cpu: pretend AVX-512 is disabled on Darwin
Darwin doesn't save/restore the AVX-512 mask registers when
processing a signal. Go generates lots of signals, which cause
the mask registers to randomly get clobbered. Better to pretend
that AVX-512 isn't supported.
Update golang/go#49233
Change-Id: I0dda77a6f205e10eefccd82e6f4f0f184dae42d9
Reviewed-on: https://go-review.googlesource.com/c/sys/+/361255
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Martin Möhrmann <martin@golang.org>
diff --git a/cpu/cpu_x86.go b/cpu/cpu_x86.go
index 5ea287b..f5aacfc 100644
--- a/cpu/cpu_x86.go
+++ b/cpu/cpu_x86.go
@@ -90,9 +90,10 @@
osSupportsAVX = isSet(1, eax) && isSet(2, eax)
if runtime.GOOS == "darwin" {
- // Check darwin commpage for AVX512 support. Necessary because:
- // https://github.com/apple/darwin-xnu/blob/0a798f6738bc1db01281fc08ae024145e84df927/osfmk/i386/fpu.c#L175-L201
- osSupportsAVX512 = osSupportsAVX && darwinSupportsAVX512()
+ // Darwin doesn't save/restore AVX-512 mask registers correctly across signal handlers.
+ // Since users can't rely on mask register contents, let's not advertise AVX-512 support.
+ // See issue 49233.
+ osSupportsAVX512 = false
} else {
// Check if OPMASK and ZMM registers have OS support.
osSupportsAVX512 = osSupportsAVX && isSet(5, eax) && isSet(6, eax) && isSet(7, eax)
diff --git a/cpu/cpu_x86.s b/cpu/cpu_x86.s
index b748ba5..39acab2 100644
--- a/cpu/cpu_x86.s
+++ b/cpu/cpu_x86.s
@@ -26,27 +26,3 @@
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
