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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.
53 lines
1.8 KiB
C
53 lines
1.8 KiB
C
/* Initialize CPU feature data via IFUNC relocation.
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Copyright (C) 2015-2021 Free Software Foundation, Inc.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <ldsodefs.h>
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#ifdef SHARED
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# include <cpu-features.c>
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/* NB: Normally, DL_PLATFORM_INIT calls init_cpu_features to initialize
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CPU features in dynamic executable. But when loading ld.so inside of
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static executable, DL_PLATFORM_INIT isn't called and IFUNC relocation
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is used to call init_cpu_features. In static executable, it is called
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once by IFUNC relocation. In dynamic executable, it is called twice
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by DL_PLATFORM_INIT and by IFUNC relocation. */
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extern void __x86_cpu_features (void) attribute_hidden;
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const void (*__x86_cpu_features_p) (void) attribute_hidden
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= __x86_cpu_features;
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void
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_dl_x86_init_cpu_features (void)
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{
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struct cpu_features *cpu_features = __get_cpu_features ();
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if (cpu_features->basic.kind == arch_kind_unknown)
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init_cpu_features (cpu_features);
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}
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__ifunc (__x86_cpu_features, __x86_cpu_features, NULL, void,
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_dl_x86_init_cpu_features);
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#endif
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#undef _dl_x86_get_cpu_features
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const struct cpu_features *
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_dl_x86_get_cpu_features (void)
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{
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return &GLRO(dl_x86_cpu_features);
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}
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