   * the value of `Var2' is a copy of the value of variable `Var'
     defined in the project file `base.gpr', concatenated with `".new"'

   * attribute `Default_Qualifiers ("Ada")' in package `Builder' is a
     string list that includes in its value a copy of variable
     `Ada_Qualifiers' defined in the `Builder' package in project file
     `imported.gpr' plus two new elements: `"/STYLE=GNAT"' and `"-v"';

   * attribute `Default_Qualifiers ("Ada")' in package `Compiler' is a
     copy of the variable `Ada_Qualifiers' defined in the `Compiler'
     package in project file `base.gpr', the project being extended.


File: gnat_ug_vms.info,  Node: Naming Schemes,  Next: Library Projects,  Prev: Variables from Imported Projects,  Up: GNAT Project Manager

Naming Schemes
==============

Sometimes an Ada software system is ported from a foreign compilation
environment to GNAT, with file names that do not use the default GNAT
conventions. Instead of changing all the file names (which for a
variety of reasons might not be possible), you can define the relevant
file naming scheme in the `Naming' package in your project file.  For
example, the following package models the Apex file naming rules:

       package Naming is
         for Casing                        use "lowercase";
         for Dot_Replacement               use ".";
         for Specification_Suffix ("Ada")  use ".1.ADA";
         for Implementation_Suffix ("Ada") use ".2.ADA";
       end Naming;

You can define the following attributes in package `Naming':

`CASING'
     This must be a string with one of the three values `"lowercase"',
     `"uppercase"' or `"mixedcase"'; these strings are case insensitive.

     If CASING is not specified, then the default is `"lowercase"'.

`DOT_REPLACEMENT'
     This must be a string whose value satisfies the following
     conditions:

        * It must not be empty

        * It cannot start or end with an alphanumeric character

        * It cannot be a single underscore

        * It cannot start with an underscore followed by an alphanumeric

        * It cannot contain a dot `'.'' except if it the entire string
          is `"."'

     If `Dot_Replacement' is not specified, then the default is `"-"'.

`SPECIFICATION_SUFFIX'
     This is an associative array (indexed by the programming language
     name, case insensitive) whose value is a string that must satisfy
     the following conditions:

        * It must not be empty

        * It cannot start with an alphanumeric character

        * It cannot start with an underscore followed by an
          alphanumeric character

     If `Specification_Suffix ("Ada")' is not specified, then the
     default is `".ADS"'.

`IMPLEMENTATION_SUFFIX'
     This is an associative array (indexed by the programming language
     name, case insensitive) whose value is a string that must satisfy
     the following conditions:

        * It must not be empty

        * It cannot start with an alphanumeric character

        * It cannot start with an underscore followed by an
          alphanumeric character

        * It cannot be a suffix of `Specification_Suffix'

     If `Implementation_Suffix ("Ada")' is not specified, then the
     default is `".ADB"'.

`SEPARATE_SUFFIX'
     This must be a string whose value satisfies the same conditions as
     `Implementation_Suffix'.

     If `Separate_Suffix ("Ada")' is not specified, then it defaults to
     same value as `Implementation_Suffix ("Ada")'.

`SPECIFICATION'
     You can use the `Specification' attribute, an associative array,
     to define the source file name for an individual Ada compilation
     unit's spec. The array index must be a string literal that
     identifies the Ada unit (case insensitive).  The value of this
     attribute must be a string that identifies the file that contains
     this unit's spec (case sensitive or insensitive depending on the
     operating system).

             for Specification ("MyPack.MyChild") use "mypack.mychild.spec";

`IMPLEMENTATION'
     You can use the `Implementation' attribute, an associative array,
     to define the source file name for an individual Ada compilation
     unit's body (possibly a subunit).  The array index must be a
     string literal that identifies the Ada unit (case insensitive).
     The value of this attribute must be a string that identifies the
     file that contains this unit's body or subunit (case sensitive or
     insensitive depending on the operating system).

             for Implementation ("MyPack.MyChild") use "mypack.mychild.body";


File: gnat_ug_vms.info,  Node: Library Projects,  Next: Qualifiers Related to Project Files,  Prev: Naming Schemes,  Up: GNAT Project Manager

Library Projects
================

_Library projects_ are projects whose object code is placed in a
library.  (Note that this facility is not yet supported on all
platforms)

   To create a library project, you need to define in its project file
two project-level attributes: `Library_Name' and `Library_Dir'.
Additionally, you may define the library-related attributes
`Library_Kind', `Library_Version' and `Library_Elaboration'.

   The `Library_Name' attribute has a string value that must start with
a letter and include only letters and digits.

   The `Library_Dir' attribute has a string value that designates the
path (absolute or relative) of the directory where the library will
reside.  It must designate an existing directory, and this directory
needs to be different from the project's object directory. It also
needs to be writable.

   If both `Library_Name' and `Library_Dir' are specified and are
legal, then the project file defines a library project.  The optional
library-related attributes are checked only for such project files.

   The `Library_Kind' attribute has a string value that must be one of
the following (case insensitive): `"static"', `"dynamic"' or
`"relocatable"'. If this attribute is not specified, the library is a
static library. Otherwise, the library may be dynamic or relocatable.
Depending on the operating system, there may or may not be a distinction
between dynamic and relocatable libraries. For example, on Unix there
is no such distinction.

   The `Library_Version' attribute has a string value whose
interpretation is platform dependent. On Unix, it is used only for
dynamic/relocatable libraries as the internal name of the library (the
`"soname"'). If the library file name (built from the `Library_Name')
is different from the `Library_Version', then the library file will be
a symbolic link to the actual file whose name will be `Library_Version'.

   Example (on Unix):

     project Plib is
     
        Version := "1";
     
        for Library_Dir use "lib_dir";
        for Library_Name use "dummy";
        for Library_Kind use "relocatable";
        for Library_Version use "libdummy.so." & Version;
     
     end Plib;

Directory `lib_dir' will contain the internal library file whose name
will be `libdummy.so.1', and `libdummy.so' will be a symbolic link to
`libdummy.so.1'.

   When `GNAT MAKE' detects that a project file (not the main project
file) is a library project file, it will check all immediate sources of
the project and rebuild the library if any of the sources have been
recompiled.  All `ALI' files will also be copied from the object
directory to the library directory. To build executables, `GNAT MAKE'
will use the library rather than the individual object files.


File: gnat_ug_vms.info,  Node: Qualifiers Related to Project Files,  Next: Tools Supporting Project Files,  Prev: Library Projects,  Up: GNAT Project Manager

Qualifiers Related to Project Files
===================================

The following qualifiers are used by GNAT tools that support project
files:

``-PPROJECT''
     Indicates the name of a project file. This project file will be
     parsed with the verbosity indicated by `-vP_x_', if any, and using
     the external references indicated by `-X' qualifiers, if any.

     There must be only one `-P' qualifier on the command line.

     Since the Project Manager parses the project file only after all
     the qualifiers on the command line are checked, the order of the
     qualifiers `-P', `-Vp_x_' or `-X' is not significant.

``-XNAME=VALUE''
     Indicates that external variable NAME has the value VALUE.  The
     Project Manager will use this value for occurrences of
     `external(name)' when parsing the project file.

     If NAME or VALUE includes a space, then NAME=VALUE should be put
     between quotes.
            -XOS=NT
            -X"user=John Doe"

     Several `-X' qualifiers can be used simultaneously.  If several
     `-X' qualifiers specify the same NAME, only the last one is used.

     An external variable specified with a `-X' qualifier takes
     precedence over the value of the same name in the environment.

``-vP_x_''
     Indicates the verbosity of the parsing of GNAT project files.
     `-vP0' means Default (no output for syntactically correct project
     files); `-vP1' means Medium; `-vP2' means High.

     The default is Default.

     If several `-vP_x_' qualifiers are present, only the last one is
     used.



File: gnat_ug_vms.info,  Node: Tools Supporting Project Files,  Next: An Extended Example,  Prev: Qualifiers Related to Project Files,  Up: GNAT Project Manager

Tools Supporting Project Files
==============================

* Menu:

* GNAT MAKE and Project Files::
* The GNAT Driver and Project Files::


File: gnat_ug_vms.info,  Node: GNAT MAKE and Project Files,  Next: The GNAT Driver and Project Files,  Up: Tools Supporting Project Files

GNAT MAKE and Project Files
---------------------------

This section covers two topics related to `GNAT MAKE' and project files:
defining qualifiers for `GNAT MAKE' and for the tools that it invokes;
and the use of the `Main' attribute.

* Menu:

* Qualifiers and Project Files::
* Project Files and Main Subprograms::


File: gnat_ug_vms.info,  Node: Qualifiers and Project Files,  Next: Project Files and Main Subprograms,  Up: GNAT MAKE and Project Files

Qualifiers and Project Files
............................

For each of the packages `Builder', `Compiler', `Binder', and `Linker',
you can specify a `Default_Qualifiers' attribute, a `Qualifiers'
attribute, or both; as their names imply, these qualifier-related
attributes affect which qualifiers are used for which files when `GNAT
MAKE' is invoked.  As will be explained below, these
package-contributed qualifiers precede the qualifiers passed on the
`GNAT MAKE' command line.

   The `Default_Qualifiers' attribute is an associative array indexed by
language name (case insensitive) and returning a string list.  For
example:

     package Compiler is
       for Default_Qualifiers ("Ada") use ("/STYLE=", "-v");
     end Compiler;

The `Qualifiers' attribute is also an associative array, indexed by a
file name (which may or may not be case sensitive, depending on the
operating system) and returning a string list.  For example:

     package Builder is
        for Qualifiers ("MAIN1.ADB") use ("/OPTIMIZE=ALL");
        for Qualifiers ("MAIN2.ADB") use ("-g");
     end Builder;

For the `Builder' package, the file names should designate source files
for main subprograms.  For the `Binder' and `Linker' packages, the file
names should designate `ALI' or source files for main subprograms.  In
each case just the file name (without explicit extension) is acceptable.

   For each tool used in a program build (`GNAT MAKE', the compiler, the
binder, and the linker), its corresponding package "contributes" a set
of qualifiers for each file on which the tool is invoked, based on the
qualifier-related attributes defined in the package. In particular, the
qualifiers that each of these packages contributes for a given file F
comprise:

   * the value of attribute `Qualifiers (F)', if it is specified in the
     package for the given file,

   * otherwise, the value of `Default_Qualifiers ("Ada")', if it is
     specified in the package.

If neither of these attributes is defined in the package, then the
package does not contribute any qualifiers for the given file.

   When `GNAT MAKE' is invoked on a file, the qualifiers comprise two
sets, in the following order: those contributed for the file by the
`Builder' package; and the qualifiers passed on the command line.

   When `GNAT MAKE' invokes a tool (compiler, binder, linker) on a file,
the qualifiers passed to the tool comprise three sets, in the following
order:

  1. the applicable qualifiers contributed for the file by the
     `Builder' package in the project file supplied on the command line;

  2. those contributed for the file by the package (in the relevant
     project file - see below) corresponding to the tool; and

  3. the applicable qualifiers passed on the command line.

The term _applicable qualifiers_ reflects the fact that `GNAT MAKE'
qualifiers may or may not be passed to individual tools, depending on
the individual qualifier.

   `GNAT MAKE' may invoke the compiler on source files from different
projects. The Project Manager will use the appropriate project file to
determine the `Compiler' package for each source file being compiled.
Likewise for the `Binder' and `Linker' packages.

   As an example, consider the following package in a project file:

     project Proj1 is
        package Compiler is
           for Default_Qualifiers ("Ada") use ("-g");
           for Qualifiers ("A.ADB") use ("/OPTIMIZE=SOME");
           for Qualifiers ("B.ADB") use ("/OPTIMIZE=ALL", "/STYLE=");
        end Compiler;
     end Proj1;

If `GNAT MAKE' is invoked with this project file, and it needs to
compile, say, the files `A.ADB', `B.ADB', and `C.ADB', then `A.ADB'
will be compiled with the qualifier `/OPTIMIZE=SOME', `B.ADB' with
qualifiers `/OPTIMIZE=ALL' and `/STYLE=', and `C.ADB' with `-g'.

   Another example illustrates the ordering of the qualifiers
contributed by different packages:

     project Proj2 is
        package Builder is
           for Qualifiers ("MAIN.ADB") use ("-g", "/OPTIMIZE=SOME", "-f");
        end Builder;
     
        package Compiler is
           for Qualifiers ("MAIN.ADB") use ("/OPTIMIZE=ALL");
        end Compiler;
     end Proj2;

If you issue the command:

         GNAT MAKE -PProj2 /OPTIMIZE=NONE main

then the compiler will be invoked on `MAIN.ADB' with the following
sequence of qualifiers

        -g /OPTIMIZE=SOME /OPTIMIZE=ALL /OPTIMIZE=NONE

   with the last `-O' qualifier having precedence over the earlier ones;
several other qualifiers (such as `-c') are added implicitly.

   The qualifiers `-g' and `/OPTIMIZE=SOME' are contributed by package
`Builder',  `/OPTIMIZE=ALL' is contributed by the package `Compiler'
and `/OPTIMIZE=NONE' comes from the command line.

   The `-g' qualifier will also be passed in the invocation of `GNAT
LINK.'

   A final example illustrates qualifier contributions from packages in
different project files:

     project Proj3 is
        for Source_Files use ("PACK.ADS", "PACK.ADB");
        package Compiler is
           for Default_Qualifiers ("Ada") use ("/CHECKS=ASSERTIONS");
        end Compiler;
     end Proj3;
     
     with "Proj3";
     project Proj4 is
        for Source_Files use ("FOO_MAIN.ADB", "BAR_MAIN.ADB");
        package Builder is
           for Qualifiers ("FOO_MAIN.ADB") use ("-s", "-g");
        end Builder;
     end Proj4;
     
     -- Ada source file:
     with Pack;
     procedure Foo_Main is
        ...
     end Foo_Main;

   If the command is
     GNAT MAKE -PProj4 FOO_MAIN.ADB /COMPILER_QUALIFIERS /CHECKS=OVERFLOW

then the qualifiers passed to the compiler for `FOO_MAIN.ADB' are `-g'
(contributed by the package `Proj4.Builder') and `/CHECKS=OVERFLOW'
(passed on the command line).  When the imported package `Pack' is
compiled, the qualifiers used are `-g' from `Proj4.Builder',
`/CHECKS=ASSERTIONS' (contributed from package `Proj3.Compiler', and
`/CHECKS=OVERFLOW' from the command line.


File: gnat_ug_vms.info,  Node: Project Files and Main Subprograms,  Prev: Qualifiers and Project Files,  Up: GNAT MAKE and Project Files

Project Files and Main Subprograms
..................................

When using a project file, you can invoke `GNAT MAKE' with several main
subprograms, by specifying their source files on the command line.
Each of these needs to be an immediate source file of the project.

         GNAT MAKE -Pprj main1 main2 main3

When using a project file, you can also invoke `GNAT MAKE' without
explicitly specifying any main, and the effect depends on whether you
have defined the `Main' attribute.  This attribute has a string list
value, where each element in the list is the name of a source file (the
file extension is optional) containing a main subprogram.

   If the `Main' attribute is defined in a project file as a non-empty
string list and the qualifier `-u' is not used on the command line, then
invoking `GNAT MAKE' with this project file but without any main on the
command line is equivalent to invoking `GNAT MAKE' with all the file
names in the `Main' attribute on the command line.

   Example:
        project Prj is
           for Main use ("main1", "main2", "main3");
        end Prj;

With this project file, `"GNAT MAKE -Pprj"' is equivalent to `"GNAT
MAKE -Pprj main1 main2 main3"'.

   When the project attribute `Main' is not specified, or is specified
as an empty string list, or when the qualifier `-u' is used on the
command line, then invoking `GNAT MAKE' with no main on the command
line will result in all immediate sources of the project file being
checked, and potentially recompiled. Depending on the presence of the
qualifier `-u', sources from other project files on which the immediate
sources of the main project file depend are also checked and
potentially recompiled. In other words, the `-u' qualifier is applied
to all of the immediate sources of themain project file.


File: gnat_ug_vms.info,  Node: The GNAT Driver and Project Files,  Prev: GNAT MAKE and Project Files,  Up: Tools Supporting Project Files

The GNAT Driver and Project Files
---------------------------------

A number of GNAT tools, other than `GNAT MAKE' are project-aware: `GNAT
BIND', `GNAT FIND', `GNAT LINK', `GNAT LIST' and `GNAT XREF'. However,
none of these tools can be invoked directly with a project file
qualifier (`-P'). They need to be invoke through the `gnat' driver.

   The `gnat' driver is a front-end that accepts a number of commands
and call the corresponding tool. It has been designed initially for VMS
to convert VMS style qualifiers to Unix style qualifiers, but it is now
available to all the GNAT supported platforms.

   On non VMS platforms, the `gnat' driver accepts the following
commands (case insensitive):

   * BIND to invoke `GNAT BIND'

   * CHOP to invoke `GNAT CHOP'

   * COMP or COMPILE to invoke the compiler

   * ELIM to invoke `GNAT ELIM'

   * FIND to invoke `GNAT FIND'

   * KR or KRUNCH to invoke `GNAT KRUNCH'

   * LINK to invoke `GNAT LINK'

   * LS or LIST to invoke `GNAT LIST'

   * MAKE to invoke `GNAT MAKE'

   * NAME to invoke `gnatname'

   * PREP or PREPROCESS to invoke `GNAT PREPROCESS'

   * PSTA or STANDARD to invoke `GNAT STANDARD'

   * STUB to invoke `GNAT STUB'

   * XREF to invoke `GNAT XREF'

Note that the compiler is invoked using the command `GNAT MAKE -f -u'.

Following the command, you may put qualifiers and arguments for the
invoked tool.

       gnat bind -C MAIN.ALI
       gnat ls -a main
       gnat chop foo.txt

In addition, for command BIND, FIND, LS or LIST, LINK and XREF, the
project file related qualifiers (`-P', `-X' and `-vPx') may be used in
addition to the qualifiers of the invoking tool.

For each of these command, there is possibly a package in the main
project that corresponds to the invoked tool.

   * package `Binder' for command BIND (invoking `GNAT BIND')

   * package `Finder' for command FIND (invoking `GNAT FIND')

   * package `GNAT LIST' for command LS or LIST (invoking `GNAT LIST')

   * package `Linker' for command LINK (invoking `GNAT LINK')

   * package `Cross_Reference' for command XREF (invoking `GNAT LINK')


Package `GNAT LIST' has a unique attribute `Qualifiers', a simple
variable with a string list value. It contains qualifiers for the
invocation of `GNAT LIST'.

     project Proj1 is
        package GNAT LIST is
           for Qualifiers use ("-a", "-v");
        end GNAT LIST;
     end Proj1;

All other packages contains a qualifier `Default_Qualifiers', an
associative array, indexed by the programming language (case
insensitive) and having a string list value. `Default_Qualifiers
("Ada")' contains the qualifiers for the invocation of the tool
corresponding to the package.

     project Proj is
     
        for Source_Dirs use ("./**");
     
        package GNAT LIST is
           for Qualifiers use ("-a", "-v");
        end GNAT LIST;
     
        package Binder is
           for Default_Qualifiers ("Ada") use ("-C", "-e");
        end Binder;
     
        package Linker is
           for Default_Qualifiers ("Ada") use ("-C");
        end Linker;
     
        package Finder is
           for Default_Qualifiers ("Ada") use ("-a", "-f");
        end Finder;
     
        package Cross_Reference is
           for Default_Qualifiers ("Ada") use ("-a", "-f", "-d", "-u");
        end Cross_Reference;
     end Proj;

With the above project file, commands such as

        gnat ls -Pproj main
        gnat xref -Pproj main
        gnat bind -Pproj MAIN.ALI

will set up the environment properly and invoke the tool with the
qualifiers found in the package corresponding to the tool.


File: gnat_ug_vms.info,  Node: An Extended Example,  Next: Project File Complete Syntax,  Prev: Tools Supporting Project Files,  Up: GNAT Project Manager

An Extended Example
===================

Suppose that we have two programs, PROG1 and PROG2, with the sources in
the respective directories. We would like to build them with a single
`GNAT MAKE' command, and we would like to place their object files into
`.build' subdirectories of the source directories. Furthermore, we would
like to have to have two separate subdirectories in `.build'  -
`release' and `debug' - which will contain the object files compiled
with different set of compilation flags.

   In other words, we have the following structure:

        main
          |- prog1
          |    |- .build
          |         | debug
          |         | release
          |- prog2
               |- .build
                    | debug
                    | release

Here are the project files that we need to create in a directory `main'
to maintain this structure:

  1. We create a `Common' project with a package `Compiler' that
     specifies the compilation qualifiers:

          File "common.gpr":
          project Common is
          
             for Source_Dirs use (); -- No source files
          
             type Build_Type is ("release", "debug");
             Build : Build_Type := External ("BUILD", "debug");
             package Compiler is
                case Build is
                   when "release" =>
                     for Default_Qualifiers ("Ada") use ("/OPTIMIZE=ALL");
                   when "debug"   =>
                     for Default_Qualifiers ("Ada") use ("-g");
                end case;
             end Compiler;
          
          end Common;

  2. We create separate projects for the two programs:

          File "prog1.gpr":
          
          with "common";
          project Prog1 is
          
              for Source_Dirs use ("prog1");
              for Object_Dir  use "prog1/.build/" & Common.Build;
          
              package Compiler renames Common.Compiler;
          
          end Prog1;

          File "prog2.gpr":
          
          with "common";
          project Prog2 is
          
              for Source_Dirs use ("prog2");
              for Object_Dir  use "prog2/.build/" & Common.Build;
          
              package Compiler renames Common.Compiler;
          end Prog2;

  3. We create a wrapping project MAIN:

          File "main.gpr":
          
          with "common";
          with "prog1";
          with "prog2";
          project Main is
          
             package Compiler renames Common.Compiler;
          
          end Main;

  4. Finally we need to create a dummy procedure that `with's (either
     explicitly or implicitly) all the sources of our two programs.


Now we can build the programs using the command

        GNAT MAKE -Pmain dummy

for the Debug mode, or

        GNAT MAKE -Pmain -XBUILD=release

for the Release mode.


File: gnat_ug_vms.info,  Node: Project File Complete Syntax,  Prev: An Extended Example,  Up: GNAT Project Manager

Project File Complete Syntax
============================

     project ::=
       context_clause project_declaration
     
     context_clause ::=
       {with_clause}
     
     with_clause ::=
       with literal_string { , literal_string } ;
     
     project_declaration ::=
       project <project_>simple_name [ extends literal_string ] is
         {declarative_item}
       end <project_>simple_name;
     
     declarative_item ::=
       package_declaration |
       typed_string_declaration |
       other_declarative_item
     
     package_declaration ::=
       package <package_>simple_name package_completion
     
     package_completion ::=
       package_body | package_renaming
     
     package body ::=
       is
         {other_declarative_item}
       end <package_>simple_name ;
     
     package_renaming ::==
       renames <project_>simple_name.<package_>simple_name ;
     
     typed_string_declaration ::=
       type <typed_string_>_simple_name is
        ( literal_string {, literal_string} );
     
     other_declarative_item ::=
       attribute_declaration |
       typed_variable_declaration |
       variable_declaration |
       case_construction
     
     attribute_declaration ::=
       for attribute use expression ;
     
     attribute ::=
       <simple_attribute_>simple_name |
       <associative_array_attribute_>simple_name ( literal_string )
     
     typed_variable_declaration ::=
       <typed_variable_>simple_name : <typed_string_>name :=  string_expression ;
     
     variable_declaration ::=
       <variable_>simple_name := expression;
     
     expression ::=
       term {& term}
     
     term ::=
       literal_string |
       string_list |
       <variable_>name |
       external_value |
       attribute_reference
     
     literal_string ::=
       (same as Ada)
     
     string_list ::=
       ( <string_>expression { , <string_>expression } )
     
     external_value ::=
       external ( literal_string [, literal_string] )
     
     attribute_reference ::=
       attribute_parent ' <simple_attribute_>simple_name [ ( literal_string ) ]
     
     attribute_parent ::=
       project |
       <project_or_package>simple_name |
       <project_>simple_name . <package_>simple_name
     
     case_construction ::=
       case <typed_variable_>name is
         {case_item}
       end case ;
     
     case_item ::=
       when discrete_choice_list => {case_construction | attribute_declaration}
     
     discrete_choice_list ::=
       literal_string {| literal_string}
     
     name ::=
       simple_name {. simple_name}
     
     simple_name ::=
       identifier (same as Ada)


File: gnat_ug_vms.info,  Node: Elaboration Order Handling in GNAT,  Next: The Cross-Referencing Tools GNAT XREF and GNAT FIND,  Prev: GNAT Project Manager,  Up: Top

Elaboration Order Handling in GNAT
**********************************

* Menu:

* Elaboration Code in Ada 95::
* Checking the Elaboration Order in Ada 95::
* Controlling the Elaboration Order in Ada 95::
* Controlling Elaboration in GNAT - Internal Calls::
* Controlling Elaboration in GNAT - External Calls::
* Default Behavior in GNAT - Ensuring Safety::
* Elaboration Issues for Library Tasks::
* Mixing Elaboration Models::
* What to Do If the Default Elaboration Behavior Fails::
* Elaboration for Access-to-Subprogram Values::
* Summary of Procedures for Elaboration Control::
* Other Elaboration Order Considerations::

This chapter describes the handling of elaboration code in Ada 95 and
in GNAT, and discusses how the order of elaboration of program units can
be controlled in GNAT, either automatically or with explicit programming
features.


File: gnat_ug_vms.info,  Node: Elaboration Code in Ada 95,  Next: Checking the Elaboration Order in Ada 95,  Up: Elaboration Order Handling in GNAT

Elaboration Code in Ada 95
==========================

Ada 95 provides rather general mechanisms for executing code at
elaboration time, that is to say before the main program starts
executing. Such code arises in three contexts:

Initializers for variables.
     Variables declared at the library level, in package specs or
     bodies, can require initialization that is performed at
     elaboration time, as in:
          Sqrt_Half : Float := Sqrt (0.5);

Package initialization code
     Code in a `BEGIN-END' section at the outer level of a package body
     is executed as part of the package body elaboration code.

Library level task allocators
     Tasks that are declared using task allocators at the library level
     start executing immediately and hence can execute at elaboration
     time.

Subprogram calls are possible in any of these contexts, which means that
any arbitrary part of the program may be executed as part of the
elaboration code. It is even possible to write a program which does all
its work at elaboration time, with a null main program, although
stylistically this would usually be considered an inappropriate way to
structure a program.

   An important concern arises in the context of elaboration code: we
have to be sure that it is executed in an appropriate order. What we
have is a series of elaboration code sections, potentially one section
for each unit in the program. It is important that these execute in the
correct order. Correctness here means that, taking the above example of
the declaration of `Sqrt_Half', if some other piece of elaboration code
references `Sqrt_Half', then it must run after the section of
elaboration code that contains the declaration of `Sqrt_Half'.

   There would never be any order of elaboration problem if we made a
rule that whenever you `with' a unit, you must elaborate both the spec
and body of that unit before elaborating the unit doing the `with''ing:

     with Unit_1;
     package Unit_2 is ...

would require that both the body and spec of `Unit_1' be elaborated
before the spec of `Unit_2'. However, a rule like that would be far too
restrictive. In particular, it would make it impossible to have routines
in separate packages that were mutually recursive.

   You might think that a clever enough compiler could look at the
actual elaboration code and determine an appropriate correct order of
elaboration, but in the general case, this is not possible. Consider
the following example.

   In the body of `Unit_1', we have a procedure `Func_1' that references
the variable `Sqrt_1', which is declared in the elaboration code of the
body of `Unit_1':

     Sqrt_1 : Float := Sqrt (0.1);

The elaboration code of the body of `Unit_1' also contains:

     if expression_1 = 1 then
        Q := Unit_2.Func_2;
     end if;

`Unit_2' is exactly parallel, it has a procedure `Func_2' that
references the variable `Sqrt_2', which is declared in the elaboration
code of the body `Unit_2':

     Sqrt_2 : Float := Sqrt (0.1);

The elaboration code of the body of `Unit_2' also contains:

     if expression_2 = 2 then
        Q := Unit_1.Func_1;
     end if;

Now the question is, which of the following orders of elaboration is
acceptable:

     Spec of Unit_1
     Spec of Unit_2
     Body of Unit_1
     Body of Unit_2

or

     Spec of Unit_2
     Spec of Unit_1
     Body of Unit_2
     Body of Unit_1

If you carefully analyze the flow here, you will see that you cannot
tell at compile time the answer to this question.  If `expression_1' is
not equal to 1, and `expression_2' is not equal to 2, then either order
is acceptable, because neither of the function calls is executed. If
both tests evaluate to true, then neither order is acceptable and in
fact there is no correct order.

   If one of the two expressions is true, and the other is false, then
one of the above orders is correct, and the other is incorrect. For
example, if `expression_1' = 1 and `expression_2' /= 2, then the call
to `Func_2' will occur, but not the call to `Func_1.' This means that
it is essential to elaborate the body of `Unit_1' before the body of
`Unit_2', so the first order of elaboration is correct and the second
is wrong.

   By making `expression_1' and `expression_2' depend on input data, or
perhaps the time of day, we can make it impossible for the compiler or
binder to figure out which of these expressions will be true, and hence
it is impossible to guarantee a safe order of elaboration at run time.


File: gnat_ug_vms.info,  Node: Checking the Elaboration Order in Ada 95,  Next: Controlling the Elaboration Order in Ada 95,  Prev: Elaboration Code in Ada 95,  Up: Elaboration Order Handling in GNAT

Checking the Elaboration Order in Ada 95
========================================

In some languages that involve the same kind of elaboration problems,
e.g. Java and C++, the programmer is expected to worry about these
ordering problems himself, and it is common to write a program in which
an incorrect elaboration order  gives surprising results, because it
references variables before they are initialized.  Ada 95 is designed
to be a safe language, and a programmer-beware approach is clearly not
sufficient. Consequently, the language provides three lines of defense:

Standard rules
     Some standard rules restrict the possible choice of elaboration
     order. In particular, if you `with' a unit, then its spec is always
     elaborated before the unit doing the `with'. Similarly, a parent
     spec is always elaborated before the child spec, and finally a
     spec is always elaborated before its corresponding body.

Dynamic elaboration checks
     Dynamic checks are made at run time, so that if some entity is
     accessed before it is elaborated (typically  by means of a
     subprogram call) then the exception (`Program_Error') is raised.

Elaboration control
     Facilities are provided for the programmer to specify the desired
     order of elaboration.

   Let's look at these facilities in more detail. First, the rules for
dynamic checking. One possible rule would be simply to say that the
exception is raised if you access a variable which has not yet been
elaborated. The trouble with this approach is that it could require
expensive checks on every variable reference. Instead Ada 95 has two
rules which are a little more restrictive, but easier to check, and
easier to state:

Restrictions on calls
     A subprogram can only be called at elaboration time if its body
     has been elaborated. The rules for elaboration given above
     guarantee that the spec of the subprogram has been elaborated
     before the call, but not the body. If this rule is violated, then
     the exception `Program_Error' is raised.

Restrictions on instantiations
     A generic unit can only be instantiated if the body of the generic
     unit has been elaborated. Again, the rules for elaboration given
     above guarantee that the spec of the generic unit has been
     elaborated before the instantiation, but not the body. If this
     rule is violated, then the exception `Program_Error' is raised.

The idea is that if the body has been elaborated, then any variables it
references must have been elaborated; by checking for the body being
elaborated we guarantee that none of its references causes any trouble.
As we noted above, this is a little too restrictive, because a
subprogram that has no non-local references in its body may in fact be
safe to call. However, it really would be unsafe to rely on this,
because it would mean that the caller was aware of details of the
implementation in the body. This goes against the basic tenets of Ada.

   A plausible implementation can be described as follows.  A Boolean
variable is associated with each subprogram and each generic unit. This
variable is initialized to False, and is set to True at the point body
is elaborated. Every call or instantiation checks the variable, and
raises `Program_Error' if the variable is False.

   Note that one might think that it would be good enough to have one
Boolean variable for each package, but that would not deal with cases
of trying to call a body in the same package as the call that has not
been elaborated yet.  Of course a compiler may be able to do enough
analysis to optimize away some of the Boolean variables as unnecessary,
and `GNAT' indeed does such optimizations, but still the easiest
conceptual model is to think of there being one variable per subprogram.


File: gnat_ug_vms.info,  Node: Controlling the Elaboration Order in Ada 95,  Next: Controlling Elaboration in GNAT - Internal Calls,  Prev: Checking the Elaboration Order in Ada 95,  Up: Elaboration Order Handling in GNAT

Controlling the Elaboration Order in Ada 95
===========================================

In the previous section we discussed the rules in Ada 95 which ensure
that `Program_Error' is raised if an incorrect elaboration order is
chosen. This prevents erroneous executions, but we need mechanisms to
specify a correct execution and avoid the exception altogether.  To
achieve this, Ada 95 provides a number of features for controlling the
order of elaboration. We discuss these features in this section.

   First, there are several ways of indicating to the compiler that a
given unit has no elaboration problems:

packages that do not require a body
     In Ada 95, a library package that does not require a body does not
     permit a body. This means that if we have a such a package, as in:

          package Definitions is
             generic
                type m is new integer;
             package Subp is
                type a is array (1 .. 10) of m;
                type b is array (1 .. 20) of m;
             end Subp;
          end Definitions;

     A package that `with''s `Definitions' may safely instantiate
     `Definitions.Subp' because the compiler can determine that there
     definitely is no package body to worry about in this case

pragma Pure
     Places sufficient restrictions on a unit to guarantee that no call
     to any subprogram in the unit can result in an elaboration
     problem. This means that the compiler does not need to worry about
     the point of elaboration of such units, and in particular, does
     not need to check any calls to any subprograms in this unit.

pragma Preelaborate
     This pragma places slightly less stringent restrictions on a unit
     than does pragma Pure, but these restrictions are still sufficient
     to ensure that there are no elaboration problems with any calls to
     the unit.

pragma Elaborate_Body
     This pragma requires that the body of a unit be elaborated
     immediately after its spec. Suppose a unit `A' has such a pragma,
     and unit `B' does a `with' of unit `A'. Recall that the standard
     rules require the spec of unit `A' to be elaborated before the
     `with''ing unit; given the pragma in `A', we also know that the
     body of `A' will be elaborated before `B', so that calls to `A'
     are safe and do not need a check.

Note that, unlike pragma `Pure' and pragma `Preelaborate', the use of
`Elaborate_Body' does not guarantee that the program is free of
elaboration problems, because it may not be possible to satisfy the
requested elaboration order.  Let's go back to the example with
`Unit_1' and `Unit_2'.  If a programmer marks `Unit_1' as
`Elaborate_Body', and not `Unit_2,' then the order of elaboration will
be:

     Spec of Unit_2
     Spec of Unit_1
     Body of Unit_1
     Body of Unit_2

Now that means that the call to `Func_1' in `Unit_2' need not be
checked, it must be safe. But the call to `Func_2' in `Unit_1' may
still fail if `Expression_1' is equal to 1, and the programmer must
still take responsibility for this not being the case.

   If all units carry a pragma `Elaborate_Body', then all problems are
eliminated, except for calls entirely within a body, which are in any
case fully under programmer control. However, using the pragma
everywhere is not always possible.  In particular, for our
`Unit_1'/`Unit_2' example, if we marked both of them as having pragma
`Elaborate_Body', then clearly there would be no possible elaboration
order.

   The above pragmas allow a server to guarantee safe use by clients,
and clearly this is the preferable approach. Consequently a good rule in
Ada 95 is to mark units as `Pure' or `Preelaborate' if possible, and if
this is not possible, mark them as `Elaborate_Body' if possible.  As we
have seen, there are situations where neither of these three pragmas
can be used.  So we also provide methods for clients to control the
order of elaboration of the servers on which they depend:

pragma Elaborate (unit)
     This pragma is placed in the context clause, after a `with' clause,
     and it requires that the body of the named unit be elaborated
     before the unit in which the pragma occurs. The idea is to use
     this pragma if the current unit calls at elaboration time,
     directly or indirectly, some subprogram in the named unit.

pragma Elaborate_All (unit)
     This is a stronger version of the Elaborate pragma. Consider the
     following example:

          Unit A `with''s unit B and calls B.Func in elab code
          Unit B `with''s unit C, and B.Func calls C.Func

     Now if we put a pragma `Elaborate (B)' in unit `A', this ensures
     that the body of `B' is elaborated before the call, but not the
     body of `C', so the call to `C.Func' could still cause
     `Program_Error' to be raised.

     The effect of a pragma `Elaborate_All' is stronger, it requires
     not only that the body of the named unit be elaborated before the
     unit doing the `with', but also the bodies of all units that the
     named unit uses, following `with' links transitively. For example,
     if we put a pragma `Elaborate_All (B)' in unit `A', then it
     requires not only that the body of `B' be elaborated before `A',
     but also the body of `C', because `B' `with''s `C'.

We are now in a position to give a usage rule in Ada 95 for avoiding
elaboration problems, at least if dynamic dispatching and access to
subprogram values are not used. We will handle these cases separately
later.

   The rule is simple. If a unit has elaboration code that can directly
or indirectly make a call to a subprogram in a `with''ed unit, or
instantiate a generic unit in a `with''ed unit, then if the `with''ed
unit does not have pragma `Pure' or `Preelaborate', then the client
should have a pragma `Elaborate_All' for the `with''ed unit. By
following this rule a client is assured that calls can be made without
risk of an exception.  If this rule is not followed, then a program may
be in one of four states:

No order exists
     No order of elaboration exists which follows the rules, taking into
     account any `Elaborate', `Elaborate_All', or `Elaborate_Body'
     pragmas. In this case, an Ada 95 compiler must diagnose the
     situation at bind time, and refuse to build an executable program.

One or more orders exist, all incorrect
     One or more acceptable elaboration orders exists, and all of them
     generate an elaboration order problem. In this case, the binder
     can build an executable program, but `Program_Error' will be raised
     when the program is run.

Several orders exist, some right, some incorrect
     One or more acceptable elaboration orders exists, and some of them
     work, and some do not. The programmer has not controlled the order
     of elaboration, so the binder may or may not pick one of the
     correct orders, and the program may or may not raise an exception
     when it is run. This is the worst case, because it means that the
     program may fail when moved to another compiler, or even another
     version of the same compiler.

One or more orders exists, all correct
     One ore more acceptable elaboration orders exist, and all of them
     work. In this case the program runs successfully. This state of
     affairs can be guaranteed by following the rule we gave above, but
     may be true even if the rule is not followed.

Note that one additional advantage of following our Elaborate_All rule
is that the program continues to stay in the ideal (all orders OK) state
even if maintenance changes some bodies of some subprograms.
Conversely, if a program that does not follow this rule happens to be
safe at some point, this state of affairs may deteriorate silently as a
result of maintenance changes.

   You may have noticed that the above discussion did not mention the
use of `Elaborate_Body'. This was a deliberate omission. If you `with'
an `Elaborate_Body' unit, it still may be the case that code in the
body makes calls to some other unit, so it is still necessary to use
`Elaborate_All' on such units.


File: gnat_ug_vms.info,  Node: Controlling Elaboration in GNAT - Internal Calls,  Next: Controlling Elaboration in GNAT - External Calls,  Prev: Controlling the Elaboration Order in Ada 95,  Up: Elaboration Order Handling in GNAT

Controlling Elaboration in GNAT - Internal Calls
================================================

In the case of internal calls, i.e. calls within a single package, the
programmer has full control over the order of elaboration, and it is up
to the programmer to elaborate declarations in an appropriate order. For
example writing:

     function One return Float;
     
     Q : Float := One;
     
     function One return Float is
     begin
          return 1.0;
     end One;

will obviously raise `Program_Error' at run time, because function One
will be called before its body is elaborated. In this case GNAT will
generate a warning that the call will raise `Program_Error':

      1. procedure y is
      2.    function One return Float;
      3.
      4.    Q : Float := One;
                         |
         >>> warning: cannot call "One" before body is elaborated
         >>> warning: Program_Error will be raised at run time
     
      5.
      6.    function One return Float is
      7.    begin
      8.         return 1.0;
      9.    end One;
     10.
     11. begin
     12.    null;
     13. end;

Note that in this particular case, it is likely that the call is safe,
because the function `One' does not access any global variables.
Nevertheless in Ada 95, we do not want the validity of the check to
depend on the contents of the body (think about the separate
compilation case), so this is still wrong, as we discussed in the
previous sections.

