go/src/runtime/os_linux_arm64.go

// Copyright 2015 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 runtime

const (
	_ARM64_FEATURE_HAS_CRC32 = 0x80
)

var randomNumber uint32
var supportCRC32 bool

func archauxv(tag, val uintptr) {
	switch tag {
	case _AT_RANDOM:
		// sysargs filled in startupRandomData, but that
		// pointer may not be word aligned, so we must treat
		// it as a byte array.
		randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
			uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
	case _AT_HWCAP:
		supportCRC32 = val&_ARM64_FEATURE_HAS_CRC32 != 0
	}
}

//go:nosplit
func cputicks() int64 {
	// Currently cputicks() is used in blocking profiler and to seed fastrand().
	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
	// randomNumber provides better seeding of fastrand.
	return nanotime() + int64(randomNumber)
}