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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
/* Architecture-specific glibc-hwcaps subdirectories. x86 version.
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Copyright (C) 2020-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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 <dl-hwcaps.h>
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#include <cpu-features.h>
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#include <ldsodefs.h>
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#include <get-isa-level.h>
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const char _dl_hwcaps_subdirs[] = "x86-64-v4:x86-64-v3:x86-64-v2";
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enum { subdirs_count = 3 }; /* Number of components in _dl_hwcaps_subdirs. */
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uint32_t
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_dl_hwcaps_subdirs_active (void)
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{
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const struct cpu_features *cpu_features = __get_cpu_features ();
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unsigned int isa_level = get_isa_level (cpu_features);
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int active = 0;
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/* Test in reverse preference order. */
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/* x86-64-v2. */
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if (!(isa_level & GNU_PROPERTY_X86_ISA_1_V2))
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return _dl_hwcaps_subdirs_build_bitmask (subdirs_count, active);
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++active;
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/* x86-64-v3. */
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if (!(isa_level & GNU_PROPERTY_X86_ISA_1_V3))
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return _dl_hwcaps_subdirs_build_bitmask (subdirs_count, active);
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++active;
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/* x86-64-v4. */
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if (!(isa_level & GNU_PROPERTY_X86_ISA_1_V4))
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return _dl_hwcaps_subdirs_build_bitmask (subdirs_count, active);
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++active;
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return _dl_hwcaps_subdirs_build_bitmask (subdirs_count, active);
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}
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