   The error is easily corrected by rearranging the declarations so
that the body of One appears before the declaration containing the call
(note that in Ada 95, declarations can appear in any order, so there is
no restriction that would prevent this reordering, and if we write:

     function One return Float;
     
     function One return Float is
     begin
          return 1.0;
     end One;
     
     Q : Float := One;

then all is well, no warning is generated, and no `Program_Error'
exception will be raised.  Things are more complicated when a chain of
subprograms is executed:

     function A return Integer;
     function B return Integer;
     function C return Integer;
     
     function B return Integer is begin return A; end;
     function C return Integer is begin return B; end;
     
     X : Integer := C;
     
     function A return Integer is begin return 1; end;

Now the call to `C' at elaboration time in the declaration of `X' is
correct, because the body of `C' is already elaborated, and the call to
`B' within the body of `C' is correct, but the call to `A' within the
body of `B' is incorrect, because the body of `A' has not been
elaborated, so `Program_Error' will be raised on the call to `A'.  In
this case GNAT will generate a warning that `Program_Error' may be
raised at the point of the call. Let's look at the warning:

      1. procedure x is
      2.    function A return Integer;
      3.    function B return Integer;
      4.    function C return Integer;
      5.
      6.    function B return Integer is begin return A; end;
                                                         |
         >>> warning: call to "A" before body is elaborated may
                      raise Program_Error
         >>> warning: "B" called at line 7
         >>> warning: "C" called at line 9
     
      7.    function C return Integer is begin return B; end;
      8.
      9.    X : Integer := C;
     10.
     11.    function A return Integer is begin return 1; end;
     12.
     13. begin
     14.    null;
     15. end;

Note that the message here says "may raise", instead of the direct case,
where the message says "will be raised". That's because whether `A' is
actually called depends in general on run-time flow of control.  For
example, if the body of `B' said

     function B return Integer is
     begin
        if some-condition-depending-on-input-data then
           return A;
        else
           return 1;
        end if;
     end B;

then we could not know until run time whether the incorrect call to A
would actually occur, so `Program_Error' might or might not be raised.
It is possible for a compiler to do a better job of analyzing bodies, to
determine whether or not `Program_Error' might be raised, but it
certainly couldn't do a perfect job (that would require solving the
halting problem and is provably impossible), and because this is a
warning anyway, it does not seem worth the effort to do the analysis.
Cases in which it would be relevant are rare.

   In practice, warnings of either of the forms given above will
usually correspond to real errors, and should be examined carefully and
eliminated.  In the rare case where a warning is bogus, it can be
suppressed by any of the following methods:

   * Compile with the `/WARNINGS=SUPPRESS' qualifier set

   * Suppress `Elaboration_Checks' for the called subprogram

   * Use pragma `Warnings_Off' to turn warnings off for the call

For the internal elaboration check case, GNAT by default generates the
necessary run-time checks to ensure that `Program_Error' is raised if
any call fails an elaboration check. Of course this can only happen if a
warning has been issued as described above. The use of pragma `Suppress
(Elaboration_Checks)' may (but is not guaranteed to) suppress some of
these checks, meaning that it may be possible (but is not guaranteed)
for a program to be able to call a subprogram whose body is not yet
elaborated, without raising a `Program_Error' exception.


File: gnat_ug_vms.info,  Node: Controlling Elaboration in GNAT - External Calls,  Next: Default Behavior in GNAT - Ensuring Safety,  Prev: Controlling Elaboration in GNAT - Internal Calls,  Up: Elaboration Order Handling in GNAT

Controlling Elaboration in GNAT - External Calls
================================================

The previous section discussed the case in which the execution of a
particular thread of elaboration code occurred entirely within a single
unit. This is the easy case to handle, because a programmer has direct
and total control over the order of elaboration, and furthermore,
checks need only be generated in cases which are rare and which the
compiler can easily detect.  The situation is more complex when
separate compilation is taken into account.  Consider the following:

     package Math is
        function Sqrt (Arg : Float) return Float;
     end Math;
     
     package body Math is
        function Sqrt (Arg : Float) return Float is
        begin
              ...
        end Sqrt;
     end Math;

     with Math;
     package Stuff is
        X : Float := Math.Sqrt (0.5);
     end Stuff;
     
     with Stuff;
     procedure Main is
     begin
        ...
     end Main;

where `Main' is the main program. When this program is executed, the
elaboration code must first be executed, and one of the jobs of the
binder is to determine the order in which the units of a program are to
be elaborated. In this case we have four units: the spec and body of
`Math', the spec of `Stuff' and the body of `Main').  In what order
should the four separate sections of elaboration code be executed?

   There are some restrictions in the order of elaboration that the
binder can choose. In particular, if unit U has a `with' for a package
`X', then you are assured that the spec of `X' is elaborated before U ,
but you are not assured that the body of `X' is elaborated before U.
This means that in the above case, the binder is allowed to choose the
order:

     spec of Math
     spec of Stuff
     body of Math
     body of Main

but that's not good, because now the call to `Math.Sqrt' that happens
during the elaboration of the `Stuff' spec happens before the body of
`Math.Sqrt' is elaborated, and hence causes `Program_Error' exception
to be raised.  At first glance, one might say that the binder is
misbehaving, because obviously you want to elaborate the body of
something you `with' first, but that is not a general rule that can be
followed in all cases. Consider

     package X is ...
     
     package Y is ...
     
     with X;
     package body Y is ...
     
     with Y;
     package body X is ...

This is a common arrangement, and, apart from the order of elaboration
problems that might arise in connection with elaboration code, this
works fine.  A rule that says that you must first elaborate the body of
anything you `with' cannot work in this case: the body of `X' `with''s
`Y', which means you would have to elaborate the body of `Y' first, but
that `with''s `X', which means you have to elaborate the body of `X'
first, but ... and we have a loop that cannot be broken.

   It is true that the binder can in many cases guess an order of
elaboration that is unlikely to cause a `Program_Error' exception to be
raised, and it tries to do so (in the above example of
`Math/Stuff/Spec', the GNAT binder will by default elaborate the body
of `Math' right after its spec, so all will be well).

   However, a program that blindly relies on the binder to be helpful
can get into trouble, as we discussed in the previous sections, so GNAT
provides a number of facilities for assisting the programmer in
developing programs that are robust with respect to elaboration order.


File: gnat_ug_vms.info,  Node: Default Behavior in GNAT - Ensuring Safety,  Next: Elaboration Issues for Library Tasks,  Prev: Controlling Elaboration in GNAT - External Calls,  Up: Elaboration Order Handling in GNAT

Default Behavior in GNAT - Ensuring Safety
==========================================

The default behavior in GNAT ensures elaboration safety. In its default
mode GNAT implements the rule we previously described as the right
approach. Let's restate it:

   * _If a unit has elaboration code that can directly or indirectly
     make a call to a subprogram in a `with''ed unit, or instantiate a
     generic unit in a `with''ed unit, then if the `with''ed unit does
     not have pragma `Pure' or `Preelaborate', then the client should
     have an `Elaborate_All' for the `with''ed unit._

By following this rule a client is assured that calls and
instantiations can be made without risk of an exception.

   In this mode GNAT traces all calls that are potentially made from
elaboration code, and puts in any missing implicit `Elaborate_All'
pragmas.  The advantage of this approach is that no elaboration problems
are possible if the binder can find an elaboration order that is
consistent with these implicit `Elaborate_All' pragmas. The
disadvantage of this approach is that no such order may exist.

   If the binder does not generate any diagnostics, then it means that
it has found an elaboration order that is guaranteed to be safe.
However, the binder may still be relying on implicitly generated
`Elaborate_All' pragmas so portability to other compilers than GNAT is
not guaranteed.

   If it is important to guarantee portability, then the compilations
should use the `/WARNINGS=ELABORATION' (warn on elaboration problems)
qualifier. This will cause warning messages to be generated indicating
the missing `Elaborate_All' pragmas.  Consider the following source
program:

     with k;
     package j is
       m : integer := k.r;
     end;

where it is clear that there should be a pragma `Elaborate_All' for
unit `k'. An implicit pragma will be generated, and it is likely that
the binder will be able to honor it. However, it is safer to include
the pragma explicitly in the source. If this unit is compiled with the
`/WARNINGS=ELABORATION' qualifier, then the compiler outputs a warning:

     1. with k;
     2. package j is
     3.   m : integer := k.r;
                          |
        >>> warning: call to "r" may raise Program_Error
        >>> warning: missing pragma Elaborate_All for "k"
     
     4. end;

and these warnings can be used as a guide for supplying manually the
missing pragmas.

   This default mode is more restrictive than the Ada Reference Manual,
and it is possible to construct programs which will compile using the
dynamic model described there, but will run into a circularity using
the safer static model we have described.

   Of course any Ada compiler must be able to operate in a mode
consistent with the requirements of the Ada Reference Manual, and in
particular must have the capability of implementing the standard
dynamic model of elaboration with run-time checks.

   In GNAT, this standard mode can be achieved either by the use of the
`/CHECKS=ELABORATION' qualifier on the compiler (`GNAT COMPILE' or
`GNAT MAKE') command, or by the use of the configuration pragma:

     pragma Elaboration_Checks (RM);

Either approach will cause the unit affected to be compiled using the
standard dynamic run-time elaboration checks described in the Ada
Reference Manual. The static model is generally preferable, since it is
clearly safer to rely on compile and link time checks rather than
run-time checks. However, in the case of legacy code, it may be
difficult to meet the requirements of the static model. This issue is
further discussed in *Note What to Do If the Default Elaboration
Behavior Fails::.

   Note that the static model provides a strict subset of the allowed
behavior and programs of the Ada Reference Manual, so if you do adhere
to the static model and no circularities exist, then you are assured
that your program will work using the dynamic model.


File: gnat_ug_vms.info,  Node: Elaboration Issues for Library Tasks,  Next: Mixing Elaboration Models,  Prev: Default Behavior in GNAT - Ensuring Safety,  Up: Elaboration Order Handling in GNAT

Elaboration Issues for Library Tasks
====================================

In this section we examine special elaboration issues that arise for
programs that declare library level tasks.

   Generally the model of execution of an Ada program is that all units
are elaborated, and then execution of the program starts. However, the
declaration of library tasks definitely does not fit this model. The
reason for this is that library tasks start as soon as they are declared
(more precisely, as soon as the statement part of the enclosing package
body is reached), that is to say before elaboration of the program is
complete. This means that if such a task calls a subprogram, or an
entry in another task, the callee may or may not be elaborated yet, and
in the standard Reference Manual model of dynamic elaboration checks,
you can even get timing dependent Program_Error exceptions, since there
can be a race between the elaboration code and the task code.

   The static model of elaboration in GNAT seeks to avoid all such
dynamic behavior, by being conservative, and the conservative approach
in this particular case is to assume that all the code in a task body
is potentially executed at elaboration time if a task is declared at
the library level.

   This can definitely result in unexpected circularities. Consider the
following example

     package Decls is
       task Lib_Task is
          entry Start;
       end Lib_Task;
     
       type My_Int is new Integer;
     
       function Ident (M : My_Int) return My_Int;
     end Decls;
     
     with Utils;
     package body Decls is
       task body Lib_Task is
       begin
          accept Start;
          Utils.Put_Val (2);
       end Lib_Task;
     
       function Ident (M : My_Int) return My_Int is
       begin
          return M;
       end Ident;
     end Decls;
     
     with Decls;
     package Utils is
       procedure Put_Val (Arg : Decls.My_Int);
     end Utils;
     
     with Text_IO;
     package body Utils is
       procedure Put_Val (Arg : Decls.My_Int) is
       begin
          Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
       end Put_Val;
     end Utils;
     
     with Decls;
     procedure Main is
     begin
        Decls.Lib_Task.Start;
     end;

If the above example is compiled in the default static elaboration
mode, then a circularity occurs. The circularity comes from the call
`Utils.Put_Val' in the task body of `Decls.Lib_Task'. Since this call
occurs in elaboration code, we need an implicit pragma `Elaborate_All'
for `Utils'. This means that not only must the spec and body of `Utils'
be elaborated before the body of `Decls', but also the spec and body of
any unit that is `with'ed' by the body of `Utils' must also be
elaborated before the body of `Decls'. This is the transitive
implication of pragma `Elaborate_All' and it makes sense, because in
general the body of `Put_Val' might have a call to something in a
`with'ed' unit.

   In this case, the body of Utils (actually its spec) `with's'
`Decls'. Unfortunately this means that the body of `Decls' must be
elaborated before itself, in case there is a call from the body of
`Utils'.

   Here is the exact chain of events we are worrying about:

  1. In the body of `Decls' a call is made from within the body of a
     library task to a subprogram in the package `Utils'. Since this
     call may occur at elaboration time (given that the task is
     activated at elaboration time), we have to assume the worst, i.e.
     that the call does happen at elaboration time.

  2. This means that the body and spec of `Util' must be elaborated
     before the body of `Decls' so that this call does not cause an
     access before elaboration.

  3. Within the body of `Util', specifically within the body of
     `Util.Put_Val' there may be calls to any unit `with''ed by this
     package.

  4. One such `with''ed package is package `Decls', so there might be a
     call to a subprogram in `Decls' in `Put_Val'.  In fact there is
     such a call in this example, but we would have to assume that
     there was such a call even if it were not there, since we are not
     supposed to write the body of `Decls' knowing what is in the body
     of `Utils'; certainly in the case of the static elaboration model,
     the compiler does not know what is in other bodies and must assume
     the worst.

  5. This means that the spec and body of `Decls' must also be
     elaborated before we elaborate the unit containing the call, but
     that unit is `Decls'! This means that the body of `Decls' must be
     elaborated before itself, and that's a circularity.

Indeed, if you add an explicit pragma Elaborate_All for `Utils' in the
body of `Decls' you will get a true Ada Reference Manual circularity
that makes the program illegal.

   In practice, we have found that problems with the static model of
elaboration in existing code often arise from library tasks, so we must
address this particular situation.

   Note that if we compile and run the program above, using the dynamic
model of elaboration (that is to say use the `/CHECKS=ELABORATION'
qualifier), then it compiles, binds, links, and runs, printing the
expected result of 2. Therefore in some sense the circularity here is
only apparent, and we need to capture the properties of this program
that  distinguish it from other library-level tasks that have real
elaboration problems.

   We have four possible answers to this question:

   * Use the dynamic model of elaboration.

     If we use the `/CHECKS=ELABORATION' qualifier, then as noted
     above, the program works.  Why is this? If we examine the task
     body, it is apparent that the task cannot proceed past the
     `accept' statement until after elaboration has been completed,
     because the corresponding entry call comes from the main program,
     not earlier.  This is why the dynamic model works here. But that's
     really giving up on a precise analysis, and we prefer to take this
     approach only if we cannot solve the problem in any other manner.
     So let us examine two ways to reorganize the program to avoid the
     potential elaboration problem.

   * Split library tasks into separate packages.

     Write separate packages, so that library tasks are isolated from
     other declarations as much as possible. Let us look at a variation
     on the above program.

          package Decls1 is
            task Lib_Task is
               entry Start;
            end Lib_Task;
          end Decls1;
          
          with Utils;
          package body Decls1 is
            task body Lib_Task is
            begin
               accept Start;
               Utils.Put_Val (2);
            end Lib_Task;
          end Decls1;
          
          package Decls2 is
            type My_Int is new Integer;
            function Ident (M : My_Int) return My_Int;
          end Decls2;
          
          with Utils;
          package body Decls2 is
            function Ident (M : My_Int) return My_Int is
            begin
               return M;
            end Ident;
          end Decls2;
          
          with Decls2;
          package Utils is
            procedure Put_Val (Arg : Decls2.My_Int);
          end Utils;
          
          with Text_IO;
          package body Utils is
            procedure Put_Val (Arg : Decls2.My_Int) is
            begin
               Text_IO.Put_Line (Decls2.My_Int'Image (Decls2.Ident (Arg)));
            end Put_Val;
          end Utils;
          
          with Decls1;
          procedure Main is
          begin
             Decls1.Lib_Task.Start;
          end;

     All we have done is to split `Decls' into two packages, one
     containing the library task, and one containing everything else.
     Now there is no cycle, and the program compiles, binds, links and
     executes using the default static model of elaboration.

   * Declare separate task types.

     A significant part of the problem arises because of the use of the
     single task declaration form. This means that the elaboration of
     the task type, and the elaboration of the task itself (i.e. the
     creation of the task) happen at the same time. A good rule of
     style in Ada 95 is to always create explicit task types. By
     following the additional step of placing task objects in separate
     packages from the task type declaration, many elaboration problems
     are avoided. Here is another modified example of the example
     program:

          package Decls is
            task type Lib_Task_Type is
               entry Start;
            end Lib_Task_Type;
          
            type My_Int is new Integer;
          
            function Ident (M : My_Int) return My_Int;
          end Decls;
          
          with Utils;
          package body Decls is
            task body Lib_Task_Type is
            begin
               accept Start;
               Utils.Put_Val (2);
            end Lib_Task_Type;
          
            function Ident (M : My_Int) return My_Int is
            begin
               return M;
            end Ident;
          end Decls;
          
          with Decls;
          package Utils is
            procedure Put_Val (Arg : Decls.My_Int);
          end Utils;
          
          with Text_IO;
          package body Utils is
            procedure Put_Val (Arg : Decls.My_Int) is
            begin
               Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
            end Put_Val;
          end Utils;
          
          with Decls;
          package Declst is
             Lib_Task : Decls.Lib_Task_Type;
          end Declst;
          
          with Declst;
          procedure Main is
          begin
             Declst.Lib_Task.Start;
          end;

     What we have done here is to replace the `task' declaration in
     package `Decls' with a `task type' declaration. Then we introduce
     a separate package `Declst' to contain the actual task object.
     This separates the elaboration issues for the `task type'
     declaration, which causes no trouble, from the elaboration issues
     of the task object, which is also unproblematic, since it is now
     independent of the elaboration of  `Utils'.  This separation of
     concerns also corresponds to a generally sound engineering
     principle of separating declarations from instances. This version
     of the program also compiles, binds, links, and executes,
     generating the expected output.

   * Use No_Entry_Calls_In_Elaboration_Code restriction.

     The previous two approaches described how a program can be
     restructured to avoid the special problems caused by library task
     bodies. in practice, however, such restructuring may be difficult
     to apply to existing legacy code, so we must consider solutions
     that do not require massive rewriting.

     Let us consider more carefully why our original sample program
     works under the dynamic model of elaboration. The reason is that
     the code in the task body blocks immediately on the `accept'
     statement. Now of course there is nothing to prohibit elaboration
     code from making entry calls (for example from another library
     level task), so we cannot tell in isolation that the task will not
     execute the accept statement  during elaboration.

     However, in practice it is very unusual to see elaboration code
     make any entry calls, and the pattern of tasks starting at
     elaboration time and then immediately blocking on `accept' or
     `select' statements is very common. What this means is that the
     compiler is being too pessimistic when it analyzes the whole
     package body as though it might be executed at elaboration time.

     If we know that the elaboration code contains no entry calls, (a
     very safe assumption most of the time, that could almost be made
     the default behavior), then we can compile all units of the
     program under control of the following configuration pragma:

          pragma Restrictions (No_Entry_Calls_In_Elaboration_Code);

     This pragma can be placed in the `GNAT.ADC' file in the usual
     manner. If we take our original unmodified program and compile it
     in the presence of a `GNAT.ADC' containing the above pragma, then
     once again, we can compile, bind, link, and execute, obtaining the
     expected result. In the presence of this pragma, the compiler does
     not trace calls in a task body, that appear after the first
     `accept' or `select' statement, and therefore does not report a
     potential circularity in the original program.

     The compiler will check to the extent it can that the above
     restriction is not violated, but it is not always possible to do a
     complete check at compile time, so it is important to use this
     pragma only if the stated restriction is in fact met, that is to
     say no task receives an entry call before elaboration of all units
     is completed.



File: gnat_ug_vms.info,  Node: Mixing Elaboration Models,  Next: What to Do If the Default Elaboration Behavior Fails,  Prev: Elaboration Issues for Library Tasks,  Up: Elaboration Order Handling in GNAT

Mixing Elaboration Models
=========================

So far, we have assumed that the entire program is either compiled
using the dynamic model or static model, ensuring consistency. It is
possible to mix the two models, but rules have to be followed if this
mixing is done to ensure that elaboration checks are not omitted.

   The basic rule is that _a unit compiled with the static model cannot
be `with'ed' by a unit compiled with the dynamic model_. The reason for
this is that in the static model, a unit assumes that its clients
guarantee to use (the equivalent of) pragma `Elaborate_All' so that no
elaboration checks are required in inner subprograms, and this
assumption is violated if the client is compiled with dynamic checks.

   The precise rule is as follows. A unit that is compiled with dynamic
checks can only `with' a unit that meets at least one of the following
criteria:

   * The `with'ed' unit is itself compiled with dynamic elaboration
     checks (that is with the `/CHECKS=ELABORATION' qualifier.

   * The `with'ed' unit is an internal GNAT implementation unit from
     the System, Interfaces, Ada, or GNAT hierarchies.

   * The `with'ed' unit has pragma Preelaborate or pragma Pure.

   * The `with'ing' unit (that is the client) has an explicit pragma
     `Elaborate_All' for the `with'ed' unit.


If this rule is violated, that is if a unit with dynamic elaboration
checks `with's' a unit that does not meet one of the above four
criteria, then the binder (`GNAT BIND') will issue a warning similar to
that in the following example:

     warning: "X.ADS" has dynamic elaboration checks and with's
     warning:   "Y.ADS" which has static elaboration checks

These warnings indicate that the rule has been violated, and that as a
result elaboration checks may be missed in the resulting executable
file.  This warning may be suppressed using the `-ws' binder qualifier
in the usual manner.

   One useful application of this mixing rule is in the case of a
subsystem which does not itself `with' units from the remainder of the
application. In this case, the entire subsystem can be compiled with
dynamic checks to resolve a circularity in the subsystem, while
allowing the main application that uses this subsystem to be compiled
using the more reliable default static model.


File: gnat_ug_vms.info,  Node: What to Do If the Default Elaboration Behavior Fails,  Next: Elaboration for Access-to-Subprogram Values,  Prev: Mixing Elaboration Models,  Up: Elaboration Order Handling in GNAT

What to Do If the Default Elaboration Behavior Fails
====================================================

If the binder cannot find an acceptable order, it outputs detailed
diagnostics. For example:
     error: elaboration circularity detected
     info:   "proc (body)" must be elaborated before "pack (body)"
     info:     reason: Elaborate_All probably needed in unit "pack (body)"
     info:     recompile "pack (body)" with /WARNINGS=ELABORATION
     info:                             for full details
     info:       "proc (body)"
     info:         is needed by its spec:
     info:       "proc (spec)"
     info:         which is withed by:
     info:       "pack (body)"
     info:  "pack (body)" must be elaborated before "proc (body)"
     info:     reason: pragma Elaborate in unit "proc (body)"


In this case we have a cycle that the binder cannot break. On the one
hand, there is an explicit pragma Elaborate in `proc' for `pack'. This
means that the body of `pack' must be elaborated before the body of
`proc'. On the other hand, there is elaboration code in `pack' that
calls a subprogram in `proc'. This means that for maximum safety, there
should really be a pragma Elaborate_All in `pack' for `proc' which
would require that the body of `proc' be elaborated before the body of
`pack'. Clearly both requirements cannot be satisfied.  Faced with a
circularity of this kind, you have three different options.

Fix the program
     The most desirable option from the point of view of long-term
     maintenance is to rearrange the program so that the elaboration
     problems are avoided.  One useful technique is to place the
     elaboration code into separate child packages. Another is to move
     some of the initialization code to explicitly called subprograms,
     where the program controls the order of initialization explicitly.
     Although this is the most desirable option, it may be impractical
     and involve too much modification, especially in the case of
     complex legacy code.

Perform dynamic checks
     If the compilations are done using the `/CHECKS=ELABORATION'
     (dynamic elaboration check) qualifier, then GNAT behaves in a
     quite different manner. Dynamic checks are generated for all calls
     that could possibly result in raising an exception. With this
     qualifier, the compiler does not generate implicit `Elaborate_All'
     pragmas.  The behavior then is exactly as specified in the Ada 95
     Reference Manual.  The binder will generate an executable program
     that may or may not raise `Program_Error', and then it is the
     programmer's job to ensure that it does not raise an exception.
     Note that it is important to compile all units with the qualifier,
     it cannot be used selectively.

Suppress checks
     The drawback of dynamic checks is that they generate a significant
     overhead at run time, both in space and time. If you are
     absolutely sure that your program cannot raise any elaboration
     exceptions, and you still want to use the dynamic elaboration
     model, then you can use the configuration pragma `Suppress
     (Elaboration_Checks)' to suppress all such checks. For example
     this pragma could be placed in the `GNAT.ADC' file.

Suppress checks selectively
     When you know that certain calls in elaboration code cannot
     possibly lead to an elaboration error, and the binder nevertheless
     generates warnings on those calls and inserts Elaborate_All
     pragmas that lead to elaboration circularities, it is possible to
     remove those warnings locally and obtain a program that will bind.
     Clearly this can be unsafe, and it is the responsibility of the
     programmer to make sure that the resulting program has no
     elaboration anomalies. The pragma `Suppress (Elaboration_Check)'
     can be used with different granularity to suppress warnings and
     break elaboration circularities:

        * Place the pragma that names the called subprogram in the
          declarative part that contains the call.

        * Place the pragma in the declarative part, without naming an
          entity. This disables warnings on all calls in the
          corresponding  declarative region.

        * Place the pragma in the package spec that declares the called
          subprogram, and name the subprogram. This disables warnings
          on all elaboration calls to that subprogram.

        * Place the pragma in the package spec that declares the called
          subprogram, without naming any entity. This disables warnings
          on all elaboration calls to all subprograms declared in this
          spec.

     These four cases are listed in order of decreasing safety, and
     therefore require increasing programmer care in their application.
     Consider the following program:

          package Pack1 is
            function F1 return Integer;
            X1 : Integer;
          end Pack1;
          
          package Pack2 is
            function F2 return Integer;
            function Pure (x : integer) return integer;
            --  pragma Suppress (Elaboration_Check, On => Pure);  -- (3)
            --  pragma Suppress (Elaboration_Check);              -- (4)
          end Pack2;
          
          with Pack2;
          package body Pack1 is
            function F1 return Integer is
            begin
              return 100;
            end F1;
            Val : integer := Pack2.Pure (11);    --  Elab. call (1)
          begin
            declare
              --  pragma Suppress(Elaboration_Check, Pack2.F2);   -- (1)
              --  pragma Suppress(Elaboration_Check);             -- (2)
            begin
              X1 := Pack2.F2 + 1;                --  Elab. call (2)
            end;
          end Pack1;
          
          with Pack1;
          package body Pack2 is
            function F2 return Integer is
            begin
               return Pack1.F1;
            end F2;
            function Pure (x : integer) return integer is
            begin
               return x ** 3 - 3 * x;
            end;
          end Pack2;
          
          with Pack1, Ada.Text_IO;
          procedure Proc3 is
          begin
            Ada.Text_IO.Put_Line(Pack1.X1'Img); -- 101
          end Proc3;
     In the absence of any pragmas, an attempt to bind this program
     produces the following diagnostics:
          error: elaboration circularity detected
          info:    "pack1 (body)" must be elaborated before "pack1 (body)"
          info:       reason: Elaborate_All probably needed in unit "pack1 (body)"
          info:       recompile "pack1 (body)" with /WARNINGS=ELABORATION for full details
          info:          "pack1 (body)"
          info:             must be elaborated along with its spec:
          info:          "pack1 (spec)"
          info:             which is withed by:
          info:          "pack2 (body)"
          info:             which must be elaborated along with its spec:
          info:          "pack2 (spec)"
          info:             which is withed by:
          info:          "pack1 (body)"
     The sources of the circularity are the two calls to
     `Pack2.Pure' and `Pack2.F2' in the body of `Pack1'. We can see
     that the call to F2 is safe, even though F2 calls F1, because the
     call appears after the elaboration of the body of F1. Therefore
     the pragma (1) is safe, and will remove the warning on the call.
     It is also possible to use pragma (2) because there are no other
     potentially unsafe calls in the block.

     The call to `Pure' is safe because this function does not depend
     on the state of `Pack2'. Therefore any call to this function is
     safe, and it is correct to place pragma (3) in the corresponding
     package spec.

     Finally, we could place pragma (4) in the spec of `Pack2' to
     disable warnings on all calls to functions declared therein. Note
     that this is not necessarily safe, and requires more detailed
     examination of the subprogram bodies involved. In particular, a
     call to `F2' requires that `F1' be already elaborated.

It is hard to generalize on which of these four approaches should be
taken. Obviously if it is possible to fix the program so that the
default treatment works, this is preferable, but this may not always be
practical.  It is certainly simple enough to use `/CHECKS=ELABORATION'
but the danger in this case is that, even if the GNAT binder finds a
correct elaboration order, it may not always do so, and certainly a
binder from another Ada compiler might not. A combination of testing
and analysis (for which the warnings generated with the
`/WARNINGS=ELABORATION' qualifier can be useful) must be used to ensure
that the program is free of errors. One qualifier that is useful in
this testing is the `/PESSIMISTIC_ELABORATION_ORDER' qualifier for
`GNAT BIND'.  Normally the binder tries to find an order that has the
best chance of of avoiding elaboration problems. With this qualifier,
the binder plays a devil's advocate role, and tries to choose the order
that has the best chance of failing. If your program works even with
this qualifier, then it has a better chance of being error free, but
this is still not a guarantee.

   For an example of this approach in action, consider the C-tests
(executable tests) from the ACVC suite. If these are compiled and run
with the default treatment, then all but one of them succeed without
generating any error diagnostics from the binder. However, there is one
test that fails, and this is not surprising, because the whole point of
this test is to ensure that the compiler can handle cases where it is
impossible to determine a correct order statically, and it checks that
an exception is indeed raised at run time.

   This one test must be compiled and run using the
`/CHECKS=ELABORATION' qualifier, and then it passes. Alternatively, the
entire suite can be run using this qualifier. It is never wrong to run
with the dynamic elaboration qualifier if your code is correct, and we
assume that the C-tests are indeed correct (it is less efficient, but
efficiency is not a factor in running the ACVC tests.)


File: gnat_ug_vms.info,  Node: Elaboration for Access-to-Subprogram Values,  Next: Summary of Procedures for Elaboration Control,  Prev: What to Do If the Default Elaboration Behavior Fails,  Up: Elaboration Order Handling in GNAT

Elaboration for Access-to-Subprogram Values
===========================================

The introduction of access-to-subprogram types in Ada 95 complicates
the handling of elaboration. The trouble is that it becomes impossible
to tell at compile time which procedure is being called. This means
that it is not possible for the binder to analyze the elaboration
requirements in this case.

   If at the point at which the access value is created (i.e., the
evaluation of `P'Access' for a subprogram `P'), the body of the
subprogram is known to have been elaborated, then the access value is
safe, and its use does not require a check. This may be achieved by
appropriate arrangement of the order of declarations if the subprogram
is in the current unit, or, if the subprogram is in another unit, by
using pragma `Pure', `Preelaborate', or `Elaborate_Body' on the
referenced unit.

   If the referenced body is not known to have been elaborated at the
point the access value is created, then any use of the access value
must do a dynamic check, and this dynamic check will fail and raise a
`Program_Error' exception if the body has not been elaborated yet.
GNAT will generate the necessary checks, and in addition, if the
`/WARNINGS=ELABORATION' qualifier is set, will generate warnings that
such checks are required.

   The use of dynamic dispatching for tagged types similarly generates
a requirement for dynamic checks, and premature calls to any primitive
operation of a tagged type before the body of the operation has been
elaborated, will result in the raising of `Program_Error'.


File: gnat_ug_vms.info,  Node: Summary of Procedures for Elaboration Control,  Next: Other Elaboration Order Considerations,  Prev: Elaboration for Access-to-Subprogram Values,  Up: Elaboration Order Handling in GNAT

Summary of Procedures for Elaboration Control
=============================================

First, compile your program with the default options, using none of the
special elaboration control qualifiers. If the binder successfully
binds your program, then you can be confident that, apart from issues
raised by the use of access-to-subprogram types and dynamic dispatching,
the program is free of elaboration errors. If it is important that the
program be portable, then use the `/WARNINGS=ELABORATION' qualifier to
generate warnings about missing `Elaborate_All' pragmas, and supply the
missing pragmas.

   If the program fails to bind using the default static elaboration
handling, then you can fix the program to eliminate the binder message,
or recompile the entire program with the `/CHECKS=ELABORATION'
qualifier to generate dynamic elaboration checks, and, if you are sure
there really are no elaboration problems, use a global pragma `Suppress
(Elaboration_Checks)'.


File: gnat_ug_vms.info,  Node: Other Elaboration Order Considerations,  Prev: Summary of Procedures for Elaboration Control,  Up: Elaboration Order Handling in GNAT

Other Elaboration Order Considerations
======================================

This section has been entirely concerned with the issue of finding a
valid elaboration order, as defined by the Ada Reference Manual. In a
case where several elaboration orders are valid, the task is to find one
of the possible valid elaboration orders (and the static model in GNAT
will ensure that this is achieved).

   The purpose of the elaboration rules in the Ada Reference Manual is
to make sure that no entity is accessed before it has been elaborated.
For a subprogram, this means that the spec and body must have been
elaborated before the subprogram is called. For an object, this means
that the object must have been elaborated before its value is read or
written. A violation of either of these two requirements is an access
before elaboration order, and this section has been all about avoiding
such errors.

   In the case where more than one order of elaboration is possible, in
the sense that access before elaboration errors are avoided, then any
one of the orders is "correct" in the sense that it meets the
requirements of the Ada Reference Manual, and no such error occurs.

   However, it may be the case for a given program, that there are
constraints on the order of elaboration that come not from consideration
of avoiding elaboration errors, but rather from extra-lingual logic
requirements. Consider this example:

     with Init_Constants;
     package Constants is
        X : Integer := 0;
        Y : Integer := 0;
     end Constants;
     
     package Init_Constants is
        procedure Calc;
     end Init_Constants;
     
     with Constants;
     package body Init_Constants is
        procedure Calc is begin null; end;
     begin
        Constants.X := 3;
        Constants.Y := 4;
     end Init_Constants;
     
     with Constants;
     package Calc is
        Z : Integer := Constants.X + Constants.Y;
     end Calc;
     
     with Calc;
     with Text_IO; use Text_IO;
     procedure Main is
     begin
        Put_Line (Calc.Z'Img);
     end Main;

In this example, there is more than one valid order of elaboration. For
example both the following are correct orders:

     Init_Constants spec
     Constants spec
     Calc spec
     Main body
     Init_Constants body
     
       and
     
     Init_Constants spec
     Init_Constants body
     Constants spec
     Calc spec
     Main body

There is no language rule to prefer one or the other, both are correct
from an order of elaboration point of view. But the programmatic effects
of the two orders are very different. In the first, the elaboration
routine of `Calc' initializes `Z' to zero, and then the main program
runs with this value of zero. But in the second order, the elaboration
routine of `Calc' runs after the body of Init_Constants has set `X' and
`Y' and thus `Z' is set to 7 before `Main' runs.

   One could perhaps by applying pretty clever non-artificial
intelligence to the situation guess that it is more likely that the
second order of elaboration is the one desired, but there is no formal
linguistic reason to prefer one over the other. In fact in this
particular case, GNAT will prefer the second order, because of the rule
that bodies are elaborated as soon as possible, but it's just luck that
this is what was wanted (if indeed the second order was preferred).

   If the program cares about the order of elaboration routines in a
case like this, it is important to specify the order required. In this
particular case, that could have been achieved by adding to the spec of
Calc:

     pragma Elaborate_All (Constants);

which requires that the body (if any) and spec of `Constants', as well
as the body and spec of any unit `with''ed by `Constants' be elaborated
before `Calc' is elaborated.

   Clearly no automatic method can always guess which alternative you
require, and if you are working with legacy code that had constraints
of this kind which were not properly specified by adding `Elaborate' or
`Elaborate_All' pragmas, then indeed it is possible that two different
compilers can choose different orders.

   The `GNAT BIND' `/PESSIMISTIC_ELABORATION' qualifier may be useful
in smoking out problems. This qualifier causes bodies to be elaborated
as late as possible instead of as early as possible. In the example
above, it would have forced the choice of the first elaboration order.
If you get different results when using this qualifier, and
particularly if one set of results is right, and one is wrong as far as
you are concerned, it shows that you have some missing `Elaborate'
pragmas. For the example above, we have the following output:

     GNAT MAKE -f -q main
     main
      7
     GNAT MAKE -f -q main /BINDER_QUALIFIERS -p
     main
      0

It is of course quite unlikely that both these results are correct, so
it is up to you in a case like this to investigate the source of the
difference, by looking at the two elaboration orders that are chosen,
and figuring out which is correct, and then adding the necessary
`Elaborate_All' pragmas to ensure the desired order.


File: gnat_ug_vms.info,  Node: The Cross-Referencing Tools GNAT XREF and GNAT FIND,  Next: File Name Krunching Using GNAT KRUNCH,  Prev: Elaboration Order Handling in GNAT,  Up: Top

The Cross-Referencing Tools `GNAT XREF' and `GNAT FIND'
*******************************************************

The compiler generates cross-referencing information (unless you set
the `/XREF=SUPPRESS' qualifier), which are saved in the `.ALI' files.
This information indicates where in the source each entity is declared
and referenced. Note that entities in package Standard are not
included, but entities in all other predefined units are included in
the output.

   Before using any of these two tools, you need to compile
successfully your application, so that GNAT gets a chance to generate
the cross-referencing information.

   The two tools `GNAT XREF' and `GNAT FIND' take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that `GNAT FIND' is intended for locating
definitions and/or references to a specified entity or entities, whereas
`GNAT XREF' is oriented to generating a full report of all
cross-references.

   To use these tools, you must not compile your application using the
`/XREF=SUPPRESS' qualifier on the `GNAT MAKE' command line (*note
(gnat_ug)The GNAT Make Program GNAT MAKE::). Otherwise,
cross-referencing information will not be generated.

* Menu:

* GNAT XREF Qualifiers::
* GNAT FIND Qualifiers::
* Project Files for GNAT XREF and GNAT FIND::
* Regular Expressions in GNAT FIND and GNAT XREF::
* Examples of GNAT XREF Usage::
* Examples of GNAT FIND Usage::


File: gnat_ug_vms.info,  Node: GNAT XREF Qualifiers,  Next: GNAT FIND Qualifiers,  Up: The Cross-Referencing Tools GNAT XREF and GNAT FIND

`GNAT XREF' Qualifiers
======================

The command lines for `GNAT XREF' is:
     $ GNAT XREF [qualifiers] sourcefile1 [sourcefile2 ...]

where

`sourcefile1, sourcefile2'
     identifies the source files for which a report is to be generated.
     The 'with'ed units will be processed too. You must provide at
     least one file.

     These file names are considered to be regular expressions, so for
     instance specifying 'source*.ADB' is the same as giving every file
     in the current directory whose name starts with 'source' and whose
     extension is 'adb'.


The qualifiers can be :
`/ALL_FILES'
     If this qualifier is present, `GNAT FIND' and `GNAT XREF' will
     parse the read-only files found in the library search path.
     Otherwise, these files will be ignored. This option can be used to
     protect Gnat sources or your own libraries from being parsed, thus
     making `GNAT FIND' and `GNAT XREF' much faster, and their output
     much smaller.

`/SOURCE_SEARCH=direc'
     When looking for source files also look in directory DIR. The
     order in which source file search is undertaken is the same as for
     `GNAT MAKE'.

`/OBJECT_SEARCH=direc'
     When searching for library and object files, look in directory
     DIR. The order in which library files are searched is the same as
     for `GNAT MAKE'.

`/NOSTD_INCLUDES'
     Do not look for sources in the system default directory.

`/NOSTD_LIBRARIES'
     Do not look for library files in the system default directory.

`/RUNTIME_SYSTEM=RTS-PATH'
     Specifies the default location of the runtime library. Same
     meaning as the equivalent `GNAT MAKE' flag (see *Note Qualifiers
     for GNAT MAKE::).

`-d'
     If this qualifier is set `GNAT XREF' will output the parent type
     reference for each matching derived types.

`/FULL_PATHNAME'
     If this qualifier is set, the output file names will be preceded
     by their directory (if the file was found in the search path). If
     this qualifier is not set, the directory will not be printed.

