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* build-aux/gendocs.sh (version): * doc/gendocs_template: * doc/gendocs_template_min: * doc/gnulib.texi: * lib/version-etc.c (COPYRIGHT_YEAR): Update copyright dates by hand in templates and the like. * all files: Run 'make update-copyright'.
69 lines
2.5 KiB
C
69 lines
2.5 KiB
C
/* Return a pointer to a zero-size object in memory.
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Copyright (C) 2009-2017 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* ISO C 99 does not allow memcmp(), memchr() etc. to be invoked with a NULL
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argument. Therefore this file produces a non-NULL pointer which cannot
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be dereferenced, if possible. */
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#include <stdlib.h>
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/* Test whether mmap() and mprotect() are available.
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We don't use HAVE_MMAP, because AC_FUNC_MMAP would not define it on HP-UX.
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HAVE_MPROTECT is not enough, because mingw does not have mmap() but has an
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mprotect() function in libgcc.a. */
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#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
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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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/* Define MAP_FILE when it isn't otherwise. */
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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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/* Return a pointer to a zero-size object in memory (that is, actually, a
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pointer to a page boundary where the previous page is readable and writable
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and the next page is neither readable not writable), if possible.
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Return NULL otherwise. */
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static void *
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zerosize_ptr (void)
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{
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/* Use mmap and mprotect when they exist. Don't test HAVE_MMAP, because it is
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not defined on HP-UX 11 (since it does not support MAP_FIXED). */
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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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return two_pages + pagesize;
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}
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#endif
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return NULL;
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}
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