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[PATCH] Add Prefer_MAP_32BIT_EXEC for Silvermont

From: "H.J. Lu" <hongjiu dot lu at intel dot com>

To: GNU C Library <libc-alpha at sourceware dot org>

Date: Fri, 11 Dec 2015 06:37:06 -0800

Subject: [PATCH] Add Prefer_MAP_32BIT_EXEC for Silvermont

Authentication-results: sourceware.org; auth=none

Reply-to: "H.J. Lu" <hjl dot tools at gmail dot com>

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. Set the Prefer_MAP_32BIT_EXEC bit for Silvermont so that mmap will try to map executable pages with MAP_32BIT first. Also enable Silvermont optimizations for Knights Landing. Prefer_MAP_32BIT_EXEC reduces bits available for address space layout randomization (ASLR), which can be disabled by setting environment variable, LD_DISABLE_PREFER_MAP_32BIT_EXEC. On Fedora 23, this patch speeds up GCC 5 testsuite by 3% on Silvermont. Tested on ia32, x32 and x86-64. H.J. --- * sysdeps/unix/sysv/linux/x86_64/64/mmap.c: New file. * sysdeps/x86/cpu-features.c (get_prefer_map_32bit_exec): New function. (init_cpu_features): Set the Prefer_MAP_32BIT_EXEC bit for Silvermont. Enable Silvermont optimizations for Knights Landing. * sysdeps/x86/cpu-features.h (bit_Prefer_MAP_32BIT_EXEC): New. (index_Prefer_MAP_32BIT_EXEC): Likewise. --- sysdeps/unix/sysv/linux/x86_64/64/mmap.c | 49 ++++++++++++++++++++++++++++++++ sysdeps/x86/cpu-features.c | 44 ++++++++++++++++++++++++++-- sysdeps/x86/cpu-features.h | 3 ++ 3 files changed, 94 insertions(+), 2 deletions(-) create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/mmap.c 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..57de010 --- /dev/null +++ b/sysdeps/unix/sysv/linux/x86_64/64/mmap.c @@ -0,0 +1,49 @@ +/* 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 <sys/syscall.h> +#include <sysdep.h> +#include <unistd.h> +#include <ldsodefs.h> +#include <cpu-features.h> + +__ptr_t +__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset) +{ + /* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages + with MAP_32BIT first. */ + if (addr == NULL + && (prot & PROT_EXEC) != 0 + && HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC)) + { + addr = (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, + flags | MAP_32BIT, + fd, offset); + if (addr != MAP_FAILED) + return addr; + } + 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/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index fba3ef0..6a132f7 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -39,6 +39,33 @@ get_common_indeces (struct cpu_features *cpu_features, } } +/* Prefer_MAP_32BIT_EXEC reduces bits available for address space layout + randomization (ASLR), which can be disabled by setting environment + variable, LD_DISABLE_PREFER_MAP_32BIT_EXEC. */ + +static inline unsigned int +get_prefer_map_32bit_exec (void) +{ +#if defined __LP64__ && IS_IN (rtld) + extern char **__environ attribute_hidden; + for (char **current = __environ; *current != NULL; ++current) + { + /* Check LD_DISABLE_PREFER_MAP_32BIT_EXEC=. */ + static const char *disable = "LD_DISABLE_PREFER_MAP_32BIT_EXEC="; + for (size_t i = 0; ; i++) + { + if (disable[i] != (*current)[i]) + break; + if ((*current)[i] == '=') + return 0; + } + } + return bit_Prefer_MAP_32BIT_EXEC; +#else + return 0; +#endif +} + static inline void init_cpu_features (struct cpu_features *cpu_features) { @@ -78,22 +105,35 @@ init_cpu_features (struct cpu_features *cpu_features) cpu_features->feature[index_Slow_BSF] |= bit_Slow_BSF; break; + case 0x57: + /* Knights Landing. Enable Silvermont optimizations. */ + case 0x37: case 0x4a: case 0x4d: case 0x5a: case 0x5d: - /* Unaligned load versions are faster than SSSE3 - on Silvermont. */ + /* Unaligned load versions are faster than SSSE3 on + Silvermont. 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. Set 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. */ #if index_Fast_Unaligned_Load != index_Prefer_PMINUB_for_stringop # error index_Fast_Unaligned_Load != index_Prefer_PMINUB_for_stringop #endif +#if index_Fast_Unaligned_Load != index_Prefer_MAP_32BIT_EXEC +# error index_Fast_Unaligned_Load != index_Prefer_MAP_32BIT_EXEC +#endif #if index_Fast_Unaligned_Load != index_Slow_SSE4_2 # error index_Fast_Unaligned_Load != index_Slow_SSE4_2 #endif cpu_features->feature[index_Fast_Unaligned_Load] |= (bit_Fast_Unaligned_Load | bit_Prefer_PMINUB_for_stringop + | get_prefer_map_32bit_exec () | bit_Slow_SSE4_2); break; 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