cpu: support darwin/arm64 feature detection

cpu/cpu.go

@@ -76,7 +76,7 @@ var X86 struct {
 }
 
 // ARM64 contains the supported CPU features of the
-// current ARMv8(aarch64) platform. If the current platform
+// current ARMv8 (aarch64) platform. If the current platform
 // is not arm64 then all feature flags are false.
 var ARM64 struct {
 	_           CacheLinePad

cpu/cpu_arm64.go

@@ -45,7 +45,7 @@ func archInit() {
 	switch runtime.GOOS {
 	case "freebsd":
 		readARM64Registers()
-	case "linux", "netbsd", "openbsd":
+	case "darwin", "linux", "netbsd", "openbsd":
 		doinit()
 	default:
 		// Many platforms don't seem to allow reading these registers.

cpu/cpu_darwin_arm64.go

@@ -0,0 +1,65 @@
+// 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.
+
+package cpu
+
+func doinit() {
+	c := readCaps()
+	ARM64.HasFP = c.has(commpageHasVFP)
+	ARM64.HasASIMD = c.has(commpageHasNeon)
+	ARM64.HasCRC32 = c.has(commpageHasARMv8CRC32)
+	ARM64.HasATOMICS = c.has(commpageHasARMv81Atomics)
+	ARM64.HasFPHP = c.has(commpageHasNeonFP16)
+	ARM64.HasASIMDHP = c.has(commpageHasNeonHPFP)
+	ARM64.HasSHA3 = c.has(commpageHasARMv82SHA3)
+	ARM64.HasSHA512 = c.has(commpageHasARMv82SHA512)
+	ARM64.HasASIMDFHM = c.has(commpageHasARMv82FHM)
+	ARM64.HasSVE = c.has(commpageHasEvent)
+
+	// As of xnu-7195.101.1, there aren't any commpage values for
+	// the following features.
+	//
+	// Assume the following features are available on Apple M1.
+	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
+}
+
+// Constants taken from
+// https://github.com/apple-oss-distributions/xnu/blob/1031c584a5e37aff177559b9f69dbd3c8c3fd30a/osfmk/arm/cpu_capabilities.h
+const (
+	commpageHasNeonFP16      caps = 0x00000008         // ARM v8.2 NEON FP16
+	commpageHasNeon          caps = 0x00000100         // Advanced SIMD
+	commpageHasNeonHPFP      caps = 0x00000200         // Advanced SIMD half-precision
+	commpageHasVFP           caps = 0x00000400         // VFP
+	commpageHasEvent         caps = 0x00001000         // WFE/SVE and period event wakeup
+	commpageHasFMA           caps = 0x00002000         // Fused multiply add
+	commpageHasARMv82FHM     caps = 0x00004000         // Optional ARMv8.2 FMLAL/FMLSL instructions (required in ARMv8.4)
+	commpageHasARMv8Crypto   caps = 0x01000000         // Optional ARMv8 Crypto extensions
+	commpageHasARMv81Atomics caps = 0x02000000         // ARMv8.1 Atomic instructions
+	commpageHasARMv8CRC32    caps = 0x04000000         // Optional ARMv8 crc32 instructions (required in ARMv8.1)
+	commpageHasARMv82SHA512  caps = 0x80000000         // Optional ARMv8.2 SHA512 instructions
+	commpageHasARMv82SHA3    caps = 0x0000000100000000 // Optional ARMv8.2 SHA3 instructions
+)
+
+// caps is the set of commpage capabilities.
+type caps uint64
+
+// has reports whether the capability is enabled.
+func (c caps) has(x caps) bool {
+	return c&x == x
+}
+
+// readCaps loads the current capabilities from commmpage.
+func readCaps() (res caps)

cpu/cpu_darwin_arm64.s

@@ -0,0 +1,48 @@
+// 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.
+
+#include "textflag.h"
+
+// Constants taken from
+// https://github.com/apple-oss-distributions/xnu/blob/1031c584a5e37aff177559b9f69dbd3c8c3fd30a/osfmk/arm/cpu_capabilities.h
+
+#define _COMM_PAGE64_BASE_ADDRESS     0x0000000FFFFFC000
+#define _COMM_PAGE_START_ADDRESS      _COMM_PAGE64_BASE_ADDRESS
+#define _COMM_PAGE_CPU_CAPABILITIES64 (_COMM_PAGE_START_ADDRESS+0x010)
+#define _COMM_PAGE_CPU_CAPABILITIES32 (_COMM_PAGE_START_ADDRESS+0x020)
+#define _COMM_PAGE_VERSION            (_COMM_PAGE_START_ADDRESS+0x01E)
+
+// func readCaps() (res caps)
+TEXT ·readCaps(SB), NOSPLIT, $0-8
+#define ptr R0
+#define caps R1
+
+	MOVD ZR, ptr
+	MOVD ZR, caps
+
+	// We can't check the 64-bit capabilities on iOS because they
+	// might not exist. They were added in xnu-7195.50.7.100.1
+	// (iOS 14 and macOS 11), and Go supports older iOS versions.
+	// _COMM_PAGE_VERSION has stayed the same (3) across kernel
+	// versions, so there doesn't appear to be a way to determine
+	// whether the 64-bit capabilities exist.
+	//
+	// The story is different for macOS because Apple's M1 CPUs
+	// only support Big Sur and newer.
+#ifdef GOOS_ios
+	MOVWU $_COMM_PAGE_CPU_CAPABILITIES32, ptr
+	MOVWU (ptr), caps
+
+#else
+	MOVD $_COMM_PAGE_CPU_CAPABILITIES64, ptr
+	MOVD (ptr), caps
+
+#endif
+
+done:
+	MOVD caps, res+0(FP)
+	RET
+
+#undef ptr
+#undef caps

cpu/cpu_other_arm64.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 !linux && !netbsd && !openbsd && arm64
+//go:build !darwin && !linux && !netbsd && !openbsd && 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 == "ios" {
+	if runtime.GOARCH != "arm64" {
 		return
 	}
 	if !cpu.ARM64.HasASIMD {