`/IGNORE_LOCALS'
     If this qualifier is set, information is output only for
     library-level entities, ignoring local entities. The use of this
     qualifier may accelerate `GNAT FIND' and `GNAT XREF'.

`/SEARCH=direc'
     Equivalent to `/OBJECT_SEARCH=direc /SOURCE_SEARCH=direc'.

`/PROJECT=file'
     Specify a project file to use *Note Project Files::.  By default,
     `GNAT XREF' and `GNAT FIND' will try to locate a project file in
     the current directory.

     If a project file is either specified or found by the tools, then
     the content of the source directory and object directory lines are
     added as if they had been specified respectively by
     `/SOURCE_SEARCH' and `OBJECT_SEARCH'.

`/UNUSED'
     Output only unused symbols. This may be really useful if you give
     your main compilation unit on the command line, as `GNAT XREF'
     will then display every unused entity and 'with'ed package.


   All these qualifiers may be in any order on the command line, and
may even appear after the file names. They need not be separated by
spaces, thus you can say `GNAT XREF /ALL_FILES/IGNORE_LOCALS' instead of
`GNAT XREF /ALL_FILES /IGNORE_LOCALS'.


File: gnat_ug_vms.info,  Node: GNAT FIND Qualifiers,  Next: Project Files for GNAT XREF and GNAT FIND,  Prev: GNAT XREF Qualifiers,  Up: The Cross-Referencing Tools GNAT XREF and GNAT FIND

`GNAT FIND' Qualifiers
======================

The command line for `GNAT FIND' is:

     $ GNAT FIND [qualifiers] pattern[:sourcefile[:line[:column]]]
           [file1 file2 ...]

where

`pattern'
     An entity will be output only if it matches the regular expression
     found in `pattern', see *Note Regular Expressions in GNAT FIND and
     GNAT XREF::.

     Omitting the pattern is equivalent to specifying `*', which will
     match any entity. Note that if you do not provide a pattern, you
     have to provide both a sourcefile and a line.

     Entity names are given in Latin-1, with uppercase/lowercase
     equivalence for matching purposes. At the current time there is no
     support for 8-bit codes other than Latin-1, or for wide characters
     in identifiers.

`sourcefile'
     `GNAT FIND' will look for references, bodies or declarations of
     symbols referenced in `sourcefile', at line `line' and column
     `column'. See *note Examples of GNAT FIND Usage:: for syntax
     examples.

`line'
     is a decimal integer identifying the line number containing the
     reference to the entity (or entities) to be located.

`column'
     is a decimal integer identifying the exact location on the line of
     the first character of the identifier for the entity reference.
     Columns are numbered from 1.

`file1 file2 ...'
     The search will be restricted to these files. If none are given,
     then the search will be done for every library file in the search
     path.  These file must appear only after the pattern or sourcefile.

     These file names are considered to be regular expressions, so for
     instance specifying 'source*.ADB' is the same as giving every file
     in the current directory whose name starts with 'source' and whose
     extension is 'adb'.

     Not that if you specify at least one file in this part, `GNAT
     FIND' may sometimes not be able to find the body of the
     subprograms...


   At least one of 'sourcefile' or 'pattern' has to be present on the
command line.

   The following qualifiers are available:
`/ALL_FILES'
     If this qualifier is present, `GNAT FIND' and `GNAT XREF' will
     parse the read-only files found in the library search path.
     Otherwise, these files will be ignored. This option can be used to
     protect Gnat sources or your own libraries from being parsed, thus
     making `GNAT FIND' and `GNAT XREF' much faster, and their output
     much smaller.

`/SOURCE_SEARCH=direc'
     When looking for source files also look in directory DIR. The
     order in which source file search is undertaken is the same as for
     `GNAT MAKE'.

`/OBJECT_SEARCH=direc'
     When searching for library and object files, look in directory
     DIR. The order in which library files are searched is the same as
     for `GNAT MAKE'.

`/NOSTD_INCLUDES'
     Do not look for sources in the system default directory.

`/NOSTD_LIBRARIES'
     Do not look for library files in the system default directory.

`/RUNTIME_SYSTEM=RTS-PATH'
     Specifies the default location of the runtime library. Same
     meaning as the equivalent `GNAT MAKE' flag (see *Note Qualifiers
     for GNAT MAKE::).

`-d'
     If this qualifier is set, then `GNAT FIND' will output the parent
     type reference for each matching derived types.

`/EXPRESSIONS'
     By default, `GNAT FIND' accept the simple regular expression set
     for `pattern'. If this qualifier is set, then the pattern will be
     considered as full Unix-style regular expression.

`/FULL_PATHNAME'
     If this qualifier is set, the output file names will be preceded
     by their directory (if the file was found in the search path). If
     this qualifier is not set, the directory will not be printed.

`/IGNORE_LOCALS'
     If this qualifier is set, information is output only for
     library-level entities, ignoring local entities. The use of this
     qualifier may accelerate `GNAT FIND' and `GNAT XREF'.

`/SEARCH=direc'
     Equivalent to `/OBJECT_SEARCH=direc /SOURCE_SEARCH=direc'.

`/PROJECT=file'
     Specify a project file (*note Project Files::) to use.  By
     default, `GNAT XREF' and `GNAT FIND' will try to locate a project
     file in the current directory.

     If a project file is either specified or found by the tools, then
     the content of the source directory and object directory lines are
     added as if they had been specified respectively by
     `/SOURCE_SEARCH' and `/OBJECT_SEARCH'.

`/REFERENCES'
     By default, `GNAT FIND' will output only the information about the
     declaration, body or type completion of the entities. If this
     qualifier is set, the `GNAT FIND' will locate every reference to
     the entities in the files specified on the command line (or in
     every file in the search path if no file is given on the command
     line).

`/PRINT_LINES'
     If this qualifier is set, then `GNAT FIND' will output the content
     of the Ada source file lines were the entity was found.

`-t'
     If this qualifier is set, then `GNAT FIND' will output the type
     hierarchy for the specified type. It act like -d option but
     recursively from parent type to parent type. When this qualifier
     is set it is not possible to specify more than one file.


   All these qualifiers may be in any order on the command line, and
may even appear after the file names. They need not be separated by
spaces, thus you can say `GNAT XREF /ALL_FILES/IGNORE_LOCALS' instead of
`GNAT XREF /ALL_FILES /IGNORE_LOCALS'.

   As stated previously, GNAT FIND will search in every directory in the
search path. You can force it to look only in the current directory if
you specify `*' at the end of the command line.


File: gnat_ug_vms.info,  Node: Project Files for GNAT XREF and GNAT FIND,  Next: Regular Expressions in GNAT FIND and GNAT XREF,  Prev: GNAT FIND Qualifiers,  Up: The Cross-Referencing Tools GNAT XREF and GNAT FIND

Project Files for `GNAT XREF' and `GNAT FIND'
=============================================

Project files allow a programmer to specify how to compile its
application, where to find sources,... These files are used primarily by
the Glide Ada mode, but they can also be used by the two tools `GNAT
XREF' and `GNAT FIND'.

   A project file name must end with `.adp'. If a single one is present
in the current directory, then `GNAT XREF' and `GNAT FIND' will extract
the information from it. If multiple project files are found, none of
them is read, and you have to use the `-p' qualifier to specify the one
you want to use.

   The following lines can be included, even though most of them have
default values which can be used in most cases.  The lines can be
entered in any order in the file.  Except for `src_dir' and `obj_dir',
you can only have one instance of each line. If you have multiple
instances, only the last one is taken into account.

`src_dir=DIR         [default: "[]"]'
     specifies a directory where to look for source files. Multiple
     src_dir lines can be specified and they will be searched in the
     order they are specified.

`obj_dir=DIR         [default: "[]"]'
     specifies a directory where to look for object and library files.
     Multiple obj_dir lines can be specified and they will be searched
     in the order they are specified

`comp_opt=SWITCHES   [default: ""]'
     creates a variable which can be referred to subsequently by using
     the `${comp_opt}' notation. This is intended to store the default
     qualifiers given to `GNAT MAKE' and `GNAT COMPILE'.

`bind_opt=SWITCHES   [default: ""]'
     creates a variable which can be referred to subsequently by using
     the `${bind_opt}' notation. This is intended to store the default
     qualifiers given to `GNAT BIND'.

`link_opt=SWITCHES   [default: ""]'
     creates a variable which can be referred to subsequently by using
     the `${link_opt}' notation. This is intended to store the default
     qualifiers given to `GNAT LINK'.

`main=EXECUTABLE     [default: ""]'
     specifies the name of the executable for the application. This
     variable can be referred to in the following lines by using the
     `${main}' notation.

`comp_cmd=COMMAND    [default: "GNAT COMPILE /SEARCH=${src_dir} /DEBUG /TRY_SEMANTICS"]'
     specifies the command used to compile a single file in the
     application.

`make_cmd=COMMAND    [default: "GNAT MAKE ${main} /SOURCE_SEARCH=${src_dir} /OBJECT_SEARCH=${obj_dir} /DEBUG /TRY_SEMANTICS /COMPILER_QUALIFIERS ${comp_opt} /BINDER_QUALIFIERS ${bind_opt} /LINKER_QUALIFIERS ${link_opt}"]'
     specifies the command used to recompile the whole application.

`run_cmd=COMMAND     [default: "${main}"]'
     specifies the command used to run the application.

`debug_cmd=COMMAND   [default: "GDB ${main}"]'
     specifies the command used to debug the application


   `GNAT XREF' and `GNAT FIND' only take into account the `src_dir' and
`obj_dir' lines, and ignore the others.


File: gnat_ug_vms.info,  Node: Regular Expressions in GNAT FIND and GNAT XREF,  Next: Examples of GNAT XREF Usage,  Prev: Project Files for GNAT XREF and GNAT FIND,  Up: The Cross-Referencing Tools GNAT XREF and GNAT FIND

Regular Expressions in `GNAT FIND' and `GNAT XREF'
==================================================

As specified in the section about `GNAT FIND', the pattern can be a
regular expression. Actually, there are to set of regular expressions
which are recognized by the program :

`globbing patterns'
     These are the most usual regular expression. They are the same
     that you generally used in a Unix shell command line, or in a DOS
     session.

     Here is a more formal grammar :
          regexp ::= term
          term   ::= elmt            -- matches elmt
          term   ::= elmt elmt       -- concatenation (elmt then elmt)
          term   ::= *               -- any string of 0 or more characters
          term   ::= ?               -- matches any character
          term   ::= [char {char}] -- matches any character listed
          term   ::= [char - char]   -- matches any character in range

`full regular expression'
     The second set of regular expressions is much more powerful. This
     is the type of regular expressions recognized by utilities such a
     `grep'.

     The following is the form of a regular expression, expressed in Ada
     reference manual style BNF is as follows

          regexp ::= term {| term} -- alternation (term or term ...)
          
          term ::= item {item}     -- concatenation (item then item)
          
          item ::= elmt              -- match elmt
          item ::= elmt *            -- zero or more elmt's
          item ::= elmt +            -- one or more elmt's
          item ::= elmt ?            -- matches elmt or nothing
          elmt ::= nschar            -- matches given character
          elmt ::= [nschar {nschar}]   -- matches any character listed
          elmt ::= [^ nschar {nschar}] -- matches any character not listed
          elmt ::= [char - char]     -- matches chars in given range
          elmt ::= \ char            -- matches given character
          elmt ::= .                 -- matches any single character
          elmt ::= ( regexp )        -- parens used for grouping
          
          char ::= any character, including special characters
          nschar ::= any character except ()[].*+?^

     Following are a few examples :

    `abcde|fghi'
          will match any of the two strings 'abcde' and 'fghi'.

    `abc*d'
          will match any string like 'abd', 'abcd', 'abccd', 'abcccd',
          and so on

    `[a-z]+'
          will match any string which has only lowercase characters in
          it (and at least one character



File: gnat_ug_vms.info,  Node: Examples of GNAT XREF Usage,  Next: Examples of GNAT FIND Usage,  Prev: Regular Expressions in GNAT FIND and GNAT XREF,  Up: The Cross-Referencing Tools GNAT XREF and GNAT FIND

Examples of `GNAT XREF' Usage
=============================

General Usage
-------------

For the following examples, we will consider the following units :

     MAIN.ADS:
     1: with Bar;
     2: package Main is
     3:     procedure Foo (B : in Integer);
     4:     C : Integer;
     5: private
     6:     D : Integer;
     7: end Main;
     
     MAIN.ADB:
     1: package body Main is
     2:     procedure Foo (B : in Integer) is
     3:     begin
     4:        C := B;
     5:        D := B;
     6:        Bar.Print (B);
     7:        Bar.Print (C);
     8:     end Foo;
     9: end Main;
     
     BAR.ADS:
     1: package Bar is
     2:     procedure Print (B : Integer);
     3: end bar;

     The first thing to do is to recompile your application (for
     instance, in that case just by doing a `GNAT MAKE main', so that
     GNAT generates the cross-referencing information.  You can then
     issue any of the following commands:

`GNAT XREF MAIN.ADB'
     `GNAT XREF' generates cross-reference information for MAIN.ADB and
     every unit 'with'ed by MAIN.ADB.

     The output would be:
          B                                                      Type: Integer
            Decl: BAR.ADS           2:22
          B                                                      Type: Integer
            Decl: MAIN.ADS          3:20
            Body: MAIN.ADB          2:20
            Ref:  MAIN.ADB          4:13     5:13     6:19
          Bar                                                    Type: Unit
            Decl: BAR.ADS           1:9
            Ref:  MAIN.ADB          6:8      7:8
                 MAIN.ADS           1:6
          C                                                      Type: Integer
            Decl: MAIN.ADS          4:5
            Modi: MAIN.ADB          4:8
            Ref:  MAIN.ADB          7:19
          D                                                      Type: Integer
            Decl: MAIN.ADS          6:5
            Modi: MAIN.ADB          5:8
          Foo                                                    Type: Unit
            Decl: MAIN.ADS          3:15
            Body: MAIN.ADB          2:15
          Main                                                    Type: Unit
            Decl: MAIN.ADS          2:9
            Body: MAIN.ADB          1:14
          Print                                                   Type: Unit
            Decl: BAR.ADS           2:15
            Ref:  MAIN.ADB          6:12     7:12

     that is the entity `Main' is declared in MAIN.ADS, line 2, column
     9, its body is in MAIN.ADB, line 1, column 14 and is not
     referenced any where.

     The entity `Print' is declared in BAR.ADS, line 2, column 15 and it
     it referenced in MAIN.ADB, line 6 column 12 and line 7 column 12.

`GNAT XREF PACKAGE1.ADB PACKAGE2.ADS'
     `GNAT XREF' will generates cross-reference information for
     PACKAGE1.ADB, PACKAGE2.ADS and any other package 'with'ed by any
     of these.



File: gnat_ug_vms.info,  Node: Examples of GNAT FIND Usage,  Prev: Examples of GNAT XREF Usage,  Up: The Cross-Referencing Tools GNAT XREF and GNAT FIND

Examples of `GNAT FIND' Usage
=============================

`GNAT FIND /FULL_PATHNAME xyz:MAIN.ADB'
     Find declarations for all entities xyz referenced at least once in
     MAIN.ADB. The references are search in every library file in the
     search path.

     The directories will be printed as well (as the `/FULL_PATHNAME'
     qualifier is set)

     The output will look like:
          [directory]MAIN.ADS:106:14: xyz <= declaration
          [directory]MAIN.ADB:24:10: xyz <= body
          [directory]FOO.ADS:45:23: xyz <= declaration

     that is to say, one of the entities xyz found in MAIN.ADB is
     declared at line 12 of MAIN.ADS (and its body is in MAIN.ADB), and
     another one is declared at line 45 of FOO.ADS

`GNAT FIND /FULL_PATHNAME/SOURCE_LINE xyz:MAIN.ADB'
     This is the same command as the previous one, instead `GNAT FIND'
     will display the content of the Ada source file lines.

     The output will look like:

          [directory]MAIN.ADS:106:14: xyz <= declaration
             procedure xyz;
          [directory]MAIN.ADB:24:10: xyz <= body
             procedure xyz is
          [directory]FOO.ADS:45:23: xyz <= declaration
             xyz : Integer;

     This can make it easier to find exactly the location your are
     looking for.

`GNAT FIND /REFERENCES "*x*":MAIN.ADS:123 FOO.ADB'
     Find references to all entities containing an x that are
     referenced on line 123 of MAIN.ADS.  The references will be
     searched only in MAIN.ADB and FOO.ADB.

`GNAT FIND MAIN.ADS:123'
     Find declarations and bodies for all entities that are referenced
     on line 123 of MAIN.ADS.

     This is the same as `GNAT FIND "*":MAIN.ADB:123'.

`GNAT FIND [mydir]MAIN.ADB:123:45'
     Find the declaration for the entity referenced at column 45 in
     line 123 of file MAIN.ADB in directory mydir. Note that it is
     usual to omit the identifier name when the column is given, since
     the column position identifies a unique reference.

     The column has to be the beginning of the identifier, and should
     not point to any character in the middle of the identifier.



File: gnat_ug_vms.info,  Node: File Name Krunching Using GNAT KRUNCH,  Next: Preprocessing Using GNAT PREPROCESS,  Prev: The Cross-Referencing Tools GNAT XREF and GNAT FIND,  Up: Top

File Name Krunching Using `GNAT KRUNCH'
***************************************

This chapter discusses the method used by the compiler to shorten the
default file names chosen for Ada units so that they do not exceed the
maximum length permitted. It also describes the `GNAT KRUNCH' utility
that can be used to determine the result of applying this shortening.

* Menu:

* About GNAT KRUNCH::
* Using GNAT KRUNCH::
* Krunching Method::
* Examples of GNAT KRUNCH Usage::


File: gnat_ug_vms.info,  Node: About GNAT KRUNCH,  Next: Using GNAT KRUNCH,  Up: File Name Krunching Using GNAT KRUNCH

About `GNAT KRUNCH'
===================

The default file naming rule in GNAT is that the file name must be
derived from the unit name. The exact default rule is as follows:
   * Take the unit name and replace all dots by hyphens.

   * If such a replacement occurs in the second character position of a
     name, and the first character is A, G, S, or I then replace the
     dot by the character $ (dollar sign) instead of a minus.
   The reason for this exception is to avoid clashes with the standard
names for children of System, Ada, Interfaces, and GNAT, which use the
prefixes S- A- I- and G- respectively.

   The `/FILE_NAME_MAX_LENGTH=NN' qualifier of the compiler activates a
"krunching" circuit that limits file names to nn characters (where nn
is a decimal integer). For example, using OpenVMS, where the maximum
file name length is 39, the value of nn is usually set to 39, but if
you want to generate a set of files that would be usable if ported to a
system with some different maximum file length, then a different value
can be specified.  The default value of 39 for OpenVMS need not be
specified.

   The `GNAT KRUNCH' utility can be used to determine the krunched name
for a given file, when krunched to a specified maximum length.


File: gnat_ug_vms.info,  Node: Using GNAT KRUNCH,  Next: Krunching Method,  Prev: About GNAT KRUNCH,  Up: File Name Krunching Using GNAT KRUNCH

Using `GNAT KRUNCH'
===================

The `GNAT KRUNCH' command has the form

     $ GNAT KRUNCH NAME /COUNT=nn

NAME can be an Ada name with dots or the GNAT name of the unit, where
the dots representing child units or subunit are replaced by hyphens.
The only confusion arises if a name ends in `.ADS' or `.ADB'. `GNAT
KRUNCH' takes this to be an extension if there are no other dots in the
name.

   LENGTH represents the length of the krunched name. The default when
no argument is given is 39 characters. A length of zero stands for
unlimited, in other words do not chop except for system files which are
always 39.

The output is the krunched name. The output has an extension only if the
original argument was a file name with an extension.


File: gnat_ug_vms.info,  Node: Krunching Method,  Next: Examples of GNAT KRUNCH Usage,  Prev: Using GNAT KRUNCH,  Up: File Name Krunching Using GNAT KRUNCH

Krunching Method
================

The initial file name is determined by the name of the unit that the
file contains. The name is formed by taking the full expanded name of
the unit and replacing the separating dots with hyphens and using
uppercase for all letters, except that a hyphen in the second character
position is replaced by a dollar sign if the first character is A, I,
G, or S.  The extension is `.ADS' for a specification and `.ADB' for a
body.  Krunching does not affect the extension, but the file name is
shortened to the specified length by following these rules:

   * The name is divided into segments separated by hyphens, tildes or
     underscores and all hyphens, tildes, and underscores are
     eliminated. If this leaves the name short enough, we are done.

   * If the name is too long, the longest segment is located (left-most
     if there are two of equal length), and shortened by dropping its
     last character. This is repeated until the name is short enough.

     As an example, consider the krunching of
     `OUR-STRINGS-WIDE_FIXED.ADB' to fit the name into 8 characters as
     required by some operating systems.

          our-strings-wide_fixed 22
          our strings wide fixed 19
          our string  wide fixed 18
          our strin   wide fixed 17
          our stri    wide fixed 16
          our stri    wide fixe  15
          our str     wide fixe  14
          our str     wid  fixe  13
          our str     wid  fix   12
          ou  str     wid  fix   11
          ou  st      wid  fix   10
          ou  st      wi   fix   9
          ou  st      wi   fi    8
          Final file name: OUSTWIFI.ADB

   * The file names for all predefined units are always krunched to
     eight characters. The krunching of these predefined units uses the
     following special prefix replacements:

    `ada-'
          replaced by `A-'

    `gnat-'
          replaced by `G-'

    `interfaces-'
          replaced by `I-'

    `system-'
          replaced by `S-'

     These system files have a hyphen in the second character position.
     That is why normal user files replace such a character with a
     dollar sign, to avoid confusion with system file names.

     As an example of this special rule, consider
     `ADA-STRINGS-WIDE_FIXED.ADB', which gets krunched as follows:

          ada-strings-wide_fixed 22
          a-  strings wide fixed 18
          a-  string  wide fixed 17
          a-  strin   wide fixed 16
          a-  stri    wide fixed 15
          a-  stri    wide fixe  14
          a-  str     wide fixe  13
          a-  str     wid  fixe  12
          a-  str     wid  fix   11
          a-  st      wid  fix   10
          a-  st      wi   fix   9
          a-  st      wi   fi    8
          Final file name: A-STWIFI.ADB

   Of course no file shortening algorithm can guarantee uniqueness over
all possible unit names, and if file name krunching is used then it is
your responsibility to ensure that no name clashes occur. The utility
program `GNAT KRUNCH' is supplied for conveniently determining the
krunched name of a file.


File: gnat_ug_vms.info,  Node: Examples of GNAT KRUNCH Usage,  Prev: Krunching Method,  Up: File Name Krunching Using GNAT KRUNCH

Examples of `GNAT KRUNCH' Usage
===============================

     $ GNAT KRUNCH VERY_LONG_UNIT_NAME.ADS/count=6 --> VLUNNA.ADS
     $ GNAT KRUNCH VERY_LONG_UNIT_NAME.ADS/count=0 --> VERY_LONG_UNIT_NAME.ADS


File: gnat_ug_vms.info,  Node: Preprocessing Using GNAT PREPROCESS,  Next: The GNAT Run-Time Library Builder GNAT LIBRARY,  Prev: File Name Krunching Using GNAT KRUNCH,  Up: Top

Preprocessing Using `GNAT PREPROCESS'
*************************************

The `GNAT PREPROCESS' utility provides a simple preprocessing
capability for Ada programs.  It is designed for use with GNAT, but is
not dependent on any special features of GNAT.

* Menu:

* Using GNAT PREPROCESS::
* Qualifiers for GNAT PREPROCESS::
* Form of Definitions File::
* Form of Input Text for GNAT PREPROCESS::


File: gnat_ug_vms.info,  Node: Using GNAT PREPROCESS,  Next: Qualifiers for GNAT PREPROCESS,  Up: Preprocessing Using GNAT PREPROCESS

Using `GNAT PREPROCESS'
=======================

To call `GNAT PREPROCESS' use

     $ GNAT PREPROCESS [-bcrsu] [-Dsymbol=value] infile outfile [deffile]

where
`infile'
     is the full name of the input file, which is an Ada source file
     containing preprocessor directives.

`outfile'
     is the full name of the output file, which is an Ada source in
     standard Ada form. When used with GNAT, this file name will
     normally have an ads or adb suffix.

`deffile'
     is the full name of a text file containing definitions of symbols
     to be referenced by the preprocessor. This argument is optional,
     and can be replaced by the use of the `-D' qualifier.

`qualifiers'
     is an optional sequence of qualifiers as described in the next
     section.


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT PREPROCESS,  Next: Form of Definitions File,  Prev: Using GNAT PREPROCESS,  Up: Preprocessing Using GNAT PREPROCESS

Qualifiers for `GNAT PREPROCESS'
================================

`/BLANK_LINES'
     Causes both preprocessor lines and the lines deleted by
     preprocessing to be replaced by blank lines in the output source
     file, preserving line numbers in the output file.

`/COMMENTS'
     Causes both preprocessor lines and the lines deleted by
     preprocessing to be retained in the output source as comments
     marked with the special string "-! ". This option will result in
     line numbers being preserved in the output file.

`-Dsymbol=value'
     Defines a new symbol, associated with value. If no value is given
     on the command line, then symbol is considered to be `True'. This
     qualifier can be used in place of a definition file.

`/REMOVE (default)'
     This is the default setting which causes lines deleted by
     preprocessing to be entirely removed from the output file.

`/REFERENCE'
     Causes a `Source_Reference' pragma to be generated that references
     the original input file, so that error messages will use the file
     name of this original file. The use of this qualifier implies that
     preprocessor lines are not to be removed from the file, so its use
     will force `/BLANK_LINES' mode if `/COMMENTS' has not been
     specified explicitly.

     Note that if the file to be preprocessed contains multiple units,
     then it will be necessary to `GNAT CHOP' the output file from
     `GNAT PREPROCESS'. If a `Source_Reference' pragma is present in
     the preprocessed file, it will be respected by `GNAT CHOP
     /REFERENCE' so that the final chopped files will correctly refer
     to the original input source file for `GNAT PREPROCESS'.

`/SYMBOLS'
     Causes a sorted list of symbol names and values to be listed on
     the standard output file.

`/UNDEFINED'
     Causes undefined symbols to be treated as having the value FALSE
     in the context of a preprocessor test. In the absence of this
     option, an undefined symbol in a `#if' or `#elsif' test will be
     treated as an error.



File: gnat_ug_vms.info,  Node: Form of Definitions File,  Next: Form of Input Text for GNAT PREPROCESS,  Prev: Qualifiers for GNAT PREPROCESS,  Up: Preprocessing Using GNAT PREPROCESS

Form of Definitions File
========================

The definitions file contains lines of the form

     symbol := value

where symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and value is one of the following:

   * Empty, corresponding to a null substitution

   * A string literal using normal Ada syntax

   * Any sequence of characters from the set (letters, digits, period,
     underline).

Comment lines may also appear in the definitions file, starting with
the usual `--', and comments may be added to the definitions lines.


File: gnat_ug_vms.info,  Node: Form of Input Text for GNAT PREPROCESS,  Prev: Form of Definitions File,  Up: Preprocessing Using GNAT PREPROCESS

Form of Input Text for `GNAT PREPROCESS'
========================================

The input text may contain preprocessor conditional inclusion lines, as
well as general symbol substitution sequences.

   The preprocessor conditional inclusion commands have the form

     #if expression [then]
        lines
     #elsif expression [then]
        lines
     #elsif expression [then]
        lines
     ...
     #else
        lines
     #end if;

In this example, expression is defined by the following grammar:
     expression ::=  <symbol>
     expression ::=  <symbol> = "<value>"
     expression ::=  <symbol> = <symbol>
     expression ::=  <symbol> 'Defined
     expression ::=  not expression
     expression ::=  expression and expression
     expression ::=  expression or expression
     expression ::=  expression and then expression
     expression ::=  expression or else expression
     expression ::=  ( expression )

For the first test (expression ::= <symbol>) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals `True'
or `False'. If the value is true, then the corresponding lines are
included, and if the value is false, they are excluded.

   The test (expression ::= <symbol> `'Defined') is true only if the
symbol has been defined in the definition file or by a `-D' qualifier
on the command line. Otherwise, the test is false.

   The equality tests are case insensitive, as are all the preprocessor
lines.

   If the symbol referenced is not defined in the symbol definitions
file, then the effect depends on whether or not qualifier `-u' is
specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this qualifier is not specified, then it
is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than `True' or
`False'.

   The use of the `not' operator inverts the sense of this logical
test, so that the lines are included only if the symbol is not defined.
The `then' keyword is optional as shown

   The `#' must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the `#' and the keyword. The keywords and the symbols are case
insensitive as in normal Ada code. Comments may be used on a
preprocessor line, but other than that, no other tokens may appear on a
preprocessor line. Any number of `elsif' clauses can be present,
including none at all. The `else' is optional, as in Ada.

   The `#' marking the start of a preprocessor line must be the first
non-blank character on the line, i.e. it must be preceded only by
spaces or horizontal tabs.

   Symbol substitution outside of preprocessor lines is obtained by
using the sequence

     $symbol

anywhere within a source line, except in a comment or within a string
literal. The identifier following the `$' must match one of the symbols
defined in the symbol definition file, and the result is to substitute
the value of the symbol in place of `$symbol' in the output file.

   Note that although the substitution of strings within a string
literal is not possible, it is possible to have a symbol whose defined
value is a string literal. So instead of setting XYZ to `hello' and
writing:

     Header : String := "$XYZ";

you should set XYZ to `"hello"' and write:

     Header : String := $XYZ;

and then the substitution will occur as desired.


File: gnat_ug_vms.info,  Node: The GNAT Run-Time Library Builder GNAT LIBRARY,  Next: The GNAT Library Browser GNAT LIST,  Prev: Preprocessing Using GNAT PREPROCESS,  Up: Top

The GNAT Run-Time Library Builder `GNAT LIBRARY'
************************************************

`GNAT LIBRARY' is a tool for rebuilding the GNAT run time with user
supplied configuration pragmas.

* Menu:

* Running GNAT LIBRARY::
* Qualifiers for GNAT LIBRARY::
* Examples of GNAT LIBRARY Usage::


File: gnat_ug_vms.info,  Node: Running GNAT LIBRARY,  Next: Qualifiers for GNAT LIBRARY,  Up: The GNAT Run-Time Library Builder GNAT LIBRARY

Running `GNAT LIBRARY'
======================

The `GNAT LIBRARY' command has the form

     $ GNAT LIBRARY /[CREATE | SET | DELETE]=directory [/CONFIG=file]


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT LIBRARY,  Next: Examples of GNAT LIBRARY Usage,  Prev: Running GNAT LIBRARY,  Up: The GNAT Run-Time Library Builder GNAT LIBRARY

Qualifiers for `GNAT LIBRARY'
=============================

`GNAT LIBRARY' recognizes the following qualifiers:

`/CREATE=directory'
     Create the new run-time library in the specified directory.

`/SET=directory'
     Make the library in the specified directory the current run-time
       library.

`/DELETE=directory'
     Delete the run-time library in the specified directory.

`/CONFIG=file'
     With /CREATE:      Use the configuration pragmas in the specified
     file when building      the library.

     With /SET:      Use the configuration pragmas in the specified
     file when compiling.



File: gnat_ug_vms.info,  Node: Examples of GNAT LIBRARY Usage,  Prev: Qualifiers for GNAT LIBRARY,  Up: The GNAT Run-Time Library Builder GNAT LIBRARY

Example of `GNAT LIBRARY' Usage
===============================

     Contents of VAXFLOAT.ADC:
     pragma Float_Representation (VAX_Float);
     
     $ GNAT LIBRARY /CREATE=[.VAXFLOAT] /CONFIG=VAXFLOAT.ADC
     
     GNAT LIBRARY rebuilds the run-time library in directory [.VAXFLOAT]


File: gnat_ug_vms.info,  Node: The GNAT Library Browser GNAT LIST,  Next: Finding Memory Problems with GNAT Debug Pool,  Prev: The GNAT Run-Time Library Builder GNAT LIBRARY,  Up: Top

The GNAT Library Browser `GNAT LIST'
************************************

`GNAT LIST' is a tool that outputs information about compiled units. It
gives the relationship between objects, unit names and source files. It
can also be used to check the source dependencies of a unit as well as
various characteristics.

* Menu:

* Running GNAT LIST::
* Qualifiers for GNAT LIST::
* Examples of GNAT LIST Usage::


File: gnat_ug_vms.info,  Node: Running GNAT LIST,  Next: Qualifiers for GNAT LIST,  Up: The GNAT Library Browser GNAT LIST

Running `GNAT LIST'
===================

The `GNAT LIST' command has the form

     $ GNAT LIST qualifiers OBJECT_OR_ALI_FILE

The main argument is the list of object or `ali' files (*note The Ada
Library Information Files::) for which information is requested.

   In normal mode, without additional option, `GNAT LIST' produces a
four-column listing. Each line represents information for a specific
object. The first column gives the full path of the object, the second
column gives the name of the principal unit in this object, the third
column gives the status of the source and the fourth column gives the
full path of the source representing this unit.  Here is a simple
example of use:

     $ GNAT LIST *.OBJ
     []DEMO1.OBJ            demo1            DIF DEMO1.ADB
     []DEMO2.OBJ            demo2             OK DEMO2.ADB
     []HELLO.OBJ            h1                OK HELLO.ADB
     []INSTR-CHILD.OBJ      instr.child      MOK INSTR-CHILD.ADB
     []INSTR.OBJ            instr             OK INSTR.ADB
     []TEF.OBJ              tef              DIF TEF.ADB
     []TEXT_IO_EXAMPLE.OBJ  text_io_example   OK TEXT_IO_EXAMPLE.ADB
     []TGEF.OBJ             tgef             DIF TGEF.ADB

The first line can be interpreted as follows: the main unit which is
contained in object file `DEMO1.OBJ' is demo1, whose main source is in
`DEMO1.ADB'. Furthermore, the version of the source used for the
compilation of demo1 has been modified (DIF). Each source file has a
status qualifier which can be:

`OK (unchanged)'
     The version of the source file used for the compilation of the
     specified unit corresponds exactly to the actual source file.

`MOK (slightly modified)'
     The version of the source file used for the compilation of the
     specified unit differs from the actual source file but not enough
     to require recompilation. If you use GNAT MAKE with the qualifier
     `/MINIMAL_RECOMPILATION', a file marked MOK will not be recompiled.

`DIF (modified)'
     No version of the source found on the path corresponds to the
     source used to build this object.

`??? (file not found)'
     No source file was found for this unit.

`HID (hidden,  unchanged version not first on PATH)'
     The version of the source that corresponds exactly to the source
     used for compilation has been found on the path but it is hidden
     by another version of the same source that has been modified.



File: gnat_ug_vms.info,  Node: Qualifiers for GNAT LIST,  Next: Examples of GNAT LIST Usage,  Prev: Running GNAT LIST,  Up: The GNAT Library Browser GNAT LIST

Qualifiers for `GNAT LIST'
==========================

`GNAT LIST' recognizes the following qualifiers:

`/ALL_UNITS'
     Consider all units, including those of the predefined Ada library.
     Especially useful with `/DEPENDENCIES'.

`/DEPENDENCIES'
     List sources from which specified units depend on.

`/OUTPUT=OPTIONS'
     Output the list of options.

`/OUTPUT=OBJECTS'
     Only output information about object files.

`/OUTPUT=SOURCES'
     Only output information about source files.

`/OUTPUT=UNITS'
     Only output information about compilation units.

`/OBJECT_SEARCH=DIR'
`/SOURCE_SEARCH=DIR'
`/SEARCH=DIR'
`/NOCURRENT_DIRECTORY'
`/NOSTD_INCLUDES'
     Source path manipulation. Same meaning as the equivalent `GNAT
     MAKE' flags (see *Note Qualifiers for GNAT MAKE::).

`/RUNTIME_SYSTEM=RTS-PATH'
     Specifies the default location of the runtime library. Same
     meaning as the equivalent `GNAT MAKE' flag (see *Note Qualifiers
     for GNAT MAKE::).

`/OUTPUT=VERBOSE'
     Verbose mode. Output the complete source and object paths. Do not
     use the default column layout but instead use long format giving
     as much as information possible on each requested units, including
     special characteristics such as:

    `Preelaborable'
          The unit is preelaborable in the Ada 95 sense.

    `No_Elab_Code'
          No elaboration code has been produced by the compiler for
          this unit.

    `Pure'
          The unit is pure in the Ada 95 sense.

    `Elaborate_Body'
          The unit contains a pragma Elaborate_Body.

    `Remote_Types'
          The unit contains a pragma Remote_Types.

    `Shared_Passive'
          The unit contains a pragma Shared_Passive.

    `Predefined'
          This unit is part of the predefined environment and cannot be
          modified by the user.

    `Remote_Call_Interface'
          The unit contains a pragma Remote_Call_Interface.




File: gnat_ug_vms.info,  Node: Examples of GNAT LIST Usage,  Prev: Qualifiers for GNAT LIST,  Up: The GNAT Library Browser GNAT LIST

Example of `GNAT LIST' Usage
============================

     GNAT LIST /DEPENDENCIES /OUTPUT=SOURCES /ALL_UNITS DEMO1.ADB
     
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]ADA.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]A-FINALI.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]A-FILICO.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]A-STREAM.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]A-TAGS.ADS
     DEMO1.ADB
     GEN_LIST.ADS
     GEN_LIST.ADB
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]GNAT.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]G-IO.ADS
     INSTR.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]SYSTEM.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-EXCTAB.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-FINIMP.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-FINROO.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-SECSTA.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-STALIB.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-STOELE.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-STRATT.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-TASOLI.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]S-UNSTYP.ADS
     GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]UNCHCONV.ADS


File: gnat_ug_vms.info,  Node: Finding Memory Problems with GNAT Debug Pool,  Next: Creating Sample Bodies Using GNAT STUB,  Prev: The GNAT Library Browser GNAT LIST,  Up: Top

Finding Memory Problems with GNAT Debug Pool
********************************************

The use of unchecked deallocation and unchecked conversion can easily
lead to incorrect memory references. The problems generated by such
references are usually difficult to tackle because the symptoms can be
very remote from the origin of the problem. In such cases, it is very
helpful to detect the problem as early as possible. This is the purpose
of the Storage Pool provided by `GNAT.Debug_Pools'.

In order to use the GNAT specific debugging pool, the user must
associate a debug pool object with each of the access types that may be
related to suspected memory problems. See Ada Reference Manual 13.11.
     type Ptr is access Some_Type;
     Pool : GNAT.Debug_Pools.Debug_Pool;
     for Ptr'Storage_Pool use Pool;

   `GNAT.Debug_Pools' is derived from of a GNAT-specific kind of pool:
the Checked_Pool. Such pools, like standard Ada storage pools, allow
the user to redefine allocation and deallocation strategies. They also
provide a checkpoint for each dereference, through the use of the
primitive operation `Dereference' which is implicitly called at each
dereference of an access value.

