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-rw-r--r--tests/zerosize-ptr.h68
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diff --git a/tests/zerosize-ptr.h b/tests/zerosize-ptr.h
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+/* Return a pointer to a zero-size object in memory.
+ Copyright (C) 2009 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+/* ISO C 99 does not allow memcmp(), memchr() etc. to be invoked with a NULL
+ argument. Therefore this file produces a non-NULL pointer which cannot
+ be dereferenced, if possible. */
+
+#include <stdlib.h>
+
+/* Test whether mmap() and mprotect() are available.
+ We don't use HAVE_MMAP, because AC_FUNC_MMAP would not define it on HP-UX.
+ HAVE_MPROTECT is not enough, because mingw does not have mmap() but has an
+ mprotect() function in libgcc.a. */
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# include <fcntl.h>
+# include <unistd.h>
+# include <sys/types.h>
+# include <sys/mman.h>
+/* Define MAP_FILE when it isn't otherwise. */
+# ifndef MAP_FILE
+# define MAP_FILE 0
+# endif
+#endif
+
+/* Return a pointer to a zero-size object in memory (that is, actually, a
+ pointer to a page boundary where the previous page is readable and writable
+ and the next page is neither readable not writable), if possible.
+ Return NULL otherwise. */
+
+static void *
+zerosize_ptr (void)
+{
+/* Use mmap and mprotect when they exist. Don't test HAVE_MMAP, because it is
+ not defined on HP-UX 11 (since it does not support MAP_FIXED). */
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# if HAVE_MAP_ANONYMOUS
+ const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+ const int fd = -1;
+# else /* !HAVE_MAP_ANONYMOUS */
+ const int flags = MAP_FILE | MAP_PRIVATE;
+ int fd = open ("/dev/zero", O_RDONLY, 0666);
+ if (fd >= 0)
+# endif
+ {
+ int pagesize = getpagesize ();
+ char *two_pages =
+ (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
+ flags, fd, 0);
+ if (two_pages != (char *)(-1)
+ && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
+ return two_pages + pagesize;
+ }
+#endif
+ return NULL;
+}