Fix wordsize-32 mmap offset for negative value (BZ#18877)

This patch fixes the default wordsize-32 mmap implementation offset
calculation for negative values.  Current code uses signed shift
operation to calculate the multiple size to use with syscall and
it is implementation defined.  Change it to use a division base
on mmap page size (default being as before, 4096).

Tested on armv7hf.

	[BZ #18877]
	* posix/Makefile (tests): Add tst-mmap-offset.
	* posix/tst-mmap.c: New file.
	* sysdeps/unix/sysv/linux/generic/wordsize-32/mmap.c (__mmap): Fix
	offset calculation for negative values.

1 files changed, 67 insertions, 0 deletions

diff --git a/posix/tst-mmap-offset.c b/posix/tst-mmap-offset.c
new file mode 100644
index 0000000000..2af8a671c3
--- /dev/null
+++ b/posix/tst-mmap-offset.c
@@ -0,0 +1,67 @@
+/* BZ #18877 mmap offset test.
+
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+static int
+printmsg (int rc, const char *msg)
+{
+  printf ("%s failed: %m\n", msg);
+  return rc;
+}
+
+/* Check if negative offsets are handled correctly by mmap.  */
+static int
+do_test (void)
+{
+  const int prot = PROT_READ | PROT_WRITE;
+  const int flags = MAP_SHARED;
+  const unsigned long length = 0x10000;
+  const unsigned long offset = 0xace00000;
+  const unsigned long size = offset + length;
+  void *addr;
+  int fd;
+  char fname[] = "tst-mmap-offset-XXXXXX";
+
+  fd = mkstemp64 (fname);
+  if (fd < 0)
+    return printmsg (1, "mkstemp");
+
+  if (unlink (fname))
+    return printmsg (1, "unlink");
+
+  if (ftruncate64 (fd, size))
+    return printmsg (0, "ftruncate64");
+
+  addr = mmap (NULL, length, prot, flags, fd, offset);
+  if (MAP_FAILED == addr)
+    return printmsg (1, "mmap");
+
+  /* This memcpy is likely to SIGBUS if mmap has messed up with offset.  */
+  memcpy (addr, fname, sizeof (fname));
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"