1# memchr.m4 serial 18 2dnl Copyright (C) 2002-2004, 2009-2021 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_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. 104AC_DEFUN([gl_PREREQ_MEMCHR], [ 105 AC_CHECK_HEADERS([bp-sym.h]) 106]) 107