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cpu: fix AVX512 support detection on Darwin

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Summary: On darwin/amd64, it is not adequate to use OSXSAVE
bits to determine AVX512 availabilty. The reason is involved.
See github issue for details.

The fix consists of implementing Apple's recommended approach
using the process commpage cpu_capabilities bits to determine
availability of AVX512.

Fixes golang/go#43089

Change-Id: I1ba89965498863d268fbf2e427dbfd6429c7409f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/285572
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Martin Möhrmann <moehrmann@google.com>
This commit is contained in:
Vaughn Iverson
2021-05-03 07:37:44 +00:00
committed by Martin Möhrmann
parent 71e4cd670f
commit b677753862
4 changed files with 42 additions and 2 deletions
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cpu/cpu_x86.s
+24
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@@ -26,3 +26,27 @@ TEXT ·xgetbv(SB),NOSPLIT,$0-8
MOVL AX, eax+0(FP)
MOVL DX, edx+4(FP)
RET
// func darwinSupportsAVX512() bool
TEXT ·darwinSupportsAVX512(SB), NOSPLIT, $0-1
MOVB $0, ret+0(FP) // default to false
#ifdef GOOS_darwin // return if not darwin
#ifdef GOARCH_amd64 // return if not amd64
// These values from:
// https://github.com/apple/darwin-xnu/blob/xnu-4570.1.46/osfmk/i386/cpu_capabilities.h
#define commpage64_base_address 0x00007fffffe00000
#define commpage64_cpu_capabilities64 (commpage64_base_address+0x010)
#define commpage64_version (commpage64_base_address+0x01E)
#define hasAVX512F 0x0000004000000000
MOVQ $commpage64_version, BX
CMPW (BX), $13 // cpu_capabilities64 undefined in versions < 13
JL no_avx512
MOVQ $commpage64_cpu_capabilities64, BX
MOVQ $hasAVX512F, CX
TESTQ (BX), CX
JZ no_avx512
MOVB $1, ret+0(FP)
no_avx512:
#endif
#endif
RET