gnulib/import/m4/memchr.m4

   1 # memchr.m4 serial 15
   2 dnl Copyright (C) 2002-2004, 2009-2019 Free Software Foundation, Inc.
   3 dnl This file is free software; the Free Software Foundation
   4 dnl gives unlimited permission to copy and/or distribute it,
   5 dnl with or without modifications, as long as this notice is preserved.
   6
   7 AC_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 native Windows.
  96             mingw*)          gl_cv_func_memchr_works="guessing yes" ;;
  97                              # If we don't know, obey --enable-cross-guesses.
  98             *)               gl_cv_func_memchr_works="$gl_cross_guess_normal" ;;
  99           esac
 100          ])
 101       ])
 102     case "$gl_cv_func_memchr_works" in
 103       *yes) ;;
 104       *) REPLACE_MEMCHR=1 ;;
 105     esac
 106   fi
 107 ])
 108
 109 # Prerequisites of lib/memchr.c.
 110 AC_DEFUN([gl_PREREQ_MEMCHR], [
 111   AC_CHECK_HEADERS([bp-sym.h])
 112 ])