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58978af429
Use 'volatile' for the CPU feature masks and dispatched function pointers. We don't need memory barriers for them, so 'volatile' is good enough to stop the compiler from inserting bogus reads/writes.
115 lines
3.4 KiB
C
115 lines
3.4 KiB
C
/*
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* x86/cpu_features.c - feature detection for x86 processors
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*
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* Copyright 2016 Eric Biggers
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following
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* conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include "cpu_features.h"
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#if X86_CPU_FEATURES_ENABLED
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volatile u32 _cpu_features = 0;
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/* With old GCC versions we have to manually save and restore the x86_32 PIC
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* register (ebx). See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47602 */
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#if defined(__i386__) && defined(__PIC__)
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# define EBX_CONSTRAINT "=r"
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#else
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# define EBX_CONSTRAINT "=b"
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#endif
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/* Execute the CPUID instruction. */
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static inline void
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cpuid(u32 leaf, u32 subleaf, u32 *a, u32 *b, u32 *c, u32 *d)
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{
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__asm__(".ifnc %%ebx, %1; mov %%ebx, %1; .endif\n"
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"cpuid \n"
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".ifnc %%ebx, %1; xchg %%ebx, %1; .endif\n"
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: "=a" (*a), EBX_CONSTRAINT (*b), "=c" (*c), "=d" (*d)
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: "a" (leaf), "c" (subleaf));
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}
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/* Read an extended control register. */
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static inline u64
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read_xcr(u32 index)
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{
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u32 edx, eax;
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/* Execute the "xgetbv" instruction. Old versions of binutils do not
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* recognize this instruction, so list the raw bytes instead. */
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__asm__ (".byte 0x0f, 0x01, 0xd0" : "=d" (edx), "=a" (eax) : "c" (index));
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return ((u64)edx << 32) | eax;
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}
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#define IS_SET(reg, bit) ((reg) & ((u32)1 << (bit)))
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/* Initialize _cpu_features with bits for interesting processor features. */
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void setup_cpu_features(void)
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{
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u32 features = 0;
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u32 dummy1, dummy2, dummy3, dummy4;
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u32 max_function;
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u32 features_1, features_2, features_3, features_4;
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bool os_saves_ymm_regs = false;
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/* Get maximum supported function */
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cpuid(0, 0, &max_function, &dummy2, &dummy3, &dummy4);
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if (max_function < 1)
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goto out;
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/* Standard feature flags */
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cpuid(1, 0, &dummy1, &dummy2, &features_2, &features_1);
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if (IS_SET(features_1, 26))
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features |= X86_CPU_FEATURE_SSE2;
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if (IS_SET(features_2, 1))
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features |= X86_CPU_FEATURE_PCLMULQDQ;
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if (IS_SET(features_2, 27)) /* OSXSAVE set? */
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if ((read_xcr(0) & 0x6) == 0x6)
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os_saves_ymm_regs = true;
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if (os_saves_ymm_regs && IS_SET(features_2, 28))
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features |= X86_CPU_FEATURE_AVX;
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if (max_function < 7)
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goto out;
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/* Extended feature flags */
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cpuid(7, 0, &dummy1, &features_3, &features_4, &dummy4);
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if (os_saves_ymm_regs && IS_SET(features_3, 5))
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features |= X86_CPU_FEATURE_AVX2;
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if (IS_SET(features_3, 8))
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features |= X86_CPU_FEATURE_BMI2;
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out:
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_cpu_features = features | X86_CPU_FEATURES_KNOWN;
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}
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#endif /* X86_CPU_FEATURES_ENABLED */
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