emacs/m4/malloc.m4

# malloc.m4
# serial 34
dnl Copyright (C) 2007, 2009-2024 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

# This is adapted with modifications from upstream Autoconf here:
# https://git.savannah.gnu.org/cgit/autoconf.git/tree/lib/autoconf/functions.m4?id=v2.70#n949
AC_DEFUN([_AC_FUNC_MALLOC_IF],
[
  AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
  AC_CACHE_CHECK([whether malloc (0) returns nonnull],
    [ac_cv_func_malloc_0_nonnull],
    [AC_RUN_IFELSE(
       [AC_LANG_PROGRAM(
          [[#include <stdlib.h>
          ]],
          [[void *p = malloc (0);
            void * volatile vp = p;
            int result = !vp;
            free (p);
            return result;]])
       ],
       [ac_cv_func_malloc_0_nonnull=yes],
       [ac_cv_func_malloc_0_nonnull=no],
       [case "$host_os" in
          # Guess yes on platforms where we know the result.
          *-gnu* | freebsd* | netbsd* | openbsd* | bitrig* \
          | gnu* | *-musl* | midipix* | midnightbsd* \
          | hpux* | solaris* | cygwin* | mingw* | windows* | msys* )
            ac_cv_func_malloc_0_nonnull="guessing yes" ;;
          # If we don't know, obey --enable-cross-guesses.
          *) ac_cv_func_malloc_0_nonnull="$gl_cross_guess_normal" ;;
        esac
       ])
    ])
  AS_CASE([$ac_cv_func_malloc_0_nonnull], [*yes], [$1], [$2])
])# _AC_FUNC_MALLOC_IF

# gl_FUNC_MALLOC_GNU
# ------------------
# Replace malloc if it is not compatible with GNU libc.
AC_DEFUN([gl_FUNC_MALLOC_GNU],
[
  AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
  AC_REQUIRE([gl_FUNC_MALLOC_POSIX])

  dnl Through the dependency on module extensions-aix, _LINUX_SOURCE_COMPAT
  dnl gets defined already before this macro gets invoked.  This helps
  dnl if !(__VEC__ || __AIXVEC), and doesn't hurt otherwise.

  REPLACE_MALLOC_FOR_MALLOC_GNU="$REPLACE_MALLOC_FOR_MALLOC_POSIX"
  if test $REPLACE_MALLOC_FOR_MALLOC_GNU = 0; then
    _AC_FUNC_MALLOC_IF([], [REPLACE_MALLOC_FOR_MALLOC_GNU=1])
  fi
])

# gl_FUNC_MALLOC_PTRDIFF
# ----------------------
# Test whether malloc (N) reliably fails when N exceeds PTRDIFF_MAX,
# and replace malloc otherwise.
AC_DEFUN([gl_FUNC_MALLOC_PTRDIFF],
[
  AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
  AC_REQUIRE([gl_CHECK_MALLOC_PTRDIFF])
  test "$gl_cv_malloc_ptrdiff" = yes || REPLACE_MALLOC_FOR_MALLOC_POSIX=1
])

# Test whether malloc, realloc, calloc refuse to create objects
# larger than what can be expressed in ptrdiff_t.
# Set gl_cv_func_malloc_gnu to yes or no accordingly.
AC_DEFUN([gl_CHECK_MALLOC_PTRDIFF],
[
  AC_CACHE_CHECK([whether malloc is ptrdiff_t safe],
    [gl_cv_malloc_ptrdiff],
    [AC_COMPILE_IFELSE(
       [AC_LANG_PROGRAM(
          [[#include <stdint.h>
          ]],
          [[/* 64-bit ptrdiff_t is so wide that no practical platform
               can exceed it.  */
            #define WIDE_PTRDIFF (PTRDIFF_MAX >> 31 >> 31 != 0)

            /* On rare machines where size_t fits in ptrdiff_t there
               is no problem.  */
            #define NARROW_SIZE (SIZE_MAX <= PTRDIFF_MAX)

