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x86_simd_caps: check max cpuid before testing AVX2

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structured extended feature flags require eax = 7; avoids incorrectly
detecting avx2 on some older processors that support avx.

from [1]:
INPUT EAX = 0: Returns CPUID’s Highest Value for Basic Processor
Information and the Vendor Identification String

[1] http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html

Change-Id: I6b4735b5f7b7729a815e428fca767d1e5a10bcab
This commit is contained in:
James Zern 2015-04-24 19:21:53 -07:00
parent b3e411e481
commit abff8b24b9
1 changed files with 8 additions and 6 deletions
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14
vpx_ports/x86.h
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@ -152,7 +152,7 @@ static INLINE int
x86_simd_caps(void) { x86_simd_caps(void) {
unsigned int flags = 0; unsigned int flags = 0;
unsigned int mask = ~0; unsigned int mask = ~0;
unsigned int reg_eax, reg_ebx, reg_ecx, reg_edx; unsigned int max_cpuid_val, reg_eax, reg_ebx, reg_ecx, reg_edx;
char *env; char *env;
(void)reg_ebx; (void)reg_ebx;
@ -168,9 +168,9 @@ x86_simd_caps(void) {
mask = strtol(env, NULL, 0); mask = strtol(env, NULL, 0);
/* Ensure that the CPUID instruction supports extended features */ /* Ensure that the CPUID instruction supports extended features */
cpuid(0, 0, reg_eax, reg_ebx, reg_ecx, reg_edx); cpuid(0, 0, max_cpuid_val, reg_ebx, reg_ecx, reg_edx);
if (reg_eax < 1) if (max_cpuid_val < 1)
return 0; return 0;
/* Get the standard feature flags */ /* Get the standard feature flags */
@ -193,10 +193,12 @@ x86_simd_caps(void) {
if ((xgetbv() & 0x6) == 0x6) { if ((xgetbv() & 0x6) == 0x6) {
flags |= HAS_AVX; flags |= HAS_AVX;
/* Get the leaf 7 feature flags. Needed to check for AVX2 support */ if (max_cpuid_val >= 7) {
cpuid(7, 0, reg_eax, reg_ebx, reg_ecx, reg_edx); /* Get the leaf 7 feature flags. Needed to check for AVX2 support */
cpuid(7, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
if (reg_ebx & BIT(5)) flags |= HAS_AVX2; if (reg_ebx & BIT(5)) flags |= HAS_AVX2;
}
} }
} }