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<sys/platform/x86.h>: Remove the C preprocessor magic

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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.
This commit is contained in:
H.J. Lu
2020-12-25 07:30:46 -08:00
parent d7ee6bd8c2
commit ff6d62e9ed
24 changed files with 1165 additions and 850 deletions
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29
sysdeps/x86/tst-get-cpu-features.c
View File

@ -1,4 +1,4 @@
/* Test case for __x86_get_cpu_features interface
/* Test case for <sys/platform/x86.h> interface
Copyright (C) 2015-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
@ -33,36 +33,9 @@
printf (" " #name "\n"); \
}
static const char * const cpu_kinds[] =
{
"Unknown",
"Intel",
"AMD",
"ZHAOXIN",
"Other",
};
static int
do_test (void)
{
const struct cpu_features *cpu_features = __x86_get_cpu_features (0);
switch (cpu_features->basic.kind)
{
case arch_kind_intel:
case arch_kind_amd:
case arch_kind_zhaoxin:
case arch_kind_other:
printf ("Vendor: %s\n", cpu_kinds[cpu_features->basic.kind]);
printf ("Family: 0x%x\n", cpu_features->basic.family);
printf ("Model: 0x%x\n", cpu_features->basic.model);
printf ("Stepping: 0x%x\n", cpu_features->basic.stepping);
break;
default:
abort ();
}
#ifdef __SSE2__
TEST_VERIFY_EXIT (HAS_CPU_FEATURE (SSE2));
#endif