Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT hjl/32bit/master

According to Silvermont software optimization guide, for 64-bit
applications, branch prediction performance can be negatively impacted
when the target of a branch is more than 4GB away from the branch.  Add
the Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
pages with MAP_32BIT first.  NB: MAP_32BIT will map to lower 2GB, not
lower 4GB, address.  Prefer_MAP_32BIT_EXEC reduces bits available for
address space layout randomization (ASLR), which is always disabled for
SUID programs and can only be enabled by setting environment variable,
LD_PREFER_MAP_32BIT_EXEC.

On Fedora 23, this patch speeds up GCC 5 testsuite by 3% on Silvermont.

	[BZ #19367]
	* sysdeps/unix/sysv/linux/wordsize-64/mmap.c: New file.
	* sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/mmap.c: Likewise.
	* sysdeps/x86/cpu-features.h (bit_Prefer_MAP_32BIT_EXEC): New.
	(index_Prefer_MAP_32BIT_EXEC): Likewise.

1 files changed, 40 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/wordsize-64/mmap.c b/sysdeps/unix/sysv/linux/wordsize-64/mmap.c
new file mode 100644
index 0000000000..e098976fbb
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/wordsize-64/mmap.c
@@ -0,0 +1,40 @@
+/* Linux mmap system call.  64-bit version.
+   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 <sys/types.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <sysdep.h>
+
+/* An architecture may override this.  */
+#ifndef MMAP_PREPARE
+# define MMAP_PREPARE(addr, len, prot, flags, fd, offset)
+#endif
+
+__ptr_t
+__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
+{
+  MMAP_PREPARE (addr, len, prot, flags, fd, offset);
+  return (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, flags,
+				   fd, offset);
+}
+
+weak_alias (__mmap, mmap)
+weak_alias (__mmap, mmap64)
+weak_alias (__mmap, __mmap64)