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Re: [PATCH] Add Prefer_MAP_32BIT_EXEC for Silvermont
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: "Carlos O'Donell" <carlos at redhat dot com>
- Cc: Jeff Law <law at redhat dot com>, Zack Weinberg <zackw at panix dot com>, Andi Kleen <andi at firstfloor dot org>, Adhemerval Zanella <adhemerval dot zanella at linaro dot org>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 15 Dec 2015 12:08:31 -0800
- Subject: Re: [PATCH] Add Prefer_MAP_32BIT_EXEC for Silvermont
- Authentication-results: sourceware.org; auth=none
- References: <CAKCAbMhMArQ9wsXhw2y+Fvv+_3O5i4g8pdDQdWo6_1YxqfVxkQ at mail dot gmail dot com> <CAMe9rOrVjSnhp-EzmAnVBg10wbqk9U4n+hL-3xF5=DPZP5co1A at mail dot gmail dot com> <CAKCAbMhk69hUBbrQ=0j0NDYjRT6R-EK1+F43+Mmi9FwS7epexQ at mail dot gmail dot com> <CAKCAbMhA6x4r6Bhw8cnAavoWzjWsm6WM8JPzrnCsrqxbEswS_g at mail dot gmail dot com> <87egeszoq3 dot fsf at tassilo dot jf dot intel dot com> <CAKCAbMibxh54DGJ6p59ah6jQK=oFkH9LCZo0UDBefQeh1y-5eg at mail dot gmail dot com> <CAMe9rOoyc4MXVz74GmjViora-iCEKitQXbpX9EB+Ln1Q_DAD_A at mail dot gmail dot com> <CAKCAbMi_noBivP+ksLaotNtfEhGrtUuUacbnZgjMg5m0PfEniw at mail dot gmail dot com> <20151211222913 dot GT15533 at two dot firstfloor dot org> <566B55DF dot 2040200 at redhat dot com> <20151212001449 dot GU15533 at two dot firstfloor dot org> <CAKCAbMgcZKr8-i2XuhHAnk4nKpJnpWEqj1XNuygkNhYzXPb8hA at mail dot gmail dot com> <566B8008 dot 6010106 at redhat dot com> <CAMe9rOofj5_TQFcU695CbMmpqcULUgD4r0O9kY2+VmsNoPJx9A at mail dot gmail dot com> <56705B8F dot 7000303 at redhat dot com> <56705E40 dot 3030307 at redhat dot com>
On Tue, Dec 15, 2015 at 10:38 AM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 12/15/2015 01:27 PM, Carlos O'Donell wrote:
>> + cpu_features->feature[index_Prefer_MAP_32BIT_EXEC]
>> + |= get_prefer_map_32bit_exec ();
>>
>> You wouldn't need get_prefer_map_32bit_exec, since this is all part of
>> the code, like dl-librecon.h, which parses the extra env var.
>
> To be clear:
>
> * Add new bit flag definitions for cpu_features.
> * Add a sysdeps/unix/sysv/linux/x86_64/dl-silvermont.h
> * Fill in EXTRA_LD_ENVVARS or add new ones.
> * Write to rtld's GLRO cpu_features the bit you need based
> on __libc_enable_secure.
>
> That should simplify and concentrate the Silvermont fixes to
> just two files, making future maintenance and documentation
> easier.
>
>
This is the updated patch. I put EXTRA_LD_ENVVARS and
EXTRA_UNSECURE_ENVVARS in x86_64/64/dl-librecon.h
to be consistent with i386/dl-librecon.h. If we ever need to
update EXTRA_LD_ENVVARS/EXTRA_UNSECURE_ENVVARS
in the future, we have a single file to change.
Tested on x86-64. OK for master?
Thanks for all the feedbacks and suggestions.
--
H.J.
From 940a29897c4018a5c13bef99d0918311629b5f10 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 21 Oct 2015 14:44:23 -0700
Subject: [PATCH] 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.
* 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.
---
sysdeps/unix/sysv/linux/wordsize-64/mmap.c | 40 ++++++++++++++++++++++
sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h | 44 +++++++++++++++++++++++++
sysdeps/unix/sysv/linux/x86_64/64/mmap.c | 37 +++++++++++++++++++++
sysdeps/x86/cpu-features.h | 3 ++
4 files changed, 124 insertions(+)
create mode 100644 sysdeps/unix/sysv/linux/wordsize-64/mmap.c
create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/mmap.c
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 0000000..e098976
--- /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)
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
new file mode 100644
index 0000000..159d0f1
--- /dev/null
+++ b/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 */
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/mmap.c b/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
new file mode 100644
index 0000000..031316c
--- /dev/null
+++ b/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>
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index 80edbee..93bee69 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -33,6 +33,7 @@
#define bit_AVX512DQ_Usable (1 << 13)
#define bit_I586 (1 << 14)
#define bit_I686 (1 << 15)
+#define bit_Prefer_MAP_32BIT_EXEC (1 << 16)
/* CPUID Feature flags. */
@@ -97,6 +98,7 @@
# define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE
# define index_I586 FEATURE_INDEX_1*FEATURE_SIZE
# define index_I686 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__
@@ -248,6 +250,7 @@ extern const struct cpu_features *__get_cpu_features (void)
# define index_AVX512DQ_Usable FEATURE_INDEX_1
# define index_I586 FEATURE_INDEX_1
# define index_I686 FEATURE_INDEX_1
+# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1
#endif /* !__ASSEMBLER__ */
--
2.5.0