1 files changed, 81 insertions, 0 deletions
diff --git a/gnulib-tests/zerosize-ptr.h b/gnulib-tests/zerosize-ptr.h
new file mode 100644
index 0000000..4a5d267
--- /dev/null
+++ b/gnulib-tests/zerosize-ptr.h
@@ -0,0 +1,81 @@
+/* Return a pointer to a zero-size object in memory.
+   Copyright (C) 2009-2020 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 <https://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.  */
+
+/* On Android, when targeting Android 4.4 or older with a GCC toolchain,
+   prevent a compilation error
+     "error: call to 'mmap' declared with attribute error: mmap is not
+      available with _FILE_OFFSET_BITS=64 when using GCC until android-21.
+      Either raise your minSdkVersion, disable _FILE_OFFSET_BITS=64, or
+      switch to Clang."
+   The files that we access in this compilation unit are less than 2 GB
+   large.  */
+#if defined __ANDROID__
+# undef _FILE_OFFSET_BITS
+# undef __USE_FILE_OFFSET64
+#endif
+
+#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;
+}