cpu: read ARM64 registers using sysctl(3) on netbsd/arm64

Use sysctl("machdep.cpu0.cpu_id") to retrieve the ARM64 cpu_id
information on netbsd/arm64. This includes the ISAR0, ISAR1 and PFR0
registers which can be parsed using existing functionality.

In order to use sysctl(3) without depending on x/sys/unix, some
functionality needed to be copied and slightly adjusted.

Change-Id: Ic9a133917ae5da516e6794f375bd7602d9bd3aa6
Reviewed-on: https://go-review.googlesource.com/c/sys/+/264378
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Trust: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>

cpu/cpu_arm64.go

@@ -39,28 +39,26 @@ func initOptions() {
 
 func archInit() {
 	switch runtime.GOOS {
-	case "android", "darwin", "ios", "netbsd", "openbsd":
+	case "freebsd":
-		// Android and iOS don't seem to allow reading these registers.
+		readARM64Registers()
-		//
+	case "linux", "netbsd":
-		// NetBSD:
+		doinit()
-		// ID_AA64ISAR0_EL1 is a privileged register and cannot be read from EL0.
+	default:
-		// It can be read via sysctl(3). Example for future implementers:
+		// Most platforms don't seem to allow reading these registers.
-		// https://nxr.netbsd.org/xref/src/usr.sbin/cpuctl/arch/aarch64.c
 		//
 		// OpenBSD:
 		// See https://golang.org/issue/31746
-		//
+		setMinimalFeatures()
-		// Fake the minimal features expected by
-		// TestARM64minimalFeatures.
-		ARM64.HasASIMD = true
-		ARM64.HasFP = true
-	case "linux":
-		doinit()
-	default:
-		readARM64Registers()
 	}
 }
 
+// setMinimalFeatures fakes the minimal ARM64 features expected by
+// TestARM64minimalFeatures.
+func setMinimalFeatures() {
+	ARM64.HasASIMD = true
+	ARM64.HasFP = true
+}
+
 func readARM64Registers() {
 	Initialized = true
 