   Once an access type has been associated with a debug pool,
operations on values of the type may raise four distinct exceptions,
which correspond to four potential kinds of memory corruption:
   * `GNAT.Debug_Pools.Accessing_Not_Allocated_Storage'

   * `GNAT.Debug_Pools.Accessing_Deallocated_Storage'

   * `GNAT.Debug_Pools.Freeing_Not_Allocated_Storage'

   * `GNAT.Debug_Pools.Freeing_Deallocated_Storage '

For types associated with a Debug_Pool, dynamic allocation is performed
using the standard GNAT allocation routine. References to all allocated
chunks of memory are kept in an internal dictionary. The deallocation
strategy consists in not releasing the memory to the underlying system
but rather to fill it with a memory pattern easily recognizable during
debugging sessions: The memory pattern is the old IBM hexadecimal
convention: 16#DEADBEEF#.  Upon each dereference, a check is made that
the access value denotes a properly allocated memory location. Here is
a complete example of use of `Debug_Pools', that includes typical
instances of  memory corruption:
     with Gnat.Io; use Gnat.Io;
     with Unchecked_Deallocation;
     with Unchecked_Conversion;
     with GNAT.Debug_Pools;
     with System.Storage_Elements;
     with Ada.Exceptions; use Ada.Exceptions;
     procedure Debug_Pool_Test is
     
        type T is access Integer;
        type U is access all T;
     
        P : GNAT.Debug_Pools.Debug_Pool;
        for T'Storage_Pool use P;
     
        procedure Free is new Unchecked_Deallocation (Integer, T);
        function UC is new Unchecked_Conversion (U, T);
        A, B : aliased T;
     
        procedure Info is new GNAT.Debug_Pools.Print_Info(Put_Line);
     
     begin
        Info (P);
        A := new Integer;
        B := new Integer;
        B := A;
        Info (P);
        Free (A);
        begin
           Put_Line (Integer'Image(B.all));
        exception
           when E : others => Put_Line ("raised: " & Exception_Name (E));
        end;
        begin
           Free (B);
        exception
           when E : others => Put_Line ("raised: " & Exception_Name (E));
        end;
        B := UC(A'Access);
        begin
           Put_Line (Integer'Image(B.all));
        exception
           when E : others => Put_Line ("raised: " & Exception_Name (E));
        end;
        begin
           Free (B);
        exception
           when E : others => Put_Line ("raised: " & Exception_Name (E));
        end;
        Info (P);
     end Debug_Pool_Test;

The debug pool mechanism provides the following precise diagnostics on
the execution of this erroneous program:
     Debug Pool info:
       Total allocated bytes :  0
       Total deallocated bytes :  0
       Current Water Mark:  0
       High Water Mark:  0
     
     Debug Pool info:
       Total allocated bytes :  8
       Total deallocated bytes :  0
       Current Water Mark:  8
       High Water Mark:  8
     
     raised: GNAT.DEBUG_POOLS.ACCESSING_DEALLOCATED_STORAGE
     raised: GNAT.DEBUG_POOLS.FREEING_DEALLOCATED_STORAGE
     raised: GNAT.DEBUG_POOLS.ACCESSING_NOT_ALLOCATED_STORAGE
     raised: GNAT.DEBUG_POOLS.FREEING_NOT_ALLOCATED_STORAGE
     Debug Pool info:
       Total allocated bytes :  8
       Total deallocated bytes :  4
       Current Water Mark:  4
       High Water Mark:  8


File: gnat_ug_vms.info,  Node: Creating Sample Bodies Using GNAT STUB,  Next: Reducing the Size of Ada Executables with GNAT ELIM,  Prev: Finding Memory Problems with GNAT Debug Pool,  Up: Top

Creating Sample Bodies Using `GNAT STUB'
****************************************

`GNAT STUB' creates body stubs, that is, empty but compilable bodies
for library unit declarations.

   To create a body stub, `GNAT STUB' has to compile the library unit
declaration. Therefore, bodies can be created only for legal library
units. Moreover, if a library unit depends semantically upon units
located outside the current directory, you have to provide the source
search path when calling `GNAT STUB', see the description of `GNAT
STUB' qualifiers below.

* Menu:

* Running GNAT STUB::
* Qualifiers for GNAT STUB::


File: gnat_ug_vms.info,  Node: Running GNAT STUB,  Next: Qualifiers for GNAT STUB,  Up: Creating Sample Bodies Using GNAT STUB

Running `GNAT STUB'
===================

`GNAT STUB' has the command-line interface of the form

     $ GNAT STUB [qualifiers] filename [directory]

where
`filename'
     is the name of the source file that contains a library unit
     declaration for which a body must be created. This name should
     follow the GNAT file name conventions. No crunching is allowed for
     this file name. The file name may contain the path information.

`directory'
     indicates the directory to place a body stub (default is the
     current directory)

`qualifiers'
     is an optional sequence of qualifiers as described in the next
     section


File: gnat_ug_vms.info,  Node: Qualifiers for GNAT STUB,  Prev: Running GNAT STUB,  Up: Creating Sample Bodies Using GNAT STUB

Qualifiers for `GNAT STUB'
==========================

`/FULL'
     If the destination directory already contains a file with a name
     of the body file for the argument spec file, replace it with the
     generated body stub.

`/HEADER=SPEC'
     Put the comment header (i.e. all the comments preceding the
     compilation unit) from the source of the library unit declaration
     into the body stub.

`/HEADER=GENERAL'
     Put a sample comment header into the body stub.

`/SEARCH=direc'
`/NOCURRENT_DIRECTORY'
     These qualifiers have the same meaning as in calls to GNAT COMPILE.
     They define the source search path in the call to GNAT COMPILE
     issued by `GNAT STUB' to compile an argument source file.

`/INDENTATION=N'
     (N is a decimal natural number). Set the indentation level in the
     generated body sample to n, '/INDENTATION=0' means "no
     indentation", the default indentation is 3.

`/TREE_FILE=SAVE'
     Do not remove the tree file (i.e. the snapshot of the compiler
     internal structures used by `GNAT STUB') after creating the body
     stub.

`/LINE_LENGTH=N'
     (N is a decimal positive number) Set the maximum line length in the
     body stub to n, the default is 78.

`/QUIET'
     Quiet mode: do not generate a confirmation when a body is
     successfully created or a message when a body is not required for
     an argument unit.

`/TREE_FILE=REUSE'
     Reuse the tree file (if it exists) instead of creating it: instead
     of creating the tree file for the library unit declaration, GNAT
     STUB tries to find it in the current directory and use it for
     creating a body. If the tree file is not found, no body is
     created. `/REUSE' also implies `/SAVE', whether or not `/SAVE' is
     set explicitly.

`/TREE_FILE=OVERWRITE'
     Overwrite the existing tree file: if the current directory already
     contains the file which, according to the GNAT file name rules
     should be considered as a tree file for the argument source file,
     GNAT STUB will refuse to create the tree file needed to create a
     body sampler, unless `-t' option is set

`/VERBOSE'
     Verbose mode: generate version information.



File: gnat_ug_vms.info,  Node: Reducing the Size of Ada Executables with GNAT ELIM,  Next: Other Utility Programs,  Prev: Creating Sample Bodies Using GNAT STUB,  Up: Top

Reducing the Size of Ada Executables with `GNAT ELIM'
*****************************************************

* Menu:

* About GNAT ELIM::
* Eliminate Pragma::
* Tree Files::
* Preparing Tree and Bind Files for GNAT ELIM::
* Running GNAT ELIM::
* Correcting the List of Eliminate Pragmas::
* Making Your Executables Smaller::
* Summary of the GNAT ELIM Usage Cycle::


File: gnat_ug_vms.info,  Node: About GNAT ELIM,  Next: Eliminate Pragma,  Up: Reducing the Size of Ada Executables with GNAT ELIM

About `GNAT ELIM'
=================

When a program shares a set of Ada packages with other programs, it may
happen that this program uses only a fraction of the subprograms
defined in these packages. The code created for these unused
subprograms increases the size of the executable.

   `GNAT ELIM' tracks unused subprograms in an Ada program and outputs
a list of GNAT-specific `Eliminate' pragmas (see next section) marking
all the subprograms that are declared but never called.  By placing the
list of `Eliminate' pragmas in the GNAT configuration file `GNAT.ADC'
and recompiling your program, you may decrease the size of its
executable, because the compiler will not generate the code for
'eliminated' subprograms.

   `GNAT ELIM' needs as its input data a set of tree files (see *Note
Tree Files::) representing all the components of a program to process
and a bind file for a main subprogram (see *Note Preparing Tree and
Bind Files for GNAT ELIM::).


File: gnat_ug_vms.info,  Node: Eliminate Pragma,  Next: Tree Files,  Prev: About GNAT ELIM,  Up: Reducing the Size of Ada Executables with GNAT ELIM

`Eliminate' Pragma
==================

The simplified syntax of the Eliminate pragma used by `GNAT ELIM' is:

     pragma Eliminate (Library_Unit_Name, Subprogram_Name);

where
`Library_Unit_Name'
     full expanded Ada name of a library unit

`Subprogram_Name'
     a simple or expanded name of a subprogram declared within this
     compilation unit


The effect of an `Eliminate' pragma placed in the GNAT configuration
file `GNAT.ADC' is:

   * If the subprogram `Subprogram_Name' is declared within the library
     unit `Library_Unit_Name', the compiler will not generate code for
     this subprogram. This applies to all overloaded subprograms denoted
     by `Subprogram_Name'.

   * If a subprogram marked by the pragma `Eliminate' is used (called)
     in a program, the compiler will produce an error message in the
     place where it is called.


File: gnat_ug_vms.info,  Node: Tree Files,  Next: Preparing Tree and Bind Files for GNAT ELIM,  Prev: Eliminate Pragma,  Up: Reducing the Size of Ada Executables with GNAT ELIM

Tree Files
==========

A tree file stores a snapshot of the compiler internal data structures
at the very end of a successful compilation. It contains all the
syntactic and semantic information for the compiled unit and all the
units upon which it depends semantically.  To use tools that make use
of tree files, you need to first produce the right set of tree files.

   GNAT produces correct tree files when /TREE_OUTPUT /NOLOAD options
are set in a GNAT COMPILE call. The tree files have an .adt extension.
Therefore, to produce a tree file for the compilation unit contained in
a file named `FOO.ADB', you must use the command

     $ GNAT COMPILE /NOLOAD /TREE_OUTPUT FOO.ADB

and you will get the tree file `foo.adt'.  compilation.


File: gnat_ug_vms.info,  Node: Preparing Tree and Bind Files for GNAT ELIM,  Next: Running GNAT ELIM,  Prev: Tree Files,  Up: Reducing the Size of Ada Executables with GNAT ELIM

Preparing Tree and Bind Files for `GNAT ELIM'
=============================================

A set of tree files covering the program to be analyzed with `GNAT
ELIM' and the bind file for the main subprogram does not have to be in
the current directory.  '-T' GNAT ELIM option may be used to provide
the search path for tree files, and '-b' option may be used to point to
the bind file to process (see *Note Running GNAT ELIM::)

   If you do not have the appropriate set of tree files and the right
bind file, you may create them in the current directory using the
following procedure.

   Let `Main_Prog' be the name of a main subprogram, and suppose this
subprogram is in a file named `MAIN_PROG.ADB'.

   To create a bind file for `GNAT ELIM', run `GNAT BIND' for the main
subprogram. `GNAT ELIM' can work with both Ada and C bind files; when
both are present, it uses the Ada bind file.  The following commands
will build the program and create the bind file:

     $ GNAT MAKE /ACTIONS=COMPILE MAIN_PROG
     $ GNAT BIND main_prog

To create a minimal set of tree files covering the whole program, call
`GNAT MAKE' for this program as follows:

     $ GNAT MAKE /FORCE_COMPILE /ACTIONS=COMPILE /NOLOAD /TREE_OUTPUT MAIN_PROG

The `/ACTIONS=COMPILE' GNAT MAKE option turns off the bind and link
steps, that are useless anyway because the sources are compiled with
`/NOLOAD' option which turns off code generation.

   The `/FORCE_COMPILE' GNAT MAKE option forces recompilation of all
the needed sources.

   This sequence of actions will create all the data needed by `GNAT
ELIM' from scratch and therefore guarantee its consistency. If you
would like to use some existing set of files as `GNAT ELIM' output, you
must make sure that the set of files is complete and consistent. You
can use the `-m' qualifier to check if there are missed tree files

   Note, that `GNAT ELIM' needs neither object nor ALI files.


File: gnat_ug_vms.info,  Node: Running GNAT ELIM,  Next: Correcting the List of Eliminate Pragmas,  Prev: Preparing Tree and Bind Files for GNAT ELIM,  Up: Reducing the Size of Ada Executables with GNAT ELIM

Running `GNAT ELIM'
===================

`GNAT ELIM' has the following command-line interface:

     $ GNAT ELIM [options] name

`name' should be a full expanded Ada name of a main subprogram of a
program (partition).

   `GNAT ELIM' options:

`/QUIET'
     Quiet mode: by default `GNAT ELIM' generates to the standard error
     stream a trace of the source file names of the compilation units
     being processed. This option turns this trace off.

`/VERBOSE'
     Verbose mode: `GNAT ELIM' version information is printed as Ada
     comments to the standard output stream.

`/ALL'
     Also look for subprograms from the GNAT run time that can be
     eliminated.

`/MISSED'
     Check if any tree files are missing for an accurate result.

`/TREE_DIRS=DIR'
     When looking for tree files also look in directory DIR

`/BIND_FILE=BIND_FILE'
     Specifies BIND_FILE as the bind file to process. If not set, the
     name of the bind file is computed from the full expanded Ada name
     of a main subprogram.

`-dX'
     Activate internal debugging qualifiers. X is a letter or digit, or
     string of letters or digits, which specifies the type of debugging
     mode desired.  Normally these are used only for internal
     development or system debugging purposes. You can find full
     documentation for these qualifiers in the body of the `GNAT
     ELIM.Options' unit in the compiler source file
     `GNATELIM-OPTIONS.ADB'.

`GNAT ELIM' sends its output to the standard output stream, and all the
tracing and debug information is sent to the standard error stream.  In
order to produce a proper GNAT configuration file `GNAT.ADC',
redirection must be used:

     $ PIPE GNAT ELIM MAIN_PROG > GNAT.ADC

In order to append the `GNAT ELIM' output to the existing contents of
`GNAT.ADC'.


File: gnat_ug_vms.info,  Node: Correcting the List of Eliminate Pragmas,  Next: Making Your Executables Smaller,  Prev: Running GNAT ELIM,  Up: Reducing the Size of Ada Executables with GNAT ELIM

Correcting the List of Eliminate Pragmas
========================================

In some rare cases it may happen that `GNAT ELIM' will try to eliminate
subprograms which are actually called in the program. In this case, the
compiler will generate an error message of the form:

     FILE.ADB:106:07: cannot call eliminated subprogram "My_Prog"

You will need to manually remove the wrong `Eliminate' pragmas from the
`GNAT.ADC' file. It is advised that you recompile your program from
scratch after that because you need a consistent `GNAT.ADC' file during
the entire compilation.


File: gnat_ug_vms.info,  Node: Making Your Executables Smaller,  Next: Summary of the GNAT ELIM Usage Cycle,  Prev: Correcting the List of Eliminate Pragmas,  Up: Reducing the Size of Ada Executables with GNAT ELIM

Making Your Executables Smaller
===============================

In order to get a smaller executable for your program you now have to
recompile the program completely with the new `GNAT.ADC' file created
by `GNAT ELIM' in your current directory:

     $ GNAT MAKE /FORCE_COMPILE MAIN_PROG

(you will need `/FORCE_COMPILE' option for GNAT MAKE to recompile
everything with the set of pragmas `Eliminate' you have obtained with
`GNAT ELIM').

   Be aware that the set of `Eliminate' pragmas is specific to each
program. It is not recommended to merge sets of `Eliminate' pragmas
created for different programs in one `GNAT.ADC' file.


File: gnat_ug_vms.info,  Node: Summary of the GNAT ELIM Usage Cycle,  Prev: Making Your Executables Smaller,  Up: Reducing the Size of Ada Executables with GNAT ELIM

Summary of the GNAT ELIM Usage Cycle
====================================

Here is a quick summary of the steps to be taken in order to reduce the
size of your executables with `GNAT ELIM'. You may use other GNAT
options to control the optimization level, to produce the debugging
information, to set search path, etc.

  1. Produce a bind file and a set of tree files

          $ GNAT MAKE /ACTIONS=COMPILE MAIN_PROG
          $ GNAT BIND main_prog
          $ GNAT MAKE /FORCE_COMPILE /NO_LINK /NOLOAD /TREE_OUTPUT MAIN_PROG

  2. Generate a list of `Eliminate' pragmas
          $ PIPE GNAT ELIM MAIN_PROG > GNAT.ADC

  3. Recompile the application

          $ GNAT MAKE /FORCE_COMPILE MAIN_PROG



File: gnat_ug_vms.info,  Node: Other Utility Programs,  Next: Compatibility with DEC Ada,  Prev: Reducing the Size of Ada Executables with GNAT ELIM,  Up: Top

Other Utility Programs
**********************

This chapter discusses some other utility programs available in the Ada
environment.

* Menu:

* Using Other Utility Programs with GNAT::
* The GNAT STANDARD Utility Program::
* The External Symbol Naming Scheme of GNAT::
* Ada Mode for Glide::
* Converting Ada Files to html with gnathtml::
* Installing gnathtml::
* LSE::
* Profiling::


File: gnat_ug_vms.info,  Node: Using Other Utility Programs with GNAT,  Next: The GNAT STANDARD Utility Program,  Up: Other Utility Programs

Using Other Utility Programs with GNAT
======================================

The object files generated by GNAT are in standard system format and in
particular the debugging information uses this format. This means
programs generated by GNAT can be used with existing utilities that
depend on these formats.


File: gnat_ug_vms.info,  Node: The GNAT STANDARD Utility Program,  Next: The External Symbol Naming Scheme of GNAT,  Prev: Using Other Utility Programs with GNAT,  Up: Other Utility Programs

The `GNAT STANDARD' Utility Program
===================================

Many of the definitions in package Standard are
implementation-dependent.  However, the source of this package does not
exist as an Ada source file, so these values cannot be determined by
inspecting the source.  They can be determined by examining in detail
the coding of `CSTAND.ADB' which creates the image of Standard in the
compiler, but this is awkward and requires a great deal of internal
knowledge about the system.

   The `GNAT STANDARD' utility is designed to deal with this situation.
It is an Ada program that dynamically determines the values of all the
relevant parameters in Standard, and prints them out in the form of an
Ada source listing for Standard, displaying all the values of interest.
This output is generated to `SYS$OUTPUT'.

   To determine the value of any parameter in package Standard, simply
run `GNAT STANDARD' with no qualifiers or arguments, and examine the
output. This is preferable to consulting documentation, because you
know that the values you are getting are the actual ones provided by
the executing system.


File: gnat_ug_vms.info,  Node: The External Symbol Naming Scheme of GNAT,  Next: Ada Mode for Glide,  Prev: The GNAT STANDARD Utility Program,  Up: Other Utility Programs

The External Symbol Naming Scheme of GNAT
=========================================

In order to interpret the output from GNAT, when using tools that are
originally intended for use with other languages, it is useful to
understand the conventions used to generate link names from the Ada
entity names.

   All link names are in all lowercase letters. With the exception of
library procedure names, the mechanism used is simply to use the full
expanded Ada name with dots replaced by double underscores. For
example, suppose we have the following package spec:

     package QRS is
        MN : Integer;
     end QRS;

The variable `MN' has a full expanded Ada name of `QRS.MN', so the
corresponding link name is `qrs__mn'.  Of course if a `pragma Export'
is used this may be overridden:

     package Exports is
        Var1 : Integer;
        pragma Export (Var1, C, External_Name => "var1_name");
        Var2 : Integer;
        pragma Export (Var2, C, Link_Name => "var2_link_name");
     end Exports;

In this case, the link name for VAR1 is whatever link name the C
compiler would assign for the C function VAR1_NAME. This typically
would be either VAR1_NAME or _VAR1_NAME, depending on operating system
conventions, but other possibilities exist. The link name for VAR2 is
VAR2_LINK_NAME, and this is not operating system dependent.

   One exception occurs for library level procedures. A potential
ambiguity arises between the required name `_main' for the C main
program, and the name we would otherwise assign to an Ada library level
procedure called `Main' (which might well not be the main program).

   To avoid this ambiguity, we attach the prefix `_ada_' to such names.
So if we have a library level procedure such as

     procedure Hello (S : String);

the external name of this procedure will be _ADA_HELLO.


File: gnat_ug_vms.info,  Node: Ada Mode for Glide,  Next: Converting Ada Files to html with gnathtml,  Prev: The External Symbol Naming Scheme of GNAT,  Up: Other Utility Programs

Ada Mode for `Glide'
====================

The Glide mode for programming in Ada (both, Ada83 and Ada95) helps the
user in understanding existing code and facilitates writing new code. It
furthermore provides some utility functions for easier integration of
standard EMACS features when programming in Ada.

General Features:
-----------------

   * Full Integrated Development Environment :

        * support of 'project files' for the configuration (directories,
          compilation options,...)

        * compiling and stepping through error messages.

        * running and debugging your applications within Glide.

   * easy to use for beginners by pull-down menus,

   * user configurable by many user-option variables.

Ada Mode Features That Help Understanding Code:
-----------------------------------------------

   * functions for easy and quick stepping through Ada code,

   * getting cross reference information for identifiers (e.g. find the
     defining place by a keystroke),

   * displaying an index menu of types and subprograms and move point to
     the chosen one,

   * automatic color highlighting of the various entities in Ada code.

Glide Support for Writing Ada Code:
-----------------------------------

   * switching between spec and body files with possible autogeneration
     of body files,

   * automatic formating of subprograms parameter lists.

   * automatic smart indentation according to Ada syntax,

   * automatic completion of identifiers,

   * automatic casing of identifiers, keywords, and attributes,

   * insertion of statement templates,

   * filling comment paragraphs like filling normal text,

   For more information, please refer to the online Glide documentation
available in the Glide -> Help Menu.


File: gnat_ug_vms.info,  Node: Converting Ada Files to html with gnathtml,  Next: Installing gnathtml,  Prev: Ada Mode for Glide,  Up: Other Utility Programs

Converting Ada Files to html with `gnathtml'
============================================

This `Perl' script allows Ada source files to be browsed using standard
Web browsers. For installation procedure, see the section *Note
Installing gnathtml::.

   Ada reserved keywords are highlighted in a bold font and Ada
comments in a blue font. Unless your program was compiled with the GNAT
COMPILE `/XREF=SUPPRESS' qualifier to suppress the generation of
cross-referencing information, user defined variables and types will
appear in a different color; you will be able to click on any
identifier and go to its declaration.

   The command line is as follow:
     $ perl gnathtml.pl [qualifiers] ada-files

   You can pass it as many Ada files as you want. `gnathtml' will
generate an html file for every ada file, and a global file called
`index.htm'.  This file is an index of every identifier defined in the
files.

   The available qualifiers are the following ones :

`-83'
     Only the subset on the Ada 83 keywords will be highlighted, not
     the full Ada 95 keywords set.

`-cc COLOR'
     This option allows you to change the color used for comments. The
     default value is green. The color argument can be any name
     accepted by html.

`-d'
     If the ada files depend on some other files (using for instance the
     `with' command, the latter will also be converted to html.  Only
     the files in the user project will be converted to html, not the
     files in the run-time library itself.

`-D'
     This command is the same as -d above, but `gnathtml' will also look
     for files in the run-time library, and generate html files for
     them.

`-f'
     By default, gnathtml will generate html links only for global
     entities ('with'ed units, global variables and types,...). If you
     specify the `-f' on the command line, then links will be generated
     for local entities too.

`-l NUMBER'
     If this qualifier is provided and NUMBER is not 0, then `gnathtml'
     will number the html files every NUMBER line.

`-I DIR'
     Specify a directory to search for library files (`.ALI' files) and
     source files. You can provide several -I qualifiers on the command
     line, and the directories will be parsed in the order of the
     command line.

`-o DIR'
     Specify the output directory for html files. By default, gnathtml
     will saved the generated html files in a subdirectory named
     `html/'.

`-p FILE'
     If you are using EMACS and the most recent EMACS Ada mode, which
     provides a full Integrated Development Environment for compiling,
     checking, running and debugging applications, you may be using
     `.adp' files to give the directories where EMACS can find sources
     and object files.

     Using this qualifier, you can tell gnathtml to use these files.
     This allows you to get an html version of your application, even
     if it is spread over multiple directories.

`-sc COLOR'
     This option allows you to change the color used for symbol
     definitions.  The default value is red. The color argument can be
     any name accepted by html.

`-t FILE'
     This qualifier provides the name of a file. This file contains a
     list of file names to be converted, and the effect is exactly as
     though they had appeared explicitly on the command line. This is
     the recommended way to work around the command line length limit
     on some systems.



File: gnat_ug_vms.info,  Node: Installing gnathtml,  Next: LSE,  Prev: Converting Ada Files to html with gnathtml,  Up: Other Utility Programs

Installing `gnathtml'
=====================

`Perl' needs to be installed on your machine to run this script.
`Perl' is freely available for almost every architecture and Operating
System via the Internet.

   On Unix systems, you  may want to modify  the  first line of  the
script `gnathtml',  to explicitly  tell  the Operating  system  where
Perl is. The syntax of this line is :
     #!full_path_name_to_perl

Alternatively, you may run the script using the following command line:

     $ perl gnathtml.pl [qualifiers] files


File: gnat_ug_vms.info,  Node: LSE,  Next: Profiling,  Prev: Installing gnathtml,  Up: Other Utility Programs

LSE
===

The GNAT distribution provides an Ada 95 template for the Digital
Language Sensitive Editor (LSE), a component of DECset. In order to
access it, invoke LSE with the qualifier
/ENVIRONMENT=GNU:[LIB]ADA95.ENV.


File: gnat_ug_vms.info,  Node: Profiling,  Prev: LSE,  Up: Other Utility Programs

Profiling
=========

GNAT supports The Digital Performance Coverage Analyzer (PCA), a
component of DECset. To use it proceed as outlined under "HELP PCA",
except for running the collection phase with the /DEBUG qualifier.

     $ GNAT MAKE /DEBUG <PROGRAM_NAME>
     $ DEFINE LIB$DEBUG PCA$COLLECTOR
     $ RUN/DEBUG <PROGRAM_NAME>


File: gnat_ug_vms.info,  Node: Running and Debugging Ada Programs,  Next: Inline Assembler,  Prev: Compatibility with DEC Ada,  Up: Top

Running and Debugging Ada Programs
**********************************

This chapter discusses how to debug Ada programs. An incorrect Ada
program may be handled in three ways by the GNAT compiler:

  1. The illegality may be a violation of the static semantics of Ada.
     In that case GNAT diagnoses the constructs in the program that are
     illegal.  It is then a straightforward matter for the user to
     modify those parts of the program.

  2. The illegality may be a violation of the dynamic semantics of Ada.
     In that case the program compiles and executes, but may generate
     incorrect results, or may terminate abnormally with some exception.

  3. When presented with a program that contains convoluted errors, GNAT
     itself may terminate abnormally without providing full diagnostics
     on the incorrect user program.

* Menu:

* The GNAT Debugger GDB::
* Running GDB::
* Introduction to GDB Commands::
* Using Ada Expressions::
* Calling User-Defined Subprograms::
* Using the Next Command in a Function::
* Ada Exceptions::
* Ada Tasks::
* Debugging Generic Units::
* GNAT Abnormal Termination or Failure to Terminate::
* Naming Conventions for GNAT Source Files::
* Getting Internal Debugging Information::
* Stack Traceback::


File: gnat_ug_vms.info,  Node: The GNAT Debugger GDB,  Next: Running GDB,  Up: Running and Debugging Ada Programs

The GNAT Debugger GDB
=====================

`GDB' is a general purpose, platform-independent debugger that can be
used to debug mixed-language programs compiled with `GCC', and in
particular is capable of debugging Ada programs compiled with GNAT. The
latest versions of `GDB' are Ada-aware and can handle complex Ada data
structures.

   The manual `Debugging with GDB' , located in the GNU:[DOCS]
directory, contains full details on the usage of `GDB', including a
section on its usage on programs. This manual should be consulted for
full details. The section that follows is a brief introduction to the
philosophy and use of `GDB'.

   When GNAT programs are compiled, the compiler optionally writes
debugging information into the generated object file, including
information on line numbers, and on declared types and variables. This
information is separate from the generated code. It makes the object
files considerably larger, but it does not add to the size of the
actual executable that will be loaded into memory, and has no impact on
run-time performance. The generation of debug information is triggered
by the use of the /DEBUG qualifier in the GNAT COMPILE or GNAT MAKE
command used to carry out the compilations. It is important to
emphasize that the use of these options does not change the generated
code.

   The debugging information is written in standard system formats that
are used by many tools, including debuggers and profilers. The format
of the information is typically designed to describe C types and
semantics, but GNAT implements a translation scheme which allows full
details about Ada types and variables to be encoded into these standard
C formats. Details of this encoding scheme may be found in the file
EXP_DBUG.ADS in the GNAT source distribution. However, the details of
this encoding are, in general, of no interest to a user, since `GDB'
automatically performs the necessary decoding.

   When a program is bound and linked, the debugging information is
collected from the object files, and stored in the executable image of
the program. Again, this process significantly increases the size of
the generated executable file, but it does not increase the size of the
executable program itself. Furthermore, if this program is run in the
normal manner, it runs exactly as if the debug information were not
present, and takes no more actual memory.

   However, if the program is run under control of `GDB', the debugger
is activated.  The image of the program is loaded, at which point it is
ready to run.  If a run command is given, then the program will run
exactly as it would have if `GDB' were not present. This is a crucial
part of the `GDB' design philosophy.  `GDB' is entirely non-intrusive
until a breakpoint is encountered.  If no breakpoint is ever hit, the
program will run exactly as it would if no debugger were present. When
a breakpoint is hit, `GDB' accesses the debugging information and can
respond to user commands to inspect variables, and more generally to
report on the state of execution.


File: gnat_ug_vms.info,  Node: Running GDB,  Next: Introduction to GDB Commands,  Prev: The GNAT Debugger GDB,  Up: Running and Debugging Ada Programs

Running GDB
===========

The debugger can be launched directly and simply from `glide' or
through its graphical interface: `gvd'. It can also be used directly in
text mode. Here is described the basic use of `GDB' in text mode. All
the commands described below can be used in the `gvd' console window
eventhough there is usually other more graphical ways to achieve the
same goals.

The command to run `GDB' in text mode is

     $ $ GDB PROGRAM

where `PROGRAM' is the name of the executable file. This activates the
debugger and results in a prompt for debugger commands.  The simplest
command is simply `run', which causes the program to run exactly as if
the debugger were not present. The following section describes some of
the additional commands that can be given to `GDB'.


File: gnat_ug_vms.info,  Node: Introduction to GDB Commands,  Next: Using Ada Expressions,  Prev: Running GDB,  Up: Running and Debugging Ada Programs

Introduction to GDB Commands
============================

`GDB' contains a large repertoire of commands. The manual `Debugging
with GDB' , located in the GNU:[DOCS] directory, includes extensive
documentation on the use of these commands, together with examples of
their use. Furthermore, the command HELP invoked from within `GDB'
activates a simple help facility which summarizes the available
commands and their options.  In this section we summarize a few of the
most commonly used commands to give an idea of what `GDB' is about. You
should create a simple program with debugging information and
experiment with the use of these `GDB' commands on the program as you
read through the following section.

`set args ARGUMENTS'
     The ARGUMENTS list above is a list of arguments to be passed to
     the program on a subsequent run command, just as though the
     arguments had been entered on a normal invocation of the program.
     The `set args' command is not needed if the program does not
     require arguments.

`run'
     The `run' command causes execution of the program to start from
     the beginning. If the program is already running, that is to say if
     you are currently positioned at a breakpoint, then a prompt will
     ask for confirmation that you want to abandon the current
     execution and restart.

`breakpoint LOCATION'
     The breakpoint command sets a breakpoint, that is to say a point
     at which execution will halt and `GDB' will await further
     commands. LOCATION is either a line number within a file, given in
     the format `file:linenumber', or it is the name of a subprogram.
     If you request that a breakpoint be set on a subprogram that is
     overloaded, a prompt will ask you to specify on which of those
     subprograms you want to breakpoint. You can also specify that all
     of them should be breakpointed. If the program is run and
     execution encounters the breakpoint, then the program stops and
     `GDB' signals that the breakpoint was encountered by printing the
     line of code before which the program is halted.

`breakpoint exception NAME'
     A special form of the breakpoint command which breakpoints whenever
     exception NAME is raised.  If NAME is omitted, then a breakpoint
     will occur when any exception is raised.

`print EXPRESSION'
     This will print the value of the given expression. Most simple Ada
     expression formats are properly handled by `GDB', so the expression
     can contain function calls, variables, operators, and attribute
     references.

`continue'
     Continues execution following a breakpoint, until the next
     breakpoint or the termination of the program.

`step'
     Executes a single line after a breakpoint. If the next statement
     is a subprogram call, execution continues into (the first
     statement of) the called subprogram.

`next'
     Executes a single line. If this line is a subprogram call,
     executes and returns from the call.

`list'
     Lists a few lines around the current source location. In practice,
     it is usually more convenient to have a separate edit window open
     with the relevant source file displayed. Successive applications
     of this command print subsequent lines. The command can be given
     an argument which is a line number, in which case it displays a
     few lines around the specified one.

`backtrace'
     Displays a backtrace of the call chain. This command is typically
     used after a breakpoint has occurred, to examine the sequence of
     calls that leads to the current breakpoint. The display includes
     one line for each activation record (frame) corresponding to an
     active subprogram.

`up'
     At a breakpoint, `GDB' can display the values of variables local
     to the current frame. The command `up' can be used to examine the
     contents of other active frames, by moving the focus up the stack,
     that is to say from callee to caller, one frame at a time.

`down'
     Moves the focus of `GDB' down from the frame currently being
     examined to the frame of its callee (the reverse of the previous
     command),

`frame N'
     Inspect the frame with the given number. The value 0 denotes the
     frame of the current breakpoint, that is to say the top of the
     call stack.


   The above list is a very short introduction to the commands that
`GDB' provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in `Debugging with GDB'.  Note that
most commands can be abbreviated (for example, c for continue, bt for
backtrace).


File: gnat_ug_vms.info,  Node: Using Ada Expressions,  Next: Calling User-Defined Subprograms,  Prev: Introduction to GDB Commands,  Up: Running and Debugging Ada Programs

Using Ada Expressions
=====================

`GDB' supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is

   * That `GDB' should provide basic literals and access to operations
     for arithmetic, dereferencing, field selection, indexing, and
     subprogram calls, leaving more sophisticated computations to
     subprograms written into the program (which therefore may be
     called from `GDB').

   * That type safety and strict adherence to Ada language restrictions
     are not particularly important to the `GDB' user.

   * That brevity is important to the `GDB' user.

   Thus, for brevity, the debugger acts as if there were implicit
`with' and `use' clauses in effect for all user-written packages, thus
making it unnecessary to fully qualify most names with their packages,
regardless of context. Where this causes ambiguity, `GDB' asks the
user's intent.

   For details on the supported Ada syntax, see `Debugging with GDB'.


File: gnat_ug_vms.info,  Node: Calling User-Defined Subprograms,  Next: Using the Next Command in a Function,  Prev: Using Ada Expressions,  Up: Running and Debugging Ada Programs

Calling User-Defined Subprograms
================================

An important capability of `GDB' is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering a
subprogram call statement in the form:

     call subprogram-name (parameters)

The keyword `call' can be omitted in the normal case where the
`subprogram-name' does not coincide with any of the predefined `GDB'
commands.

   The effect is to invoke the given subprogram, passing it the list of
parameters that is supplied. The parameters can be expressions and can
include variables from the program being debugged. The subprogram must
be defined at the library level within your program, and `GDB' will
call the subprogram within the environment of your program execution
(which means that the subprogram is free to access or even modify
variables within your program).

   The most important use of this facility is in allowing the inclusion
of debugging routines that are tailored to particular data structures
in your program. Such debugging routines can be written to provide a
suitably high-level description of an abstract type, rather than a
low-level dump of its physical layout. After all, the standard `GDB
print' command only knows the physical layout of your types, not their
abstract meaning. Debugging routines can provide information at the
desired semantic level and are thus enormously useful.

   For example, when debugging GNAT itself, it is crucial to have
access to the contents of the tree nodes used to represent the program
internally.  But tree nodes are represented simply by an integer value
(which in turn is an index into a table of nodes).  Using the `print'
command on a tree node would simply print this integer value, which is
not very useful. But the PN routine (defined in file TREEPR.ADB in the
GNAT sources) takes a tree node as input, and displays a useful high
level representation of the tree node, which includes the syntactic
category of the node, its position in the source, the integers that
denote descendant nodes and parent node, as well as varied semantic
information. To study this example in more detail, you might want to
look at the body of the PN procedure in the stated file.


File: gnat_ug_vms.info,  Node: Using the Next Command in a Function,  Next: Ada Exceptions,  Prev: Calling User-Defined Subprograms,  Up: Running and Debugging Ada Programs

Using the Next Command in a Function
====================================

When you use the `next' command in a function, the current source
location will advance to the next statement as usual. A special case
arises in the case of a `return' statement.

   Part of the code for a return statement is the "epilog" of the
function.  This is the code that returns to the caller. There is only
one copy of this epilog code, and it is typically associated with the
last return statement in the function if there is more than one return.
In some implementations, this epilog is associated with the first
statement of the function.

   The result is that if you use the `next' command from a return
statement that is not the last return statement of the function you may
see a strange apparent jump to the last return statement or to the
start of the function. You should simply ignore this odd jump.  The
value returned is always that from the first return statement that was
stepped through.


File: gnat_ug_vms.info,  Node: Ada Exceptions,  Next: Ada Tasks,  Prev: Using the Next Command in a Function,  Up: Running and Debugging Ada Programs

Breaking on Ada Exceptions
==========================

You can set breakpoints that trip when your program raises selected
exceptions.

`break exception'
     Set a breakpoint that trips whenever (any task in the) program
     raises any exception.

`break exception NAME'
     Set a breakpoint that trips whenever (any task in the) program
     raises the exception NAME.

`break exception unhandled'
     Set a breakpoint that trips whenever (any task in the) program
     raises an exception for which there is no handler.

`info exceptions'
`info exceptions REGEXP'
     The `info exceptions' command permits the user to examine all
     defined exceptions within Ada programs. With a regular expression,
     REGEXP, as argument, prints out only those exceptions whose name
     matches REGEXP.


File: gnat_ug_vms.info,  Node: Ada Tasks,  Next: Debugging Generic Units,  Prev: Ada Exceptions,  Up: Running and Debugging Ada Programs

Ada Tasks
=========

`GDB' allows the following task-related commands:

`info tasks'
     This command shows a list of current Ada tasks, as in the
     following example:

          (GDB) info tasks
            ID       TID P-ID   Thread Pri State                 Name
             1   8088000   0   807e000  15 Child Activation Wait main_task
             2   80a4000   1   80ae000  15 Accept/Select Wait    b
             3   809a800   1   80a4800  15 Child Activation Wait a
          *  4   80ae800   3   80b8000  15 Running               c

     In this listing, the asterisk before the first task indicates it
     to be the currently running task. The first column lists the task
     ID that is used to refer to tasks in the following commands.

`break LINESPEC task TASKID'
`break LINESPEC task TASKID if ...'
     These commands are like the `break ... thread ...'.  LINESPEC
     specifies source lines.

     Use the qualifier `task TASKID' with a breakpoint command to
     specify that you only want `GDB' to stop the program when a
     particular Ada task reaches this breakpoint. TASKID is one of the
     numeric task identifiers assigned by `GDB', shown in the first
     column of the `info tasks' display.

     If you do not specify `task TASKID' when you set a breakpoint, the
     breakpoint applies to _all_ tasks of your program.

     You can use the `task' qualifier on conditional breakpoints as
     well; in this case, place `task TASKID' before the breakpoint
     condition (before the `if').

`task TASKNO'
     This command allows to qualifier to the task referred by TASKNO. In
     particular, This allows to browse the backtrace of the specified
     task. It is advised to qualifier back to the original task before
     continuing execution otherwise the scheduling of the program may be
     perturbated.

For more detailed information on the tasking support, see `Debugging
with GDB'.


File: gnat_ug_vms.info,  Node: Debugging Generic Units,  Next: GNAT Abnormal Termination or Failure to Terminate,  Prev: Ada Tasks,  Up: Running and Debugging Ada Programs

Debugging Generic Units
=======================

GNAT always uses code expansion for generic instantiation. This means
that each time an instantiation occurs, a complete copy of the original
code is made, with appropriate substitutions of formals by actuals.

   It is not possible to refer to the original generic entities in
`GDB', but it is always possible to debug a particular instance of a
generic, by using the appropriate expanded names. For example, if we
have

     procedure g is
     
        generic package k is
           procedure kp (v1 : in out integer);
        end k;
     
        package body k is
           procedure kp (v1 : in out integer) is
           begin
              v1 := v1 + 1;
           end kp;
        end k;
     
        package k1 is new k;
        package k2 is new k;
     
        var : integer := 1;
     
     begin
        k1.kp (var);
        k2.kp (var);
        k1.kp (var);
        k2.kp (var);
     end;

Then to break on a call to procedure kp in the k2 instance, simply use
the command:

     (GDB) break g.k2.kp

When the breakpoint occurs, you can step through the code of the
instance in the normal manner and examine the values of local
variables, as for other units.


File: gnat_ug_vms.info,  Node: GNAT Abnormal Termination or Failure to Terminate,  Next: Naming Conventions for GNAT Source Files,  Prev: Debugging Generic Units,  Up: Running and Debugging Ada Programs

GNAT Abnormal Termination or Failure to Terminate
=================================================

When presented with programs that contain serious errors in syntax or
semantics, GNAT may on rare occasions  experience problems in
operation, such as aborting with a segmentation fault or illegal memory
access, raising an internal exception, terminating abnormally, or
failing to terminate at all.  In such cases, you can activate various
features of GNAT that can help you pinpoint the construct in your
program that is the likely source of the problem.

