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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. |
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| sh | ||
| sysv/linux | ||
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| confstr.h | ||
| get_child_max.c | ||
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| getpagesize.c | ||
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| ifreq.c | ||
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| make-syscalls.sh | ||
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| setxid.h | ||
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| syscall-template.S | ||
| syscall.S | ||
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| sysdep.h | ||