2 dnl Copyright (C) 2002-2004, 2009-2020 Free Software Foundation, Inc.
3 dnl This file is free software; the Free Software Foundation
4 dnl gives unlimited permission to copy and/or distribute it,
5 dnl with or without modifications, as long as this notice is preserved.
7 AC_DEFUN_ONCE([gl_FUNC_MEMCHR],
9 AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
11 dnl Check for prerequisites for memory fence checks.
13 AC_CHECK_HEADERS_ONCE([sys/mman.h])
14 AC_CHECK_FUNCS_ONCE([mprotect])
16 AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
17 m4_ifdef([gl_FUNC_MEMCHR_OBSOLETE], [
18 dnl These days, we assume memchr is present. But if support for old
19 dnl platforms is desired:
20 AC_CHECK_FUNCS_ONCE([memchr])
21 if test $ac_cv_func_memchr = no; then
25 if test $HAVE_MEMCHR = 1; then
26 # Detect platform-specific bugs in some versions of glibc:
27 # memchr should not dereference anything with length 0
28 # https://bugzilla.redhat.com/show_bug.cgi?id=499689
29 # memchr should not dereference overestimated length after a match
30 # https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
31 # https://sourceware.org/bugzilla/show_bug.cgi?id=10162
32 # memchr should cast the second argument to 'unsigned char'.
33 # This bug exists in Android 4.3.
34 # Assume that memchr works on platforms that lack mprotect.
35 AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
36 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
41 # include <sys/types.h>
42 # include <sys/mman.h>
50 #if HAVE_SYS_MMAN_H && HAVE_MPROTECT
51 # if HAVE_MAP_ANONYMOUS
52 const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
54 # else /* !HAVE_MAP_ANONYMOUS */
55 const int flags = MAP_FILE | MAP_PRIVATE;
56 int fd = open ("/dev/zero", O_RDONLY, 0666);
60 int pagesize = getpagesize ();
62 (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
64 if (two_pages != (char *)(-1)
65 && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
66 fence = two_pages + pagesize;
71 if (memchr (fence, 0, 0))
73 strcpy (fence - 9, "12345678");
74 if (memchr (fence - 9, 0, 79) != fence - 1)
76 if (memchr (fence - 1, 0, 3) != fence - 1)
79 /* Test against bug on Android 4.3. */
85 if (memchr (input, 0x789abc00 | 'b', 3) != input + 1)
90 [gl_cv_func_memchr_works=yes],
91 [gl_cv_func_memchr_works=no],
93 # Guess no on Android.
94 linux*-android*) gl_cv_func_memchr_works="guessing no" ;;
95 # Guess yes on native Windows.
96 mingw*) gl_cv_func_memchr_works="guessing yes" ;;
97 # If we don't know, obey --enable-cross-guesses.
98 *) gl_cv_func_memchr_works="$gl_cross_guess_normal" ;;
102 case "$gl_cv_func_memchr_works" in
104 *) REPLACE_MEMCHR=1 ;;
109 # Prerequisites of lib/memchr.c.
110 AC_DEFUN([gl_PREREQ_MEMCHR], [
111 AC_CHECK_HEADERS([bp-sym.h])