   The following strategies are presented in increasing order of
difficulty, corresponding to your experience in using GNAT and your
familiarity with compiler internals.

  1. Run `GNAT COMPILE' with the `/REPORT_ERRORS=FULL'. This first
     qualifier causes all errors on a given line to be reported. In its
     absence, only the first error on a line is displayed.

     The `/REPORT_ERRORS=IMMEDIATE' qualifier causes errors to be
     displayed as soon as they are encountered, rather than after
     compilation is terminated. If GNAT terminates prematurely or goes
     into an infinite loop, the last error message displayed may help
     to pinpoint the culprit.

  2. Run `GNAT COMPILE' with the `/VERBOSE' qualifier. In this mode,
     `GNAT COMPILE' produces ongoing information about the progress of
     the compilation and provides the name of each procedure as code is
     generated. This qualifier allows you to find which Ada procedure
     was being compiled when it encountered a code generation problem.

  3. Run `GNAT COMPILE' with the `/TRACE_UNITS' qualifier. This is a
     GNAT specific qualifier that does for the front-end what `VERBOSE'
     does for the back end.  The system prints the name of each unit,
     either a compilation unit or nested unit, as it is being analyzed.

  4. Finally, you can start `GDB' directly on the `GNAT1' executable.
     `GNAT1' is the front-end of GNAT, and can be run independently
     (normally it is just called from `GNAT COMPILE'). You can use
     `GDB' on `GNAT1' as you would on a C program (but *note The GNAT
     Debugger GDB:: for caveats). The `where' command is the first line
     of attack; the variable `lineno' (seen by `print lineno'), used by
     the second phase of `GNAT1' and by the `GNAT COMPILE' backend,
     indicates the source line at which the execution stopped, and
     `input_file name' indicates the name of the source file.


File: gnat_ug_vms.info,  Node: Naming Conventions for GNAT Source Files,  Next: Getting Internal Debugging Information,  Prev: GNAT Abnormal Termination or Failure to Terminate,  Up: Running and Debugging Ada Programs

Naming Conventions for GNAT Source Files
========================================

In order to examine the workings of the GNAT system, the following
brief description of its organization may be helpful:

   * Files with prefix `SC' contain the lexical scanner.

   * All files prefixed with `PAR' are components of the parser. The
     numbers correspond to chapters of the Ada 95 Reference Manual. For
     example, parsing of select statements can be found in
     `PAR-CH9.ADB'.

   * All files prefixed with `SEM' perform semantic analysis. The
     numbers correspond to chapters of the Ada standard. For example,
     all issues involving context clauses can be found in
     `SEM_CH10.ADB'. In addition, some features of the language require
     sufficient special processing to justify their own semantic files:
     sem_aggr for aggregates, sem_disp for dynamic dispatching, etc.

   * All files prefixed with `EXP' perform normalization and expansion
     of the intermediate representation (abstract syntax tree, or AST).
     these files use the same numbering scheme as the parser and
     semantics files.  For example, the construction of record
     initialization procedures is done in `EXP_CH3.ADB'.

   * The files prefixed with `BIND' implement the binder, which
     verifies the consistency of the compilation, determines an order of
     elaboration, and generates the bind file.

   * The files `ATREE.ADS' and `ATREE.ADB' detail the low-level data
     structures used by the front-end.

   * The files `SINFO.ADS' and `SINFO.ADB' detail the structure of the
     abstract syntax tree as produced by the parser.

   * The files `EINFO.ADS' and `EINFO.ADB' detail the attributes of all
     entities, computed during semantic analysis.

   * Library management issues are dealt with in files with prefix
     `LIB'.

   * Ada files with the prefix `A-' are children of `Ada', as defined
     in Annex A.

   * Files with prefix `I-' are children of `Interfaces', as defined in
     Annex B.

   * Files with prefix `S-' are children of `System'. This includes
     both language-defined children and GNAT run-time routines.

   * Files with prefix `G-' are children of `GNAT'. These are useful
     general-purpose packages, fully documented in their
     specifications. All the other `.C' files are modifications of
     common `GNAT COMPILE' files.


File: gnat_ug_vms.info,  Node: Getting Internal Debugging Information,  Next: Stack Traceback,  Prev: Naming Conventions for GNAT Source Files,  Up: Running and Debugging Ada Programs

Getting Internal Debugging Information
======================================

Most compilers have internal debugging qualifiers and modes. GNAT does
also, except GNAT internal debugging qualifiers and modes are not
secret. A summary and full description of all the compiler and binder
debug flags are in the file `DEBUG.ADB'. You must obtain the sources of
the compiler to see the full detailed effects of these flags.

   The qualifiers that print the source of the program (reconstructed
from the internal tree) are of general interest for user programs, as
are the options to print the full internal tree, and the entity table
(the symbol table information). The reconstructed source provides a
readable version of the program after the front-end has completed
analysis and  expansion, and is useful when studying the performance of
specific constructs. For example, constraint checks are indicated,
complex aggregates are replaced with loops and assignments, and tasking
primitives are replaced with run-time calls.


File: gnat_ug_vms.info,  Node: Stack Traceback,  Prev: Getting Internal Debugging Information,  Up: Running and Debugging Ada Programs

Stack Traceback
===============

Traceback is a mechanism to display the sequence of subprogram calls
that leads to a specified execution point in a program. Often (but not
always) the execution point is an instruction at which an exception has
been raised.  This mechanism is also known as stack unwinding because
it obtains its information by scanning the run-time stack and
recovering the activation records of all active subprograms. Stack
unwinding is one of the most important tools for program debugging.

The first entry stored in traceback corresponds to the deepest calling
level, that is to say the subprogram currently executing the instruction
from which we want to obtain the traceback.

Note that there is no runtime performance penalty when stack traceback
is enabled and no exception are raised during program execution.

* Menu:

* Non-Symbolic Traceback::
* Symbolic Traceback::


File: gnat_ug_vms.info,  Node: Non-Symbolic Traceback,  Next: Symbolic Traceback,  Up: Stack Traceback

Non-Symbolic Traceback
----------------------

Note: this feature is not supported on all platforms. See
`GNAT.Traceback spec in G-TRACEB.ADS' for a complete list of supported
platforms.

* Menu:

* Tracebacks From an Unhandled Exception::
* Tracebacks From Exception Occurrences (non-symbolic)::
* Tracebacks From Anywhere in a Program (non-symbolic)::


File: gnat_ug_vms.info,  Node: Tracebacks From an Unhandled Exception,  Next: Tracebacks From Exception Occurrences (non-symbolic),  Up: Non-Symbolic Traceback

Tracebacks From an Unhandled Exception
......................................

A runtime non-symbolic traceback is a list of addresses of call
instructions.  To enable this feature you must use the `-E' `GNAT
BIND''s option. With this option a stack traceback is stored as part of
exception information. It is possible to retrieve this information
using the standard `Ada.Exception.Exception_Information' routine.

Let's have a look at a simple example:

     procedure STB is
     
        procedure P1 is
        begin
           raise Constraint_Error;
        end P1;
     
        procedure P2 is
        begin
           P1;
        end P2;
     
     begin
        P2;
     end STB;

     $ GNAT MAKE stb /BINDER_QUALIFIERS -E
     $ stb
     
     Execution terminated by unhandled exception
     Exception name: CONSTRAINT_ERROR
     Message: STB.ADB:5
     Call stack traceback locations:
     0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4

As we see the traceback lists a sequence of addresses for the unhandled
exception `CONSTAINT_ERROR' raised in procedure P1. It is easy to guess
that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the `addr2line'
tool, described below, is invaluable. The use of this tool requires the
program to be compiled with debug information.

     $ GNAT MAKE -g stb /BINDER_QUALIFIERS -E
     $ stb
     
     Execution terminated by unhandled exception
     Exception name: CONSTRAINT_ERROR
     Message: STB.ADB:5
     Call stack traceback locations:
     0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4
     
     $ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4
        0x4011f1 0x77e892a4
     
     00401373 at d:/stb/STB.ADB:5
     0040138B at d:/stb/STB.ADB:10
     0040139C at d:/stb/STB.ADB:14
     00401335 at d:/stb/B~STB.ADB:104
     004011C4 at /build/.../CRT1.C:200
     004011F1 at /build/.../CRT1.C:222
     77E892A4 in ?? at ??:0

`addr2line' has a number of other useful options:

`--functions'
     to get the function name corresponding to any location

`--demangle=gnat'
     to use the gnat decoding mode for the function names. Note that
     for binutils version 2.9.x the option is simply `--demangle'.

     $ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b
        0x40139c 0x401335 0x4011c4 0x4011f1
     
     00401373 in stb.p1 at d:/stb/STB.ADB:5
     0040138B in stb.p2 at d:/stb/STB.ADB:10
     0040139C in stb at d:/stb/STB.ADB:14
     00401335 in main at d:/stb/B~STB.ADB:104
     004011C4 in <__mingw_CRTStartup> at /build/.../CRT1.C:200
     004011F1 in <mainCRTStartup> at /build/.../CRT1.C:222

From this traceback we can see that the exception was raised in
`STB.ADB' at line 5, which was reached from a procedure call in
`STB.ADB' at line 10, and so on. The `B~STD.ADB' is the binder file,
which contains the call to the main program.  *note Running GNAT
BIND::. The remaining entries are assorted runtime routines, and the
output will vary from platform to platform.

It is also possible to use `GDB' with these traceback addresses to debug
the program. For example, we can break at a given code location, as
reported in the stack traceback:

     $ GDB -nw stb
     
     (GDB) break *0x401373
     Breakpoint 1 at 0x401373: file STB.ADB, line 5.

It is important to note that the stack traceback addresses do not
change when debug information is included. This is particularly useful
because it makes it possible to release software without debug
information (to minimize object size), get a field report that includes
a stack traceback whenever an internal bug occurs, and then be able to
retrieve the sequence of calls with the same program compiled with
debug information.


File: gnat_ug_vms.info,  Node: Tracebacks From Exception Occurrences (non-symbolic),  Next: Tracebacks From Anywhere in a Program (non-symbolic),  Prev: Tracebacks From an Unhandled Exception,  Up: Non-Symbolic Traceback

Tracebacks From Exception Occurrences
.....................................

Non-symbolic tracebacks are obtained by using the `-E' binder argument.
The stack traceback is attached to the exception information string,
and can be retrieved in an exception handler within the Ada program, by
means of the Ada95 facilities defined in `Ada.Exceptions'. Here is a
simple example:

     with Ada.Text_IO;
     with Ada.Exceptions;
     
     procedure STB is
     
        use Ada;
        use Ada.Exceptions;
     
        procedure P1 is
           K : Positive := 1;
        begin
           K := K - 1;
        exception
           when E : others =>
              Text_IO.Put_Line (Exception_Information (E));
        end P1;
     
        procedure P2 is
        begin
           P1;
        end P2;
     
     begin
        P2;
     end STB;

This program will output:

     $ stb
     
     Exception name: CONSTRAINT_ERROR
     Message: STB.ADB:12
     Call stack traceback locations:
     0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4


File: gnat_ug_vms.info,  Node: Tracebacks From Anywhere in a Program (non-symbolic),  Prev: Tracebacks From Exception Occurrences (non-symbolic),  Up: Non-Symbolic Traceback

Tracebacks From Anywhere in a Program
.....................................

It is also possible to retrieve a stack traceback from anywhere in a
program. For this you need to use the `GNAT.Traceback' API. This
package includes a procedure called `Call_Chain' that computes a
complete stack traceback, as well as useful display procedures
described below. It is not necessary to use the `-E GNAT BIND' option
in this case, because the stack traceback mechanism is invoked
explicitly.

In the following example we compute a traceback at a specific location
in the program, and we display it using `GNAT.Debug_Utilities.Image' to
convert addresses to strings:

     with Ada.Text_IO;
     with GNAT.Traceback;
     with GNAT.Debug_Utilities;
     
     procedure STB is
     
        use Ada;
        use GNAT;
        use GNAT.Traceback;
     
        procedure P1 is
           TB  : Tracebacks_Array (1 .. 10);
           --  We are asking for a maximum of 10 stack frames.
           Len : Natural;
           --  Len will receive the actual number of stack frames returned.
        begin
           Call_Chain (TB, Len);
     
           Text_IO.Put ("In STB.P1 : ");
     
           for K in 1 .. Len loop
              Text_IO.Put (Debug_Utilities.Image (TB (K)));
              Text_IO.Put (' ');
           end loop;
     
           Text_IO.New_Line;
        end P1;
     
        procedure P2 is
        begin
           P1;
        end P2;
     
     begin
        P2;
     end STB;

     $ GNAT MAKE stb
     $ stb
     
     In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C#
     16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4#


File: gnat_ug_vms.info,  Node: Symbolic Traceback,  Prev: Non-Symbolic Traceback,  Up: Stack Traceback

Symbolic Traceback
------------------

A symbolic traceback is a stack traceback in which procedure names are
associated with each code location.

Note that this feature is not supported on all platforms. See
`GNAT.Traceback.Symbolic spec in G-TRASYM.ADS' for a complete list of
currently supported platforms.

Note that the symbolic traceback requires that the program be compiled
with debug information. If it is not compiled with debug information
only the non-symbolic information will be valid.

* Menu:

* Tracebacks From Exception Occurrences (symbolic)::
* Tracebacks From Anywhere in a Program (symbolic)::


File: gnat_ug_vms.info,  Node: Tracebacks From Exception Occurrences (symbolic),  Next: Tracebacks From Anywhere in a Program (symbolic),  Up: Symbolic Traceback

Tracebacks From Exception Occurrences
.....................................

     with Ada.Text_IO;
     with GNAT.Traceback.Symbolic;
     
     procedure STB is
     
        procedure P1 is
        begin
           raise Constraint_Error;
        end P1;
     
        procedure P2 is
        begin
           P1;
        end P2;
     
        procedure P3 is
        begin
           P2;
        end P3;
     
     begin
        P3;
     exception
        when E : others =>
           Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E));
     end STB;

     $ GNAT MAKE -g stb /BINDER_QUALIFIERS -E /LINKER_QUALIFIERS -lgnat -laddr2line -lintl
     $ stb
     
     0040149F in stb.p1 at STB.ADB:8
     004014B7 in stb.p2 at STB.ADB:13
     004014CF in stb.p3 at STB.ADB:18
     004015DD in ada.stb at STB.ADB:22
     00401461 in main at B~STB.ADB:168
     004011C4 in __mingw_CRTStartup at CRT1.C:200
     004011F1 in mainCRTStartup at CRT1.C:222
     77E892A4 in ?? at ??:0

The exact sequence of linker options may vary from platform to platform.
The above `/LINKER_QUALIFIERS' section is for Windows platforms. By
contrast, under Unix there is no need for the `/LINKER_QUALIFIERS'
section.  Differences across platforms are due to details of linker
implementation.


File: gnat_ug_vms.info,  Node: Tracebacks From Anywhere in a Program (symbolic),  Prev: Tracebacks From Exception Occurrences (symbolic),  Up: Symbolic Traceback

Tracebacks From Anywhere in a Program
.....................................

It is possible to get a symbolic stack traceback from anywhere in a
program, just as for non-symbolic tracebacks.  The first step is to
obtain a non-symbolic traceback, and then call `Symbolic_Traceback' to
compute the symbolic information. Here is an example:

     with Ada.Text_IO;
     with GNAT.Traceback;
     with GNAT.Traceback.Symbolic;
     
     procedure STB is
     
        use Ada;
        use GNAT.Traceback;
        use GNAT.Traceback.Symbolic;
     
        procedure P1 is
           TB  : Tracebacks_Array (1 .. 10);
           --  We are asking for a maximum of 10 stack frames.
           Len : Natural;
           --  Len will receive the actual number of stack frames returned.
        begin
           Call_Chain (TB, Len);
           Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len)));
        end P1;
     
        procedure P2 is
        begin
           P1;
        end P2;
     
     begin
        P2;
     end STB;


File: gnat_ug_vms.info,  Node: Compatibility with DEC Ada,  Next: Running and Debugging Ada Programs,  Prev: Other Utility Programs,  Up: Top

Compatibility with DEC Ada
**************************

This section of the manual compares DEC Ada for OpenVMS Alpha and GNAT
OpenVMS Alpha. GNAT achieves a high level of compatibility with DEC
Ada, and it should generally be straightforward to port code from the
DEC Ada environment to GNAT. However, there are a few language and
implementation differences of which the user must be aware. These
differences are discussed in this section. In addition, the operating
environment and command structure for the compiler are different, and
these differences are also discussed.

   Note that this discussion addresses specifically the implementation
of Ada 83 for DIGITAL OpenVMS Alpha Systems. In cases where the
implementation of DEC Ada differs between OpenVMS Alpha Systems and
OpenVMS VAX Systems, GNAT always follows the Alpha implementation.

* Menu:

* Ada 95 Compatibility::
* Differences in the Definition of Package System::
* Language-Related Features::
* The Package STANDARD::
* The Package SYSTEM::
* Tasking and Task-Related Features::
* Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems::
* Pragmas and Pragma-Related Features::
* Library of Predefined Units::
* Bindings::
* Main Program Definition::
* Implementation-Defined Attributes::
* Compiler and Run-Time Interfacing::
* Program Compilation and Library Management::
* Input-Output::
* Implementation Limits::
* Tools::


File: gnat_ug_vms.info,  Node: Ada 95 Compatibility,  Next: Differences in the Definition of Package System,  Up: Compatibility with DEC Ada

Ada 95 Compatibility
====================

GNAT is an Ada 95 compiler, and DEC Ada is an Ada 83 compiler. Ada 95
is almost completely upwards compatible with Ada 83, and therefore Ada
83 programs will compile and run under GNAT with no changes or only
minor changes. The Ada 95 Reference Manual (ANSI/ISO/IEC-8652:1995)
provides details on specific incompatibilities.

   GNAT provides the qualifier /83 on the GNAT COMPILE command, as well
as the pragma ADA_83, to force the compiler to operate in Ada 83 mode.
This mode does not guarantee complete conformance to Ada 83, but in
practice is sufficient to eliminate most sources of incompatibilities.
In particular, it eliminates the recognition of the additional Ada 95
keywords, so that their use as identifiers in Ada83 program is legal,
and handles the cases of packages with optional bodies, and generics
that instantiate unconstrained types without the use of `(<>)'.


File: gnat_ug_vms.info,  Node: Differences in the Definition of Package System,  Next: Language-Related Features,  Prev: Ada 95 Compatibility,  Up: Compatibility with DEC Ada

Differences in the Definition of Package System
===============================================

Both the Ada 95 and Ada 83 reference manuals permit a compiler to add
implementation-dependent declarations to package System. In normal mode,
GNAT does not take advantage of this permission, and the version of
System provided by GNAT exactly matches that in the Ada 95 Reference
Manual.

   However, DEC Ada adds an extensive set of declarations to package
System, as fully documented in the DEC Ada manuals. To minimize changes
required for programs that make use of these extensions, GNAT provides
the pragma Extend_System for extending the definition of package
System. By using:

     pragma Extend_System (Aux_DEC);

The set of definitions in System is extended to include those in package
`System.Aux_DEC'.  These definitions are incorporated directly into
package System, as though they had been declared there in the first
place. For a list of the declarations added, see the specification of
this package, which can be found in the file `S-AUXDEC.ADS' in the GNAT
library.  The pragma Extend_System is a configuration pragma, which
means that it can be placed in the file `GNAT.ADC', so that it will
automatically apply to all subsequent compilations. See the section on
Configuration Pragmas for further details.

   An alternative approach that avoids the use of the non-standard
Extend_System pragma is to add a context clause to the unit that
references these facilities:

     with System.Aux_DEC;
     use  System.Aux_DEC;

The effect is not quite semantically identical to incorporating the
declarations directly into package `System', but most programs will not
notice a difference unless they use prefix notation (e.g.
`System.Integer_8') to reference the entities directly in package
`System'.  For units containing such references, the prefixes must
either be removed, or the pragma `Extend_System' must be used.


File: gnat_ug_vms.info,  Node: Language-Related Features,  Next: The Package STANDARD,  Prev: Differences in the Definition of Package System,  Up: Compatibility with DEC Ada

Language-Related Features
=========================

The following sections highlight differences in types, representations
of types, operations, alignment, and related topics.

* Menu:

* Integer Types and Representations::
* Floating-Point Types and Representations::
* Pragmas Float_Representation and Long_Float::
* Fixed-Point Types and Representations::
* Record and Array Component Alignment::
* Address Clauses::
* Other Representation Clauses::


File: gnat_ug_vms.info,  Node: Integer Types and Representations,  Next: Floating-Point Types and Representations,  Up: Language-Related Features

Integer Types and Representations
---------------------------------

The set of predefined integer types is identical in DEC Ada and GNAT.
Furthermore the representation of these integer types is also identical,
including the capability of size clauses forcing biased representation.

   In addition, DEC Ada for OpenVMS Alpha systems has defined the
following additional integer types in package System:

   * INTEGER_8

   * INTEGER_16

   * INTEGER_32

   * INTEGER_64

   * LARGEST_INTEGER

When using GNAT, the first four of these types may be obtained from the
standard Ada 95 package `Interfaces'.  Alternatively, by use of the
pragma `Extend_System', identical declarations can be referenced
directly in package `System'.  On both GNAT and DEC Ada, the maximum
integer size is 64 bits.


File: gnat_ug_vms.info,  Node: Floating-Point Types and Representations,  Next: Pragmas Float_Representation and Long_Float,  Prev: Integer Types and Representations,  Up: Language-Related Features

Floating-Point Types and Representations
----------------------------------------

The set of predefined floating-point types is identical in DEC Ada and
GNAT.  Furthermore the representation of these floating-point types is
also identical. One important difference is that the default
representation for DEC Ada is VAX_Float, but the default representation
for GNAT is IEEE.

   Specific types may be declared to be VAX_Float or IEEE, using the
pragma `Float_Representation' as described in the DEC Ada documentation.
For example, the declarations:

     type F_Float is digits 6;
     pragma Float_Representation (VAX_Float, F_Float);

declare a type F_Float that will be represented in VAX_Float format.
This set of declarations actually appears in System.Aux_DEC, which
provides the full set of additional floating-point declarations
provided in the DEC Ada version of package System. This and similar
declarations may be accessed in a user program by using pragma
`Extend_System'. The use of this pragma, and the related pragma
`Long_Float' is described in further detail in the following section.


File: gnat_ug_vms.info,  Node: Pragmas Float_Representation and Long_Float,  Next: Fixed-Point Types and Representations,  Prev: Floating-Point Types and Representations,  Up: Language-Related Features

Pragmas Float_Representation and Long_Float
-------------------------------------------

DEC Ada provides the pragma `Float_Representation', which acts as a
program library qualifier to allow control over the internal
representation chosen for the predefined floating-point types declared
in the package `Standard'.  The format of this pragma is as follows:

     pragma `Float_Representation'(VAX_Float | IEEE_Float);

This pragma controls the representation of floating-point types as
follows:

   * `VAX_Float' specifies that floating-point types are represented by
     default with the VAX hardware types F-floating, D-floating,
     G-floating. Note that the H-floating type is available only on
     DIGITAL Vax systems, and is not available in either DEC Ada or
     GNAT for Alpha systems.

   * `IEEE_Float' specifies that floating-point types are represented
     by default with the IEEE single and double floating-point types.

GNAT provides an identical implementation of the pragma
`Float_Representation', except that it functions as a configuration
pragma, as defined by Ada 95. Note that the notion of configuration
pragma corresponds closely to the DEC Ada notion of a program library
qualifier.

   When no pragma is used in GNAT, the default is IEEE_Float, which is
different from DEC Ada 83, where the default is VAX_Float. In addition,
the predefined libraries in GNAT are built using IEEE_Float, so it is
not advisable to change the format of numbers passed to standard library
routines, and if necessary explicit type conversions may be needed.

   The use of IEEE_Float is recommended in GNAT since it is more
efficient, and (given that it conforms to an international standard)
potentially more portable. The situation in which VAX_Float may be
useful is in interfacing to existing code and data that expects the use
of VAX_Float. There are two possibilities here. If the requirement for
the use of VAX_Float is localized, then the best approach is to use the
predefined VAX_Float types in package `System', as extended by
`Extend_System'. For example, use `System.F_Float' to specify the
32-bit `F-Float' format.

   Alternatively, if an entire program depends heavily on the use of
the `VAX_Float' and in particular assumes that the types in package
`Standard' are in `Vax_Float' format, then it may be desirable to
reconfigure GNAT to assume Vax_Float by default.  This is done by using
the GNAT LIBRARY command to rebuild the library, and then using the
general form of the `Float_Representation' pragma to ensure that this
default format is used throughout.  The form of the GNAT LIBRARY
command is:

     GNAT LIBRARY /CONFIG=file /CREATE=directory

where file contains the new configuration pragmas and directory is the
directory to be created to contain the new library.

On OpenVMS systems, DEC Ada provides the pragma `Long_Float' to allow
control over the internal representation chosen for the predefined type
`Long_Float' and for floating-point type declarations with digits
specified in the range 7 .. 15.  The format of this pragma is as
follows:

     pragma Long_Float (D_FLOAT | G_FLOAT);


File: gnat_ug_vms.info,  Node: Fixed-Point Types and Representations,  Next: Record and Array Component Alignment,  Prev: Pragmas Float_Representation and Long_Float,  Up: Language-Related Features

Fixed-Point Types and Representations
-------------------------------------

On DEC Ada for OpenVMS Alpha systems, rounding is away from zero for
both positive and negative numbers.  Therefore, +0.5 rounds to 1 and
-0.5 rounds to -1.

   On GNAT for OpenVMS Alpha, the results of operations on fixed-point
types are in accordance with the Ada 95 rules. In particular, results
of operations on decimal fixed-point types are truncated.


File: gnat_ug_vms.info,  Node: Record and Array Component Alignment,  Next: Address Clauses,  Prev: Fixed-Point Types and Representations,  Up: Language-Related Features

Record and Array Component Alignment
------------------------------------

On DEC Ada for OpenVMS Alpha, all non composite components are aligned
on natural boundaries. For example, 1-byte components are aligned on
byte boundaries, 2-byte components on 2-byte boundaries, 4-byte
components on 4-byte byte boundaries, and so on. The OpenVMS Alpha
hardware runs more efficiently with naturally aligned data.

   ON GNAT for OpenVMS Alpha, alignment rules are compatible with DEC
Ada for OpenVMS Alpha.


File: gnat_ug_vms.info,  Node: Address Clauses,  Next: Other Representation Clauses,  Prev: Record and Array Component Alignment,  Up: Language-Related Features

Address Clauses
---------------

In DEC Ada and GNAT, address clauses are supported for objects and
imported subprograms.  The predefined type `System.Address' is a
private type in both compilers, with the same representation (it is
simply a machine pointer). Addition, subtraction, and comparison
operations are available in the standard Ada 95 package
`System.Storage_Elements', or in package `System' if it is extended to
include `System.Aux_DEC' using a pragma `Extend_System' as previously
described.

   Note that code that with's both this extended package `System' and
the package `System.Storage_Elements' should not `use' both packages,
or ambiguities will result. In general it is better not to mix these
two sets of facilities. The Ada 95 package was designed specifically to
provide the kind of features that DEC Ada adds directly to package
`System'.

   GNAT is compatible with DEC Ada in its handling of address clauses,
except for some limitations in the form of address clauses for
composite objects with initialization. Such address clauses are easily
replaced by the use of an explicitly-defined constant as described in
the Ada 95 Reference Manual (13.1(22)). For example, the sequence of
declarations:

     X, Y : Integer := Init_Func;
     Q : String (X .. Y) := "abc";
     ...
     for Q'Address use Compute_Address;

will be rejected by GNAT, since the address cannot be computed at the
time that Q is declared. To achieve the intended effect, write instead:

     X, Y : Integer := Init_Func;
     Q_Address : constant Address := Compute_Address;
     Q : String (X .. Y) := "abc";
     ...
     for Q'Address use Q_Address;

which will be accepted by GNAT (and other Ada 95 compilers), and is also
backwards compatible with Ada 83. A fuller description of the
restrictions on address specifications is found in the GNAT Reference
Manual.


File: gnat_ug_vms.info,  Node: Other Representation Clauses,  Prev: Address Clauses,  Up: Language-Related Features

Other Representation Clauses
----------------------------

GNAT supports in a compatible manner all the representation clauses
supported by DEC Ada. In addition, it supports representation clause
forms that are new in Ada 95 including COMPONENT_SIZE and SIZE clauses
for objects.


File: gnat_ug_vms.info,  Node: The Package STANDARD,  Next: The Package SYSTEM,  Prev: Language-Related Features,  Up: Compatibility with DEC Ada

The Package STANDARD
====================

The package STANDARD, as implemented by DEC Ada, is fully described in
the Reference Manual for the Ada Programming Language
(ANSI/MIL-STD-1815A-1983) and in the DEC Ada Language Reference Manual.
As implemented by GNAT, the package STANDARD is described in the Ada 95
Reference Manual.

   In addition, DEC Ada supports the Latin-1 character set in the type
CHARACTER. GNAT supports the Latin-1 character set in the type
CHARACTER and also Unicode (ISO 10646 BMP) in the type WIDE_CHARACTER.

   The floating-point types supported by GNAT are those supported by
DEC Ada, but defaults are different, and are controlled by pragmas. See
*note Floating-Point Types and Representations:: for details.


File: gnat_ug_vms.info,  Node: The Package SYSTEM,  Next: Tasking and Task-Related Features,  Prev: The Package STANDARD,  Up: Compatibility with DEC Ada

The Package SYSTEM
==================

DEC Ada provides a system-specific version of the package SYSTEM for
each platform on which the language ships.  For the complete
specification of the package SYSTEM, see Appendix F of the DEC Ada
Language Reference Manual.

   On DEC Ada, the package SYSTEM includes the following conversion
functions:
   * TO_ADDRESS(INTEGER)

   * TO_ADDRESS(UNSIGNED_LONGWORD)

   * TO_ADDRESS(universal_integer)

   * TO_INTEGER(ADDRESS)

   * TO_UNSIGNED_LONGWORD(ADDRESS)

   * Function IMPORT_VALUE return UNSIGNED_LONGWORD and the
         functions IMPORT_ADDRESS and IMPORT_LARGEST_VALUE

By default, GNAT supplies a version of SYSTEM that matches the
definition given in the Ada 95 Reference Manual.  This is a subset of
the DIGITAL system definitions, which is as close as possible to the
original definitions. The only difference is that the definition of
SYSTEM_NAME is different:

     type Name is (SYSTEM_NAME_GNAT);
     System_Name : constant Name := SYSTEM_NAME_GNAT;

Also, GNAT adds the new Ada 95 declarations for BIT_ORDER and
DEFAULT_BIT_ORDER.

   However, the use of the following pragma causes GNAT to extend the
definition of package SYSTEM so that it encompasses the full set of
DIGITAL-specific extensions, including the functions listed above:

     pragma Extend_System (Aux_DEC);

The pragma Extend_System is a configuration pragma that is most
conveniently placed in the `GNAT.ADC' file. See the GNAT Reference
Manual for further details.

   DEC Ada does not allow the recompilation of the package SYSTEM.
Instead DEC Ada provides several pragmas (SYSTEM_ NAME, STORAGE_UNIT,
and MEMORY_SIZE) to modify values in the package SYSTEM. On OpenVMS
Alpha systems, the pragma SYSTEM_NAME takes the enumeration literal
OPENVMS_AXP as its single argument.

   GNAT does permit the recompilation of package SYSTEM using a special
qualifier (/STYLE=GNAT) and this qualifier can be used if it is
necessary to change constants in SYSTEM. GNAT does not permit the
specification of SYSTEM_NAME, STORAGE_UNIT or MEMORY_SIZE by any other
means.

   On GNAT systems, the pragma SYSTEM_NAME takes the enumeration
literal SYSTEM_NAME_GNAT.

   The definitions provided by the use of

     pragma Extend_System (AUX_Dec);

are virtually identical to those provided by the DEC Ada 83 package
System. One important difference is that the name of the TO_ADDRESS
function for type UNSIGNED_LONGWORD is changed to TO_ADDRESS_LONG.  See
the GNAT Reference manual for a discussion of why this change was
necessary.

The version of TO_ADDRESS taking a universal integer argument is in fact
an extension to Ada 83 not strictly compatible with the reference
manual.  In GNAT, we are constrained to be exactly compatible with the
standard, and this means we cannot provide this capability. In DEC Ada
83, the point of this definition is to deal with a call like:

     TO_ADDRESS (16#12777#);

Normally, according to the Ada 83 standard, one would expect this to be
ambiguous, since it matches both the INTEGER and UNSIGNED_LONGWORD forms
of TO_ADDRESS. However, in DEC Ada 83, there is no ambiguity, since the
definition using universal_integer takes precedence.

   In GNAT, since the version with universal_integer cannot be
supplied, it is not possible to be 100% compatible. Since there are
many programs using numeric constants for the argument to TO_ADDRESS,
the decision in GNAT was to change the name of the function in the
UNSIGNED_LONGWORD case, so the declarations provided in the GNAT
version of AUX_Dec are:

     function To_Address (X : Integer) return Address;
     pragma Pure_Function (To_Address);
     
     function To_Address_Long (X : Unsigned_Longword) return Address;
     pragma Pure_Function (To_Address_Long);

This means that programs using TO_ADDRESS for UNSIGNED_LONGWORD must
change the name to TO_ADDRESS_LONG.


File: gnat_ug_vms.info,  Node: Tasking and Task-Related Features,  Next: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems,  Prev: The Package SYSTEM,  Up: Compatibility with DEC Ada

Tasking and Task-Related Features
=================================

The concepts relevant to a comparison of tasking on GNAT and on DEC Ada
for OpenVMS Alpha systems are discussed in the following sections.

   For detailed information on concepts related to tasking in DEC Ada,
see the DEC Ada Language Reference Manual and the relevant run-time
reference manual.


File: gnat_ug_vms.info,  Node: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems,  Next: Pragmas and Pragma-Related Features,  Prev: Tasking and Task-Related Features,  Up: Compatibility with DEC Ada

Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems
============================================================

On OpenVMS Alpha systems, each Ada task (except a passive task) is
implemented as a single stream of execution that is created and managed
by the kernel. On these systems, DEC Ada tasking support is based on
DECthreads, an implementation of the POSIX standard for threads.

   Although tasks are implemented as threads, all tasks in an Ada
program are part of the same process. As a result, resources such as
open files and virtual memory can be shared easily among tasks. Having
all tasks in one process allows better integration with the programming
environment (the shell and the debugger, for example).

   Also, on OpenVMS Alpha systems, DEC Ada tasks and foreign code that
calls DECthreads routines can be used together.  The interaction
between Ada tasks and DECthreads routines can have some benefits. For
example when on OpenVMS Alpha, DEC Ada can call C code that is already
threaded.  GNAT on OpenVMS Alpha uses the facilities of DECthreads, and
Ada tasks are mapped to threads.

* Menu:

* Assigning Task IDs::
* Task IDs and Delays::
* Task-Related Pragmas::
* Scheduling and Task Priority::
* The Task Stack::
* External Interrupts::


File: gnat_ug_vms.info,  Node: Assigning Task IDs,  Next: Task IDs and Delays,  Up: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

Assigning Task IDs
------------------

The DEC Ada Run-Time Library always assigns %TASK 1 to the environment
task that executes the main program. On OpenVMS Alpha systems, %TASK 0
is often used for tasks that have been created but are not yet
activated.

   On OpenVMS Alpha systems, task IDs are assigned at activation. On
GNAT systems, task IDs are also assigned at task creation but do not
have the same form or values as task ID values in DEC Ada. There is no
null task, and the environment task does not have a specific task ID
value.


File: gnat_ug_vms.info,  Node: Task IDs and Delays,  Next: Task-Related Pragmas,  Prev: Assigning Task IDs,  Up: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

Task IDs and Delays
-------------------

On OpenVMS Alpha systems, tasking delays are implemented using Timer
System Services. The Task ID is used for the identification of the
timer request (the REQIDT parameter).  If Timers are used in the
application take care not to use 0 for the identification, because
cancelling such a timer will cancel all timers and may lead to
unpredictable results.


File: gnat_ug_vms.info,  Node: Task-Related Pragmas,  Next: Scheduling and Task Priority,  Prev: Task IDs and Delays,  Up: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

Task-Related Pragmas
--------------------

Ada supplies the pragma TASK_STORAGE, which allows specification of the
size of the guard area for a task stack. (The guard area forms an area
of memory that has no read or write access and thus helps in the
detection of stack overflow.) On OpenVMS Alpha systems, if the pragma
TASK_STORAGE specifies a value of zero, a minimal guard area is
created. In the absence of a pragma TASK_STORAGE, a default guard area
is created.

   GNAT supplies the following task-related pragmas:

   * TASK_INFO

     This pragma appears within a task definition and
     applies to the task in which it appears. The argument
     must be of type SYSTEM.TASK_INFO.TASK_INFO_TYPE.

   * TASK_STORAGE

     GNAT implements pragma TASK_STORAGE in the same way as
      DEC Ada.                Both DEC Ada and GNAT supply the pragmas
     PASSIVE,               SUPPRESS, and VOLATILE.


File: gnat_ug_vms.info,  Node: Scheduling and Task Priority,  Next: The Task Stack,  Prev: Task-Related Pragmas,  Up: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

Scheduling and Task Priority
----------------------------

DEC Ada implements the Ada language requirement that when two tasks are
eligible for execution and they have different priorities, the lower
priority task does not execute while the higher priority task is
waiting. The DEC Ada Run-Time Library keeps a task running until either
the task is suspended or a higher priority task becomes ready.

   On OpenVMS Alpha systems, the default strategy is round- robin with
preemption. Tasks of equal priority take turns at the processor. A task
is run for a certain period of time and then placed at the rear of the
ready queue for its priority level.

   DEC Ada provides the implementation-defined pragma TIME_SLICE, which
can be used to enable or disable round-robin scheduling of tasks with
the same priority.  See the relevant DEC Ada run-time reference manual
for information on using the pragmas to control DEC Ada task scheduling.

   GNAT follows the scheduling rules of Annex D (real-time Annex) of
the Ada 95 Reference Manual. In general, this scheduling strategy is
fully compatible with DEC Ada although it provides some additional
constraints (as fully documented in Annex D).  GNAT implements time
slicing control in a manner compatible with DEC Ada 83, by means of the
pragma Time_Slice, whose semantics are identical to the DEC Ada 83
pragma of the same name.  Note that it is not possible to mix GNAT
tasking and DEC Ada 83 tasking in the same program, since the two run
times are not compatible.


File: gnat_ug_vms.info,  Node: The Task Stack,  Next: External Interrupts,  Prev: Scheduling and Task Priority,  Up: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

The Task Stack
--------------

In DEC Ada, a task stack is allocated each time a non passive task is
activated. As soon as the task is terminated, the storage for the task
stack is deallocated.  If you specify a size of zero (bytes) with
T'STORAGE_SIZE, a default stack size is used. Also, regardless of the
size specified, some additional space is allocated for task management
purposes. On OpenVMS Alpha systems, at least one page is allocated.

   GNAT handles task stacks in a similar manner. According to the Ada
95 rules, it provides the pragma STORAGE_SIZE as an alternative method
for controlling the task stack size.  The specification of the
attribute T'STORAGE_SIZE is also supported in a manner compatible with
DEC Ada.


File: gnat_ug_vms.info,  Node: External Interrupts,  Prev: The Task Stack,  Up: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems

External Interrupts
-------------------

On DEC Ada, external interrupts can be associated with task entries.
GNAT is compatible with DEC Ada in its handling of external interrupts.


File: gnat_ug_vms.info,  Node: Pragmas and Pragma-Related Features,  Next: Library of Predefined Units,  Prev: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems,  Up: Compatibility with DEC Ada

Pragmas and Pragma-Related Features
===================================

Both DEC Ada and GNAT supply all language-defined pragmas as specified
by the Ada 83 standard. GNAT also supplies all language-defined pragmas
specified in the Ada 95 Reference Manual.  In addition, GNAT implements
the implementation-defined pragmas from DEC Ada 83.

