cpu: support reading arm64 CPU feature registers

This allows to detect ARM64 CPU features on non-Linux systems. On Linux,
this is used in case /proc/self/auxv cannot be read.

Change-Id: I67d55e989f2beda0c05a97ca5e55781840a8e01c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/209478
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

cpu/cpu_arm64.go

@@ -0,0 +1,134 @@
+// Copyright 2019 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.
+
+package cpu
+
+import "runtime"
+
+const cacheLineSize = 64
+
+func init() {
+	switch runtime.GOOS {
+	case "darwin":
+		// iOS does not seem to allow reading these registers
+	case "android", "linux":
+		doinit()
+	default:
+		readARM64Registers()
+	}
+}
+
+func readARM64Registers() {
+	Initialized = true
+
+	// ID_AA64ISAR0_EL1
+	isar0 := getisar0()
+
+	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:
+		ARM64.HasSHA2 = true
+	case 2:
+		ARM64.HasSHA2 = true
+		ARM64.HasSHA512 = true
+	}
+
+	switch extractBits(isar0, 16, 19) {
+	case 1:
+		ARM64.HasCRC32 = true
+	}
+
+	switch extractBits(isar0, 20, 23) {
+	case 2:
+		ARM64.HasATOMICS = true
+	}
+
+	switch extractBits(isar0, 28, 31) {
+	case 1:
+		ARM64.HasASIMDRDM = true
+	}
+
+	switch extractBits(isar0, 32, 35) {
+	case 1:
+		ARM64.HasSHA3 = true
+	}
+
+	switch extractBits(isar0, 36, 39) {
+	case 1:
+		ARM64.HasSM3 = true
+	}
+
+	switch extractBits(isar0, 40, 43) {
+	case 1:
+		ARM64.HasSM4 = true
+	}
+
+	switch extractBits(isar0, 44, 47) {
+	case 1:
+		ARM64.HasASIMDDP = true
+	}
+
+	// ID_AA64ISAR1_EL1
+	isar1 := getisar1()
+
+	switch extractBits(isar1, 0, 3) {
+	case 1:
+		ARM64.HasDCPOP = true
+	}
+
+	switch extractBits(isar1, 12, 15) {
+	case 1:
+		ARM64.HasJSCVT = true
+	}
+
+	switch extractBits(isar1, 16, 19) {
+	case 1:
+		ARM64.HasFCMA = true
+	}
+
+	switch extractBits(isar1, 20, 23) {
+	case 1:
+		ARM64.HasLRCPC = true
+	}
+
+	// ID_AA64PFR0_EL1
+	pfr0 := getpfr0()
+
+	switch extractBits(pfr0, 16, 19) {
+	case 0:
+		ARM64.HasFP = true
+	case 1:
+		ARM64.HasFP = true
+		ARM64.HasFPHP = true
+	}
+
+	switch extractBits(pfr0, 20, 23) {
+	case 0:
+		ARM64.HasASIMD = true
+	case 1:
+		ARM64.HasASIMD = true
+		ARM64.HasASIMDHP = true
+	}
+
+	switch extractBits(pfr0, 32, 35) {
+	case 1:
+		ARM64.HasSVE = true
+	}
+}
+
+func extractBits(data uint64, start, end uint) uint {
+	return (uint)(data>>start) & ((1 << (end - start + 1)) - 1)
+}