            /* glibc 2.30 and later malloc refuses to exceed ptrdiff_t
               bounds even on 32-bit platforms.  We don't know which
               non-glibc systems are safe.  */
            #define KNOWN_SAFE (2 < __GLIBC__ + (30 <= __GLIBC_MINOR__))

            #if WIDE_PTRDIFF || NARROW_SIZE || KNOWN_SAFE
              return 0;
            #else
              #error "malloc might not be ptrdiff_t safe"
              syntax error
            #endif
          ]])],
       [gl_cv_malloc_ptrdiff=yes],
       [gl_cv_malloc_ptrdiff=no])
    ])
])

# gl_FUNC_MALLOC_POSIX
# --------------------
# Test whether 'malloc' is POSIX compliant (sets errno to ENOMEM when it
# fails, and doesn't mess up with ptrdiff_t overflow), and replace
# malloc if it is not.
AC_DEFUN([gl_FUNC_MALLOC_POSIX],
[
  AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
  AC_REQUIRE([gl_FUNC_MALLOC_PTRDIFF])
  AC_REQUIRE([gl_CHECK_MALLOC_POSIX])
  if test "$gl_cv_func_malloc_posix" = yes; then
    AC_DEFINE([HAVE_MALLOC_POSIX], [1],
      [Define if malloc, realloc, and calloc set errno on allocation failure.])
  else
    REPLACE_MALLOC_FOR_MALLOC_POSIX=1
  fi
])

# Test whether malloc, realloc, calloc set errno to ENOMEM on failure.
# Set gl_cv_func_malloc_posix to yes or no accordingly.
AC_DEFUN([gl_CHECK_MALLOC_POSIX],
[
  AC_REQUIRE([AC_CANONICAL_HOST])
  AC_CACHE_CHECK([whether malloc, realloc, calloc set errno on failure],
    [gl_cv_func_malloc_posix],
    [
      dnl It is too dangerous to try to allocate a large amount of memory:
      dnl some systems go to their knees when you do that. So assume that
      dnl all Unix implementations of the function set errno on failure,
      dnl except on those platforms where we have seen 'test-malloc-gnu',
      dnl 'test-realloc-gnu', 'test-calloc-gnu' fail.
      case "$host_os" in
        mingw* | windows*)
          gl_cv_func_malloc_posix=no ;;
        irix* | solaris*)
          dnl On IRIX 6.5, the three functions return NULL with errno unset
          dnl when the argument is larger than PTRDIFF_MAX.
          dnl On Solaris 11.3, the three functions return NULL with errno set
          dnl to EAGAIN, not ENOMEM, when the argument is larger than
          dnl PTRDIFF_MAX.
          dnl Here is a test program:
m4_divert_push([KILL])
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#define ptrdiff_t long
#ifndef PTRDIFF_MAX
# define PTRDIFF_MAX ((ptrdiff_t) ((1UL << (8 * sizeof (ptrdiff_t) - 1)) - 1))
#endif

int main ()
{
  void *p;

  fprintf (stderr, "PTRDIFF_MAX = %lu\n", (unsigned long) PTRDIFF_MAX);

  errno = 0;
  p = malloc ((unsigned long) PTRDIFF_MAX + 1);
  fprintf (stderr, "p=%p errno=%d\n", p, errno);

  errno = 0;
  p = calloc (PTRDIFF_MAX / 2 + 1, 2);
  fprintf (stderr, "p=%p errno=%d\n", p, errno);

  errno = 0;
  p = realloc (NULL, (unsigned long) PTRDIFF_MAX + 1);
  fprintf (stderr, "p=%p errno=%d\n", p, errno);

  return 0;
}
m4_divert_pop([KILL])
          gl_cv_func_malloc_posix=no ;;
        *)
          gl_cv_func_malloc_posix=yes ;;
      esac
    ])
])