   * AST_ENTRY

   * COMMON_OBJECT

   * COMPONENT_ALIGNMENT

   * EXPORT_EXCEPTION

   * EXPORT_FUNCTION

   * EXPORT_OBJECT

   * EXPORT_PROCEDURE

   * EXPORT_VALUED_PROCEDURE

   * FLOAT_REPRESENTATION

   * IDENT

   * IMPORT_EXCEPTION

   * IMPORT_FUNCTION

   * IMPORT_OBJECT

   * IMPORT_PROCEDURE

   * IMPORT_VALUED_PROCEDURE

   * INLINE_GENERIC

   * INTERFACE_NAME

   * LONG_FLOAT

   * MAIN_STORAGE

   * PASSIVE

   * PSET_OBJECT

   * SHARE_GENERIC

   * SUPPRESS_ALL

   * TASK_STORAGE

   * TIME_SLICE

   * TITLE

These pragmas are all fully implemented, with the exception of `Title',
`Passive', and `Share_Generic', which are recognized, but which have no
effect in GNAT. The effect of `Passive' may be obtained by the use of
protected objects in Ada 95. In GNAT, all generics are inlined.

   Unlike DEC Ada, the GNAT 'EXPORT_subprogram' pragmas require a
separate subprogram specification which must appear before the
subprogram body.

   GNAT also supplies a number of implementation-defined pragmas as
follows:
   * C_PASS_BY_COPY

   * EXTEND_SYSTEM

   * SOURCE_FILE_NAME

   * UNSUPPRESS

   * WARNINGS

   * ABORT_DEFER

   * ADA_83

   * ADA_95

   * ANNOTATE

   * ASSERT

   * CPP_CLASS

   * CPP_CONSTRUCTOR

   * CPP_DESTRUCTOR

   * CPP_VIRTUAL

   * CP_VTABLE

   * DEBUG

   * LINKER_ALIAS

   * LINKER_SECTION

   * MACHINE_ATTRIBUTE

   * NO_RETURN

   * PURE_FUNCTION

   * SOURCE_REFERENCE

   * TASK_INFO

   * UNCHECKED_UNION

   * UNIMPLEMENTED_UNIT

   * WEAK_EXTERNAL

For full details on these GNAT implementation-defined pragmas, see the
GNAT Reference Manual.

* Menu:

* Restrictions on the Pragma INLINE::
* Restrictions on the Pragma INTERFACE::
* Restrictions on the Pragma SYSTEM_NAME::


File: gnat_ug_vms.info,  Node: Restrictions on the Pragma INLINE,  Next: Restrictions on the Pragma INTERFACE,  Up: Pragmas and Pragma-Related Features

Restrictions on the Pragma INLINE
---------------------------------

DEC Ada applies the following restrictions to the pragma INLINE:
   * Parameters cannot be a task type.

   * Function results cannot be task types, unconstrained array types,
     or unconstrained types with discriminants.

   * Bodies cannot declare the following:
        * Subprogram body or stub (imported subprogram is allowed)

        * Tasks

        * Generic declarations

        * Instantiations

        * Exceptions

        * Access types (types derived from access types allowed)

        * Array or record types

        * Dependent tasks

        * Direct recursive calls of subprogram or containing
          subprogram, directly or via a renaming


In GNAT, the only restriction on pragma INLINE is that the body must
occur before the call if both are in the same unit, and the size must
be appropriately small. There are no other specific restrictions which
cause subprograms to be incapable of being inlined.


File: gnat_ug_vms.info,  Node: Restrictions on the Pragma INTERFACE,  Next: Restrictions on the Pragma SYSTEM_NAME,  Prev: Restrictions on the Pragma INLINE,  Up: Pragmas and Pragma-Related Features

Restrictions on the Pragma INTERFACE
------------------------------------

The following lists and describes the restrictions on the pragma
INTERFACE on DEC Ada and GNAT:
   * Languages accepted: Ada, Bliss, C, Fortran, Default.  Default is
     the default on OpenVMS Alpha systems.

   * Parameter passing: Language specifies default mechanisms but can
     be overridden with an EXPORT pragma.

        * Ada: Use internal Ada rules.

        * Bliss, C: Parameters must be mode `in'; cannot be record or
          task type. Result cannot be a string, an array, or a record.

        * Fortran: Parameters cannot be a task. Result cannot be a
          string, an array, or a record.

GNAT is entirely upwards compatible with DEC Ada, and in addition allows
record parameters for all languages.


File: gnat_ug_vms.info,  Node: Restrictions on the Pragma SYSTEM_NAME,  Prev: Restrictions on the Pragma INTERFACE,  Up: Pragmas and Pragma-Related Features

Restrictions on the Pragma SYSTEM_NAME
--------------------------------------

For DEC Ada for OpenVMS Alpha, the enumeration literal for the type
NAME is OPENVMS_AXP. In GNAT, the enumeration literal for the type NAME
is SYSTEM_NAME_GNAT.


File: gnat_ug_vms.info,  Node: Library of Predefined Units,  Next: Bindings,  Prev: Pragmas and Pragma-Related Features,  Up: Compatibility with DEC Ada

Library of Predefined Units
===========================

A library of predefined units is provided as part of the DEC Ada and
GNAT implementations. DEC Ada does not provide the package MACHINE_CODE
but instead recommends importing assembler code.

   The GNAT versions of the DEC Ada Run-Time Library (ADA$PREDEFINED:)
units are taken from the OpenVMS Alpha version, not the OpenVMS VAX
version. During GNAT installation, the DEC Ada Predefined Library units
are copied into the GNU:[LIB.OPENVMS7_x.2_8_x.DECLIB] (aka DECLIB)
directory and patched to remove Ada 95 incompatibilities and to make
them interoperable with GNAT, *note Changes to DECLIB:: for details.

   The GNAT RTL is contained in the GNU:[LIB.OPENVMS7_x.2_8_x.ADALIB]
(aka ADALIB) directory and the default search path is set up to find
DECLIB units in preference to ADALIB units with the same name (TEXT_IO,
SEQUENTIAL_IO, and DIRECT_IO, for example).

   However, it is possible to change the default so that the reverse is
true, or even to mix them using child package notation. The DEC Ada 83
units are available as DEC.xxx where xxx is the package name, and the
Ada units are available in the standard manner defined for Ada 95, that
is to say as Ada.xxx. To change the default, set ADA_INCLUDE_PATH and
ADA_OBJECTS_PATH appropriately. For example, to change the default to
use the Ada95 versions do:

     $ DEFINE ADA_INCLUDE_PATH GNU:[LIB.OPENVMS7_1.2_8_1.ADAINCLUDE],-
                               GNU:[LIB.OPENVMS7_1.2_8_1.DECLIB]
     $ DEFINE ADA_OBJECTS_PATH GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB],-
                               GNU:[LIB.OPENVMS7_1.2_8_1.DECLIB]

* Menu:

* Changes to DECLIB::


File: gnat_ug_vms.info,  Node: Changes to DECLIB,  Up: Library of Predefined Units

Changes to DECLIB
-----------------

The changes made to the DEC Ada predefined library for GNAT and Ada 95
compatibility are minor and include the following:

   * Adjusting the location of pragmas and record representation
     clauses to obey Ada 95 rules

   * Adding the proper notation to generic formal parameters that take
     unconstrained types in instantiation

   * Adding pragma ELABORATE_BODY to package specifications that have
     package bodies not otherwise allowed

   * Occurrences of the identifier "PROTECTED" are renamed to
     "PROTECTD".  Currently these are found only in the STARLET package
     spec.

None of the above changes is visible to users.


File: gnat_ug_vms.info,  Node: Bindings,  Next: Main Program Definition,  Prev: Library of Predefined Units,  Up: Compatibility with DEC Ada

Bindings
========

On OpenVMS Alpha, DEC Ada provides the following strongly-typed
bindings:
   * Command Language Interpreter (CLI interface)

   * DECtalk Run-Time Library (DTK interface)

   * Librarian utility routines (LBR interface)

   * General Purpose Run-Time Library (LIB interface)

   * Math Run-Time Library (MTH interface)

   * National Character Set Run-Time Library (NCS interface)

   * Compiled Code Support Run-Time Library (OTS interface)

   * Parallel Processing Run-Time Library (PPL interface)

   * Screen Management Run-Time Library (SMG interface)

   * Sort Run-Time Library (SOR interface)

   * String Run-Time Library (STR interface)

   * STARLET System Library

   * X Window System Version 11R4 and 11R5 (X, XLIB interface)

   * X Windows Toolkit (XT interface)

   * X/Motif Version 1.1.3 and 1.2 (XM interface)

GNAT provides implementations of these DEC bindings in the DECLIB
directory.

   The X/Motif bindings used to build DECLIB are whatever versions are
in the DEC Ada ADA$PREDEFINED directory with extension .ADC. The build
script will automatically add a pragma Linker_Options to packages Xm,
Xt, and X_Lib causing the default X/Motif shareable image libraries to
be linked in. This is done via options files named xm.opt, xt.opt, and
x_lib.opt (also located in the DECLIB directory).

   It may be necessary to edit these options files to update or correct
the library names if, for example, the newer X/Motif bindings from
ADA$EXAMPLES had been (previous to installing GNAT) copied and renamed
to superseded the default ADA$PREDEFINED versions.

* Menu:

* Shared Libraries and Options Files::
* Interfaces to C::


File: gnat_ug_vms.info,  Node: Shared Libraries and Options Files,  Next: Interfaces to C,  Up: Bindings

Shared Libraries and Options Files
----------------------------------

When using the DEC Ada predefined X and Motif bindings, the linking
with their shareable images is done automatically by GNAT LINK. When
using other X and Motif bindings, it is necessary to add the
corresponding shareable images to the command line for GNAT LINK. When
linking with shared libraries, or with .OPT files, it is also necessary
to add them to the command line for GNAT LINK.

   A shared library to be used with GNAT is built in the same way as
other libraries under VMS. The VMS Link command can be used in standard
fashion.


File: gnat_ug_vms.info,  Node: Interfaces to C,  Prev: Shared Libraries and Options Files,  Up: Bindings

Interfaces to C
---------------

DEC Ada provides the following Ada types and operations:

   * C types package (C_TYPES)

   * C strings (C_TYPES.NULL_TERMINATED)

   * Other_types (SHORT_INT)

Interfacing to C with GNAT, one can use the above approach described
for DEC Ada or the facilities of Annex B of the Ada 95 Reference Manual
(packages INTERFACES.C, INTERFACES.C.STRINGS and
INTERFACES.C.POINTERS). For more information, see the section
"Interfacing to C" in the GNAT Reference Manual.

   The `/UPPERCASE_EXTERNALS' qualifier forces default and explicit
`External_Name' parameters in pragmas Import and Export to be
uppercased for compatibility with the default behavior of DEC C. The
qualifier has no effect on `Link_Name' parameters.


File: gnat_ug_vms.info,  Node: Main Program Definition,  Next: Implementation-Defined Attributes,  Prev: Bindings,  Up: Compatibility with DEC Ada

Main Program Definition
=======================

The following section discusses differences in the definition of main
programs on DEC Ada and GNAT.  On DEC Ada, main programs are defined to
meet the following conditions:
   * Procedure with no formal parameters (returns 0 upon        normal
     completion)

   * Procedure with no formal parameters (returns 42 when
     unhandled exceptions are raised)

   * Function with no formal parameters whose returned value        is
     of a discrete type

   * Procedure with one OUT formal of a discrete type for        which
     a specification of pragma EXPORT_VALUED_PROCEDURE is given.


When declared with the pragma EXPORT_VALUED_PROCEDURE, a main function
or main procedure returns a discrete value whose size is less than 64
bits (32 on VAX systems), the value is zero- or sign-extended as
appropriate.  On GNAT, main programs are defined as follows:
   * Must be a non-generic, parameter-less subprogram that is either a
     procedure or function returning an Ada STANDARD.INTEGER (the
     predefined type)

   * Cannot be a generic subprogram or an instantiation of a generic
     subprogram


File: gnat_ug_vms.info,  Node: Implementation-Defined Attributes,  Next: Compiler and Run-Time Interfacing,  Prev: Main Program Definition,  Up: Compatibility with DEC Ada

Implementation-Defined Attributes
=================================

GNAT provides all DEC Ada implementation-defined attributes.


File: gnat_ug_vms.info,  Node: Compiler and Run-Time Interfacing,  Next: Program Compilation and Library Management,  Prev: Implementation-Defined Attributes,  Up: Compatibility with DEC Ada

Compiler and Run-Time Interfacing
=================================

DEC Ada provides the following ways to pass options to the linker (ACS
LINK):
   * /WAIT and /SUBMIT qualifiers

   * /COMMAND qualifier

   * /[NO]MAP qualifier

   * /OUTPUT=file-spec

   * /[NO]DEBUG and /[NO]TRACEBACK qualifiers

To pass options to the linker, GNAT provides the following qualifiers:

   * /EXECUTABLE=exec-name

   * /VERBOSE qualifier

   * /[NO]DEBUG and /[NO]TRACEBACK qualifiers

For more information on these qualifiers, see the section "Qualifiers
for GNAT LINK" in the corresponding section of this Guide.  In DEC Ada,
the command-line qualifier /OPTIMIZE is available to control
optimization. DEC Ada also supplies the following pragmas:
   * OPTIMIZE

   * INLINE

   * INLINE_GENERIC

   * SUPPRESS_ALL

   * PASSIVE

In GNAT, optimization is controlled strictly by command line
parameters, as described in the corresponding section of this guide.
The DIGITAL pragmas for control of optimization are recognized but
ignored.

   Note that in GNAT, the default is optimization off, whereas in DEC
Ada 83, the default is that optimization is turned on.


File: gnat_ug_vms.info,  Node: Program Compilation and Library Management,  Next: Input-Output,  Prev: Compiler and Run-Time Interfacing,  Up: Compatibility with DEC Ada

Program Compilation and Library Management
==========================================

DEC Ada and GNAT provide a comparable set of commands to build
programs. DEC Ada also provides a program library, which is a concept
that does not exist on GNAT. Instead, GNAT provides directories of
sources that are compiled as needed.

   The following table summarizes the DEC Ada commands and provides
equivalent GNAT commands. In this table, some GNAT equivalents reflect
the fact that GNAT does not use the concept of a program library.
Instead, it uses a model in which collections of source and object
files are used in a manner consistent with other languages like C and
Fortran. Therefore, standard system file commands are used to
manipulate these elements. Those GNAT commands are marked with an
asterisk in the table that follows.  Note that, unlike DEC Ada,  none
of the GNAT commands accepts wild cards.

*DEC_Ada_Command*      *GNAT_Equivalent*      *Description*
ADA                    GNAT COMPILE           Invokes the compiler to
                                              compile one or more Ada
                                              source files.
ACS ATTACH             No equivalent          Qualifiers control of
                                              terminal from current
                                              process running the program
                                                                 library
                                              manager.
ACS CHECK              GNAT MAKE              Forms the execution closure
                       /DEPENDENCY_LIST       of one           or more
                                              compiled units and checks
                                              completeness and currency.
ACS COMPILE            GNAT MAKE              Forms the execution closure
                       /ACTIONS=COMPILE       of one or           more
                                              specified units, checks
                                              completeness and currency,
                                                      identifies units
                                              that have revised source
                                              files, compiles same,
                                                 and recompiles units
                                              that are or will become
                                              obsolete.            Also
                                              completes incomplete
                                              generic instantiations.
ACS COPY FOREIGN       Copy (*)               Copies a foreign object
                                              file into the program
                                              library as a
                                              library unit body.
ACS COPY UNIT          Copy (*)               Copies a compiled unit from
                                              one program library to
                                              another.
ACS CREATE LIBRARY     Create /directory (*)  Creates a program library.
ACS CREATE SUBLIBRARY  Create /directory (*)  Creates a program
                                              sublibrary.
ACS DELETE LIBRARY                            Deletes a program library
                                              and its contents.
ACS DELETE SUBLIBRARY                         Deletes a program
                                              sublibrary and its contents.
ACS DELETE UNIT        Delete file (*)        On OpenVMS systems, deletes
                                              one or more compiled units
                                              from           the current
                                              program library.
ACS DIRECTORY          Directory (*)          On OpenVMS systems, lists
                                              units contained in the
                                              current            program
                                              library.
ACS ENTER FOREIGN      Copy (*)               Allows the import of a
                                              foreign body as an Ada
                                              library
                                              specification and enters a
                                              reference to a pointer.
ACS ENTER UNIT         Copy (*)               Enters a reference
                                              (pointer) from the current
                                              program library to
                                              a unit compiled into
                                              another program library.
ACS EXIT               No equivalent          Exits from the program
                                              library manager.
ACS EXPORT             Copy (*)               Creates an object file that
                                              contains system-specific
                                              object code           for
                                              one or more units. With
                                              GNAT, object files can
                                              simply be copied
                                              into the desired directory.
ACS EXTRACT SOURCE     Copy (*)               Allows access to the copied
                                              source file for each Ada
                                              compilation unit
ACS HELP               HELP GNAT              Provides online help.
ACS LINK               GNAT LINK              Links an object file
                                              containing Ada units into
                                              an executable
                                              file.
ACS LOAD               Copy (*)               Loads (partially compiles)
                                              Ada units into the program
                                              library.             Allows
                                              loading a program from a
                                              collection of files into a
                                              library            without
                                              knowing the relationship
                                              among units.
ACS MERGE              Copy (*)               Merges into the current
                                              program library, one or
                                              more units from
                                              another library where they
                                              were modified.
ACS RECOMPILE          GNAT MAKE              Recompiles from   external
                       /ACTIONS=COMPILE       or copied source files any
                                              obsolete            unit in
                                              the closure. Also,
                                              completes any incomplete
                                              generic
                                              instantiations.
ACS REENTER            GNAT MAKE              Reenters current references
                                              to units compiled after
                                              last entered
                                              with the ACS ENTER UNIT
                                              command.
ACS SET LIBRARY        Set default (*)        Defines a program library
                                              to be the compilation
                                              context as well
                                              as the target library for
                                              compiler output and
                                              commands in general.
ACS SET PRAGMA         Edit GNAT.ADC (*)      Redefines specified  values
                                              of the library
                                              characteristics
                                              LONG_ FLOAT, MEMORY_SIZE,
                                              SYSTEM_NAME, and
                                              `Float_Representation'.
ACS SET SOURCE         define                 Defines the source file
                       ADA_INCLUDE_PATH path  search list for the ACS
                       (*)                    COMPILE  command.
ACS SHOW LIBRARY       Directory (*)          Lists information about one
                                              or more program libraries.
ACS SHOW PROGRAM       No equivalent          Lists information about the
                                              execution closure of one or
                                                        more units in
                                              the program library.
ACS SHOW SOURCE        Show logical           Shows the source file
                       ADA_INCLUDE_PATH       search used when compiling
                                              units.
ACS SHOW VERSION       Compile with VERBOSE   Displays the version number
                       option                 of the compiler and program
                                              library            manager
                                              used.
ACS SPAWN              No equivalent          Creates a subprocess of the
                                              current process (same as
                                              DCL SPAWN
                                              command).
ACS VERIFY             No equivalent          Performs a series of
                                              consistency checks on a
                                              program library to
                                               determine whether the
                                              library structure and
                                              library files are in
                                                 valid_form.


File: gnat_ug_vms.info,  Node: Input-Output,  Next: Implementation Limits,  Prev: Program Compilation and Library Management,  Up: Compatibility with DEC Ada

Input-Output
============

On OpenVMS Alpha systems, DEC Ada uses OpenVMS Record Management
Services (RMS) to perform operations on external files.

DEC Ada and GNAT predefine an identical set of input- output packages.
To make the use of the generic TEXT_IO operations more convenient, DEC
Ada provides predefined library packages that instantiate the integer
and floating-point operations for the predefined integer and
floating-point types as shown in the following table.

`Package_Name'
     Instantiation

`INTEGER_TEXT_IO'
     INTEGER_IO(INTEGER)

`SHORT_INTEGER_TEXT_IO'
     INTEGER_IO(SHORT_INTEGER)

`SHORT_SHORT_INTEGER_TEXT_IO'
     INTEGER_IO(SHORT_SHORT_ INTEGER)

`FLOAT_TEXT_IO'
     FLOAT_IO(FLOAT)

`LONG_FLOAT_TEXT_IO'
     FLOAT_IO(LONG_FLOAT)

The DEC Ada predefined packages and their operations are implemented
using OpenVMS Alpha files and input- output facilities. DEC Ada
supports asynchronous input- output on OpenVMS Alpha. Familiarity with
the following is recommended:
   * RMS file organizations and access methods

   * OpenVMS file specifications and directories

   * OpenVMS File Definition Language (FDL)

GNAT provides I/O facilities that are completely compatible with DEC
Ada. The distribution includes the standard DEC Ada versions of all I/O
packages, operating in a manner compatible with DEC Ada. In particular,
the following packages are by default the DEC Ada (Ada 83) versions of
these packages rather than the renamings suggested in annex J of the
Ada 95 Reference Manual:
   * TEXT_IO

   * SEQUENTIAL_IO

   * DIRECT_IO

The use of the standard Ada 95 syntax for child packages (for example,
ADA.TEXT_IO) retrieves the Ada 95 versions of these packages, as
defined in the Ada 95 Reference Manual.  GNAT provides
DIGITAL-compatible predefined instantiations of the TEXT_IO packages,
and also provides the standard predefined instantiations required by
the Ada 95 Reference Manual.

   For further information on how GNAT interfaces to the file system or
how I/O is implemented in programs written in mixed languages, see the
chapter "Implementation of the Standard I/O" in the GNAT Reference
Manual.  This chapter covers the following:
   * Standard I/O packages

   * FORM strings

   * DIRECT_IO

   * SEQUENTIAL_IO

   * TEXT_IO

   * Stream pointer positioning

   * Reading and writing non-regular files

   * GET_IMMEDIATE

   * Treating TEXT_IO files as streams

   * Shared files

   * Open modes


File: gnat_ug_vms.info,  Node: Implementation Limits,  Next: Tools,  Prev: Input-Output,  Up: Compatibility with DEC Ada

Implementation Limits
=====================

The following table lists implementation limits for DEC Ada and GNAT
systems.
Compilation Parameter                       DEC Ada        GNAT
In a subprogram or entry  declaration,      32             No set limit
maximum number of        formal parameters                 
that are of an unconstrained record type                   
Maximum identifier length (number of        255            255
characters)                                                
Maximum number of characters in a source    255            255
line                                                       
Maximum collection size   (number of bytes) 2**31-1        2**31-1
Maximum number of discriminants for a       245            No set limit
record type                                                
Maximum number of formal parameters in an   246            No set limit
entry or        subprogram declaration                     
Maximum number of dimensions in an array    255            No set limit
type                                                       
Maximum number of library  units and        4095           No set limit
subunits in a compilation.                                 
Maximum number of library units and         16383          No set limit
subunits in an execution.                                  
Maximum number of objects declared with     32757          No set limit
the pragma COMMON_OBJECT        or                         
PSECT_OBJECT                                               
Maximum number of enumeration literals in   65535          No set limit
an enumeration type        definition                      
Maximum number of lines in a source file    65534          No set limit
Maximum number of bits in any object        2**31-1        2**31-1
Maximum size of the static portion of a     2**31-1        2**31-1
stack frame (approximate)                                  


File: gnat_ug_vms.info,  Node: Tools,  Prev: Implementation Limits,  Up: Compatibility with DEC Ada

Tools
=====


File: gnat_ug_vms.info,  Node: Inline Assembler,  Next: Performance Considerations,  Prev: Running and Debugging Ada Programs,  Up: Top

Inline Assembler
****************

If you need to write low-level software that interacts directly with
the hardware, Ada provides two ways to incorporate assembly language
code into your program.  First, you can import and invoke external
routines written in assembly language, an Ada feature fully supported
by GNAT.  However, for small sections of code it may be simpler or more
efficient to include assembly language statements directly in your Ada
source program, using the facilities of the implementation-defined
package `System.Machine_Code', which incorporates the GNAT COMPILE
Inline Assembler.  The Inline Assembler approach offers a number of
advantages, including the following:

   * No need to use non-Ada tools

   * Consistent interface over different targets

   * Automatic usage of the proper calling conventions

   * Access to Ada constants and variables

   * Definition of intrinsic routines

   * Possibility of inlining a subprogram comprising assembler code

   * Code optimizer can take Inline Assembler code into account

   This chapter presents a series of examples to show you how to use
the Inline Assembler.  Although it focuses on the Intel x86, the
general approach applies also to other processors.  It is assumed that
you are familiar with Ada and with assembly language programming.

* Menu:

* Basic Assembler Syntax::
* A Simple Example of Inline Assembler::
* Output Variables in Inline Assembler::
* Input Variables in Inline Assembler::
* Inlining Inline Assembler Code::
* Other Asm Functionality::
* A Complete Example::


File: gnat_ug_vms.info,  Node: Basic Assembler Syntax,  Next: A Simple Example of Inline Assembler,  Up: Inline Assembler

Basic Assembler Syntax
======================

The assembler used by GNAT and GNAT COMPILE is based not on the Intel
assembly language, but rather on a language that descends from the AT&T
Unix assembler _as_ (and which is often referred to as "AT&T syntax").
The following table summarizes the main features of _as_ syntax and
points out the differences from the Intel conventions.  See the GNAT
COMPILE _as_ and _gas_ (an _as_ macro pre-processor) documentation for
further information.

Register names
     GNAT COMPILE / _as_: Prefix with "%"; for example `%eax'
     Intel: No extra punctuation; for example `eax'

Immediate operand
     GNAT COMPILE / _as_: Prefix with "$"; for example `$4'
     Intel: No extra punctuation; for example `4'

Address
     GNAT COMPILE / _as_: Prefix with "$"; for example `$loc'
     Intel: No extra punctuation; for example `loc'

Memory contents
     GNAT COMPILE / _as_: No extra punctuation; for example `loc'
     Intel: Square brackets; for example `[loc]'

Register contents
     GNAT COMPILE / _as_: Parentheses; for example `(%eax)'
     Intel: Square brackets; for example `[eax]'

Hexadecimal numbers
     GNAT COMPILE / _as_: Leading "0x" (C language syntax); for example
     `0xA0'
     Intel: Trailing "h"; for example `A0h'

Operand size
     GNAT COMPILE / _as_: Explicit in op code; for example `movw' to
     move a 16-bit word
     Intel: Implicit, deduced by assembler; for example `mov'

Instruction repetition
     GNAT COMPILE / _as_: Split into two lines; for example
     `rep'
     `stosl'
     Intel: Keep on one line; for example `rep stosl'

Order of operands
     GNAT COMPILE / _as_: Source first; for example `movw $4, %eax'
     Intel: Destination first; for example `mov eax, 4'


File: gnat_ug_vms.info,  Node: A Simple Example of Inline Assembler,  Next: Output Variables in Inline Assembler,  Prev: Basic Assembler Syntax,  Up: Inline Assembler

A Simple Example of Inline Assembler
====================================

The following example will generate a single assembly language
statement, `nop', which does nothing.  Despite its lack of run-time
effect, the example will be useful in illustrating the basics of the
Inline Assembler facility.

     with System.Machine_Code; use System.Machine_Code;
     procedure Nothing is
     begin
        Asm ("nop");
     end Nothing;

   `Asm' is a procedure declared in package `System.Machine_Code'; here
it takes one parameter, a _template string_ that must be a static
expression and that will form the generated instruction.  `Asm' may be
regarded as a compile-time procedure that parses the template string
and additional parameters (none here), from which it generates a
sequence of assembly language instructions.

   The examples in this chapter will illustrate several of the forms
for invoking `Asm'; a complete specification of the syntax is found in
the `GNAT Reference Manual'.

   Under the standard GNAT conventions, the `Nothing' procedure should
be in a file named `NOTHING.ADB'.  You can build the executable in the
usual way:
     GNAT MAKE nothing
   However, the interesting aspect of this example is not its run-time
behavior but rather the generated assembly code.  To see this output,
invoke the compiler as follows:
        GNAT COMPILE -S -fomit-frame-pointer /CHECKS=SUPPRESS_ALL `NOTHING.ADB'
   where the options are:

`-c'
     compile only (no bind or link)

`-S'
     generate assembler listing

`-fomit-frame-pointer'
     do not set up separate stack frames

`/CHECKS=SUPPRESS_ALL'
     do not add runtime checks

   This gives a human-readable assembler version of the code. The
resulting file will have the same name as the Ada source file, but with
a `.s' extension.  In our example, the file `nothing.s' has the
following contents:

     .file "NOTHING.ADB"
     gcc2_compiled.:
     ___gnu_compiled_ada:
     .text
        .align 4
     .globl __ada_nothing
     __ada_nothing:
     #APP
        nop
     #NO_APP
        jmp L1
        .align 2,0x90
     L1:
        ret

   The assembly code you included is clearly indicated by the compiler,
between the `#APP' and `#NO_APP' delimiters. The character before the
'APP' and 'NOAPP' can differ on different targets. For example, Linux
uses '#APP' while on NT you will see '/APP'.

   If you make a mistake in your assembler code (such as using the
wrong size modifier, or using a wrong operand for the instruction) GNAT
will report this error in a temporary file, which will be deleted when
the compilation is finished.  Generating an assembler file will help in
such cases, since you can assemble this file separately using the _as_
assembler that comes with GNAT COMPILE.

   Assembling the file using the command

     as `nothing.s'

will give you error messages whose lines correspond to the assembler
input file, so you can easily find and correct any mistakes you made.
If there are no errors, _as_ will generate an object file `nothing.out'.


File: gnat_ug_vms.info,  Node: Output Variables in Inline Assembler,  Next: Input Variables in Inline Assembler,  Prev: A Simple Example of Inline Assembler,  Up: Inline Assembler

Output Variables in Inline Assembler
====================================

The examples in this section, showing how to access the processor
flags, illustrate how to specify the destination operands for assembly
language statements.

     with Interfaces; use Interfaces;
     with Ada.Text_IO; use Ada.Text_IO;
     with System.Machine_Code; use System.Machine_Code;
     procedure Get_Flags is
        Flags : Unsigned_32;
        use ASCII;
     begin
        Asm ("pushfl"          & LF & HT & -- push flags on stack
             "popl %%eax"      & LF & HT & -- load eax with flags
             "movl %%eax, %0",             -- store flags in variable
             Outputs => Unsigned_32'Asm_Output ("=g", Flags));
        Put_Line ("Flags register:" & Flags'Img);
     end Get_Flags;

   In order to have a nicely aligned assembly listing, we have separated
multiple assembler statements in the Asm template string with linefeed
(ASCII.LF) and horizontal tab (ASCII.HT) characters.  The resulting
section of the assembly output file is:

     #APP
        pushfl
        popl %eax
        movl %eax, -40(%ebp)
     #NO_APP

   It would have been legal to write the Asm invocation as:

     Asm ("pushfl popl %%eax movl %%eax, %0")

   but in the generated assembler file, this would come out as:

     #APP
        pushfl popl %eax movl %eax, -40(%ebp)
     #NO_APP

   which is not so convenient for the human reader.

   We use Ada comments at the end of each line to explain what the
assembler instructions actually do.  This is a useful convention.

   When writing Inline Assembler instructions, you need to precede each
register and variable name with a percent sign.  Since the assembler
already requires a percent sign at the beginning of a register name,
you need two consecutive percent signs for such names in the Asm
template string, thus `%%eax'.  In the generated assembly code, one of
the percent signs will be stripped off.

   Names such as `%0', `%1', `%2', etc., denote input or output
variables: operands you later define using `Input' or `Output'
parameters to `Asm'.  An output variable is illustrated in the third
statement in the Asm template string:
     movl %%eax, %0
   The intent is to store the contents of the eax register in a
variable that can be accessed in Ada.  Simply writing `movl %%eax,
Flags' would not necessarily work, since the compiler might optimize by
using a register to hold Flags, and the expansion of the `movl'
instruction would not be aware of this optimization.  The solution is
not to store the result directly but rather to advise the compiler to
choose the correct operand form; that is the purpose of the `%0' output
variable.

   Information about the output variable is supplied in the `Outputs'
parameter to `Asm':
     Outputs => Unsigned_32'Asm_Output ("=g", Flags));

   The output is defined by the `Asm_Output' attribute of the target
type; the general format is
     Type'Asm_Output (constraint_string, variable_name)

   The constraint string directs the compiler how to store/access the
associated variable.  In the example
     Unsigned_32'Asm_Output ("=m", Flags);
   the `"m"' (memory) constraint tells the compiler that the variable
`Flags' should be stored in a memory variable, thus preventing the
optimizer from keeping it in a register.  In contrast,
     Unsigned_32'Asm_Output ("=r", Flags);
   uses the `"r"' (register) constraint, telling the compiler to store
the variable in a register.

   If the constraint is preceded by the equal character (*=*), it tells
the compiler that the variable will be used to store data into it.

   In the `Get_Flags' example, we used the "g" (global) constraint,
allowing the optimizer to choose whatever it deems best.

   There are a fairly large number of constraints, but the ones that
are most useful (for the Intel x86 processor) are the following:

`='
     output constraint

`g'
     global (i.e. can be stored anywhere)

`m'
     in memory

`I'
     a constant

`a'
     use eax

`b'
     use ebx

`c'
     use ecx

`d'
     use edx

`S'
     use esi

`D'
     use edi

`r'
     use one of eax, ebx, ecx or edx

`q'
     use one of eax, ebx, ecx, edx, esi or edi

   The full set of constraints is described in the GNAT COMPILE and
_as_ documentation; note that it is possible to combine certain
constraints in one constraint string.

   You specify the association of an output variable with an assembler
operand through the `%'_n_ notation, where _n_ is a non-negative
integer.  Thus in
     Asm ("pushfl"          & LF & HT & -- push flags on stack
          "popl %%eax"      & LF & HT & -- load eax with flags
          "movl %%eax, %0",             -- store flags in variable
          Outputs => Unsigned_32'Asm_Output ("=g", Flags));

`%0' will be replaced in the expanded code by the appropriate operand,
whatever the compiler decided for the `Flags' variable.

   In general, you may have any number of output variables:
   * Count the operands starting at 0; thus `%0', `%1', etc.

   * Specify the `Outputs' parameter as a parenthesized comma-separated
     list of `Asm_Output' attributes

   For example:
     Asm ("movl %%eax, %0" & LF & HT &
          "movl %%ebx, %1" & LF & HT &
          "movl %%ecx, %2",
          Outputs => (Unsigned_32'Asm_Output ("=g", Var_A),   --  %0 = Var_A
                      Unsigned_32'Asm_Output ("=g", Var_B),   --  %1 = Var_B
                      Unsigned_32'Asm_Output ("=g", Var_C))); --  %2 = Var_C

where `Var_A', `Var_B', and `Var_C' are variables in the Ada program.

   As a variation on the `Get_Flags' example, we can use the
constraints string to direct the compiler to store the eax register
into the `Flags' variable, instead of including the store instruction
explicitly in the `Asm' template string:

     with Interfaces; use Interfaces;
     with Ada.Text_IO; use Ada.Text_IO;
     with System.Machine_Code; use System.Machine_Code;
     procedure Get_Flags_2 is
        Flags : Unsigned_32;
        use ASCII;
     begin
        Asm ("pushfl"      & LF & HT & -- push flags on stack
             "popl %%eax",             -- save flags in eax
             Outputs => Unsigned_32'Asm_Output ("=a", Flags));
        Put_Line ("Flags register:" & Flags'Img);
     end Get_Flags_2;

The `"a"' constraint tells the compiler that the `Flags' variable will
come from the eax register. Here is the resulting code:

     #APP
        pushfl
        popl %eax
     #NO_APP
        movl %eax,-40(%ebp)

The compiler generated the store of eax into Flags after expanding the
assembler code.

   Actually, there was no need to pop the flags into the eax register;
more simply, we could just pop the flags directly into the program
variable:

     with Interfaces; use Interfaces;
     with Ada.Text_IO; use Ada.Text_IO;
     with System.Machine_Code; use System.Machine_Code;
     procedure Get_Flags_3 is
        Flags : Unsigned_32;
        use ASCII;
     begin
        Asm ("pushfl"  & LF & HT & -- push flags on stack
             "pop %0",             -- save flags in Flags
             Outputs => Unsigned_32'Asm_Output ("=g", Flags));
        Put_Line ("Flags register:" & Flags'Img);
     end Get_Flags_3;


File: gnat_ug_vms.info,  Node: Input Variables in Inline Assembler,  Next: Inlining Inline Assembler Code,  Prev: Output Variables in Inline Assembler,  Up: Inline Assembler

Input Variables in Inline Assembler
===================================

The example in this section illustrates how to specify the source
operands for assembly language statements.  The program simply
increments its input value by 1:

     with Interfaces; use Interfaces;
     with Ada.Text_IO; use Ada.Text_IO;
     with System.Machine_Code; use System.Machine_Code;
     procedure Increment is
     
        function Incr (Value : Unsigned_32) return Unsigned_32 is
           Result : Unsigned_32;
        begin
           Asm ("incl %0",
                Inputs  => Unsigned_32'Asm_Input ("a", Value),
                Outputs => Unsigned_32'Asm_Output ("=a", Result));
           return Result;
        end Incr;
     
        Value : Unsigned_32;
     
     begin
        Value := 5;
        Put_Line ("Value before is" & Value'Img);
        Value := Incr (Value);
        Put_Line ("Value after is" & Value'Img);
     end Increment;

   The `Outputs' parameter to `Asm' specifies that the result will be
in the eax register and that it is to be stored in the `Result'
variable.

   The `Inputs' parameter looks much like the `Outputs' parameter, but
with an `Asm_Input' attribute. The `"="' constraint, indicating an
output value, is not present.

   You can have multiple input variables, in the same way that you can
have more than one output variable.

   The parameter count (%0, %1) etc, now starts at the first input
statement, and continues with the output statements.  When both
parameters use the same variable, the compiler will treat them as the
same %n operand, which is the case here.

   Just as the `Outputs' parameter causes the register to be stored
into the target variable after execution of the assembler statements,
so does the `Inputs' parameter cause its variable to be loaded into the
register before execution of the assembler statements.

   Thus the effect of the `Asm' invocation is:
  1. load the 32-bit value of `Value' into eax

  2. execute the `incl %eax' instruction

  3. store the contents of eax into the `Result' variable

   The resulting assembler file (with `/OPTIMIZE=ALL' optimization)
contains:
     _increment__incr.1:
        subl $4,%esp
        movl 8(%esp),%eax
     #APP
        incl %eax
     #NO_APP
        movl %eax,%edx
        movl %ecx,(%esp)
        addl $4,%esp
        ret


File: gnat_ug_vms.info,  Node: Inlining Inline Assembler Code,  Next: Other Asm Functionality,  Prev: Input Variables in Inline Assembler,  Up: Inline Assembler

Inlining Inline Assembler Code
==============================

For a short subprogram such as the `Incr' function in the previous
section, the overhead of the call and return (creating / deleting the
stack frame) can be significant, compared to the amount of code in the
subprogram body.  A solution is to apply Ada's `Inline' pragma to the
subprogram, which directs the compiler to expand invocations of the
subprogram at the point(s) of call, instead of setting up a stack frame
for out-of-line calls.  Here is the resulting program:

     with Interfaces; use Interfaces;
     with Ada.Text_IO; use Ada.Text_IO;
     with System.Machine_Code; use System.Machine_Code;
     procedure Increment_2 is
     
        function Incr (Value : Unsigned_32) return Unsigned_32 is
           Result : Unsigned_32;
        begin
           Asm ("incl %0",
                Inputs  => Unsigned_32'Asm_Input ("a", Value),
                Outputs => Unsigned_32'Asm_Output ("=a", Result));
           return Result;
        end Incr;
        pragma Inline (Increment);
     
        Value : Unsigned_32;
     
     begin
        Value := 5;
        Put_Line ("Value before is" & Value'Img);
        Value := Increment (Value);
        Put_Line ("Value after is" & Value'Img);
     end Increment_2;

   Compile the program with both optimization (`/OPTIMIZE=ALL') and
inlining enabled (`-gnatpn' instead of `/CHECKS=SUPPRESS_ALL').

   The `Incr' function is still compiled as usual, but at the point in
`Increment' where our function used to be called:

     pushl %edi
     call _increment__incr.1

the code for the function body directly appears:

     movl %esi,%eax
     #APP
        incl %eax
     #NO_APP
        movl %eax,%edx

thus saving the overhead of stack frame setup and an out-of-line call.


File: gnat_ug_vms.info,  Node: Other Asm Functionality,  Next: A Complete Example,  Prev: Inlining Inline Assembler Code,  Up: Inline Assembler

Other `Asm' Functionality
=========================

This section describes two important parameters to the `Asm' procedure:
`Clobber', which identifies register usage; and `Volatile', which
inhibits unwanted optimizations.

