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.
This commit is contained in:
H.J. Lu
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c9afcaaafa
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b9eb92ab05
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/* Linux mmap system call. 64-bit version.
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Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <sys/types.h>
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#include <sys/mman.h>
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#include <errno.h>
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#include <sysdep.h>
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/* An architecture may override this. */
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#ifndef MMAP_PREPARE
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# define MMAP_PREPARE(addr, len, prot, flags, fd, offset)
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#endif
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__ptr_t
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__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
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{
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MMAP_PREPARE (addr, len, prot, flags, fd, offset);
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return (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, flags,
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fd, offset);
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}
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weak_alias (__mmap, mmap)
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weak_alias (__mmap, mmap64)
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weak_alias (__mmap, __mmap64)
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@ -0,0 +1,44 @@
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/* Optional code to distinguish library flavours. x86-64 version.
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Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _DL_LIBRECON_H
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#include <sysdeps/unix/sysv/linux/dl-librecon.h>
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/* Recognizing extra environment variables. For 64-bit applications,
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branch prediction performance may be negatively impacted when the
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target of a branch is more than 4GB away from the branch. Add the
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Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
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pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB,
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not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available
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for address space layout randomization (ASLR). Prefer_MAP_32BIT_EXEC
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is always disabled for SUID programs and can be enabled by setting
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environment variable, LD_PREFER_MAP_32BIT_EXEC. */
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#define EXTRA_LD_ENVVARS \
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case 21: \
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if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \
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GLRO(dl_x86_cpu_features).feature[index_Prefer_MAP_32BIT_EXEC] \
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= bit_Prefer_MAP_32BIT_EXEC; \
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break;
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/* Extra unsecure variables. The names are all stuffed in a single
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string which means they have to be terminated with a '\0' explicitly. */
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#define EXTRA_UNSECURE_ENVVARS \
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"LD_PREFER_MAP_32BIT_EXEC\0"
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#endif /* dl-librecon.h */
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@ -0,0 +1,37 @@
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/* Linux mmap system call. x86-64 version.
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Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <ldsodefs.h>
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/* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages
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with MAP_32BIT first. */
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#define MMAP_PREPARE(addr, len, prot, flags, fd, offset) \
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if ((addr) == NULL \
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&& ((prot) & PROT_EXEC) != 0 \
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&& HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC)) \
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{ \
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__ptr_t ret = (__ptr_t) INLINE_SYSCALL (mmap, 6, (addr), (len), \
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(prot), \
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(flags) | MAP_32BIT, \
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(fd), (offset)); \
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if (ret != MAP_FAILED) \
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return ret; \
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}
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#include <sysdeps/unix/sysv/linux/wordsize-64/mmap.c>
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@ -33,6 +33,7 @@
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#define bit_AVX512DQ_Usable (1 << 13)
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#define bit_I586 (1 << 14)
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#define bit_I686 (1 << 15)
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#define bit_Prefer_MAP_32BIT_EXEC (1 << 16)
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/* CPUID Feature flags. */
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@ -97,6 +98,7 @@
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# define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE
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# define index_I586 FEATURE_INDEX_1*FEATURE_SIZE
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# define index_I686 FEATURE_INDEX_1*FEATURE_SIZE
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# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1*FEATURE_SIZE
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# if defined (_LIBC) && !IS_IN (nonlib)
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# ifdef __x86_64__
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@ -248,6 +250,7 @@ extern const struct cpu_features *__get_cpu_features (void)
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# define index_AVX512DQ_Usable FEATURE_INDEX_1
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# define index_I586 FEATURE_INDEX_1
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# define index_I686 FEATURE_INDEX_1
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# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1
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#endif /* !__ASSEMBLER__ */
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