H.J. Lu 317f1c0a8a x86-64: Add glibc.cpu.prefer_map_32bit_exec [BZ #28656] ... Crossing 2GB boundaries with indirect calls and jumps can use more branch prediction resources on Intel Golden Cove CPU (see the "Misprediction for Branches >2GB" section in Intel 64 and IA-32 Architectures Optimization Reference Manual.) There is visible performance improvement on workloads with many PLT calls when executable and shared libraries are mmapped below 2GB. Add the Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable or denywrite pages in shared libraries with MAP_32BIT first. NB: 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 the tunable, glibc.cpu.prefer_map_32bit_exec, or the environment variable, LD_PREFER_MAP_32BIT_EXEC. This works only between shared libraries or between shared libraries and executables with addresses below 2GB. PIEs are usually loaded at a random address above 4GB by the kernel.		2023-02-22 18:28:37 -08:00
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cpu-features-preferred_feature_index_1.def	x86-64: Add glibc.cpu.prefer_map_32bit_exec [BZ #28656]	2023-02-22 18:28:37 -08:00
cpu-features.h	Update copyright dates with scripts/update-copyrights	2023-01-06 21:14:39 +00:00