* Menu:

* The Clobber Parameter::
* The Volatile Parameter::


File: gnat_ug_vms.info,  Node: The Clobber Parameter,  Next: The Volatile Parameter,  Up: Other Asm Functionality

The `Clobber' Parameter
-----------------------

One of the dangers of intermixing assembly language and a compiled
language such as Ada is that the compiler needs to be aware of which
registers are being used by the assembly code.  In some cases, such as
the earlier examples, the constraint string is sufficient to indicate
register usage (e.g. "a" for the eax register).  But more generally, the
compiler needs an explicit identification of the registers that are
used by the Inline Assembly statements.

   Using a register that the compiler doesn't know about could be a
side effect of an instruction (like `mull' storing its result in both
eax and edx).  It can also arise from explicit register usage in your
assembly code; for example:
     Asm ("movl %0, %%ebx" & LF & HT &
          "movl %%ebx, %1",
          Inputs  => Unsigned_32'Asm_Input  ("g", Var_In),
          Outputs => Unsigned_32'Asm_Output ("=g", Var_Out));

where the compiler (since it does not analyze the `Asm' template string)
does not know you are using the ebx register.

   In such cases you need to supply the `Clobber' parameter to `Asm',
to identify the registers that will be used by your assembly code:

     Asm ("movl %0, %%ebx" & LF & HT &
          "movl %%ebx, %1",
          Inputs  => Unsigned_32'Asm_Input  ("g", Var_In),
          Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
          Clobber => "ebx");

   The Clobber parameter is a static string expression specifying the
register(s) you are using.  Note that register names are _not_ prefixed
by a percent sign.  Also, if more than one register is used then their
names are separated by commas; e.g., `"eax, ebx"'

   The `Clobber' parameter has several additional uses:
  1. Use the "register" name `cc' to indicate that flags might have
     changed

  2. Use the "register" name `memory' if you changed a memory location


File: gnat_ug_vms.info,  Node: The Volatile Parameter,  Prev: The Clobber Parameter,  Up: Other Asm Functionality

The `Volatile' Parameter
------------------------

Compiler optimizations in the presence of Inline Assembler may
sometimes have unwanted effects.  For example, when an `Asm' invocation
with an input variable is inside a loop, the compiler might move the
loading of the input variable outside the loop, regarding it as a
one-time initialization.

   If this effect is not desired, you can disable such optimizations by
setting the `Volatile' parameter to `True'; for example:

     Asm ("movl %0, %%ebx" & LF & HT &
          "movl %%ebx, %1",
          Inputs   => Unsigned_32'Asm_Input  ("g", Var_In),
          Outputs  => Unsigned_32'Asm_Output ("=g", Var_Out),
          Clobber  => "ebx",
          Volatile => True);

   By default, `Volatile' is set to `False' unless there is no `Outputs'
parameter.

   Although setting `Volatile' to `True' prevents unwanted
optimizations, it will also disable other optimizations that might be
important for efficiency.  In general, you should set `Volatile' to
`True' only if the compiler's optimizations have created problems.


File: gnat_ug_vms.info,  Node: A Complete Example,  Prev: Other Asm Functionality,  Up: Inline Assembler

A Complete Example
==================

This section contains a complete program illustrating a realistic usage
of GNAT's Inline Assembler capabilities.  It comprises a main procedure
`Check_CPU' and a package `Intel_CPU'.  The package declares a
collection of functions that detect the properties of the 32-bit x86
processor that is running the program.  The main procedure invokes
these functions and displays the information.

   The Intel_CPU package could be enhanced by adding functions to
detect the type of x386 co-processor, the processor caching options and
special operations such as the SIMD extensions.

   Although the Intel_CPU package has been written for 32-bit Intel
compatible CPUs, it is OS neutral. It has been tested on DOS,
Windows/NT and Linux.

* Menu:

* Check_CPU Procedure::
* Intel_CPU Package Specification::
* Intel_CPU Package Body::


File: gnat_ug_vms.info,  Node: Check_CPU Procedure,  Next: Intel_CPU Package Specification,  Up: A Complete Example

`Check_CPU' Procedure
---------------------

     ---------------------------------------------------------------------
     --                                                                 --
     --  Uses the Intel_CPU package to identify the CPU the program is  --
     --  running on, and some of the features it supports.              --
     --                                                                 --
     ---------------------------------------------------------------------
     
     with Intel_CPU;                     --  Intel CPU detection functions
     with Ada.Text_IO;                   --  Standard text I/O
     with Ada.Command_Line;              --  To set the exit status
     
     procedure Check_CPU is
     
        Type_Found : Boolean := False;
        --  Flag to indicate that processor was identified
     
        Features   : Intel_CPU.Processor_Features;
        --  The processor features
     
        Signature  : Intel_CPU.Processor_Signature;
        --  The processor type signature
     
     begin
     
        -----------------------------------
        --  Display the program banner.  --
        -----------------------------------
     
        Ada.Text_IO.Put_Line (Ada.Command_Line.Command_Name &
                              ": check Intel CPU version and features, v1.0");
        Ada.Text_IO.Put_Line ("distribute freely, but no warranty whatsoever");
        Ada.Text_IO.New_Line;
     
        -----------------------------------------------------------------------
        --  We can safely start with the assumption that we are on at least  --
        --  a x386 processor. If the CPUID instruction is present, then we   --
        --  have a later processor type.                                     --
        -----------------------------------------------------------------------
     
        if Intel_CPU.Has_CPUID = False then
     
           --  No CPUID instruction, so we assume this is indeed a x386
           --  processor. We can still check if it has a FP co-processor.
           if Intel_CPU.Has_FPU then
              Ada.Text_IO.Put_Line
                ("x386-type processor with a FP co-processor");
           else
              Ada.Text_IO.Put_Line
                ("x386-type processor without a FP co-processor");
           end if;  --  check for FPU
     
           --  Program done
           Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Success);
           return;
     
        end if;  --  check for CPUID
     
        -----------------------------------------------------------------------
        --  If CPUID is supported, check if this is a true Intel processor,  --
        --  if it is not, display a warning.                                 --
        -----------------------------------------------------------------------
     
        if Intel_CPU.Vendor_ID /= Intel_CPU.Intel_Processor then
           Ada.Text_IO.Put_Line ("*** This is a Intel compatible processor");
           Ada.Text_IO.Put_Line ("*** Some information may be incorrect");
        end if;  --  check if Intel
     
        ----------------------------------------------------------------------
        --  With the CPUID instruction present, we can assume at least a    --
        --  x486 processor. If the CPUID support level is < 1 then we have  --
        --  to leave it at that.                                            --
        ----------------------------------------------------------------------
     
        if Intel_CPU.CPUID_Level < 1 then
     
           --  Ok, this is a x486 processor. we still can get the Vendor ID
           Ada.Text_IO.Put_Line ("x486-type processor");
           Ada.Text_IO.Put_Line ("Vendor ID is " & Intel_CPU.Vendor_ID);
     
           --  We can also check if there is a FPU present
           if Intel_CPU.Has_FPU then
              Ada.Text_IO.Put_Line ("Floating-Point support");
           else
              Ada.Text_IO.Put_Line ("No Floating-Point support");
           end if;  --  check for FPU
     
           --  Program done
           Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Success);
           return;
     
        end if;  --  check CPUID level
     
        ---------------------------------------------------------------------
        --  With a CPUID level of 1 we can use the processor signature to  --
        --  determine it's exact type.                                     --
        ---------------------------------------------------------------------
     
        Signature := Intel_CPU.Signature;
     
        ----------------------------------------------------------------------
        --  Ok, now we go into a lot of messy comparisons to get the        --
        --  processor type. For clarity, no attememt to try to optimize the --
        --  comparisons has been made. Note that since Intel_CPU does not   --
        --  support getting cache info, we cannot distinguish between P5    --
        --  and Celeron types yet.                                          --
        ----------------------------------------------------------------------
     
        --  x486SL
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0100# and
          Signature.Model           = 2#0100# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("x486SL processor");
        end if;
     
        --  x486DX2 Write-Back
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0100# and
          Signature.Model           = 2#0111# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("Write-Back Enhanced x486DX2 processor");
        end if;
     
        --  x486DX4
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0100# and
          Signature.Model           = 2#1000# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("x486DX4 processor");
        end if;
     
        --  x486DX4 Overdrive
        if Signature.Processor_Type = 2#01#   and
          Signature.Family          = 2#0100# and
          Signature.Model           = 2#1000# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("x486DX4 OverDrive processor");
        end if;
     
        --  Pentium (60, 66)
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0001# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("Pentium processor (60, 66)");
        end if;
     
        --  Pentium (75, 90, 100, 120, 133, 150, 166, 200)
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0010# then
           Type_Found := True;
           Ada.Text_IO.Put_Line
             ("Pentium processor (75, 90, 100, 120, 133, 150, 166, 200)");
        end if;
     
        --  Pentium OverDrive (60, 66)
        if Signature.Processor_Type = 2#01#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0001# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("Pentium OverDrive processor (60, 66)");
        end if;
     
        --  Pentium OverDrive (75, 90, 100, 120, 133, 150, 166, 200)
        if Signature.Processor_Type = 2#01#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0010# then
           Type_Found := True;
           Ada.Text_IO.Put_Line
             ("Pentium OverDrive cpu (75, 90, 100, 120, 133, 150, 166, 200)");
        end if;
     
        --  Pentium OverDrive processor for x486 processor-based systems
        if Signature.Processor_Type = 2#01#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0011# then
           Type_Found := True;
           Ada.Text_IO.Put_Line
             ("Pentium OverDrive processor for x486 processor-based systems");
        end if;
     
        --  Pentium processor with MMX technology (166, 200)
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0100# then
           Type_Found := True;
           Ada.Text_IO.Put_Line
             ("Pentium processor with MMX technology (166, 200)");
        end if;
     
        --  Pentium OverDrive with MMX for Pentium (75, 90, 100, 120, 133)
        if Signature.Processor_Type = 2#01#   and
          Signature.Family          = 2#0101# and
          Signature.Model           = 2#0100# then
           Type_Found := True;
           Ada.Text_IO.Put_Line
             ("Pentium OverDrive processor with MMX " &
              "technology for Pentium processor (75, 90, 100, 120, 133)");
        end if;
     
        --  Pentium Pro processor
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0110# and
          Signature.Model           = 2#0001# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("Pentium Pro processor");
        end if;
     
        --  Pentium II processor, model 3
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0110# and
          Signature.Model           = 2#0011# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("Pentium II processor, model 3");
        end if;
     
        --  Pentium II processor, model 5 or Celeron processor
        if Signature.Processor_Type = 2#00#   and
          Signature.Family          = 2#0110# and
          Signature.Model           = 2#0101# then
           Type_Found := True;
           Ada.Text_IO.Put_Line
             ("Pentium II processor, model 5 or Celeron processor");
        end if;
     
        --  Pentium Pro OverDrive processor
        if Signature.Processor_Type = 2#01#   and
          Signature.Family          = 2#0110# and
          Signature.Model           = 2#0011# then
           Type_Found := True;
           Ada.Text_IO.Put_Line ("Pentium Pro OverDrive processor");
        end if;
     
        --  If no type recognized, we have an unknown. Display what
        --  we _do_ know
        if Type_Found = False then
           Ada.Text_IO.Put_Line ("Unknown processor");
        end if;
     
        -----------------------------------------
        --  Display processor stepping level.  --
        -----------------------------------------
     
        Ada.Text_IO.Put_Line ("Stepping level:" & Signature.Stepping'Img);
     
        ---------------------------------
        --  Display vendor ID string.  --
        ---------------------------------
     
        Ada.Text_IO.Put_Line ("Vendor ID: " & Intel_CPU.Vendor_ID);
     
        ------------------------------------
        --  Get the processors features.  --
        ------------------------------------
     
        Features := Intel_CPU.Features;
     
        -----------------------------
        --  Check for a FPU unit.  --
        -----------------------------
     
        if Features.FPU = True then
           Ada.Text_IO.Put_Line ("Floating-Point unit available");
        else
           Ada.Text_IO.Put_Line ("no Floating-Point unit");
        end if;  --  check for FPU
     
        --------------------------------
        --  List processor features.  --
        --------------------------------
     
        Ada.Text_IO.Put_Line ("Supported features: ");
     
        --  Virtual Mode Extension
        if Features.VME = True then
           Ada.Text_IO.Put_Line ("    VME    - Virtual Mode Extension");
        end if;
     
        --  Debugging Extension
        if Features.DE = True then
           Ada.Text_IO.Put_Line ("    DE     - Debugging Extension");
        end if;
     
        --  Page Size Extension
        if Features.PSE = True then
           Ada.Text_IO.Put_Line ("    PSE    - Page Size Extension");
        end if;
     
        --  Time Stamp Counter
        if Features.TSC = True then
           Ada.Text_IO.Put_Line ("    TSC    - Time Stamp Counter");
        end if;
     
        --  Model Specific Registers
        if Features.MSR = True then
           Ada.Text_IO.Put_Line ("    MSR    - Model Specific Registers");
        end if;
     
        --  Physical Address Extension
        if Features.PAE = True then
           Ada.Text_IO.Put_Line ("    PAE    - Physical Address Extension");
        end if;
     
        --  Machine Check Extension
        if Features.MCE = True then
           Ada.Text_IO.Put_Line ("    MCE    - Machine Check Extension");
        end if;
     
        --  CMPXCHG8 instruction supported
        if Features.CX8 = True then
           Ada.Text_IO.Put_Line ("    CX8    - CMPXCHG8 instruction");
        end if;
     
        --  on-chip APIC hardware support
        if Features.APIC = True then
           Ada.Text_IO.Put_Line ("    APIC   - on-chip APIC hardware support");
        end if;
     
        --  Fast System Call
        if Features.SEP = True then
           Ada.Text_IO.Put_Line ("    SEP    - Fast System Call");
        end if;
     
        --  Memory Type Range Registers
        if Features.MTRR = True then
           Ada.Text_IO.Put_Line ("    MTTR   - Memory Type Range Registers");
        end if;
     
        --  Page Global Enable
        if Features.PGE = True then
           Ada.Text_IO.Put_Line ("    PGE    - Page Global Enable");
        end if;
     
        --  Machine Check Architecture
        if Features.MCA = True then
           Ada.Text_IO.Put_Line ("    MCA    - Machine Check Architecture");
        end if;
     
        --  Conditional Move Instruction Supported
        if Features.CMOV = True then
           Ada.Text_IO.Put_Line
             ("    CMOV   - Conditional Move Instruction Supported");
        end if;
     
        --  Page Attribute Table
        if Features.PAT = True then
           Ada.Text_IO.Put_Line ("    PAT    - Page Attribute Table");
        end if;
     
        --  36-bit Page Size Extension
        if Features.PSE_36 = True then
           Ada.Text_IO.Put_Line ("    PSE_36 - 36-bit Page Size Extension");
        end if;
     
        --  MMX technology supported
        if Features.MMX = True then
           Ada.Text_IO.Put_Line ("    MMX    - MMX technology supported");
        end if;
     
        --  Fast FP Save and Restore
        if Features.FXSR = True then
           Ada.Text_IO.Put_Line ("    FXSR   - Fast FP Save and Restore");
        end if;
     
        ---------------------
        --  Program done.  --
        ---------------------
     
        Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Success);
     
     exception
     
        when others =>
           Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Failure);
           raise;
     
     end Check_CPU;


File: gnat_ug_vms.info,  Node: Intel_CPU Package Specification,  Next: Intel_CPU Package Body,  Prev: Check_CPU Procedure,  Up: A Complete Example

`Intel_CPU' Package Specification
---------------------------------

     -------------------------------------------------------------------------
     --                                                                     --
     --  file: INTEL_CPU.ADS                                                --
     --                                                                     --
     --           *********************************************             --
     --           * WARNING: for 32-bit Intel processors only *             --
     --           *********************************************             --
     --                                                                     --
     --  This package contains a number of subprograms that are useful in   --
     --  determining the Intel x86 CPU (and the features it supports) on    --
     --  which the program is running.                                      --
     --                                                                     --
     --  The package is based upon the information given in the Intel       --
     --  Application Note AP-485: "Intel Processor Identification and the   --
     --  CPUID Instruction" as of April 1998. This application note can be  --
     --  found on www.intel.com.                                            --
     --                                                                     --
     --  It currently deals with 32-bit processors only, will not detect    --
     --  features added after april 1998, and does not guarantee proper     --
     --  results on Intel-compatible processors.                            --
     --                                                                     --
     --  Cache info and x386 fpu type detection are not supported.          --
     --                                                                     --
     --  This package does not use any privileged instructions, so should   --
     --  work on any OS running on a 32-bit Intel processor.                --
     --                                                                     --
     -------------------------------------------------------------------------
     
     with Interfaces;             use Interfaces;
     --  for using unsigned types
     
     with System.Machine_Code;    use System.Machine_Code;
     --  for using inline assembler code
     
     with Ada.Characters.Latin_1; use Ada.Characters.Latin_1;
     --  for inserting control characters
     
     package Intel_CPU is
     
        ----------------------
        --  Processor bits  --
        ----------------------
     
        subtype Num_Bits is Natural range 0 .. 31;
        --  the number of processor bits (32)
     
        --------------------------
        --  Processor register  --
        --------------------------
     
        --  define a processor register type for easy access to
        --  the individual bits
     
        type Processor_Register is array (Num_Bits) of Boolean;
        pragma Pack (Processor_Register);
        for Processor_Register'Size use 32;
     
        -------------------------
        --  Unsigned register  --
        -------------------------
     
        --  define a processor register type for easy access to
        --  the individual bytes
     
        type Unsigned_Register is
           record
              L1 : Unsigned_8;
              H1 : Unsigned_8;
              L2 : Unsigned_8;
              H2 : Unsigned_8;
           end record;
     
        for Unsigned_Register use
           record
              L1 at 0 range  0 ..  7;
              H1 at 0 range  8 .. 15;
              L2 at 0 range 16 .. 23;
              H2 at 0 range 24 .. 31;
           end record;
     
        for Unsigned_Register'Size use 32;
     
        ---------------------------------
        --  Intel processor vendor ID  --
        ---------------------------------
     
        Intel_Processor : constant String (1 .. 12) := "GenuineIntel";
        --  indicates an Intel manufactured processor
     
        ------------------------------------
        --  Processor signature register  --
        ------------------------------------
     
        --  a register type to hold the processor signature
     
        type Processor_Signature is
           record
              Stepping       : Natural range 0 .. 15;
              Model          : Natural range 0 .. 15;
              Family         : Natural range 0 .. 15;
              Processor_Type : Natural range 0 .. 3;
              Reserved       : Natural range 0 .. 262143;
           end record;
     
        for Processor_Signature use
           record
              Stepping       at 0 range  0 ..  3;
              Model          at 0 range  4 ..  7;
              Family         at 0 range  8 .. 11;
              Processor_Type at 0 range 12 .. 13;
              Reserved       at 0 range 14 .. 31;
           end record;
     
        for Processor_Signature'Size use 32;
     
        -----------------------------------
        --  Processor features register  --
        -----------------------------------
     
        --  a processor register to hold the processor feature flags
     
        type Processor_Features is
           record
              FPU    : Boolean;                --  floating point unit on chip
              VME    : Boolean;                --  virtual mode extension
              DE     : Boolean;                --  debugging extension
              PSE    : Boolean;                --  page size extension
              TSC    : Boolean;                --  time stamp counter
              MSR    : Boolean;                --  model specific registers
              PAE    : Boolean;                --  physical address extension
              MCE    : Boolean;                --  machine check extension
              CX8    : Boolean;                --  cmpxchg8 instruction
              APIC   : Boolean;                --  on-chip apic hardware
              Res_1  : Boolean;                --  reserved for extensions
              SEP    : Boolean;                --  fast system call
              MTRR   : Boolean;                --  memory type range registers
              PGE    : Boolean;                --  page global enable
              MCA    : Boolean;                --  machine check architecture
              CMOV   : Boolean;                --  conditional move supported
              PAT    : Boolean;                --  page attribute table
              PSE_36 : Boolean;                --  36-bit page size extension
              Res_2  : Natural range 0 .. 31;  --  reserved for extensions
              MMX    : Boolean;                --  MMX technology supported
              FXSR   : Boolean;                --  fast FP save and restore
              Res_3  : Natural range 0 .. 127; --  reserved for extensions
           end record;
     
        for Processor_Features use
           record
              FPU    at 0 range  0 ..  0;
              VME    at 0 range  1 ..  1;
              DE     at 0 range  2 ..  2;
              PSE    at 0 range  3 ..  3;
              TSC    at 0 range  4 ..  4;
              MSR    at 0 range  5 ..  5;
              PAE    at 0 range  6 ..  6;
              MCE    at 0 range  7 ..  7;
              CX8    at 0 range  8 ..  8;
              APIC   at 0 range  9 ..  9;
              Res_1  at 0 range 10 .. 10;
              SEP    at 0 range 11 .. 11;
              MTRR   at 0 range 12 .. 12;
              PGE    at 0 range 13 .. 13;
              MCA    at 0 range 14 .. 14;
              CMOV   at 0 range 15 .. 15;
              PAT    at 0 range 16 .. 16;
              PSE_36 at 0 range 17 .. 17;
              Res_2  at 0 range 18 .. 22;
              MMX    at 0 range 23 .. 23;
              FXSR   at 0 range 24 .. 24;
              Res_3  at 0 range 25 .. 31;
           end record;
     
        for Processor_Features'Size use 32;
     
        -------------------
        --  Subprograms  --
        -------------------
     
        function Has_FPU return Boolean;
        --  return True if a FPU is found
        --  use only if CPUID is not supported
     
        function Has_CPUID return Boolean;
        --  return True if the processor supports the CPUID instruction
     
        function CPUID_Level return Natural;
        --  return the CPUID support level (0, 1 or 2)
        --  can only be called if the CPUID instruction is supported
     
        function Vendor_ID return String;
        --  return the processor vendor identification string
        --  can only be called if the CPUID instruction is supported
     
        function Signature return Processor_Signature;
        --  return the processor signature
        --  can only be called if the CPUID instruction is supported
     
        function Features return Processor_Features;
        --  return the processors features
        --  can only be called if the CPUID instruction is supported
     
     private
     
        ------------------------
        --  EFLAGS bit names  --
        ------------------------
     
        ID_Flag : constant Num_Bits := 21;
        --  ID flag bit
     
     end Intel_CPU;


File: gnat_ug_vms.info,  Node: Intel_CPU Package Body,  Prev: Intel_CPU Package Specification,  Up: A Complete Example

`Intel_CPU' Package Body
------------------------

     package body Intel_CPU is
     
        ---------------------------
        --  Detect FPU presence  --
        ---------------------------
     
        --  There is a FPU present if we can set values to the FPU Status
        --  and Control Words.
     
        function Has_FPU return Boolean is
     
           Register : Unsigned_16;
           --  processor register to store a word
     
        begin
     
           --  check if we can change the status word
           Asm (
     
                --  the assembler code
                "finit"              & LF & HT &    --  reset status word
                "movw $0x5A5A, %%ax" & LF & HT &    --  set value status word
                "fnstsw %0"          & LF & HT &    --  save status word
                "movw %%ax, %0",                    --  store status word
     
                --  output stored in Register
                --  register must be a memory location
                Outputs => Unsigned_16'Asm_output ("=m", Register),
     
                --  tell compiler that we used eax
                Clobber => "eax");
     
           --  if the status word is zero, there is no FPU
           if Register = 0 then
              return False;   --  no status word
           end if;  --  check status word value
     
           --  check if we can get the control word
           Asm (
     
                --  the assembler code
                "fnstcw %0",   --  save the control word
     
                --  output into Register
                --  register must be a memory location
                Outputs => Unsigned_16'Asm_output ("=m", Register));
     
           --  check the relevant bits
           if (Register and 16#103F#) /= 16#003F# then
              return False;   --  no control word
           end if;  --  check control word value
     
           --  FPU found
           return True;
     
        end Has_FPU;
     
        --------------------------------
        --  Detect CPUID instruction  --
        --------------------------------
     
        --  The processor supports the CPUID instruction if it is possible
        --  to change the value of ID flag bit in the EFLAGS register.
     
        function Has_CPUID return Boolean is
     
           Original_Flags, Modified_Flags : Processor_Register;
           --  EFLAG contents before and after changing the ID flag
     
        begin
     
           --  try flipping the ID flag in the EFLAGS register
           Asm (
     
                --  the assembler code
                "pushfl"               & LF & HT &     --  push EFLAGS on stack
                "pop %%eax"            & LF & HT &     --  pop EFLAGS into eax
                "movl %%eax, %0"       & LF & HT &     --  save EFLAGS content
                "xor $0x200000, %%eax" & LF & HT &     --  flip ID flag
                "push %%eax"           & LF & HT &     --  push EFLAGS on stack
                "popfl"                & LF & HT &     --  load EFLAGS register
                "pushfl"               & LF & HT &     --  push EFLAGS on stack
                "pop %1",                              --  save EFLAGS content
     
                --  output values, may be anything
                --  Original_Flags is %0
                --  Modified_Flags is %1
                Outputs =>
                   (Processor_Register'Asm_output ("=g", Original_Flags),
                    Processor_Register'Asm_output ("=g", Modified_Flags)),
     
                --  tell compiler eax is destroyed
                Clobber => "eax");
     
           --  check if CPUID is supported
           if Original_Flags(ID_Flag) /= Modified_Flags(ID_Flag) then
              return True;   --  ID flag was modified
           else
              return False;  --  ID flag unchanged
           end if;  --  check for CPUID
     
        end Has_CPUID;
     
        -------------------------------
        --  Get CPUID support level  --
        -------------------------------
     
        function CPUID_Level return Natural is
     
           Level : Unsigned_32;
           --  returned support level
     
        begin
     
           --  execute CPUID, storing the results in the Level register
           Asm (
     
                --  the assembler code
                "cpuid",    --  execute CPUID
     
                --  zero is stored in eax
                --  returning the support level in eax
                Inputs => Unsigned_32'Asm_input ("a", 0),
     
                --  eax is stored in Level
                Outputs => Unsigned_32'Asm_output ("=a", Level),
     
                --  tell compiler ebx, ecx and edx registers are destroyed
                Clobber => "ebx, ecx, edx");
     
           --  return the support level
           return Natural (Level);
     
        end CPUID_Level;
     
        --------------------------------
        --  Get CPU Vendor ID String  --
        --------------------------------
     
        --  The vendor ID string is returned in the ebx, ecx and edx register
        --  after executing the CPUID instruction with eax set to zero.
        --  In case of a true Intel processor the string returned is
        --  "GenuineIntel"
     
        function Vendor_ID return String is
     
           Ebx, Ecx, Edx : Unsigned_Register;
           --  registers containing the vendor ID string
     
           Vendor_ID : String (1 .. 12);
           -- the vendor ID string
     
        begin
     
           --  execute CPUID, storing the results in the processor registers
           Asm (
     
                --  the assembler code
                "cpuid",    --  execute CPUID
     
                --  zero stored in eax
                --  vendor ID string returned in ebx, ecx and edx
                Inputs => Unsigned_32'Asm_input ("a", 0),
     
                --  ebx is stored in Ebx
                --  ecx is stored in Ecx
                --  edx is stored in Edx
                Outputs => (Unsigned_Register'Asm_output ("=b", Ebx),
                            Unsigned_Register'Asm_output ("=c", Ecx),
                            Unsigned_Register'Asm_output ("=d", Edx)));
     
           --  now build the vendor ID string
           Vendor_ID( 1) := Character'Val (Ebx.L1);
           Vendor_ID( 2) := Character'Val (Ebx.H1);
           Vendor_ID( 3) := Character'Val (Ebx.L2);
           Vendor_ID( 4) := Character'Val (Ebx.H2);
           Vendor_ID( 5) := Character'Val (Edx.L1);
           Vendor_ID( 6) := Character'Val (Edx.H1);
           Vendor_ID( 7) := Character'Val (Edx.L2);
           Vendor_ID( 8) := Character'Val (Edx.H2);
           Vendor_ID( 9) := Character'Val (Ecx.L1);
           Vendor_ID(10) := Character'Val (Ecx.H1);
           Vendor_ID(11) := Character'Val (Ecx.L2);
           Vendor_ID(12) := Character'Val (Ecx.H2);
     
           --  return string
           return Vendor_ID;
     
        end Vendor_ID;
     
        -------------------------------
        --  Get processor signature  --
        -------------------------------
     
        function Signature return Processor_Signature is
     
           Result : Processor_Signature;
           --  processor signature returned
     
        begin
     
           --  execute CPUID, storing the results in the Result variable
           Asm (
     
                --  the assembler code
                "cpuid",    --  execute CPUID
     
                --  one is stored in eax
                --  processor signature returned in eax
                Inputs => Unsigned_32'Asm_input ("a", 1),
     
                --  eax is stored in Result
                Outputs => Processor_Signature'Asm_output ("=a", Result),
     
                --  tell compiler that ebx, ecx and edx are also destroyed
                Clobber => "ebx, ecx, edx");
     
           --  return processor signature
           return Result;
     
        end Signature;
     
        ------------------------------
        --  Get processor features  --
        ------------------------------
     
        function Features return Processor_Features is
     
           Result : Processor_Features;
           --  processor features returned
     
        begin
     
           --  execute CPUID, storing the results in the Result variable
           Asm (
     
                --  the assembler code
                "cpuid",    --  execute CPUID
     
                --  one stored in eax
                --  processor features returned in edx
                Inputs => Unsigned_32'Asm_input ("a", 1),
     
                --  edx is stored in Result
                Outputs => Processor_Features'Asm_output ("=d", Result),
     
                --  tell compiler that ebx and ecx are also destroyed
                Clobber => "ebx, ecx");
     
           --  return processor signature
           return Result;
     
        end Features;
     
     end Intel_CPU;


File: gnat_ug_vms.info,  Node: Performance Considerations,  Next: GNU Free Documentation License,  Prev: Inline Assembler,  Up: Top

Performance Considerations
**************************

The GNAT system provides a number of options that allow a trade-off
between

   * performance of the generated code

   * speed of compilation

   * minimization of dependences and recompilation

   * the degree of run-time checking.

The defaults (if no options are selected) aim at improving the speed of
compilation and minimizing dependences, at the expense of performance
of the generated code:

   * no optimization

   * no inlining of subprogram calls

   * all run-time checks enabled except overflow and elaboration checks

These options are suitable for most program development purposes. This
chapter describes how you can modify these choices, and also provides
some guidelines on debugging optimized code.

* Menu:

* Controlling Run-Time Checks::
* Optimization Levels::
* Debugging Optimized Code::
* Inlining of Subprograms::
* Coverage Analysis::


File: gnat_ug_vms.info,  Node: Controlling Run-Time Checks,  Next: Optimization Levels,  Up: Performance Considerations

Controlling Run-Time Checks
===========================

By default, GNAT generates all run-time checks, except arithmetic
overflow checking for integer operations and checks for access before
elaboration on subprogram calls. The latter are not required in default
mode, because all necessary checking is done at compile time.  Two gnat
qualifiers, `/CHECKS=SUPPRESS_ALL' and `/CHECKS=OVERFLOW' allow this
default to be modified. *Note Run-Time Checks::.

   Our experience is that the default is suitable for most development
purposes.

   We treat integer overflow specially because these are quite
expensive and in our experience are not as important as other run-time
checks in the development process. Note that division by zero is not
considered an overflow check, and divide by zero checks are generated
where required by default.

   Elaboration checks are off by default, and also not needed by
default, since GNAT uses a static elaboration analysis approach that
avoids the need for run-time checking. This manual contains a full
chapter discussing the issue of elaboration checks, and if the default
is not satisfactory for your use, you should read this chapter.

   For validity checks, the minimal checks required by the Ada Reference
Manual (for case statements and assignments to array elements) are on
by default. These can be suppressed by use of the `-gnatVn' qualifier.
Note that in Ada 83, there were no validity checks, so if the Ada 83
mode is acceptable (or when comparing GNAT performance with an Ada 83
compiler), it may be reasonable to routinely use `-gnatVn'. Validity
checks are also suppressed entirely if `/CHECKS=SUPPRESS_ALL' is used.

   Note that the setting of the qualifiers controls the default setting
of the checks. They may be modified using either `pragma Suppress' (to
remove checks) or `pragma Unsuppress' (to add back suppressed checks)
in the program source.


File: gnat_ug_vms.info,  Node: Optimization Levels,  Next: Debugging Optimized Code,  Prev: Controlling Run-Time Checks,  Up: Performance Considerations

Optimization Levels
===================

The default is optimization off. This results in the fastest compile
times, but GNAT makes absolutely no attempt to optimize, and the
generated programs are considerably larger and slower than when
optimization is enabled. You can use the `/OPTIMIZE' on the `GNAT
COMPILE' command line to control the optimization level:

`/OPTIMIZE=NONE'
     no optimization (the default)

`/OPTIMIZE=SOME'
     medium level optimization

`/OPTIMIZE=ALL'
     full optimization

`/OPTIMIZE=INLINING'
     full optimization, and also attempt automatic inlining of small
     subprograms within a unit (*note Inlining of Subprograms::).

   Higher optimization levels perform more global transformations on the
program and apply more expensive analysis algorithms in order to
generate faster and more compact code. The price in compilation time,
and the resulting improvement in execution time, both depend on the
particular application and the hardware environment.  You should
experiment to find the best level for your application.

   Note: Unlike some other compilation systems, `GNAT COMPILE' has been
tested extensively at all optimization levels. There are some bugs
which appear only with optimization turned on, but there have also been
bugs which show up only in _unoptimized_ code. Selecting a lower level
of optimization does not improve the reliability of the code generator,
which in practice is highly reliable at all optimization levels.

   Note regarding the use of `/OPTIMIZE=INLINING': The use of this
optimization level is generally discouraged with GNAT, since it often
results in larger executables which run more slowly. See further
discussion of this point in *note Inlining of Subprograms::.


File: gnat_ug_vms.info,  Node: Debugging Optimized Code,  Next: Inlining of Subprograms,  Prev: Optimization Levels,  Up: Performance Considerations

Debugging Optimized Code
========================

Since the compiler generates debugging tables for a compilation unit
before it performs optimizations, the optimizing transformations may
invalidate some of the debugging data.  You therefore need to
anticipate certain anomalous situations that may arise while debugging
optimized code.  This section describes the most common cases.

  1. The "hopping Program Counter":  Repeated 'step' or 'next' commands
     show the PC bouncing back and forth in the code.  This may result
     from any of the following optimizations:

        * Common subexpression elimination: using a single instance of
          code for a quantity that the source computes several times.
          As a result you may not be able to stop on what looks like a
          statement.

        * Invariant code motion: moving an expression that does not
          change within a loop, to the beginning of the loop.

        * Instruction scheduling: moving instructions so as to overlap
          loads and stores (typically) with other code, or in general
          to move computations of values closer to their uses. Often
          this causes you to pass an assignment statement without the
          assignment happening and then later bounce back to the
          statement when the value is actually needed.  Placing a
          breakpoint on a line of code and then stepping over it may,
          therefore, not always cause all the expected side-effects.

  2. The "big leap": More commonly known as cross-jumping, in which two
     identical pieces of code are merged and the program counter
     suddenly jumps to a statement that is not supposed to be executed,
     simply because it (and the code following) translates to the same
     thing as the code that _was_ supposed to be executed.  This effect
     is typically seen in sequences that end in a jump, such as a
     `goto', a `return', or a `break' in a C `qualifier' statement.

  3. The "roving variable": The symptom is an unexpected value in a
     variable.  There are various reasons for this effect:

        * In a subprogram prologue, a parameter may not yet have been
          moved to its "home".

        * A variable may be dead, and its register re-used.  This is
          probably the most common cause.

        * As mentioned above, the assignment of a value to a variable
          may have been moved.

        * A variable may be eliminated entirely by value propagation or
          other means.  In this case, GCC may incorrectly generate
          debugging information for the variable

     In general, when an unexpected value appears for a local variable
     or parameter you should first ascertain if that value was actually
     computed by your program, as opposed to being incorrectly reported
     by the debugger.  Record fields or array elements in an object
     designated by an access value are generally less of a problem,
     once you have ascertained that the access value is sensible.
     Typically, this means checking variables in the preceding code and
     in the calling subprogram to verify that the value observed is
     explainable from other values (one must apply the procedure
     recursively to those other values); or re-running the code and
     stopping a little earlier (perhaps before the call) and stepping
     to better see how the variable obtained the value in question; or
     continuing to step _from_ the point of the strange value to see if
     code motion had simply moved the variable's assignments later.


File: gnat_ug_vms.info,  Node: Inlining of Subprograms,  Next: Coverage Analysis,  Prev: Debugging Optimized Code,  Up: Performance Considerations

Inlining of Subprograms
=======================

A call to a subprogram in the current unit is inlined if all the
following conditions are met:

   * The optimization level is at least `/OPTIMIZE=SOME'.

   * The called subprogram is suitable for inlining: It must be small
     enough and not contain nested subprograms or anything else that
     `GNAT COMPILE' cannot support in inlined subprograms.

   * The call occurs after the definition of the body of the subprogram.

   * Either `pragma Inline' applies to the subprogram or it is small
     and automatic inlining (optimization level `/OPTIMIZE=INLINING') is
     specified.

Calls to subprograms in `with''ed units are normally not inlined.  To
achieve this level of inlining, the following conditions must all be
true:

   * The optimization level is at least `/OPTIMIZE=SOME'.

   * The called subprogram is suitable for inlining: It must be small
     enough and not contain nested subprograms or anything else `GNAT
     COMPILE' cannot support in inlined subprograms.

   * The call appears in a body (not in a package spec).

   * There is a `pragma Inline' for the subprogram.

   * The `/INLINE' qualifier is used in the `GNAT COMPILE' command line

   Note that specifying the `/INLINE=PRAGMA' qualifier causes additional
compilation dependencies. Consider the following:

     package R is
        procedure Q;
        pragma Inline (Q);
     end R;
     package body R is
        ...
     end R;
     
     with R;
     procedure Main is
     begin
        ...
        R.Q;
     end Main;

With the default behavior (no `/INLINE=PRAGMA' qualifier specified), the
compilation of the `Main' procedure depends only on its own source,
`MAIN.ADB', and the spec of the package in file `R.ADS'. This means
that editing the body of `R' does not require recompiling `Main'.

   On the other hand, the call `R.Q' is not inlined under these
circumstances. If the `/INLINE=PRAGMA' qualifier is present when `Main'
is compiled, the call will be inlined if the body of `Q' is small
enough, but now `Main' depends on the body of `R' in `R.ADB' as well as
on the spec. This means that if this body is edited, the main program
must be recompiled. Note that this extra dependency occurs whether or
not the call is in fact inlined by `GNAT COMPILE'.

   The use of front end inlining with `-gnatN' generates similar
additional dependencies.

   Note: The `/INLINE=SUPPRESS' qualifier can be used to prevent all
inlining. This qualifier overrides all other conditions and ensures
that no inlining occurs. The extra dependences resulting from
`/INLINE=PRAGMA' will still be active, even if this qualifier is used
to suppress the resulting inlining actions.

   Note regarding the use of `/OPTIMIZE=INLINING': There is no
difference in inlining behavior between `/OPTIMIZE=ALL' and
`/OPTIMIZE=INLINING' for subprograms with an explicit pragma `Inline'
assuming the use of `/INLINE=PRAGMA' or `-gnatN' (the qualifiers that
activate inlining). If you have used pragma `Inline' in appropriate
cases, then it is usually much better to use `/OPTIMIZE=ALL' and
`/INLINE=PRAGMA' and avoid the use of `/OPTIMIZE=INLINING' which in
this case only has the effect of inlining subprograms you did not think
should be inlined. We often find that the use of `/OPTIMIZE=INLINING'
slows down code by performing excessive inlining, leading to increased
instruction cache pressure from the increased code size. So the bottom
line here is that you should not automatically assume that
`/OPTIMIZE=INLINING' is better than `/OPTIMIZE=ALL', and indeed you
should use `/OPTIMIZE=INLINING' only if tests show that it actually
improves performance.


File: gnat_ug_vms.info,  Node: Coverage Analysis,  Prev: Inlining of Subprograms,  Up: Performance Considerations

Coverage Analysis
=================

GNAT supports the Digital Performance Coverage Analyzer (PCA), which
allows the user to determine the distribution of execution time across
a program, *note Profiling:: for details of usage.


