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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 13:45:12 -0800 |
| commit | e4c29a1d3f7d96683582b7dbd86fb8d1ac707ea6 (patch) | |
| tree | 90197d2e3281af39c7c3b8af969f026670fc76d4 /hurd/setauth.c | |
| parent | e7b516ad591913995b928ce6db296e2c57a099e4 (diff) | |
| download | glibc-hjl/32bit/2.22.tar.gz glibc-hjl/32bit/2.22.tar.xz glibc-hjl/32bit/2.22.zip | |
Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT hjl/32bit/2.22
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. (cherry picked from commit b9eb92ab05204df772eb4929eccd018637c9f3e9)
Diffstat (limited to 'hurd/setauth.c')
0 files changed, 0 insertions, 0 deletions