cpu: avoid illegal instruction on openbsd/arm64

On OpenBSD, this package tries to read a privileged register, which
results in a SIGILL. Use the same workaround as Android, iOS and NetBSD.

Update golang/go#31746

Change-Id: I981249310169bc30b018c1a157529a4e46597d81
Reviewed-on: https://go-review.googlesource.com/c/sys/+/263337
Trust: Tobias Klauser <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Joel Sing <[email protected]>

Author: tklauser

cpu/cpu_arm64.go

@@ -39,14 +39,17 @@ func initOptions() {
 
 func archInit() {
 	switch runtime.GOOS {
-	case "android", "darwin", "ios", "netbsd":
+	case "android", "darwin", "ios", "netbsd", "openbsd":
 		// Android and iOS don't seem to allow reading these registers.
 		//
 		// NetBSD:
 		// ID_AA64ISAR0_EL1 is a privileged register and cannot be read from EL0.
 		// It can be read via sysctl(3). Example for future implementers:
 		// https://nxr.netbsd.org/xref/src/usr.sbin/cpuctl/arch/aarch64.c
 		//
+		// OpenBSD:
+		// See https://golang.org/issue/31746
+		//
 		// Fake the minimal features expected by
 		// TestARM64minimalFeatures.
 		ARM64.HasASIMD = true