/* Page fault handling library.
   Copyright (C) 1998-2021  Bruno Haible <bruno@clisp.org>

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#ifndef _SIGSEGV_H
#define _SIGSEGV_H

/* Get size_t.  */
#include <stddef.h>

/* Define the fault context structure.  */
#if defined __linux__ || defined __ANDROID__ \
    || (defined __FreeBSD__ && (defined __arm__ || defined __armhf__ || defined __arm64__)) \
    || defined __NetBSD__ \
    || defined _AIX || defined __sun \
    || defined __CYGWIN__
/* Linux, FreeBSD, NetBSD, AIX, Solaris, Cygwin */
# include <ucontext.h>
#elif (defined __APPLE__ && defined __MACH__)
/* macOS */
# include <sys/ucontext.h>
#elif defined __HAIKU__
/* Haiku */
# include <signal.h>
#endif

/* Correct the value of SIGSTKSZ on some systems.
   glibc >= 2.34: When _GNU_SOURCE is defined, SIGSTKSZ is no longer a
   compile-time constant.  But most programs need a simple constant.
   AIX 64-bit: original value 4096 is too small.
   HP-UX: original value 8192 is too small.
   Solaris 11/x86_64: original value 8192 is too small.  */
#include <signal.h>
#if __GLIBC__ >= 2
# undef SIGSTKSZ
# if defined __ia64__
#  define SIGSTKSZ 262144
# else
#  define SIGSTKSZ 65536
# endif
#endif
#if defined _AIX && defined _ARCH_PPC64
# undef SIGSTKSZ
# define SIGSTKSZ 8192
#endif
#if defined __hpux || (defined __sun && (defined __x86_64__ || defined __amd64__))
# undef SIGSTKSZ
# define SIGSTKSZ 16384
#endif

/* HAVE_SIGSEGV_RECOVERY
   is defined if the system supports catching SIGSEGV.  */
#if defined __linux__ || defined __ANDROID__ || defined __GNU__ \
    || defined __FreeBSD_kernel__ || (defined __FreeBSD__ && !(defined __sparc__ || defined __sparc64__)) || defined __DragonFly__ \
    || defined __NetBSD__ \
    || defined __OpenBSD__ \
    || (defined __APPLE__ && defined __MACH__) \
    || defined _AIX || defined __sgi || defined __sun \
    || defined __CYGWIN__ || defined __HAIKU__
/* Linux, Hurd, GNU/kFreeBSD, FreeBSD, NetBSD, OpenBSD, macOS, AIX, IRIX, Solaris, Cygwin, Haiku */
# define HAVE_SIGSEGV_RECOVERY 1
#endif

/* HAVE_STACK_OVERFLOW_RECOVERY
   is defined if stack overflow can be caught.  */
#if defined __linux__ || defined __ANDROID__ || defined __GNU__ \
    || defined __FreeBSD_kernel__ || (defined __FreeBSD__ && !(defined __sparc__ || defined __sparc64__)) || defined __DragonFly__ \
    || (defined __NetBSD__ && !(defined __sparc__ || defined __sparc64__)) \
    || defined __OpenBSD__ \
    || (defined __APPLE__ && defined __MACH__) \
    || defined _AIX || defined __sgi || defined __sun \
    || defined __CYGWIN__ || defined __HAIKU__
/* Linux, Hurd, GNU/kFreeBSD, FreeBSD, NetBSD, OpenBSD, macOS, AIX, IRIX, Solaris, Cygwin, Haiku */
# define HAVE_STACK_OVERFLOW_RECOVERY 1
#endif


#ifdef __cplusplus
extern "C" {
#endif

#define LIBSIGSEGV_VERSION 0x020D    /* version number: (major<<8) + minor */
extern int libsigsegv_version;       /* Likewise */

/* -------------------------------------------------------------------------- */

#if 1 /* really only HAVE_SIGSEGV_RECOVERY */

/*
 * The mask of bits that are set to zero in a fault address that gets passed
 * to a global SIGSEGV handler.
 * On some platforms, the precise fault address is not known, only the memory
 * page into which the fault address falls. This is apparently allowed by POSIX:
 * <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html>
 * says: "For some implementations, the value of si_addr may be inaccurate."
 * In this case, the returned fault address is rounded down to a multiple of
 * getpagesize() = sysconf(_SC_PAGESIZE).
 * On such platforms, we define SIGSEGV_FAULT_ADDRESS_ALIGNMENT to be an upper
 * bound for getpagesize() (and, like getpagesize(), also a power of 2).
 * On the platforms where the returned fault address is the precise one, we
 * define SIGSEGV_FAULT_ADDRESS_ALIGNMENT to 1.
 */
# if defined __NetBSD__ && (defined __sparc__ || defined __sparc64__)
  /* getpagesize () is 0x1000 or 0x2000, depending on hardware.  */
#  define SIGSEGV_FAULT_ADDRESS_ALIGNMENT 0x2000UL
# elif defined __linux__ && (defined __s390__ || defined __s390x__)
  /* getpagesize () is 0x1000.  */
#  define SIGSEGV_FAULT_ADDRESS_ALIGNMENT 0x1000UL
# else
#  define SIGSEGV_FAULT_ADDRESS_ALIGNMENT 1UL
# endif

