cpu: disable AVX+ on netbsd/amd64

netbsd's signal handler corrupts bits 128 and higher
in the AVX registers.

Update golang/go#80285

Change-Id: I6f486795dede81089f5ead305d10692c421d9566
Reviewed-on: https://go-review.googlesource.com/c/sys/+/797900
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Auto-Submit: Keith Randall <khr@golang.org>

cpu/cpu_netbsd_amd64.go

diff --git a/cpu/cpu_netbsd_amd64.go b/cpu/cpu_netbsd_amd64.go
new file mode 100644
index 0000000..4f981b1
--- /dev/null
+++ b/cpu/cpu_netbsd_amd64.go
@@ -0,0 +1,47 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build netbsd && amd64 && gc
+
+package cpu
+
+func doinit() {
+	// NetBSD corrupts avx registers when receiving signals.
+	// See issue 80285.
+	// TODO: when NetBSD fixes the bug, add a version
+	// check and skip here.
+	X86.HasAVX = false
+	X86.HasAVX2 = false
+	// Set these also, just to be safe
+	X86.HasAVXVNNI = false
+	X86.HasAVX512 = false
+	X86.HasAVX512F = false
+	X86.HasAVX512CD = false
+	X86.HasAVX512CD = false
+	X86.HasAVX512ER = false
+	X86.HasAVX512PF = false
+	X86.HasAVX512VL = false
+	X86.HasAVX512BW = false
+	X86.HasAVX512DQ = false
+	X86.HasAVX512IFMA = false
+	X86.HasAVX512VBMI = false
+	X86.HasAVX5124VNNIW = false
+	X86.HasAVX5124FMAPS = false
+	X86.HasAVX512VPOPCNTDQ = false
+	X86.HasAVX512VPCLMULQDQ = false
+	X86.HasAVX512VNNI = false
+	X86.HasAVX512GFNI = false
+	X86.HasAVX512VAES = false
+	X86.HasAVX512VBMI2 = false
+	X86.HasAVX512BITALG = false
+	X86.HasAVX512BF16 = false
+	X86.HasAVXIFMA = false
+	X86.HasAVXVNNI = false
+	X86.HasAVXVNNIInt8 = false
+
+}
+
+func darwinSupportsAVX512() bool {
+	panic("only implemented for gc && amd64 && darwin")
+}

cpu/cpu_other_x86.go

diff --git a/cpu/cpu_other_x86.go b/cpu/cpu_other_x86.go
index a0fd7e2..82b7580 100644
--- a/cpu/cpu_other_x86.go
+++ b/cpu/cpu_other_x86.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build 386 || amd64p32 || (amd64 && (!darwin || !gc))
+//go:build 386 || amd64p32 || (amd64 && ((!darwin && !netbsd) || !gc))
 
 package cpu