1# memchr.m4 serial 12
2dnl Copyright (C) 2002-2004, 2009-2012 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  AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
15  m4_ifdef([gl_FUNC_MEMCHR_OBSOLETE], [
16    dnl These days, we assume memchr is present.  But if support for old
17    dnl platforms is desired:
18    AC_CHECK_FUNCS_ONCE([memchr])
19    if test $ac_cv_func_memchr = no; then
20      HAVE_MEMCHR=0
21    fi
22  ])
23  if test $HAVE_MEMCHR = 1; then
24    # Detect platform-specific bugs in some versions of glibc:
25    # memchr should not dereference anything with length 0
26    #   http://bugzilla.redhat.com/499689
27    # memchr should not dereference overestimated length after a match
28    #   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
29    #   http://sourceware.org/bugzilla/show_bug.cgi?id=10162
30    # Assume that memchr works on platforms that lack mprotect.
31    AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
32      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
33#include <string.h>
34#if HAVE_SYS_MMAN_H
35# include <fcntl.h>
36# include <unistd.h>
37# include <sys/types.h>
38# include <sys/mman.h>
39# ifndef MAP_FILE
40#  define MAP_FILE 0
41# endif
42#endif
43]], [[
44  int result = 0;
45  char *fence = NULL;
46#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
47# if HAVE_MAP_ANONYMOUS
48  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
49  const int fd = -1;
50# else /* !HAVE_MAP_ANONYMOUS */
51  const int flags = MAP_FILE | MAP_PRIVATE;
52  int fd = open ("/dev/zero", O_RDONLY, 0666);
53  if (fd >= 0)
54# endif
55    {
56      int pagesize = getpagesize ();
57      char *two_pages =
58        (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
59                       flags, fd, 0);
60      if (two_pages != (char *)(-1)
61          && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
62        fence = two_pages + pagesize;
63    }
64#endif
65  if (fence)
66    {
67      if (memchr (fence, 0, 0))
68        result |= 1;
69      strcpy (fence - 9, "12345678");
70      if (memchr (fence - 9, 0, 79) != fence - 1)
71        result |= 2;
72      if (memchr (fence - 1, 0, 3) != fence - 1)
73        result |= 4;
74    }
75  return result;
76]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],
77      [dnl Be pessimistic for now.
78       gl_cv_func_memchr_works="guessing no"])])
79    if test "$gl_cv_func_memchr_works" != yes; then
80      REPLACE_MEMCHR=1
81    fi
82  fi
83])
84
85# Prerequisites of lib/memchr.c.
86AC_DEFUN([gl_PREREQ_MEMCHR], [
87  AC_CHECK_HEADERS([bp-sym.h])
88])
89