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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 /sysdeps/x86/cpu-features.h | |
| 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 'sysdeps/x86/cpu-features.h')
| -rw-r--r-- | sysdeps/x86/cpu-features.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h index 22e5abb919..f5508d1d8a 100644 --- a/sysdeps/x86/cpu-features.h +++ b/sysdeps/x86/cpu-features.h @@ -31,6 +31,7 @@ #define bit_AVX_Fast_Unaligned_Load (1 << 11) #define bit_AVX512F_Usable (1 << 12) #define bit_AVX512DQ_Usable (1 << 13) +#define bit_Prefer_MAP_32BIT_EXEC (1 << 14) /* CPUID Feature flags. */ @@ -89,6 +90,7 @@ # define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1*FEATURE_SIZE # define index_AVX512F_Usable FEATURE_INDEX_1*FEATURE_SIZE # define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE +# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1*FEATURE_SIZE # if defined (_LIBC) && !IS_IN (nonlib) # ifdef __x86_64__ @@ -234,6 +236,7 @@ extern const struct cpu_features *__get_cpu_features (void) # define index_AVX_Fast_Unaligned_Load FEATURE_INDEX_1 # define index_AVX512F_Usable FEATURE_INDEX_1 # define index_AVX512DQ_Usable FEATURE_INDEX_1 +# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1 #endif /* !__ASSEMBLER__ */ |