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# memchr.m4 serial 18 |
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dnl Copyright (C) 2002-2004, 2009-2023 Free Software Foundation, Inc. |
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dnl This file is free software; the Free Software Foundation |
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dnl gives unlimited permission to copy and/or distribute it, |
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dnl with or without modifications, as long as this notice is preserved. |
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AC_DEFUN_ONCE([gl_FUNC_MEMCHR], |
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[ |
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AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles |
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dnl Check for prerequisites for memory fence checks. |
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gl_FUNC_MMAP_ANON |
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AC_CHECK_HEADERS_ONCE([sys/mman.h]) |
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AC_CHECK_FUNCS_ONCE([mprotect]) |
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AC_REQUIRE([gl_STRING_H_DEFAULTS]) |
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# Detect platform-specific bugs in some versions of glibc: |
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# memchr should not dereference anything with length 0 |
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# https: |
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# memchr should not dereference overestimated length after a match |
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# https: |
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# https: |
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# memchr should cast the second argument to 'unsigned char'. |
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# This bug exists in Android 4.3. |
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# Assume that memchr works on platforms that lack mprotect. |
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AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works], |
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[AC_RUN_IFELSE([AC_LANG_PROGRAM([[ |
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#include <string.h> |
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#if HAVE_SYS_MMAN_H |
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# include <fcntl.h> |
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# include <unistd.h> |
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# include <sys/types.h> |
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# include <sys/mman.h> |
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# ifndef MAP_FILE |
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# define MAP_FILE 0 |
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# endif |
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#endif |
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]], [[ |
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int result = 0; |
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char *fence = NULL; |
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#if HAVE_SYS_MMAN_H && HAVE_MPROTECT |
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# if HAVE_MAP_ANONYMOUS |
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const int flags = MAP_ANONYMOUS | MAP_PRIVATE; |
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const int fd = -1; |
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# else |
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const int flags = MAP_FILE | MAP_PRIVATE; |
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int fd = open ("/dev/zero", O_RDONLY, 0666); |
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if (fd >= 0) |
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# endif |
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{ |
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int pagesize = getpagesize (); |
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char *two_pages = |
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(char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE, |
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flags, fd, 0); |
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if (two_pages != (char *)(-1) |
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&& mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0) |
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fence = two_pages + pagesize; |
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} |
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#endif |
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if (fence) |
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{ |
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if (memchr (fence, 0, 0)) |
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result |= 1; |
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strcpy (fence - 9, "12345678"); |
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if (memchr (fence - 9, 0, 79) != fence - 1) |
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result |= 2; |
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if (memchr (fence - 1, 0, 3) != fence - 1) |
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result |= 4; |
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if (memchr (fence - 4, '6', 16) != fence - 4) |
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result |= 8; |
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} |
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{ |
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char input[3]; |
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input[0] = 'a'; |
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input[1] = 'b'; |
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input[2] = 'c'; |
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if (memchr (input, 0x789abc00 | 'b', 3) != input + 1) |
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result |= 16; |
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} |
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return result; |
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]])], |
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[gl_cv_func_memchr_works=yes], |
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[gl_cv_func_memchr_works=no], |
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[case "$host_os" in |
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# Guess no on Android. |
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linux*-android*) gl_cv_func_memchr_works="guessing no" ;; |
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# Guess yes on native Windows. |
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mingw*) gl_cv_func_memchr_works="guessing yes" ;; |
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# If we don't know, obey --enable-cross-guesses. |
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*) gl_cv_func_memchr_works="$gl_cross_guess_normal" ;; |
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esac |
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]) |
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]) |
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case "$gl_cv_func_memchr_works" in |
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*yes) ;; |
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*) REPLACE_MEMCHR=1 ;; |
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esac |
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]) |
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# Prerequisites of lib/memchr.c. |
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AC_DEFUN([gl_PREREQ_MEMCHR], [ |
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AC_CHECK_HEADERS([bp-sym.h]) |
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]) |
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