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author | H.J. Lu <hjl.tools@gmail.com> | 2015-10-21 14:44:23 -0700 |
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committer | H.J. Lu <hjl.tools@gmail.com> | 2015-12-15 13:16:02 -0800 |
commit | b9eb92ab05204df772eb4929eccd018637c9f3e9 (patch) | |
tree | f272c9a3e0ef7232d0714cfda7e79b040a757fb9 /sysdeps/unix/sysv/linux/x86_64/64/mmap.c | |
parent | c9afcaaafaf9126a973883528eed8d0058a264c0 (diff) | |
download | glibc-b9eb92ab05204df772eb4929eccd018637c9f3e9.tar.gz glibc-b9eb92ab05204df772eb4929eccd018637c9f3e9.tar.xz glibc-b9eb92ab05204df772eb4929eccd018637c9f3e9.zip |
Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT hjl/32bit/master
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.
Diffstat (limited to 'sysdeps/unix/sysv/linux/x86_64/64/mmap.c')
-rw-r--r-- | sysdeps/unix/sysv/linux/x86_64/64/mmap.c | 37 |
1 files changed, 37 insertions, 0 deletions
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 0000000000..031316c85f --- /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> |