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| author | H.J. Lu <hjl.tools@gmail.com> | 2015-10-21 14:44:23 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2015-12-15 13:16:02 -0800 |
| commit | b9eb92ab05204df772eb4929eccd018637c9f3e9 (patch) | |
| tree | f272c9a3e0ef7232d0714cfda7e79b040a757fb9 /libio/tst-atime.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 'libio/tst-atime.c')
0 files changed, 0 insertions, 0 deletions