1# memchr.m4 serial 18
2dnl Copyright (C) 2002-2004, 2009-2022 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_STRING_H_DEFAULTS])
17  # Detect platform-specific bugs in some versions of glibc:
18  # memchr should not dereference anything with length 0
19  #   https://bugzilla.redhat.com/show_bug.cgi?id=499689
20  # memchr should not dereference overestimated length after a match
21  #   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
22  #   https://sourceware.org/bugzilla/show_bug.cgi?id=10162
23  # memchr should cast the second argument to 'unsigned char'.
24  #   This bug exists in Android 4.3.
25  # Assume that memchr works on platforms that lack mprotect.
26  AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
27    [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
28#include <string.h>
29#if HAVE_SYS_MMAN_H
30# include <fcntl.h>
31# include <unistd.h>
32# include <sys/types.h>
33# include <sys/mman.h>
34# ifndef MAP_FILE
35#  define MAP_FILE 0
36# endif
37#endif
38]], [[
39  int result = 0;
40  char *fence = NULL;
41#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
42# if HAVE_MAP_ANONYMOUS
43  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
44  const int fd = -1;
45# else /* !HAVE_MAP_ANONYMOUS */
46  const int flags = MAP_FILE | MAP_PRIVATE;
47  int fd = open ("/dev/zero", O_RDONLY, 0666);
48  if (fd >= 0)
49# endif
50    {
51      int pagesize = getpagesize ();
52      char *two_pages =
53        (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
54                       flags, fd, 0);
55      if (two_pages != (char *)(-1)
56          && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
57        fence = two_pages + pagesize;
58    }
59#endif
60  if (fence)
61    {
62      /* Test against bugs on glibc systems.  */
63      if (memchr (fence, 0, 0))
64        result |= 1;
65      strcpy (fence - 9, "12345678");
66      if (memchr (fence - 9, 0, 79) != fence - 1)
67        result |= 2;
68      if (memchr (fence - 1, 0, 3) != fence - 1)
69        result |= 4;
70      /* Test against bug on AIX 7.2.  */
71      if (memchr (fence - 4, '6', 16) != fence - 4)
72        result |= 8;
73    }
74  /* Test against bug on Android 4.3.  */
75  {
76    char input[3];
77    input[0] = 'a';
78    input[1] = 'b';
79    input[2] = 'c';
80    if (memchr (input, 0x789abc00 | 'b', 3) != input + 1)
81      result |= 16;
82  }
83  return result;
84]])],
85       [gl_cv_func_memchr_works=yes],
86       [gl_cv_func_memchr_works=no],
87       [case "$host_os" in
88                           # Guess no on Android.
89          linux*-android*) gl_cv_func_memchr_works="guessing no" ;;
90                           # Guess yes on native Windows.
91          mingw*)          gl_cv_func_memchr_works="guessing yes" ;;
92                           # If we don't know, obey --enable-cross-guesses.
93          *)               gl_cv_func_memchr_works="$gl_cross_guess_normal" ;;
94        esac
95       ])
96    ])
97  case "$gl_cv_func_memchr_works" in
98    *yes) ;;
99    *) REPLACE_MEMCHR=1 ;;
100  esac
101])
102
103# Prerequisites of lib/memchr.c.
104AC_DEFUN([gl_PREREQ_MEMCHR], [
105  AC_CHECK_HEADERS([bp-sym.h])
106])
107