1# memchr.m4 serial 12 2dnl Copyright (C) 2002-2004, 2009-2012 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 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. 86AC_DEFUN([gl_PREREQ_MEMCHR], [ 87 AC_CHECK_HEADERS([bp-sym.h]) 88]) 89