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Source file src/runtime/os_linux_arm64.go

Documentation: runtime

  // 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.
  
  // +build arm64
  
  package runtime
  
  // For go:linkname
  import _ "unsafe"
  
  var randomNumber uint32
  
  // arm64 doesn't have a 'cpuid' instruction equivalent and relies on
  // HWCAP/HWCAP2 bits for hardware capabilities.
  
  //go:linkname cpu_hwcap internal/cpu.arm64_hwcap
  //go:linkname cpu_hwcap2 internal/cpu.arm64_hwcap2
  var cpu_hwcap uint
  var cpu_hwcap2 uint
  
  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:
  		cpu_hwcap = uint(val)
  	case _AT_HWCAP2:
  		cpu_hwcap2 = uint(val)
  	}
  }
  
  //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)
  }
  

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