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| author | H.J. Lu <hjl.tools@gmail.com> | 2023-01-26 08:26:18 -0800 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2023-02-22 18:28:37 -0800 |
| commit | 317f1c0a8a71a862b1e600ff5386b08e02cf4b95 (patch) | |
| tree | c380e1c78d06fbb479bb39c82e8dd28119eef13f /sysdeps/x86/cpu-features.c | |
| parent | bde121872001d8f3224eeafa5b7effb871c3fbca (diff) | |
| download | glibc-317f1c0a8a71a862b1e600ff5386b08e02cf4b95.zip glibc-317f1c0a8a71a862b1e600ff5386b08e02cf4b95.tar.gz glibc-317f1c0a8a71a862b1e600ff5386b08e02cf4b95.tar.bz2 | |
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.
Diffstat (limited to 'sysdeps/x86/cpu-features.c')
| -rw-r--r-- | sysdeps/x86/cpu-features.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index a2197ed..822688e 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -27,6 +27,16 @@ extern void TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *) attribute_hidden; +# ifdef __LP64__ +static void +TUNABLE_CALLBACK (set_prefer_map_32bit_exec) (tunable_val_t *valp) +{ + if (valp->numval) + GLRO(dl_x86_cpu_features).preferred[index_arch_Prefer_MAP_32BIT_EXEC] + |= bit_arch_Prefer_MAP_32BIT_EXEC; +} +# endif + # if CET_ENABLED extern void TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *) attribute_hidden; @@ -705,6 +715,11 @@ no_cpuid: #if HAVE_TUNABLES TUNABLE_GET (hwcaps, tunable_val_t *, TUNABLE_CALLBACK (set_hwcaps)); +# ifdef __LP64__ + TUNABLE_GET (prefer_map_32bit_exec, tunable_val_t *, + TUNABLE_CALLBACK (set_prefer_map_32bit_exec)); +# endif + bool disable_xsave_features = false; if (!CPU_FEATURE_USABLE_P (cpu_features, OSXSAVE)) |