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>
golang · Nov 3, 2021 · 7861aae · 7861aae
1 parent ae416a5
commit 7861aae
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Showing 2 changed files with 4 additions and 27 deletions.
diff --git a/cpu/cpu_x86.go b/cpu/cpu_x86.go
@@ -90,9 +90,10 @@ func archInit() {
 		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
@@ -26,27 +26,3 @@ 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