cpu: support darwin/arm64 CPU feature detection

Support ARM64 features detection. The CPU features which are supported by
Apple Silicon M1 are assumed as the minimal set of features for Go programs
running on darwin/arm64.

The ARM64 supporting features are referred to
https://en.wikichip.org/wiki/arm/armv8#ARMv8_Extensions_and_Processor_Features

Author: howjmay

cpu/cpu_arm64.go

@@ -41,7 +41,7 @@ func archInit() {
 	switch runtime.GOOS {
 	case "freebsd":
 		readARM64Registers()
-	case "linux", "netbsd":
+	case "linux", "netbsd", "darwin":
 		doinit()
 	default:
 		// Most platforms don't seem to allow reading these registers.

cpu/cpu_darwin_arm64.go

@@ -0,0 +1,56 @@
+// Copyright 2021 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.
+
+// +build arm64
+// +build darwin
+// +build !ios
+
+package cpu
+
+const (
+	commpageHasNeonFP16      = 0x00000008         // ARM v8.2 NEON FP16 supported
+	commpageHasNeon          = 0x00000100         // Advanced SIMD is supported
+	commpageHasNeonHPFP      = 0x00000200         // Advanced SIMD half-precision
+	commpageHasVfp           = 0x00000400         // VFP is supported
+	commpageHasEvent         = 0x00001000         // WFE/SVE and period event wakeup
+	commpageHasARMv82FHM     = 0x00004000         // Optional ARMv8.2 FMLAL/FMLSL instructions (required in ARMv8.4)
+	commpageHasARMv8Crypto   = 0x01000000         // Optional ARMv8 Crypto extensions
+	commpageHasARMv81Atomics = 0x02000000         // ARMv8.1 Atomic instructions supported
+	commpageHasARMv8Crc32    = 0x04000000         // Optional ARMv8 crc32 instructions (required in ARMv8.1)
+	commpageHasARMv82SHA512  = 0x80000000         // Optional ARMv8.2 SHA512 instructions
+	commpageHasARMv82SHA3    = 0x0000000100000000 // Optional ARMv8.2 SHA3 instructions
+)
+
+func doinit() {
+	ARM64.HasFP = darwinCheckFeatureEnabled(commpageHasVfp)
+	ARM64.HasASIMD = darwinCheckFeatureEnabled(commpageHasNeon)
+	ARM64.HasCRC32 = darwinCheckFeatureEnabled(commpageHasARMv8Crc32)
+	ARM64.HasATOMICS = darwinCheckFeatureEnabled(commpageHasARMv81Atomics)
+	ARM64.HasFPHP = darwinCheckFeatureEnabled(commpageHasNeonFP16)
+	ARM64.HasASIMDHP = darwinCheckFeatureEnabled(commpageHasNeonHPFP)
+	ARM64.HasSHA3 = darwinCheckFeatureEnabled(commpageHasARMv82SHA3)
+	ARM64.HasSHA512 = darwinCheckFeatureEnabled(commpageHasARMv82SHA512)
+	ARM64.HasASIMDFHM = darwinCheckFeatureEnabled(commpageHasARMv82FHM)
+	ARM64.HasSVE = darwinCheckFeatureEnabled(commpageHasEvent)
+
+	// There are no hw.optional sysctl values for the below features on Mac OS 11.0
+	// to detect their supported state dynamically. Assume the CPU features that
+	// Apple Silicon M1 supports to be available as a minimal set of features
+	// to all Go programs running on darwin/arm64.
+	ARM64.HasEVTSTRM = true
+	ARM64.HasAES = true
+	ARM64.HasPMULL = true
+	ARM64.HasSHA1 = true
+	ARM64.HasSHA2 = true
+	ARM64.HasCPUID = true
+	ARM64.HasASIMDRDM = true
+	ARM64.HasJSCVT = true
+	ARM64.HasLRCPC = true
+	ARM64.HasDCPOP = true
+	ARM64.HasSM3 = true
+	ARM64.HasSM4 = true
+	ARM64.HasASIMDDP = true
+}
+
+func darwinCheckFeatureEnabled(feature_vec uint64) bool

cpu/cpu_darwin_arm64.s

@@ -0,0 +1,29 @@
+//go:build arm64 && gc
+// +build arm64
+// +build gc
+
+#include "textflag.h"
+
+// func darwinCheckFeatureEnabled(feature_vec uint64) bool
+TEXT ·darwinCheckFeatureEnabled(SB), NOSPLIT, $0-8
+    MOVD    feature_vec+0(FP), R0
+    MOVD    $0, ret+0(FP) // default to false
+    MOVD    $1, R2        // set R2 as true boolean constan
+
+#ifdef GOOS_darwin   // return if not darwin
+#ifdef GOARCH_arm64  // return if not arm64
+// These values from:
+// https://github.com/apple/darwin-xnu/blob/main/osfmk/arm/cpu_capabilities.h
+#define arm_commpage64_base_address         0x0000000fffffc000
+#define arm_commpage64_cpu_capabilities64   (arm_commpage64_base_address+0x010)
+    MOVD    $0xffffc000, R1
+    MOVK    $(0xf<<32), R1
+    MOVD    (R1), R1
+    AND   R1, R0
+    CBZ      R0, no_feature
+    MOVD    R2, ret+8(FP)
+
+no_feature:
+#endif
+#endif
+    RET

cpu/cpu_other_arm64.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !linux && !netbsd && arm64
-// +build !linux,!netbsd,arm64
+//go:build !linux && !netbsd && !darwin && arm64
+// +build !linux,!netbsd,!darwin,arm64
 
 package cpu
 

cpu/cpu_test.go

@@ -42,7 +42,7 @@ func TestAVX512HasAVX2AndAVX(t *testing.T) {
 }
 
 func TestARM64minimalFeatures(t *testing.T) {
-	if runtime.GOARCH != "arm64" || (runtime.GOOS == "darwin" || runtime.GOOS == "ios") {
+	if runtime.GOARCH != "arm64" || runtime.GOOS == "ios" {
 		return
 	}
 	if !cpu.ARM64.HasASIMD {