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/* __builtin_cpu_supports() wrapper that honors GLIBC_TUNABLES=glibc.cpu.hwcaps
Copyright 2025-2026 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#ifndef _CPU_SUPPORTS_H
# define _CPU_SUPPORTS_H
# include <string.h>
# include "attribute.h"
/* The main interface to this module is cpu_supports("feature"),
which is like __builtin_cpu_supports("feature"), but we also check if
the feature has been disabled by the GLIBC_TUNABLES env variable.
Notes:
You can call this with any "feature" accepted by __builtin_cpu_supports(),
but we only check that the feature is disabled against the set listed
in gcc_feature_to_glibc_hwcap() below.
We don't currently support amalgamated feature checks like
cpu_supports("feature1+feature2").
We do not need glibc support for GLIBC_TUNABLES,
rather mimic that functionality on all systems. */
# define cpu_supports(feature) \
(cpu_may_support (feature) && 0 < __builtin_cpu_supports (feature))
/* Check if the feature has been disabled by GLIBC_TUNABLES,
but do NOT call __builtin_cpu_supports(), as some platforms
use other interfaces like getauxval() instead. */
# define cpu_may_support(feature) \
(hwcap_allowed (gcc_feature_to_glibc_hwcap (feature)))
/* Return the glibc.cpu.hwcaps setting (prepended with "-"),
corresponding to the passed gcc _builtin_cpu_supports(FEATURE).
Supported hwcaps can be identified from the bit_cpu_* defines
in GLIBC's sysdeps/x86/include/cpu-features.h
Note this mapping should resolve at compile time. */
ATTRIBUTE_PURE
static inline char const *
gcc_feature_to_glibc_hwcap (char const *feature)
{
char const *hwcap = NULL;
if (0) {}
/* x64_64 */
else if (streq (feature, "avx")) hwcap = "-AVX";
else if (streq (feature, "avx2")) hwcap = "-AVX2";
else if (streq (feature, "avx512bw")) hwcap = "-AVX512BW";
else if (streq (feature, "avx512f")) hwcap = "-AVX512F";
else if (streq (feature, "pclmul")) hwcap = "-PCLMULQDQ";
else if (streq (feature, "vpclmulqdq")) hwcap = "-VPCLMULQDQ";
/* aarch64 */
else if (streq (feature, "pmull")) hwcap = "-PMULL";
return hwcap;
}
/* Support GLIBC's interface to disable features using:
export GLIBC_TUNABLES=glibc.cpu.hwcaps=-AVX512F,-AVX2,-AVX,-PMULL
Return true if the HWCAP is allowed. */
extern bool hwcap_allowed (char const *glibc_hwcap);
/* Set to true to enable reparsing of GLIBC_TUNABLES on each call.
This can be useful for testing. Off by default. */
extern bool hwcap_allowed_nocache;
#endif /* _CPU_SUPPORTS_H */
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