cpu/cpu_netbsd_arm64.go

@@ -0,0 +1,173 @@
+// Copyright 2020 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 (
+	"syscall"
+	"unsafe"
+)
+
+// Minimal copy of functionality from x/sys/unix so the cpu package can call
+// sysctl without depending on x/sys/unix.
+
+const (
+	_CTL_QUERY = -2
+
+	_SYSCTL_VERS_1 = 0x1000000
+)
+
+var _zero uintptr
+
+func sysctl(mib []int32, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error) {
+	var _p0 unsafe.Pointer
+	if len(mib) > 0 {
+		_p0 = unsafe.Pointer(&mib[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
+	}
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS___SYSCTL,
+		uintptr(_p0),
+		uintptr(len(mib)),
+		uintptr(unsafe.Pointer(old)),
+		uintptr(unsafe.Pointer(oldlen)),
+		uintptr(unsafe.Pointer(new)),
+		uintptr(newlen))
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
+
+type sysctlNode struct {
+	Flags          uint32
+	Num            int32
+	Name           [32]int8
+	Ver            uint32
+	__rsvd         uint32
+	Un             [16]byte
+	_sysctl_size   [8]byte
+	_sysctl_func   [8]byte
+	_sysctl_parent [8]byte
+	_sysctl_desc   [8]byte
+}
+
+func sysctlNodes(mib []int32) ([]sysctlNode, error) {
+	var olen uintptr
+
+	// Get a list of all sysctl nodes below the given MIB by performing
+	// a sysctl for the given MIB with CTL_QUERY appended.
+	mib = append(mib, _CTL_QUERY)
+	qnode := sysctlNode{Flags: _SYSCTL_VERS_1}
+	qp := (*byte)(unsafe.Pointer(&qnode))
+	sz := unsafe.Sizeof(qnode)
+	if err := sysctl(mib, nil, &olen, qp, sz); err != nil {
+		return nil, err
+	}
+
+	// Now that we know the size, get the actual nodes.
+	nodes := make([]sysctlNode, olen/sz)
+	np := (*byte)(unsafe.Pointer(&nodes[0]))
+	if err := sysctl(mib, np, &olen, qp, sz); err != nil {
+		return nil, err
+	}
+
+	return nodes, nil
+}
+
+func nametomib(name string) ([]int32, error) {
+	// Split name into components.
+	var parts []string
+	last := 0
+	for i := 0; i < len(name); i++ {
+		if name[i] == '.' {
+			parts = append(parts, name[last:i])
+			last = i + 1
+		}
+	}
+	parts = append(parts, name[last:])
+
+	mib := []int32{}
+	// Discover the nodes and construct the MIB OID.
+	for partno, part := range parts {
+		nodes, err := sysctlNodes(mib)
+		if err != nil {
+			return nil, err
+		}
+		for _, node := range nodes {
+			n := make([]byte, 0)
+			for i := range node.Name {
+				if node.Name[i] != 0 {
+					n = append(n, byte(node.Name[i]))
+				}
+			}
+			if string(n) == part {
+				mib = append(mib, int32(node.Num))
+				break
+			}
+		}
+		if len(mib) != partno+1 {
+			return nil, err
+		}
+	}
+
+	return mib, nil
+}
+
+// aarch64SysctlCPUID is struct aarch64_sysctl_cpu_id from NetBSD's <aarch64/armreg.h>
+type aarch64SysctlCPUID struct {
+	midr      uint64 /* Main ID Register */
+	revidr    uint64 /* Revision ID Register */
+	mpidr     uint64 /* Multiprocessor Affinity Register */
+	aa64dfr0  uint64 /* A64 Debug Feature Register 0 */
+	aa64dfr1  uint64 /* A64 Debug Feature Register 1 */
+	aa64isar0 uint64 /* A64 Instruction Set Attribute Register 0 */
+	aa64isar1 uint64 /* A64 Instruction Set Attribute Register 1 */
+	aa64mmfr0 uint64 /* A64 Memory Model Feature Register 0 */
+	aa64mmfr1 uint64 /* A64 Memory Model Feature Register 1 */
+	aa64mmfr2 uint64 /* A64 Memory Model Feature Register 2 */
+	aa64pfr0  uint64 /* A64 Processor Feature Register 0 */
+	aa64pfr1  uint64 /* A64 Processor Feature Register 1 */
+	aa64zfr0  uint64 /* A64 SVE Feature ID Register 0 */
+	mvfr0     uint32 /* Media and VFP Feature Register 0 */
+	mvfr1     uint32 /* Media and VFP Feature Register 1 */
+	mvfr2     uint32 /* Media and VFP Feature Register 2 */
+	pad       uint32
+	clidr     uint64 /* Cache Level ID Register */
+	ctr       uint64 /* Cache Type Register */
+}
+
+func sysctlCPUID(name string) (*aarch64SysctlCPUID, error) {
+	mib, err := nametomib(name)
+	if err != nil {
+		return nil, err
+	}
+
+	out := aarch64SysctlCPUID{}
+	n := unsafe.Sizeof(out)
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS___SYSCTL,
+		uintptr(unsafe.Pointer(&mib[0])),
+		uintptr(len(mib)),
+		uintptr(unsafe.Pointer(&out)),
+		uintptr(unsafe.Pointer(&n)),
+		uintptr(0),
+		uintptr(0))
+	if errno != 0 {
+		return nil, errno
+	}
+	return &out, nil
+}
+
+func doinit() {
+	cpuid, err := sysctlCPUID("machdep.cpu0.cpu_id")
+	if err != nil {
+		setMinimalFeatures()
+		return
+	}
+	parseARM64SystemRegisters(cpuid.aa64isar0, cpuid.aa64isar1, cpuid.aa64pfr0)
+
+	Initialized = true
+}

cpu/cpu_other_arm64.go

@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !linux,arm64
+// +build !linux,!netbsd
+// +build arm64
 
 package cpu