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>

2 files changed, 61 insertions, 1 deletions

diff --git a/src/internal/cpu/cpu_arm64_openbsd.go b/src/internal/cpu/cpu_arm64_openbsd.go
new file mode 100644
index 0000000000..2b284ebd03
--- /dev/null
+++ b/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
+	}
+}
diff --git a/src/internal/cpu/cpu_arm64_other.go b/src/internal/cpu/cpu_arm64_other.go
index d313648cb7..44592cfced 100644
--- a/src/internal/cpu/cpu_arm64_other.go
+++ b/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