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| author | H.J. Lu <hjl.tools@gmail.com> | 2020-12-25 07:30:46 -0800 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2021-01-21 05:58:17 -0800 |
| commit | ff6d62e9edb5dce537a6dd4a237d6053f331f09c (patch) | |
| tree | 0ab59c339851a55cc20ef5c06edaac0119f2b0e2 /sysdeps/x86_64 | |
| parent | d7ee6bd8c217a4deb756739039fa9c165d26ec43 (diff) | |
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<sys/platform/x86.h>: Remove the C preprocessor magic
In <sys/platform/x86.h>, define CPU features as enum instead of using
the C preprocessor magic to make it easier to wrap this functionality
in other languages. Move the C preprocessor magic to internal header
for better GCC codegen when more than one features are checked in a
single expression as in x86-64 dl-hwcaps-subdirs.c.
1. Rename COMMON_CPUID_INDEX_XXX to CPUID_INDEX_XXX.
2. Move CPUID_INDEX_MAX to sysdeps/x86/include/cpu-features.h.
3. Remove struct cpu_features and __x86_get_cpu_features from
<sys/platform/x86.h>.
4. Add __x86_get_cpuid_feature_leaf to <sys/platform/x86.h> and put it
in libc.
5. Make __get_cpu_features() private to glibc.
6. Replace __x86_get_cpu_features(N) with __get_cpu_features().
7. Add _dl_x86_get_cpu_features to GLIBC_PRIVATE.
8. Use a single enum index for each CPU feature detection.
9. Pass the CPUID feature leaf to __x86_get_cpuid_feature_leaf.
10. Return zero struct cpuid_feature for the older glibc binary with a
smaller CPUID_INDEX_MAX [BZ #27104].
11. Inside glibc, use the C preprocessor magic so that cpu_features data
can be loaded just once leading to more compact code for glibc.
256 bits are used for each CPUID leaf. Some leaves only contain a few
features. We can add exceptions to such leaves. But it will increase
code sizes and it is harder to provide backward/forward compatibilities
when new features are added to such leaves in the future.
When new leaves are added, _rtld_global_ro offsets will change which
leads to race condition during in-place updates. We may avoid in-place
updates by
1. Rename the old glibc.
2. Install the new glibc.
3. Remove the old glibc.
NB: A function, __x86_get_cpuid_feature_leaf , is used to avoid the copy
relocation issue with IFUNC resolver as shown in IFUNC resolver tests.
Diffstat (limited to 'sysdeps/x86_64')
| -rw-r--r-- | sysdeps/x86_64/dl-hwcaps-subdirs.c | 3 | ||||
| -rw-r--r-- | sysdeps/x86_64/tst-glibc-hwcaps.c | 3 |
2 files changed, 2 insertions, 4 deletions
diff --git a/sysdeps/x86_64/dl-hwcaps-subdirs.c b/sysdeps/x86_64/dl-hwcaps-subdirs.c index 4acd343183..b8f27d7f98 100644 --- a/sysdeps/x86_64/dl-hwcaps-subdirs.c +++ b/sysdeps/x86_64/dl-hwcaps-subdirs.c @@ -27,8 +27,7 @@ enum { subdirs_count = 3 }; /* Number of components in _dl_hwcaps_subdirs. */ uint32_t _dl_hwcaps_subdirs_active (void) { - const struct cpu_features *cpu_features - = __x86_get_cpu_features (COMMON_CPUID_INDEX_MAX); + const struct cpu_features *cpu_features = __get_cpu_features (); unsigned int isa_level = get_isa_level (cpu_features); int active = 0; diff --git a/sysdeps/x86_64/tst-glibc-hwcaps.c b/sysdeps/x86_64/tst-glibc-hwcaps.c index 37b61d3c84..4c8d24b3f2 100644 --- a/sysdeps/x86_64/tst-glibc-hwcaps.c +++ b/sysdeps/x86_64/tst-glibc-hwcaps.c @@ -30,8 +30,7 @@ extern int marker4 (void); static int compute_level (void) { - const struct cpu_features *cpu_features - = __x86_get_cpu_features (COMMON_CPUID_INDEX_MAX); + const struct cpu_features *cpu_features = __get_cpu_features (); unsigned int isa_level = get_isa_level (cpu_features); if (!(isa_level & GNU_PROPERTY_X86_ISA_1_V2)) |