internal/cpu: implement CPU feature detection for openbsd/arm64

OpenBSD 7.1 onwards expose the aarch64 ISAR0 and ISAR1 registers via sysctl:

  $ sysctl machdep
  machdep.compatible=apple,j274
  machdep.id_aa64isar0=153421459058925856
  machdep.id_aa64isar1=1172796674562

Implement CPU feature detection for openbsd/arm64 based on this information.

Fixes #31746

Change-Id: If8a9b2b8fc557e1aaefbcb52f4d1bd9efc43856d
Reviewed-on: https://go-review.googlesource.com/c/go/+/421875
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
Run-TryBot: Ian Lance Taylor <iant@google.com>

src/internal/cpu/cpu_arm64_openbsd.go

@@ -0,0 +1,60 @@
+// Copyright 2022 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 arm64
+
+package cpu
+
+const (
+	// From OpenBSD's sys/sysctl.h.
+	_CTL_MACHDEP = 7
+
+	// From OpenBSD's machine/cpu.h.
+	_CPU_ID_AA64ISAR0 = 2
+	_CPU_ID_AA64ISAR1 = 3
+)
+
+func extractBits(data uint64, start, end uint) uint {
+	return (uint)(data>>start) & ((1 << (end - start + 1)) - 1)
+}
+
+//go:noescape
+func sysctlUint64(mib []uint32) (uint64, bool)
+
+func osInit() {
+	// Get ID_AA64ISAR0 from sysctl.
+	isar0, ok := sysctlUint64([]uint32{_CTL_MACHDEP, _CPU_ID_AA64ISAR0})
+	if !ok {
+		return
+	}
+
+	// ID_AA64ISAR0_EL1
+	switch extractBits(isar0, 4, 7) {
+	case 1:
+		ARM64.HasAES = true
+	case 2:
+		ARM64.HasAES = true
+		ARM64.HasPMULL = true
+	}
+
+	switch extractBits(isar0, 8, 11) {
+	case 1:
+		ARM64.HasSHA1 = true
+	}
+
+	switch extractBits(isar0, 12, 15) {
+	case 1, 2:
+		ARM64.HasSHA2 = true
+	}
+
+	switch extractBits(isar0, 16, 19) {
+	case 1:
+		ARM64.HasCRC32 = true
+	}
+
+	switch extractBits(isar0, 20, 23) {
+	case 2:
+		ARM64.HasATOMICS = true
+	}
+}

src/internal/cpu/cpu_arm64_other.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 arm64 && !linux && !freebsd && !android && (!darwin || ios)
+//go:build arm64 && !linux && !freebsd && !android && (!darwin || ios) && !openbsd
 
 package cpu
 

src/runtime/os_openbsd.go

@@ -51,6 +51,21 @@ func sysctlInt(mib []uint32) (int32, bool) {
 	return out, true
 }
 
+func sysctlUint64(mib []uint32) (uint64, bool) {
+	var out uint64
+	nout := unsafe.Sizeof(out)
+	ret := sysctl(&mib[0], uint32(len(mib)), (*byte)(unsafe.Pointer(&out)), &nout, nil, 0)
+	if ret < 0 {
+		return 0, false
+	}
+	return out, true
+}
+
+//go:linkname internal_cpu_sysctlUint64 internal/cpu.sysctlUint64
+func internal_cpu_sysctlUint64(mib []uint32) (uint64, bool) {
+	return sysctlUint64(mib)
+}
+
 func getncpu() int32 {
 	// Try hw.ncpuonline first because hw.ncpu would report a number twice as
 	// high as the actual CPUs running on OpenBSD 6.4 with hyperthreading