diff options
| 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 13:16:02 -0800 |
| commit | b9eb92ab05204df772eb4929eccd018637c9f3e9 (patch) | |
| tree | f272c9a3e0ef7232d0714cfda7e79b040a757fb9 /sysdeps/x86/cpu-features.h | |
| parent | c9afcaaafaf9126a973883528eed8d0058a264c0 (diff) | |
Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT
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.
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 80edbee75c..93bee69eaf 100644 --- a/sysdeps/x86/cpu-features.h +++ b/sysdeps/x86/cpu-features.h @@ -33,6 +33,7 @@ #define bit_AVX512DQ_Usable (1 << 13) #define bit_I586 (1 << 14) #define bit_I686 (1 << 15) +#define bit_Prefer_MAP_32BIT_EXEC (1 << 16) /* CPUID Feature flags. */ @@ -97,6 +98,7 @@ # define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE # define index_I586 FEATURE_INDEX_1*FEATURE_SIZE # define index_I686 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__ @@ -248,6 +250,7 @@ extern const struct cpu_features *__get_cpu_features (void) # define index_AVX512DQ_Usable FEATURE_INDEX_1 # define index_I586 FEATURE_INDEX_1 # define index_I686 FEATURE_INDEX_1 +# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1 #endif /* !__ASSEMBLER__ */ |