b9eb92ab05
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.
41 lines
1.3 KiB
C
41 lines
1.3 KiB
C
/* 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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