m4/memchr.m4

   1 # memchr.m4 serial 12
   2 dnl Copyright (C) 2002-2004, 2009-2014 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   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.
  86 AC_DEFUN([gl_PREREQ_MEMCHR], [
  87   AC_CHECK_HEADERS([bp-sym.h])
  88 ])