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      1 # memchr.m4 serial 18
      2 dnl Copyright (C) 2002-2004, 2009-2022 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_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.
    104 AC_DEFUN([gl_PREREQ_MEMCHR], [
    105   AC_CHECK_HEADERS([bp-sym.h])
    106 ])
    107