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# memchr.m4 serial 18
dnl Copyright (C) 2002-2004, 2009-2021 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.
AC_DEFUN_ONCE([gl_FUNC_MEMCHR],
[
AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
dnl Check for prerequisites for memory fence checks.
gl_FUNC_MMAP_ANON
AC_CHECK_HEADERS_ONCE([sys/mman.h])
AC_CHECK_FUNCS_ONCE([mprotect])
AC_REQUIRE([gl_STRING_H_DEFAULTS])
# Detect platform-specific bugs in some versions of glibc:
# memchr should not dereference anything with length 0
# https://bugzilla.redhat.com/show_bug.cgi?id=499689
# memchr should not dereference overestimated length after a match
# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
# https://sourceware.org/bugzilla/show_bug.cgi?id=10162
# memchr should cast the second argument to 'unsigned char'.
# This bug exists in Android 4.3.
# Assume that memchr works on platforms that lack mprotect.
AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
[AC_RUN_IFELSE([AC_LANG_PROGRAM([[
#include <string.h>
#if HAVE_SYS_MMAN_H
# include <fcntl.h>
# include <unistd.h>
# include <sys/types.h>
# include <sys/mman.h>
# ifndef MAP_FILE
# define MAP_FILE 0
# endif
#endif
]], [[
int result = 0;
char *fence = NULL;
#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
# if HAVE_MAP_ANONYMOUS
const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
const int fd = -1;
# else /* !HAVE_MAP_ANONYMOUS */
const int flags = MAP_FILE | MAP_PRIVATE;
int fd = open ("/dev/zero", O_RDONLY, 0666);
if (fd >= 0)
# endif
{
int pagesize = getpagesize ();
char *two_pages =
(char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
flags, fd, 0);
if (two_pages != (char *)(-1)
&& mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
fence = two_pages + pagesize;
}
#endif
if (fence)
{
/* Test against bugs on glibc systems. */
if (memchr (fence, 0, 0))
result |= 1;
strcpy (fence - 9, "12345678");
if (memchr (fence - 9, 0, 79) != fence - 1)
result |= 2;
if (memchr (fence - 1, 0, 3) != fence - 1)
result |= 4;
/* Test against bug on AIX 7.2. */
if (memchr (fence - 4, '6', 16) != fence - 4)
result |= 8;
}
/* Test against bug on Android 4.3. */
{
char input[3];
input[0] = 'a';
input[1] = 'b';
input[2] = 'c';
if (memchr (input, 0x789abc00 | 'b', 3) != input + 1)
result |= 16;
}
return result;
]])],
[gl_cv_func_memchr_works=yes],
[gl_cv_func_memchr_works=no],
[case "$host_os" in
# Guess no on Android.
linux*-android*) gl_cv_func_memchr_works="guessing no" ;;
# Guess yes on native Windows.
mingw*) gl_cv_func_memchr_works="guessing yes" ;;
# If we don't know, obey --enable-cross-guesses.
*) gl_cv_func_memchr_works="$gl_cross_guess_normal" ;;
esac
])
])
case "$gl_cv_func_memchr_works" in
*yes) ;;
*) REPLACE_MEMCHR=1 ;;
esac
])
# Prerequisites of lib/memchr.c.
AC_DEFUN([gl_PREREQ_MEMCHR], [
AC_CHECK_HEADERS([bp-sym.h])
])
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