/*
 * The type of a global SIGSEGV handler.
 * The fault address, with the bits (SIGSEGV_FAULT_ADDRESS_ALIGNMENT - 1)
 * cleared, is passed as argument.
 * The access type (read access or write access) is not passed; your handler
 * has to know itself how to distinguish these two cases.
 * The second argument is 0, meaning it could also be a stack overflow, or 1,
 * meaning the handler should seriously try to fix the fault.
 * The return value should be nonzero if the handler has done its job
 * and no other handler should be called, or 0 if the handler declines
 * responsibility for the given address.
 *
 * The handler is run at a moment when nothing about the global state of the
 * program is known. Therefore it cannot use facilities that manipulate global
 * variables or locks. In particular, it cannot use malloc(); use mmap()
 * instead. It cannot use fopen(); use open() instead. Etc. All global
 * variables that are accessed by the handler should be marked 'volatile'.
 */
typedef int (*sigsegv_handler_t) (void* fault_address, int serious);

/*
 * Installs a global SIGSEGV handler.
 * This should be called once only, and it ignores any previously installed
 * SIGSEGV handler.
 * Returns 0 on success, or -1 if the system doesn't support catching SIGSEGV.
 */
extern int sigsegv_install_handler (sigsegv_handler_t handler);

/*
 * Deinstalls the global SIGSEGV handler.
 * This goes back to the state where no SIGSEGV handler is installed.
 */
extern void sigsegv_deinstall_handler (void);

/*
 * Prepares leaving a SIGSEGV handler (through longjmp or similar means).
 * Control is transferred by calling CONTINUATION with CONT_ARG1, CONT_ARG2,
 * CONT_ARG3 as arguments.
 * CONTINUATION must not return.
 * The sigsegv_leave_handler function may return if called from a SIGSEGV
 * handler; its return value should be used as the handler's return value.
 * The sigsegv_leave_handler function does not return if called from a
 * stack overflow handler.
 */
extern int sigsegv_leave_handler (void (*continuation) (void*, void*, void*), void* cont_arg1, void* cont_arg2, void* cont_arg3);

#endif /* HAVE_SIGSEGV_RECOVERY */

#if 1 /* really only HAVE_STACK_OVERFLOW_RECOVERY */

/*
 * The type of a context passed to a stack overflow handler.
 * This type is system dependent; on some platforms it is an 'ucontext_t *',
 * on some platforms it is a 'struct sigcontext *', on others merely an
 * opaque 'void *'.
 */
# if defined __linux__ || defined __ANDROID__ \
     || (defined __FreeBSD__ && (defined __arm__ || defined __armhf__ || defined __arm64__)) \
     || defined __NetBSD__ \
     || (defined __APPLE__ && defined __MACH__) \
     || defined _AIX || defined __sun \
     || defined __CYGWIN__ || defined __HAIKU__
typedef ucontext_t *stackoverflow_context_t;
# elif defined __GNU__ \
       || defined __FreeBSD_kernel__ || (defined __FreeBSD__ && !(defined __sparc__ || defined __sparc64__)) \
       || defined __OpenBSD__ || defined __sgi
typedef struct sigcontext *stackoverflow_context_t;
# else
typedef void *stackoverflow_context_t;
# endif

/*
 * The type of a stack overflow handler.
 * Such a handler should perform a longjmp call in order to reduce the amount
 * of stack needed. It must not return.
 * The emergency argument is 0 when the stack could be repared, or 1 if the
 * application should better save its state and exit now.
 *
 * The handler is run at a moment when nothing about the global state of the
 * program is known. Therefore it cannot use facilities that manipulate global
 * variables or locks. In particular, it cannot use malloc(); use mmap()
 * instead. It cannot use fopen(); use open() instead. Etc. All global
 * variables that are accessed by the handler should be marked 'volatile'.
 */
typedef void (*stackoverflow_handler_t) (int emergency, stackoverflow_context_t scp);

/*
 * Installs a stack overflow handler.
 * The extra_stack argument is a pointer to a pre-allocated area used as a
 * stack for executing the handler. It typically comes from a static variable
 * or from heap-allocated memoty; placing it on the main stack may fail on
 * some operating systems.
 * Its size, passed in extra_stack_size, should be sufficiently large.  The
 * following code determines an appropriate size:
 *   #include <signal.h>
 *   #ifndef SIGSTKSZ         / * glibc defines SIGSTKSZ for this purpose * /
 *   # define SIGSTKSZ 16384  / * on most platforms, 16 KB are sufficient * /
 *   #endif
 * Returns 0 on success, or -1 if the system doesn't support catching stack
 * overflow.
 */
extern int stackoverflow_install_handler (stackoverflow_handler_t handler,
                                          void* extra_stack, size_t extra_stack_size);

/*
 * Deinstalls the stack overflow handler.
 */
extern void stackoverflow_deinstall_handler (void);

#endif /* HAVE_STACK_OVERFLOW_RECOVERY */

/* -------------------------------------------------------------------------- */

#ifdef __cplusplus
}
#endif

#endif /* _SIGSEGV_H */