File: gnat_ug_vms.info,  Node: GNU Free Documentation License,  Next: Index,  Prev: Performance Considerations,  Up: Top

GNU Free Documentation License
******************************

                      Version 1.2, November 2002
     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

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     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
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     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
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     free program should come with manuals providing the same freedoms
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     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a computer-network location from
     which the general network-using public has access to download
     using public-standard network protocols a complete Transparent
     copy of the Document, free of added material.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
     retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
          previous versions (which should, if there were any, be listed
          in the History section of the Document).  You may use the
          same title as a previous version if the original publisher of
          that version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section Entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
          the previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
          section all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
          titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
     you are acting on behalf of, you may not add another; but you may
     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warrany Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.

ADDENDUM: How to use this License for your documents
====================================================

   To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: gnat_ug_vms.info,  Node: Index,  Prev: GNU Free Documentation License,  Up: Top

Index
*****

* Menu:

* -83 (gnathtml):                        Converting Ada Files to html with gnathtml.
* -c (gnatname):                         Qualifiers for gnatname.
* -d (gnathtml):                         Converting Ada Files to html with gnathtml.
* -D (gnatname):                         Qualifiers for gnatname.
* -d (gnatname):                         Qualifiers for gnatname.
* -f (GNAT LINK):                        Qualifiers for GNAT LINK.
* -f (gnathtml):                         Converting Ada Files to html with gnathtml.
* -fstack-check:                         Stack Overflow Checking.
* -gnatem (GNAT COMPILE):                Units to Sources Mapping Files.
* -gnatN (GNAT COMPILE):                 Subprogram Inlining Control.
* -gnatN qualifier:                      Source Dependencies.
* -gnatT (GNAT COMPILE):                 Run-Time Control.
* -gnatwP (GNAT COMPILE):                Output and Error Message Control.
* -gnatwp (GNAT COMPILE):                Output and Error Message Control.
* -h (gnatname):                         Qualifiers for gnatname.
* -I (gnathtml):                         Converting Ada Files to html with gnathtml.
* -l (gnathtml):                         Converting Ada Files to html with gnathtml.
* -o (gnathtml):                         Converting Ada Files to html with gnathtml.
* -p (gnathtml):                         Converting Ada Files to html with gnathtml.
* -P (gnatname):                         Qualifiers for gnatname.
* -sc (gnathtml):                        Converting Ada Files to html with gnathtml.
* -t (gnathtml):                         Converting Ada Files to html with gnathtml.
* -v (gnatname):                         Qualifiers for gnatname.
* -w:                                    Output and Error Message Control.
* /83 (GNAT COMPILE):                    Compiling Ada 83 Programs.
* /ACTIONS=BIND (GNAT MAKE):             Qualifiers for GNAT MAKE.
* /ACTIONS=COMPILE (GNAT MAKE):          Qualifiers for GNAT MAKE.
* /ACTIONS=LINK (GNAT MAKE):             Qualifiers for GNAT MAKE.
* /ALL_FILES (GNAT MAKE):                Qualifiers for GNAT MAKE.
* /ALL_UNITS (GNAT LIST):                Qualifiers for GNAT LIST.
* /ASM (GNAT COMPILE):                   Qualifiers for GNAT COMPILE.
* /BIND_FILE=ADA (GNAT BIND):            Output Control.
* /BIND_FILE=ADA (GNAT LINK):            Qualifiers for GNAT LINK.
* /BIND_FILE=C (GNAT BIND):              Output Control.
* /BIND_FILE=C (GNAT LINK):              Qualifiers for GNAT LINK.
* /BINDER_QUALIFIERS (GNAT MAKE):        Mode Qualifiers for GNAT MAKE.
* /CHECKS=ASSERTIONS (GNAT COMPILE):     Debugging and Assertion Control.
* /CHECKS=ELABORATION (GNAT COMPILE) <1>: Debugging Control.
* /CHECKS=ELABORATION (GNAT COMPILE):    Run-Time Checks.
* /CHECKS=OVERFLOW (GNAT COMPILE) <1>:   Controlling Run-Time Checks.
* /CHECKS=OVERFLOW (GNAT COMPILE):       Run-Time Checks.
* /CHECKS=SUPPRESS_ALL (GNAT COMPILE) <1>: Controlling Run-Time Checks.
* /CHECKS=SUPPRESS_ALL (GNAT COMPILE):   Run-Time Checks.
* /COMPILATION (GNAT CHOP):              Qualifiers for GNAT CHOP.
* /COMPILER_QUALIFIERS (GNAT MAKE):      Mode Qualifiers for GNAT MAKE.
* /CONDITIONAL_SOURCE_SEARCH (GNAT MAKE): Qualifiers for GNAT MAKE.
* /CONFIG=file (GNAT LIBRARY):           Qualifiers for GNAT LIBRARY.
* /CONTINUE_ON_ERROR (GNAT MAKE):        Qualifiers for GNAT MAKE.
* /CREATE=directory (GNAT LIBRARY):      Qualifiers for GNAT LIBRARY.
* /DEBUG (GNAT COMPILE):                 Qualifiers for GNAT COMPILE.
* /DEBUG (GNAT LINK):                    Qualifiers for GNAT LINK.
* /DEBUG=TRACEBACK (GNAT LINK):          Qualifiers for GNAT LINK.
* /DELETE=directory (GNAT LIBRARY):      Qualifiers for GNAT LIBRARY.
* /DEPENDENCIES (GNAT LIST):             Qualifiers for GNAT LIST.
* /DEPENDENCIES_LIST (GNAT MAKE):        Qualifiers for GNAT MAKE.
* /DO_OBJECT_CHECK (GNAT MAKE):          Qualifiers for GNAT MAKE.
* /ELABORATION_DEPENDENCIES (GNAT BIND): Output Control.
* /ERROR_LIMIT (GNAT COMPILE):           Output and Error Message Control.
* /EXECUTABLE (GNAT LINK):               Qualifiers for GNAT LINK.
* /EXECUTABLE (GNAT MAKE):               Qualifiers for GNAT MAKE.
* /EXPAND_SOURCE (GNAT COMPILE):         Debugging Control.
* /FILE_NAME_MAX_LENGTH (GNAT CHOP):     Qualifiers for GNAT CHOP.
* /FILE_NAME_MAX_LENGTH (GNAT COMPILE):  File Naming Control.
* /FORCE_COMPILE (GNAT MAKE):            Qualifiers for GNAT MAKE.
* /HELP (GNAT BIND):                     Output Control.
* /IDENTIFIER_CHARACTER_SET (GNAT COMPILE): Character Set Control.
* /IN_PLACE (GNAT MAKE):                 Qualifiers for GNAT MAKE.
* /INLINE=PRAGMA (GNAT COMPILE) <1>:     Inlining of Subprograms.
* /INLINE=PRAGMA (GNAT COMPILE):         Subprogram Inlining Control.
* /INLINE=PRAGMA qualifier:              Source Dependencies.
* /INLINE=SUPPRESS (GNAT COMPILE):       Inlining of Subprograms.
* /LIBRARY_SEARCH (GNAT MAKE):           Qualifiers for GNAT MAKE.
* /LINKER_OPTION_LIST (GNAT BIND):       Output Control.
* /LINKER_QUALIFIERS (GNAT MAKE):        Mode Qualifiers for GNAT MAKE.
* /LIST (GNAT COMPILE):                  Output and Error Message Control.
* /MAPPING (GNAT MAKE):                  Qualifiers for GNAT MAKE.
* /MINIMAL_RECOMPILATION (GNAT MAKE):    Qualifiers for GNAT MAKE.
* /NOCURRENT_DIRECTORY (GNAT COMPILE):   Qualifiers for GNAT COMPILE.
* /NOCURRENT_DIRECTORY (GNAT MAKE):      Qualifiers for GNAT MAKE.
* /NOLOAD (GNAT COMPILE):                Using GNAT COMPILE for Semantic Checking.
* /NOMAIN (GNAT BIND):                   Binding with Non-Ada Main Programs.
* /NOMAIN (GNAT MAKE):                   Qualifiers for GNAT MAKE.
* /NOOUTPUT (GNAT BIND):                 Output Control.
* /NOSTD_INCLUDES (GNAT MAKE):           Qualifiers for GNAT MAKE.
* /NOSTD_LIBRARIES (GNAT MAKE):          Qualifiers for GNAT MAKE.
* /NOTIME_STAMP_CHECK (GNAT BIND):       Binder Error Message Control.
* /OBJECT_LIST (GNAT BIND):              Output Control.
* /OBJECT_SEARCH (GNAT MAKE):            Qualifiers for GNAT MAKE.
* /OPTIMIZE (GNAT COMPILE):              Optimization Levels.
* /ORDER_OF_ELABORATION (GNAT BIND):     Output Control.
* /OUTPUT (GNAT BIND):                   Output Control.
* /OUTPUT=OBJECTS (GNAT LIST):           Qualifiers for GNAT LIST.
* /OUTPUT=OPTIONS (GNAT LIST):           Qualifiers for GNAT LIST.
* /OUTPUT=SOURCES (GNAT LIST):           Qualifiers for GNAT LIST.
* /OUTPUT=UNITS (GNAT LIST):             Qualifiers for GNAT LIST.
* /OUTPUT=VERBOSE (GNAT LIST):           Qualifiers for GNAT LIST.
* /OVERWRITE (GNAT CHOP):                Qualifiers for GNAT CHOP.
* /PESSIMISTIC_ELABORATION (GNAT BIND):  Elaboration Control.
* /PRESERVE (GNAT CHOP):                 Qualifiers for GNAT CHOP.
* /PROCESSES (GNAT MAKE):                Qualifiers for GNAT MAKE.
* /QUIET (GNAT CHOP):                    Qualifiers for GNAT CHOP.
* /QUIET (GNAT MAKE):                    Qualifiers for GNAT MAKE.
* /READ_SOURCES=ALL (GNAT BIND):         Consistency-Checking Modes.
* /READ_SOURCES=NONE (GNAT BIND):        Consistency-Checking Modes.
* /REASONS (GNAT MAKE):                  Qualifiers for GNAT MAKE.
* /REFERENCE (GNAT CHOP):                Qualifiers for GNAT CHOP.
* /REPORT_ERRORS=BRIEF (GNAT BIND):      Binder Error Message Control.
* /REPORT_ERRORS=FULL (GNAT COMPILE):    Output and Error Message Control.
* /REPORT_ERRORS=VERBOSE (GNAT BIND):    Binder Error Message Control.
* /REPORT_ERRORS=VERBOSE (GNAT COMPILE): Output and Error Message Control.
* /REPRESENTATION_INFO (GNAT COMPILE):   Debugging Control.
* /RESTRICTION_LIST (GNAT BIND):         Output Control.
* /RUNTIME_SYSTEM (GNAT BIND):           Summary of Binder Qualifiers.
* /RUNTIME_SYSTEM (GNAT COMPILE):        Qualifiers for GNAT COMPILE.
* /RUNTIME_SYSTEM (GNAT FIND):           GNAT FIND Qualifiers.
* /RUNTIME_SYSTEM (GNAT LIST):           Qualifiers for GNAT LIST.
* /RUNTIME_SYSTEM (GNAT MAKE):           Qualifiers for GNAT MAKE.
* /RUNTIME_SYSTEM (GNAT XREF):           GNAT XREF Qualifiers.
* /SEARCH (GNAT COMPILE):                Qualifiers for GNAT COMPILE.
* /SEARCH (GNAT MAKE):                   Qualifiers for GNAT MAKE.
* /SET=directory (GNAT LIBRARY):         Qualifiers for GNAT LIBRARY.
* /SKIP_MISSING (GNAT MAKE):             Qualifiers for GNAT MAKE.
* /SOURCE_SEARCH (GNAT MAKE):            Qualifiers for GNAT MAKE.
* /SWITCH_CHECK (GNAT MAKE):             Qualifiers for GNAT MAKE.
* /SYNTAX_ONLY (GNAT COMPILE):           Using GNAT COMPILE for Syntax Checking.
* /TRACE_UNITS qualifier:                GNAT Abnormal Termination or Failure to Terminate.
* /TREE_OUTPUT (GNAT COMPILE):           Auxiliary Output Control.
* /TRY_SEMANTICS (GNAT COMPILE):         Output and Error Message Control.
* /UNIQUE (GNAT MAKE):                   Qualifiers for GNAT MAKE.
* /UNIQUE_ERROR_TAG (GNAT COMPILE):      Output and Error Message Control.
* /UNITS_LIST (GNAT COMPILE):            Auxiliary Output Control.
* /VERBOSE (GNAT CHOP):                  Qualifiers for GNAT CHOP.
* /VERBOSE (GNAT COMPILE):               Qualifiers for GNAT COMPILE.
* /VERBOSE (GNAT LINK):                  Qualifiers for GNAT LINK.
* /WARNINGS=BIASED_ROUNDING (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=BRIEF (GNAT COMPILE):        Output and Error Message Control.
* /WARNINGS=CONDITIONALS (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=ELABORATION (GNAT COMPILE):  Output and Error Message Control.
* /WARNINGS=ERROR (GNAT BIND):           Binder Error Message Control.
* /WARNINGS=ERROR (GNAT COMPILE):        Output and Error Message Control.
* /WARNINGS=HIDING (GNAT COMPILE):       Output and Error Message Control.
* /WARNINGS=IMPLEMENTATION (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=IMPLICIT_DEREFERENCE (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOBIASED_ROUNDING (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOCONDITIONALS (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOELABORATION (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOHIDING (GNAT COMPILE):     Output and Error Message Control.
* /WARNINGS=NOIMPLEMENTATION (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOIMPLICIT_DEREFERENCE (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOOPTIONAL (GNAT COMPILE):   Output and Error Message Control.
* /WARNINGS=NOOVERLAYS (GNAT COMPILE):   Output and Error Message Control.
* /WARNINGS=NOREDUNDANT (GNAT COMPILE):  Output and Error Message Control.
* /WARNINGS=NOUNREFERENCED_FORMALS (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=NOUNUSED (GNAT COMPILE):     Output and Error Message Control.
* /WARNINGS=OPTIONAL (GNAT COMPILE):     Output and Error Message Control.
* /WARNINGS=OVERLAYS (GNAT COMPILE):     Output and Error Message Control.
* /WARNINGS=REDUNDANT (GNAT COMPILE):    Output and Error Message Control.
* /WARNINGS=SUPPRESS (GNAT BIND):        Binder Error Message Control.
* /WARNINGS=SUPPRESS (GNAT COMPILE):     Output and Error Message Control.
* /WARNINGS=UNREFERENCED_FORMALS (GNAT COMPILE): Output and Error Message Control.
* /WARNINGS=UNUSED (GNAT COMPILE):       Output and Error Message Control.
* /WIDE_CHARACTER_ENCODING (GNAT COMPILE): Character Set Control.
* /XDEBUG (GNAT COMPILE):                Debugging Control.
* /XREF=SUPPRESS (GNAT COMPILE):         Debugging Control.
* /ZERO_MAIN (GNAT BIND):                Binding Programs with No Main Subprogram.
* __gnat_finalize:                       Running GNAT BIND.
* __gnat_initialize:                     Running GNAT BIND.
* __gnat_set_globals:                    Running GNAT BIND.
* _main:                                 The External Symbol Naming Scheme of GNAT.
* Access before elaboration:             Run-Time Checks.
* Access-to-subprogram:                  Elaboration for Access-to-Subprogram Values.
* ACVC, Ada 83 tests:                    Compiling Ada 83 Programs.
* Ada <1>:                               Search Paths for GNAT BIND.
* Ada:                                   Naming Conventions for GNAT Source Files.
* Ada 83 compatibility:                  Compiling Ada 83 Programs.
* Ada 95 Language Reference Manual:      What You Should Know before Reading This Guide.
* Ada expressions:                       Using Ada Expressions.
* Ada Library Information files:         The Ada Library Information Files.
* Ada.Characters.Latin_1:                Latin-1.
* ADA_INCLUDE_PATH:                      Search Paths and the Run-Time Library (RTL).
* ADA_OBJECTS_PATH:                      Search Paths for GNAT BIND.
* adafinal <1>:                          Binding with Non-Ada Main Programs.
* adafinal:                              Running GNAT BIND.
* adainit <1>:                           Running GNAT BIND.
* adainit:                               Binding with Non-Ada Main Programs.
* Address Clauses, warnings:             Output and Error Message Control.
* ali files:                             The Ada Library Information Files.
* Annex A:                               Naming Conventions for GNAT Source Files.
* Annex B:                               Naming Conventions for GNAT Source Files.
* Arbitrary File Naming Conventions:     Handling Arbitrary File Naming Conventions Using gnatname.
* Asm:                                   Calling Conventions.
* Assert:                                Debugging and Assertion Control.
* Assertions:                            Debugging and Assertion Control.
* Biased rounding:                       Output and Error Message Control.
* Binder consistency checks:             Binder Error Message Control.
* Binder output file:                    Interfacing to C.
* Binder, multiple input files:          Binding with Non-Ada Main Programs.
* Breakpoints and tasks:                 Ada Tasks.
* C:                                     Calling Conventions.
* C++:                                   Calling Conventions.
* Calling Conventions:                   Calling Conventions.
* Check, elaboration:                    Run-Time Checks.
* Check, overflow:                       Run-Time Checks.
* Check_CPU procedure:                   Check_CPU Procedure.
* Checks, access before elaboration:     Run-Time Checks.
* Checks, division by zero:              Run-Time Checks.
* Checks, elaboration:                   Checking the Elaboration Order in Ada 95.
* Checks, overflow:                      Controlling Run-Time Checks.
* Checks, suppressing:                   Run-Time Checks.
* COBOL:                                 Calling Conventions.
* code page 437:                         Other 8-Bit Codes.
* code page 850:                         Other 8-Bit Codes.
* Command line length:                   Qualifiers for GNAT LINK.
* Compatibility:                         Compatibility with DEC Ada.
* Compilation model:                     The GNAT Compilation Model.
* Conditionals, constant:                Output and Error Message Control.
* Configuration pragmas:                 Configuration Pragmas.
* Consistency checks, in binder:         Binder Error Message Control.
* Convention Ada:                        Calling Conventions.
* Convention Asm:                        Calling Conventions.
* Convention Assembler:                  Calling Conventions.
* Convention C:                          Calling Conventions.
* Convention C++:                        Calling Conventions.
* Convention COBOL:                      Calling Conventions.
* Convention Default:                    Calling Conventions.
* Convention DLL:                        Calling Conventions.
* Convention External:                   Calling Conventions.
* Convention Fortran:                    Calling Conventions.
* Convention Stdcall:                    Calling Conventions.
* Convention Stubbed:                    Calling Conventions.
* Convention Win32:                      Calling Conventions.
* Conventions:                           Conventions.
* CR:                                    Source Representation.
* Cyrillic:                              Other 8-Bit Codes.
* Debug:                                 Debugging and Assertion Control.
* Debug Pool:                            Finding Memory Problems with GNAT Debug Pool.
* Debugger:                              Running and Debugging Ada Programs.
* Debugging:                             Running and Debugging Ada Programs.
* Debugging Generic Units:               Debugging Generic Units.
* Debugging information, including:      Qualifiers for GNAT LINK.
* Debugging options:                     Debugging Control.
* Default:                               Calling Conventions.
* Dependencies, producing list:          Qualifiers for GNAT MAKE.
* Dependency rules:                      The GNAT Make Program GNAT MAKE.
* Dereferencing, implicit:               Output and Error Message Control.
* Division by zero:                      Run-Time Checks.
* DLL:                                   Calling Conventions.
* Elaborate:                             Controlling the Elaboration Order in Ada 95.
* Elaborate_All:                         Controlling the Elaboration Order in Ada 95.
* Elaborate_Body:                        Controlling the Elaboration Order in Ada 95.
* Elaboration checks <1>:                Run-Time Checks.
* Elaboration checks:                    Checking the Elaboration Order in Ada 95.
* Elaboration control <1>:               Elaboration Order Handling in GNAT.
* Elaboration control:                   Summary of Procedures for Elaboration Control.
* Elaboration of library tasks:          Elaboration Issues for Library Tasks.
* Elaboration order control:             Comparison between GNAT and C/C++ Compilation Models.
* Elaboration, warnings:                 Output and Error Message Control.
* Eliminate:                             Eliminate Pragma.
* EMACS:                                 Editing with EMACS.
* End of source file:                    Source Representation.
* Error messages, suppressing:           Output and Error Message Control.
* EUC Coding:                            Wide Character Encodings.
* Exceptions:                            Ada Exceptions.
* Export:                                The External Symbol Naming Scheme of GNAT.
* External:                              Calling Conventions.
* FDL, GNU Free Documentation License:   GNU Free Documentation License.
* FF:                                    Source Representation.
* File names <1>:                        Alternative File Naming Schemes.
* File names:                            Using Other File Names.
* File naming schemes, alternative:      Alternative File Naming Schemes.
* Floating-Point types:                  Floating-Point Types and Representations.
* Foreign Languages:                     Calling Conventions.
* Formals, unreferenced:                 Output and Error Message Control.
* Fortran:                               Calling Conventions.
* GDB:                                   Running and Debugging Ada Programs.
* Generic formal parameters:             Compiling Ada 83 Programs.
* Generics <1>:                          Generating Object Files.
* Generics:                              Debugging Generic Units.
* GNAT <1>:                              Search Paths for GNAT BIND.
* GNAT:                                  Naming Conventions for GNAT Source Files.
* GNAT Abnormal Termination or Failure to Terminate: GNAT Abnormal Termination or Failure to Terminate.
* GNAT BIND:                             Binding Using GNAT BIND.
* GNAT CHOP:                             Renaming Files Using GNAT CHOP.
* GNAT compilation model:                The GNAT Compilation Model.
* GNAT ELIM:                             Reducing the Size of Ada Executables with GNAT ELIM.
* GNAT FIND:                             The Cross-Referencing Tools GNAT XREF and GNAT FIND.
* GNAT KRUNCH:                           File Name Krunching Using GNAT KRUNCH.
* GNAT LIBRARY:                          The GNAT Run-Time Library Builder GNAT LIBRARY.
* GNAT library:                          Comparison between GNAT and Conventional Ada Library Models.
* GNAT LINK:                             Linking Using GNAT LINK.
* GNAT LIST:                             The GNAT Library Browser GNAT LIST.
* GNAT MAKE:                             The GNAT Make Program GNAT MAKE.
* GNAT PREPROCESS:                       Preprocessing Using GNAT PREPROCESS.
* GNAT STUB:                             Creating Sample Bodies Using GNAT STUB.
* GNAT XREF:                             The Cross-Referencing Tools GNAT XREF and GNAT FIND.
* GNAT.ADC <1>:                          The Configuration Pragmas Files.
* GNAT.ADC:                              Using Other File Names.
* GNAT1:                                 Compiling Programs.
* gnat_argc:                             Command-Line Access.
* gnat_argv:                             Command-Line Access.
* GNAT_STACK_LIMIT:                      Stack Overflow Checking.
* Hiding of Declarations:                Output and Error Message Control.
* HT:                                    Source Representation.
* Implicit dereferencing:                Output and Error Message Control.
* Inline <1>:                            Source Dependencies.
* Inline:                                Inlining of Subprograms.
* Inlining:                              Comparison between GNAT and Conventional Ada Library Models.
* Inlining, warnings:                    Output and Error Message Control.
* Intel_CPU package body:                Intel_CPU Package Body.
* Intel_CPU package specification:       Intel_CPU Package Specification.
* Interfaces <1>:                        Naming Conventions for GNAT Source Files.
* Interfaces:                            Search Paths for GNAT BIND.
* Interfacing to Ada:                    Calling Conventions.
* Interfacing to Assembly:               Calling Conventions.
* Interfacing to C:                      Calling Conventions.
* Interfacing to C++:                    Calling Conventions.
* Interfacing to COBOL:                  Calling Conventions.
* Interfacing to Fortran:                Calling Conventions.
* Internal trees, writing to file:       Auxiliary Output Control.
* Latin-1 <1>:                           Source Representation.
* Latin-1:                               Latin-1.
* Latin-2:                               Other 8-Bit Codes.
* Latin-3:                               Other 8-Bit Codes.
* Latin-4:                               Other 8-Bit Codes.
* Latin-5:                               Other 8-Bit Codes.
* LF:                                    Source Representation.
* Library browser:                       The GNAT Library Browser GNAT LIST.
* Library builder:                       The GNAT Run-Time Library Builder GNAT LIBRARY.
* Library tasks, elaboration issues:     Elaboration Issues for Library Tasks.
* Linker libraries:                      Qualifiers for GNAT MAKE.
* LSE:                                   LSE.
* Machine_Overflows:                     Run-Time Checks.
* Main Program:                          Running GNAT BIND.
* Mixed Language Programming:            Mixed Language Programming.
* Multiple units, syntax checking:       Using GNAT COMPILE for Syntax Checking.
* No code generated:                     Compiling Programs.
* No_Entry_Calls_In_Elaboration_Code:    Elaboration Issues for Library Tasks.
* Object file list:                      Running GNAT BIND.
* Order of elaboration:                  Elaboration Order Handling in GNAT.
* Other Ada compilers:                   Calling Conventions.
* Overflow checks <1>:                   Controlling Run-Time Checks.
* Overflow checks:                       Run-Time Checks.
* Parallel make:                         Qualifiers for GNAT MAKE.
* PCA:                                   Profiling.
* Performance:                           Performance Considerations.
* pragma Elaborate:                      Controlling the Elaboration Order in Ada 95.
* pragma Elaborate_All:                  Controlling the Elaboration Order in Ada 95.
* pragma Elaborate_Body:                 Controlling the Elaboration Order in Ada 95.
* pragma Inline:                         Inlining of Subprograms.
* pragma Preelaborate:                   Controlling the Elaboration Order in Ada 95.
* pragma Pure:                           Controlling the Elaboration Order in Ada 95.
* pragma Suppress:                       Controlling Run-Time Checks.
* pragma Unsuppress:                     Controlling Run-Time Checks.
* Pragmas, configuration:                Configuration Pragmas.
* Preelaborate:                          Controlling the Elaboration Order in Ada 95.
* Pure:                                  Controlling the Elaboration Order in Ada 95.
* Recompilation, by GNAT MAKE:           Notes on the Command Line.
* Rounding, biased:                      Output and Error Message Control.
* RTL:                                   Qualifiers for GNAT COMPILE.
* SDP_Table_Build:                       Running GNAT BIND.
* Search paths, for GNAT MAKE:           Qualifiers for GNAT MAKE.
* Shift JIS Coding:                      Wide Character Encodings.
* Source file, end:                      Source Representation.
* Source files, suppressing search:      Qualifiers for GNAT MAKE.
* Source files, use by binder:           Running GNAT BIND.
* Source_File_Name pragma <1>:           Alternative File Naming Schemes.
* Source_File_Name pragma:               Using Other File Names.
* Source_Reference:                      Qualifiers for GNAT CHOP.
* Stack Overflow Checking:               Stack Overflow Checking.
* stack traceback:                       Stack Traceback.
* stack unwinding:                       Stack Traceback.
* Starlet:                               Bindings.
* Stdcall:                               Calling Conventions.
* storage, pool, memory corruption:      Finding Memory Problems with GNAT Debug Pool.
* Stubbed:                               Calling Conventions.
* Style checking:                        Style Checking.
* SUB:                                   Source Representation.
* Subunits:                              Generating Object Files.
* Suppress <1>:                          Run-Time Checks.
* Suppress:                              Controlling Run-Time Checks.
* Suppressing checks:                    Run-Time Checks.
* SYS$ERROR:                             Output and Error Message Control.
* SYS$OUTPUT:                            Output and Error Message Control.
* System <1>:                            Naming Conventions for GNAT Source Files.
* System:                                Search Paths for GNAT BIND.
* System.IO:                             Search Paths and the Run-Time Library (RTL).
* Task switching:                        Ada Tasks.
* Tasks:                                 Ada Tasks.
* Time Slicing:                          Run-Time Control.
* Time stamp checks, in binder:          Binder Error Message Control.
* traceback:                             Stack Traceback.
* traceback, non-symbolic:               Non-Symbolic Traceback.
* traceback, symbolic:                   Symbolic Traceback.
* Tree file:                             Tree Files.
* Typographical conventions:             Conventions.
* Unsuppress <1>:                        Controlling Run-Time Checks.
* Unsuppress:                            Run-Time Checks.
* Upper-Half Coding:                     Wide Character Encodings.
* Validity Checking:                     Validity Checking.
* Version skew (avoided by GNAT MAKE):   Running a Simple Ada Program.
* Volatile parameter:                    The Volatile Parameter.
* VT:                                    Source Representation.
* Warning messages:                      Output and Error Message Control.
* Warnings:                              Binder Error Message Control.
* Warnings, treat as error:              Output and Error Message Control.
* Win32:                                 Calling Conventions.
* Writing internal trees:                Auxiliary Output Control.
* Zero Cost Exceptions:                  Running GNAT BIND.



Tag Table:
Node: Top609
Node: About This Guide10020
Node: What This Guide Contains10554
Node: What You Should Know before Reading This Guide14536
Node: Related Information14944
Node: Conventions15780
Node: Getting Started with GNAT16674
Node: Running GNAT17105
Node: Running a Simple Ada Program17708
Node: Running a Program with Multiple Units20869
Node: Using the GNAT MAKE Utility23129
Node: Editing with EMACS25543
Node: The GNAT Compilation Model26707
Node: Source Representation28046
Node: Foreign Language Representation29832
Node: Latin-130318
Node: Other 8-Bit Codes31184
Node: Wide Character Encodings33277
Node: File Naming Rules37084
Node: Using Other File Names39386
Node: Alternative File Naming Schemes41315
Node: Generating Object Files46547
Node: Source Dependencies49267
Node: The Ada Library Information Files52821
Node: Binding an Ada Program54972
Node: Mixed Language Programming56820
Node: Interfacing to C57097
Node: Calling Conventions59706
Node: Building Mixed Ada & C++ Programs65630
Node: Interfacing to C++66711
Node: Linking a Mixed C++ & Ada Program67751
Node: A Simple Example70837
Node: Adapting the Run Time to a New C++ Compiler73756
Node: Comparison between GNAT and C/C++ Compilation Models74772
Node: Comparison between GNAT and Conventional Ada Library Models76502
Node: Compiling Using GNAT COMPILE79153
Node: Compiling Programs79698
Node: Qualifiers for GNAT COMPILE82590
Node: Output and Error Message Control91044
Node: Debugging and Assertion Control109947
Node: Validity Checking111959
Node: Style Checking118236
Node: Run-Time Checks129944
Node: Stack Overflow Checking134108
Node: Run-Time Control136230
Node: Using GNAT COMPILE for Syntax Checking137158
Node: Using GNAT COMPILE for Semantic Checking138553
Node: Compiling Ada 83 Programs140052
Node: Character Set Control141503
Node: File Naming Control144587
Node: Subprogram Inlining Control145122
Node: Auxiliary Output Control146425
Node: Debugging Control147169
Node: Units to Sources Mapping Files154497
Node: Search Paths and the Run-Time Library (RTL)155908
Node: Order of Compilation Issues159498
Node: Examples161208
Node: Binding Using GNAT BIND161826
Node: Running GNAT BIND163710
Node: Generating the Binder Program in C194514
Node: Consistency-Checking Modes211974
Node: Binder Error Message Control213670
Node: Elaboration Control215830
Node: Output Control217102
Node: Binding with Non-Ada Main Programs219697
Node: Binding Programs with No Main Subprogram222864
Node: Summary of Binder Qualifiers223704
Node: Command-Line Access227342
Node: Search Paths for GNAT BIND228367
Node: Examples of GNAT BIND Usage231597
Node: Linking Using GNAT LINK233217
Node: Running GNAT LINK233978
Node: Qualifiers for GNAT LINK236240
Node: Setting Stack Size from GNAT LINK239067
Node: Setting Heap Size from GNAT LINK239932
Node: The GNAT Make Program GNAT MAKE240755
Node: Running GNAT MAKE242222
Node: Qualifiers for GNAT MAKE243944
Node: Mode Qualifiers for GNAT MAKE256201
Node: Notes on the Command Line257489
Node: How GNAT MAKE Works260508
Node: Examples of GNAT MAKE Usage262691
Node: Renaming Files Using GNAT CHOP263902
Node: Handling Files with Multiple Units264502
Node: Operating GNAT CHOP in Compilation Mode265829
Node: Command Line for GNAT CHOP269167
Node: Qualifiers for GNAT CHOP270647
Node: Examples of GNAT CHOP Usage273964
Node: Configuration Pragmas275366
Node: Handling of Configuration Pragmas276919
Node: The Configuration Pragmas Files277780
Node: Handling Arbitrary File Naming Conventions Using gnatname279494
Node: Arbitrary File Naming Conventions279904
Node: Running gnatname281165
Node: Qualifiers for gnatname282630
Node: Examples of gnatname Usage285837
Node: GNAT Project Manager286644
Node: Introduction287308
Node: Project Files288418
Node: Examples of Project Files291642
Node: Common Sources with Different Qualifiers and Different Output Directories292118
Node: Source Files295331
Node: Specifying the Object Directory295809
Node: Specifying the Exec Directory296743
Node: Project File Packages297513
Node: Specifying Qualifier Settings298528
Node: Main Subprograms300527
Node: Source File Naming Conventions301198
Node: Source Language(s)301700
Node: Using External Variables302143
Node: Importing Other Projects305048
Node: Extending a Project308160
Node: Project File Syntax310631
Node: Basic Syntax311993
Node: Packages313001
Node: Expressions314158
Node: String Types316056
Node: Variables317359
Node: Attributes320393
Node: Associative Array Attributes325830
Node: case Constructions326697
Node: Objects and Sources in Project Files328507
Node: Object Directory329087
Node: Exec Directory330078
Node: Source Directories330907
Node: Source File Names332274
Node: Importing Projects334611
Node: Project Extension337390
Node: External References in Project Files339071
Node: Packages in Project Files340817
Node: Variables from Imported Projects343235
Node: Naming Schemes344933
Node: Library Projects348906
Node: Qualifiers Related to Project Files351804
Node: Tools Supporting Project Files353535
Node: GNAT MAKE and Project Files353842
Node: Qualifiers and Project Files354304
Node: Project Files and Main Subprograms360379
Node: The GNAT Driver and Project Files362327
Node: An Extended Example366067
Node: Project File Complete Syntax369081
Node: Elaboration Order Handling in GNAT371873
Node: Elaboration Code in Ada 95372895
Node: Checking the Elaboration Order in Ada 95377541
Node: Controlling the Elaboration Order in Ada 95381542
Node: Controlling Elaboration in GNAT - Internal Calls389859
Node: Controlling Elaboration in GNAT - External Calls395580
Node: Default Behavior in GNAT - Ensuring Safety399314
Node: Elaboration Issues for Library Tasks403457
Node: Mixing Elaboration Models416694
Node: What to Do If the Default Elaboration Behavior Fails419215
Node: Elaboration for Access-to-Subprogram Values429641
Node: Summary of Procedures for Elaboration Control431465
Node: Other Elaboration Order Considerations432663
Node: The Cross-Referencing Tools GNAT XREF and GNAT FIND437938
Node: GNAT XREF Qualifiers439652
Node: GNAT FIND Qualifiers443038
Node: Project Files for GNAT XREF and GNAT FIND448949
Node: Regular Expressions in GNAT FIND and GNAT XREF452195
Node: Examples of GNAT XREF Usage454987
Node: Examples of GNAT FIND Usage458193
Node: File Name Krunching Using GNAT KRUNCH460481
Node: About GNAT KRUNCH461139
Node: Using GNAT KRUNCH462516
Node: Krunching Method463415
Node: Examples of GNAT KRUNCH Usage466686
Node: Preprocessing Using GNAT PREPROCESS467030
Node: Using GNAT PREPROCESS467612
Node: Qualifiers for GNAT PREPROCESS468522
Node: Form of Definitions File470746
Node: Form of Input Text for GNAT PREPROCESS471508
Node: The GNAT Run-Time Library Builder GNAT LIBRARY475164
Node: Running GNAT LIBRARY475644
Node: Qualifiers for GNAT LIBRARY475947
Node: Examples of GNAT LIBRARY Usage476741
Node: The GNAT Library Browser GNAT LIST477184
Node: Running GNAT LIST477780
Node: Qualifiers for GNAT LIST480334
Node: Examples of GNAT LIST Usage482424
Node: Finding Memory Problems with GNAT Debug Pool483659
Node: Creating Sample Bodies Using GNAT STUB488362
Node: Running GNAT STUB489171
Node: Qualifiers for GNAT STUB489940
Node: Reducing the Size of Ada Executables with GNAT ELIM492254
Node: About GNAT ELIM492795
Node: Eliminate Pragma493890
Node: Tree Files494902
Node: Preparing Tree and Bind Files for GNAT ELIM495821
Node: Running GNAT ELIM497920
Node: Correcting the List of Eliminate Pragmas499930
Node: Making Your Executables Smaller500714
Node: Summary of the GNAT ELIM Usage Cycle501566
Node: Other Utility Programs502438
Node: Using Other Utility Programs with GNAT502986
Node: The GNAT STANDARD Utility Program503441
Node: The External Symbol Naming Scheme of GNAT504763
Node: Ada Mode for Glide506765
Node: Converting Ada Files to html with gnathtml508716
Node: Installing gnathtml512325
Node: LSE513003
Node: Profiling513334
Node: Running and Debugging Ada Programs513752
Node: The GNAT Debugger GDB515150
Node: Running GDB518324
Node: Introduction to GDB Commands519261
Node: Using Ada Expressions524166
Node: Calling User-Defined Subprograms525360
Node: Using the Next Command in a Function527780
Node: Ada Exceptions528945
Node: Ada Tasks529899
Node: Debugging Generic Units531968
Node: GNAT Abnormal Termination or Failure to Terminate533371
Node: Naming Conventions for GNAT Source Files536064
Node: Getting Internal Debugging Information538664
Node: Stack Traceback539873
Node: Non-Symbolic Traceback540910
Node: Tracebacks From an Unhandled Exception541371
Node: Tracebacks From Exception Occurrences (non-symbolic)545336
Node: Tracebacks From Anywhere in a Program (non-symbolic)546619
Node: Symbolic Traceback548464
Node: Tracebacks From Exception Occurrences (symbolic)549187
Node: Tracebacks From Anywhere in a Program (symbolic)550645
Node: Compatibility with DEC Ada551837
Node: Ada 95 Compatibility553386
Node: Differences in the Definition of Package System554455
Node: Language-Related Features556565
Node: Integer Types and Representations557198
Node: Floating-Point Types and Representations558142
Node: Pragmas Float_Representation and Long_Float559447
Node: Fixed-Point Types and Representations562786
Node: Record and Array Component Alignment563422
Node: Address Clauses564096
Node: Other Representation Clauses566128
Node: The Package STANDARD566528
Node: The Package SYSTEM567418
Node: Tasking and Task-Related Features571450
Node: Implementation of Tasks in DEC Ada for OpenVMS Alpha Systems572014
Node: Assigning Task IDs573500
Node: Task IDs and Delays574190
Node: Task-Related Pragmas574763
Node: Scheduling and Task Priority575860
Node: The Task Stack577557
Node: External Interrupts578471
Node: Pragmas and Pragma-Related Features578798
Node: Restrictions on the Pragma INLINE581090
Node: Restrictions on the Pragma INTERFACE582247
Node: Restrictions on the Pragma SYSTEM_NAME583249
Node: Library of Predefined Units583650
Node: Changes to DECLIB585481
Node: Bindings586248
Node: Shared Libraries and Options Files588057
Node: Interfaces to C588776
Node: Main Program Definition589632
Node: Implementation-Defined Attributes590937
Node: Compiler and Run-Time Interfacing591243
Node: Program Compilation and Library Management592589
Node: Input-Output603054
Node: Implementation Limits605671
Node: Tools607738
Node: Inline Assembler607854
Node: Basic Assembler Syntax609561
Node: A Simple Example of Inline Assembler611441
Node: Output Variables in Inline Assembler614652
Node: Input Variables in Inline Assembler622041
Node: Inlining Inline Assembler Code624559
Node: Other Asm Functionality626517
Node: The Clobber Parameter626952
Node: The Volatile Parameter628951
Node: A Complete Example630143
Node: Check_CPU Procedure631117
Node: Intel_CPU Package Specification646164
Node: Intel_CPU Package Body655592
Node: Performance Considerations664750
Node: Controlling Run-Time Checks665806
Node: Optimization Levels667836
Node: Debugging Optimized Code669736
Node: Inlining of Subprograms673472
Node: Coverage Analysis677297
Node: GNU Free Documentation License677643
Node: Index700072

End Tag Table
