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1# memchr.m4 serial 8
2dnl Copyright (C) 2002-2004, 2009-2010 Free Software Foundation, Inc.
3dnl This file is free software; the Free Software Foundation
4dnl gives unlimited permission to copy and/or distribute it,
5dnl with or without modifications, as long as this notice is preserved.
6
7AC_DEFUN_ONCE([gl_FUNC_MEMCHR],
8[
9 dnl Check for prerequisites for memory fence checks.
10 gl_FUNC_MMAP_ANON
11 AC_CHECK_HEADERS_ONCE([sys/mman.h])
12 AC_CHECK_FUNCS_ONCE([mprotect])
13
14 dnl These days, we assume memchr is present. But just in case...
15 AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
16 AC_CHECK_FUNCS_ONCE([memchr])
17 if test $ac_cv_func_memchr = yes; then
18 # Detect platform-specific bugs in some versions of glibc:
19 # memchr should not dereference anything with length 0
20 # http://bugzilla.redhat.com/499689
21 # memchr should not dereference overestimated length after a match
22 # http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
23 # http://sourceware.org/bugzilla/show_bug.cgi?id=10162
24 # Assume that memchr works on platforms that lack mprotect.
25 AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
26 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
27#include <string.h>
28#if HAVE_SYS_MMAN_H
29# include <fcntl.h>
30# include <unistd.h>
31# include <sys/types.h>
32# include <sys/mman.h>
33# ifndef MAP_FILE
34# define MAP_FILE 0
35# endif
36#endif
37]], [[
38 char *fence = NULL;
39#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
40# if HAVE_MAP_ANONYMOUS
41 const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
42 const int fd = -1;
43# else /* !HAVE_MAP_ANONYMOUS */
44 const int flags = MAP_FILE | MAP_PRIVATE;
45 int fd = open ("/dev/zero", O_RDONLY, 0666);
46 if (fd >= 0)
47# endif
48 {
49 int pagesize = getpagesize ();
50 char *two_pages =
51 (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
52 flags, fd, 0);
53 if (two_pages != (char *)(-1)
54 && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
55 fence = two_pages + pagesize;
56 }
57#endif
58 if (fence)
59 {
60 if (memchr (fence, 0, 0))
61 return 1;
62 strcpy (fence - 9, "12345678");
63 if (memchr (fence - 9, 0, 79) != fence - 1)
64 return 2;
65 }
66 return 0;
67]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],
68 [dnl Be pessimistic for now.
69 gl_cv_func_memchr_works="guessing no"])])
70 if test "$gl_cv_func_memchr_works" != yes; then
71 REPLACE_MEMCHR=1
72 fi
73 else
74 HAVE_MEMCHR=0
75 fi
76 if test $HAVE_MEMCHR = 0 || test $REPLACE_MEMCHR = 1; then
77 AC_LIBOBJ([memchr])
78 gl_PREREQ_MEMCHR
79 fi
80])
81
82# Prerequisites of lib/memchr.c.
83AC_DEFUN([gl_PREREQ_MEMCHR], [
84 AC_CHECK_HEADERS([bp-sym.h])
85])