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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. |
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| .. | ||
| bits | ||
| fpu | ||
| cpu-features-offsets.sym | ||
| cpu-features.c | ||
| cpu-features.h | ||
| dl-get-cpu-features.c | ||
| elide.h | ||
| fpu_control.h | ||
| init-arch.h | ||
| libc-start.c | ||
| linkmap.h | ||
| Makefile | ||
| rtld-global-offsets.sym | ||
| tininess.h | ||
| tst-get-cpu-features-static.c | ||
| tst-get-cpu-features.c | ||
| Versions | ||