1# memchr.m4 serial 15
2dnl Copyright (C) 2002-2004, 2009-2020 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    # memchr should cast the second argument to 'unsigned char'.
33    #   This bug exists in Android 4.3.
34    # Assume that memchr works on platforms that lack mprotect.
35    AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
36      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
37#include <string.h>
38#if HAVE_SYS_MMAN_H
39# include <fcntl.h>
40# include <unistd.h>
41# include <sys/types.h>
42# include <sys/mman.h>
43# ifndef MAP_FILE
44#  define MAP_FILE 0
45# endif
46#endif
47]], [[
48  int result = 0;
49  char *fence = NULL;
50#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
51# if HAVE_MAP_ANONYMOUS
52  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
53  const int fd = -1;
54# else /* !HAVE_MAP_ANONYMOUS */
55  const int flags = MAP_FILE | MAP_PRIVATE;
56  int fd = open ("/dev/zero", O_RDONLY, 0666);
57  if (fd >= 0)
58# endif
59    {
60      int pagesize = getpagesize ();
61      char *two_pages =
62        (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
63                       flags, fd, 0);
64      if (two_pages != (char *)(-1)
65          && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
66        fence = two_pages + pagesize;
67    }
68#endif
69  if (fence)
70    {
71      if (memchr (fence, 0, 0))
72        result |= 1;
73      strcpy (fence - 9, "12345678");
74      if (memchr (fence - 9, 0, 79) != fence - 1)
75        result |= 2;
76      if (memchr (fence - 1, 0, 3) != fence - 1)
77        result |= 4;
78    }
79  /* Test against bug on Android 4.3.  */
80  {
81    char input[3];
82    input[0] = 'a';
83    input[1] = 'b';
84    input[2] = 'c';
85    if (memchr (input, 0x789abc00 | 'b', 3) != input + 1)
86      result |= 8;
87  }
88  return result;
89]])],
90         [gl_cv_func_memchr_works=yes],
91         [gl_cv_func_memchr_works=no],
92         [case "$host_os" in
93                             # Guess no on Android.
94            linux*-android*) gl_cv_func_memchr_works="guessing no" ;;
95			     # Guess yes on bsd.
96	    *bsd*)	     gl_cv_func_memchr_works="guessing yes" ;;
97                             # Guess yes on native Windows.
98            mingw*)          gl_cv_func_memchr_works="guessing yes" ;;
99                             # If we don't know, obey --enable-cross-guesses.
100            *)               gl_cv_func_memchr_works="$gl_cross_guess_normal" ;;
101          esac
102         ])
103      ])
104    case "$gl_cv_func_memchr_works" in
105      *yes) ;;
106      *) REPLACE_MEMCHR=1 ;;
107    esac
108  fi
109])
110
111# Prerequisites of lib/memchr.c.
112AC_DEFUN([gl_PREREQ_MEMCHR], [
113  AC_CHECK_HEADERS([bp-sym.h])
114])
115