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jeremybenn |
# memchr.m4 serial 8
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dnl Copyright (C) 2002-2004, 2009-2010 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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dnl These days, we assume memchr is present. But just in case...
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AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
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AC_CHECK_FUNCS_ONCE([memchr])
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if test $ac_cv_func_memchr = yes; 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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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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return 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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return 2;
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}
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return 0;
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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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else
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HAVE_MEMCHR=0
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fi
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if test $HAVE_MEMCHR = 0 || test $REPLACE_MEMCHR = 1; then
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AC_LIBOBJ([memchr])
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gl_PREREQ_MEMCHR
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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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