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88 lines
2.7 KiB
88 lines
2.7 KiB
# memchr.m4 serial 12 |
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dnl Copyright (C) 2002-2004, 2009-2011 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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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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|
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AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS]) |
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m4_ifdef([gl_FUNC_MEMCHR_OBSOLETE], [ |
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dnl These days, we assume memchr is present. But if support for old |
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dnl platforms is desired: |
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AC_CHECK_FUNCS_ONCE([memchr]) |
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if test $ac_cv_func_memchr = no; then |
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HAVE_MEMCHR=0 |
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fi |
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]) |
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if test $HAVE_MEMCHR = 1; then |
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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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# http://bugzilla.redhat.com/499689 |
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# memchr should not dereference overestimated length after a match |
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# http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737 |
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# http://sourceware.org/bugzilla/show_bug.cgi?id=10162 |
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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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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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} |
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return result; |
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]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no], |
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[dnl Be pessimistic for now. |
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gl_cv_func_memchr_works="guessing no"])]) |
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if test "$gl_cv_func_memchr_works" != yes; then |
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REPLACE_MEMCHR=1 |
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fi |
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fi |
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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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