From ff6d62e9edb5dce537a6dd4a237d6053f331f09c Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Fri, 25 Dec 2020 07:30:46 -0800 Subject: : Remove the C preprocessor magic In , 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 . 4. Add __x86_get_cpuid_feature_leaf to 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. --- manual/platform.texi | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) (limited to 'manual') diff --git a/manual/platform.texi b/manual/platform.texi index b67683a..6caf68d 100644 --- a/manual/platform.texi +++ b/manual/platform.texi @@ -142,13 +142,10 @@ reserved. Facilities specific to X86 that are not specific to a particular operating system are declared in @file{sys/platform/x86.h}. -@deftypefun {const struct cpu_features *} __x86_get_cpu_features (unsigned int @var{max}) +@deftypefun {const struct cpuid_feature *} __x86_get_cpuid_feature_leaf (unsigned int @var{leaf}) @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} Return a pointer to x86 CPU feature structure used by query macros for x86 -CPU features. If @var{max} exceeds @code{COMMON_CPUID_INDEX_MAX} which -is the limit of the CPUID leaves supported by @Theglibc{}, the function -returns @code{NULL}, indicating that the queried processor feature is -unsupported by @Theglibc{} run-time. +CPU feature @var{leaf}. @end deftypefun @deftypefn Macro int HAS_CPU_FEATURE (@var{name}) -- cgit v1.1