1# memchr.m4 serial 13
2dnl Copyright (C) 2002-2004, 2009-2019 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  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
10
11  dnl Check for prerequisites for memory fence checks.
12  gl_FUNC_MMAP_ANON
13  AC_CHECK_HEADERS_ONCE([sys/mman.h])
14  AC_CHECK_FUNCS_ONCE([mprotect])
15
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
22      HAVE_MEMCHR=0
23    fi
24  ])
25  if test $HAVE_MEMCHR = 1; then
26    # Detect platform-specific bugs in some versions of glibc:
27    # memchr should not dereference anything with length 0
28    #   https://bugzilla.redhat.com/show_bug.cgi?id=499689
29    # memchr should not dereference overestimated length after a match
30    #   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
31    #   https://sourceware.org/bugzilla/show_bug.cgi?id=10162
32    # Assume that memchr works on platforms that lack mprotect.
33    AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
34      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
35#include <string.h>
36#if HAVE_SYS_MMAN_H
37# include <fcntl.h>
38# include <unistd.h>
39# include <sys/types.h>
40# include <sys/mman.h>
41# ifndef MAP_FILE
42#  define MAP_FILE 0
43# endif
44#endif
45]], [[
46  int result = 0;
47  char *fence = NULL;
48#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
49# if HAVE_MAP_ANONYMOUS
50  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
51  const int fd = -1;
52# else /* !HAVE_MAP_ANONYMOUS */
53  const int flags = MAP_FILE | MAP_PRIVATE;
54  int fd = open ("/dev/zero", O_RDONLY, 0666);
55  if (fd >= 0)
56# endif
57    {
58      int pagesize = getpagesize ();
59      char *two_pages =
60        (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
61                       flags, fd, 0);
62      if (two_pages != (char *)(-1)
63          && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
64        fence = two_pages + pagesize;
65    }
66#endif
67  if (fence)
68    {
69      if (memchr (fence, 0, 0))
70        result |= 1;
71      strcpy (fence - 9, "12345678");
72      if (memchr (fence - 9, 0, 79) != fence - 1)
73        result |= 2;
74      if (memchr (fence - 1, 0, 3) != fence - 1)
75        result |= 4;
76    }
77  return result;
78]])],
79         [gl_cv_func_memchr_works=yes],
80         [gl_cv_func_memchr_works=no],
81         [case "$host_os" in
82                    # Guess yes on native Windows.
83            mingw*) gl_cv_func_memchr_works="guessing yes" ;;
84                    # Be pessimistic for now.
85            *)      gl_cv_func_memchr_works="guessing no" ;;
86          esac
87         ])
88      ])
89    case "$gl_cv_func_memchr_works" in
90      *yes) ;;
91      *) REPLACE_MEMCHR=1 ;;
92    esac
93  fi
94])
95
96# Prerequisites of lib/memchr.c.
97AC_DEFUN([gl_PREREQ_MEMCHR], [
98  AC_CHECK_HEADERS([bp-sym.h])
99])
100