Home | History | Annotate | Download | only in m4 
      1 # memchr.m4 serial 12
      2 dnl Copyright (C) 2002-2004, 2009-2012 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 ])
     89