107 lines
3.3 KiB
Plaintext
107 lines
3.3 KiB
Plaintext
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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://bugzilla.redhat.com/show_bug.cgi?id=499689
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# memchr should not dereference overestimated length after a match
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# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
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# https://sourceware.org/bugzilla/show_bug.cgi?id=10162
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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 /* !HAVE_MAP_ANONYMOUS */
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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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/* Test against bugs on glibc systems. */
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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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/* Test against bug on AIX 7.2. */
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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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/* Test against bug on Android 4.3. */
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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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