commit b9eb92ab05204df772eb4929eccd018637c9f3e9
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Wed Oct 21 14:44:23 2015 -0700
Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT
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.
Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/wordsize-64/mmap.c
===================================================================
--- /dev/null
+++ glibc-2.17-c758a686/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)
Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
===================================================================
--- /dev/null
+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
@@ -0,0 +1,44 @@
+/* Optional code to distinguish library flavours. x86-64 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/>. */
+
+#ifndef _DL_LIBRECON_H
+
+#include <sysdeps/unix/sysv/linux/dl-librecon.h>
+
+/* Recognizing extra environment variables. For 64-bit applications,
+ branch prediction performance may 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). Prefer_MAP_32BIT_EXEC
+ is always disabled for SUID programs and can be enabled by setting
+ environment variable, LD_PREFER_MAP_32BIT_EXEC. */
+#define EXTRA_LD_ENVVARS \
+ case 21: \
+ if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \
+ GLRO(dl_x86_cpu_features).feature[index_Prefer_MAP_32BIT_EXEC] \
+ = bit_Prefer_MAP_32BIT_EXEC; \
+ break;
+
+/* Extra unsecure variables. The names are all stuffed in a single
+ string which means they have to be terminated with a '\0' explicitly. */
+#define EXTRA_UNSECURE_ENVVARS \
+ "LD_PREFER_MAP_32BIT_EXEC\0"
+
+#endif /* dl-librecon.h */
Index: glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
===================================================================
--- /dev/null
+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
@@ -0,0 +1,37 @@
+/* Linux mmap system call. x86-64 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 <ldsodefs.h>
+
+/* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages
+ with MAP_32BIT first. */
+#define MMAP_PREPARE(addr, len, prot, flags, fd, offset) \
+ if ((addr) == NULL \
+ && ((prot) & PROT_EXEC) != 0 \
+ && HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC)) \
+ { \
+ __ptr_t ret = (__ptr_t) INLINE_SYSCALL (mmap, 6, (addr), (len), \
+ (prot), \
+ (flags) | MAP_32BIT, \
+ (fd), (offset)); \
+ if (ret != MAP_FAILED) \
+ return ret; \
+ }
+
+#include <sysdeps/unix/sysv/linux/wordsize-64/mmap.c>
Index: glibc-2.17-c758a686/sysdeps/x86/cpu-features.h
===================================================================
--- glibc-2.17-c758a686.orig/sysdeps/x86/cpu-features.h
+++ glibc-2.17-c758a686/sysdeps/x86/cpu-features.h
@@ -32,6 +32,7 @@
#define bit_AVX_Fast_Unaligned_Load (1 << 11)
#define bit_AVX512F_Usable (1 << 12)
#define bit_AVX512DQ_Usable (1 << 13)
+#define bit_Prefer_MAP_32BIT_EXEC (1 << 16)
/* CPUID Feature flags. */
@@ -91,6 +92,7 @@
# define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1*FEATURE_SIZE
# define index_AVX512F_Usable FEATURE_INDEX_1*FEATURE_SIZE
# define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE
+# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1*FEATURE_SIZE
# if defined (_LIBC) && !IS_IN (nonlib)
# ifdef __x86_64__
@@ -267,6 +269,7 @@ extern const struct cpu_features *__get_
# define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1
# define index_AVX512F_Usable FEATURE_INDEX_1
# define index_AVX512DQ_Usable FEATURE_INDEX_1
+# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1
#endif /* !__ASSEMBLER__ */