2 dnl Copyright (C) 2002, 2003, 2004, 2009 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([gl_FUNC_MEMCHR],
9 dnl Check for prerequisites for memory fence checks.
11 AC_CHECK_HEADERS_ONCE([sys/mman.h])
12 AC_CHECK_FUNCS_ONCE([mprotect])
14 dnl These days, we assume memchr is present. But just in case...
15 AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
16 AC_REPLACE_FUNCS([memchr])
17 if test $ac_cv_func_memchr = no; then
22 if test $ac_cv_func_memchr = yes; then
23 # Detect platform-specific bugs in some versions of glibc:
24 # memchr should not dereference anything with length 0
25 # http://bugzilla.redhat.com/499689
26 # memchr should not dereference overestimated length after a match
27 # http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
28 # Assume that memchr works on platforms that lack mprotect.
29 AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
30 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
35 # include <sys/types.h>
36 # include <sys/mman.h>
43 #if HAVE_SYS_MMAN_H && HAVE_MPROTECT
44 # if HAVE_MAP_ANONYMOUS
45 const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
47 # else /* !HAVE_MAP_ANONYMOUS */
48 const int flags = MAP_FILE | MAP_PRIVATE;
49 int fd = open ("/dev/zero", O_RDONLY, 0666);
53 int pagesize = getpagesize ();
55 (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
57 if (two_pages != (char *)(-1)
58 && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
59 fence = two_pages + pagesize;
64 if (memchr (fence, 0, 0))
66 strcpy (fence - 9, "12345678");
67 if (memchr (fence - 9, 0, 79) != fence - 1)
71 ]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],
72 [dnl Be pessimistic for now.
73 gl_cv_func_memchr_works="guessing no"])])
74 if test "$gl_cv_func_memchr_works" != yes; then
82 # Prerequisites of lib/memchr.c.
83 AC_DEFUN([gl_PREREQ_MEMCHR], [
84 AC_CHECK_HEADERS([bp-sym.h])