1 # memchr.m4 serial 7 2 dnl Copyright (C) 2002, 2003, 2004, 2009 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 dnl These days, we assume memchr is present. But just in case... 15 AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS]) 16 AC_REPLACE_FUNCS([memchr]) 17 if test $ac_cv_func_memchr = no; then 18 gl_PREREQ_MEMCHR 19 REPLACE_MEMCHR=1 20 fi 21 22 if test $ac_cv_func_memchr = yes; then 23 # Detect platform-specific bugs in some versions of glibc: 24 # memchr should not dereference anything with length 0 25 # http://bugzilla.redhat.com/499689 26 # memchr should not dereference overestimated length after a match 27 # http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737 28 # http://sourceware.org/bugzilla/show_bug.cgi?id=10162 29 # Assume that memchr works on platforms that lack mprotect. 30 AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works], 31 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[ 32 #include <string.h> 33 #if HAVE_SYS_MMAN_H 34 # include <fcntl.h> 35 # include <unistd.h> 36 # include <sys/types.h> 37 # include <sys/mman.h> 38 # ifndef MAP_FILE 39 # define MAP_FILE 0 40 # endif 41 #endif 42 ]], [[ 43 char *fence = NULL; 44 #if HAVE_SYS_MMAN_H && HAVE_MPROTECT 45 # if HAVE_MAP_ANONYMOUS 46 const int flags = MAP_ANONYMOUS | MAP_PRIVATE; 47 const int fd = -1; 48 # else /* !HAVE_MAP_ANONYMOUS */ 49 const int flags = MAP_FILE | MAP_PRIVATE; 50 int fd = open ("/dev/zero", O_RDONLY, 0666); 51 if (fd >= 0) 52 # endif 53 { 54 int pagesize = getpagesize (); 55 char *two_pages = 56 (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE, 57 flags, fd, 0); 58 if (two_pages != (char *)(-1) 59 && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0) 60 fence = two_pages + pagesize; 61 } 62 #endif 63 if (fence) 64 { 65 if (memchr (fence, 0, 0)) 66 return 1; 67 strcpy (fence - 9, "12345678"); 68 if (memchr (fence - 9, 0, 79) != fence - 1) 69 return 2; 70 } 71 return 0; 72 ]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no], 73 [dnl Be pessimistic for now. 74 gl_cv_func_memchr_works="guessing no"])]) 75 if test "$gl_cv_func_memchr_works" != yes; then 76 gl_PREREQ_MEMCHR 77 REPLACE_MEMCHR=1 78 AC_LIBOBJ([memchr]) 79 fi 80 fi 81 ]) 82 83 # Prerequisites of lib/memchr.c. 84 AC_DEFUN([gl_PREREQ_MEMCHR], [ 85 AC_CHECK_HEADERS([bp-sym.h]) 86 ]) 87
