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. --- sysdeps/unix/sysv/linux/x86_64/64/libc.abilist | 1 + 1 file changed, 1 insertion(+) (limited to 'sysdeps/unix/sysv/linux/x86_64/64/libc.abilist') diff --git a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist index 4fff61818b..2744bba4af 100644 --- a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist +++ b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist @@ -2076,6 +2076,7 @@ GLIBC_2.32 sigabbrev_np F GLIBC_2.32 sigdescr_np F GLIBC_2.32 strerrordesc_np F GLIBC_2.32 strerrorname_np F +GLIBC_2.33 __x86_get_cpuid_feature_leaf F GLIBC_2.33 fstat F GLIBC_2.33 fstat64 F GLIBC_2.33 fstatat F -- cgit 1.4.1