1# memchr.m4 serial 15 2dnl Copyright (C) 2002-2004, 2009-2020 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 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_HEADER_STRING_H_DEFAULTS]) 17 m4_ifdef([gl_FUNC_MEMCHR_OBSOLETE], [ 18 dnl These days, we assume memchr is present. But if support for old 19 dnl platforms is desired: 20 AC_CHECK_FUNCS_ONCE([memchr]) 21 if test $ac_cv_func_memchr = no; then 22 HAVE_MEMCHR=0 23 fi 24 ]) 25 if test $HAVE_MEMCHR = 1; then 26 # Detect platform-specific bugs in some versions of glibc: 27 # memchr should not dereference anything with length 0 28 # https://bugzilla.redhat.com/show_bug.cgi?id=499689 29 # memchr should not dereference overestimated length after a match 30 # https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737 31 # https://sourceware.org/bugzilla/show_bug.cgi?id=10162 32 # memchr should cast the second argument to 'unsigned char'. 33 # This bug exists in Android 4.3. 34 # Assume that memchr works on platforms that lack mprotect. 35 AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works], 36 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[ 37#include <string.h> 38#if HAVE_SYS_MMAN_H 39# include <fcntl.h> 40# include <unistd.h> 41# include <sys/types.h> 42# include <sys/mman.h> 43# ifndef MAP_FILE 44# define MAP_FILE 0 45# endif 46#endif 47]], [[ 48 int result = 0; 49 char *fence = NULL; 50#if HAVE_SYS_MMAN_H && HAVE_MPROTECT 51# if HAVE_MAP_ANONYMOUS 52 const int flags = MAP_ANONYMOUS | MAP_PRIVATE; 53 const int fd = -1; 54# else /* !HAVE_MAP_ANONYMOUS */ 55 const int flags = MAP_FILE | MAP_PRIVATE; 56 int fd = open ("/dev/zero", O_RDONLY, 0666); 57 if (fd >= 0) 58# endif 59 { 60 int pagesize = getpagesize (); 61 char *two_pages = 62 (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE, 63 flags, fd, 0); 64 if (two_pages != (char *)(-1) 65 && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0) 66 fence = two_pages + pagesize; 67 } 68#endif 69 if (fence) 70 { 71 if (memchr (fence, 0, 0)) 72 result |= 1; 73 strcpy (fence - 9, "12345678"); 74 if (memchr (fence - 9, 0, 79) != fence - 1) 75 result |= 2; 76 if (memchr (fence - 1, 0, 3) != fence - 1) 77 result |= 4; 78 } 79 /* Test against bug on Android 4.3. */ 80 { 81 char input[3]; 82 input[0] = 'a'; 83 input[1] = 'b'; 84 input[2] = 'c'; 85 if (memchr (input, 0x789abc00 | 'b', 3) != input + 1) 86 result |= 8; 87 } 88 return result; 89]])], 90 [gl_cv_func_memchr_works=yes], 91 [gl_cv_func_memchr_works=no], 92 [case "$host_os" in 93 # Guess no on Android. 94 linux*-android*) gl_cv_func_memchr_works="guessing no" ;; 95 # Guess yes on bsd. 96 *bsd*) gl_cv_func_memchr_works="guessing yes" ;; 97 # Guess yes on native Windows. 98 mingw*) gl_cv_func_memchr_works="guessing yes" ;; 99 # If we don't know, obey --enable-cross-guesses. 100 *) gl_cv_func_memchr_works="$gl_cross_guess_normal" ;; 101 esac 102 ]) 103 ]) 104 case "$gl_cv_func_memchr_works" in 105 *yes) ;; 106 *) REPLACE_MEMCHR=1 ;; 107 esac 108 fi 109]) 110 111# Prerequisites of lib/memchr.c. 112AC_DEFUN([gl_PREREQ_MEMCHR], [ 113 AC_CHECK_HEADERS([bp-sym.h]) 114]) 115