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Source file src/runtime/os_linux_arm.go

Documentation: runtime

  // Copyright 2009 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
  
  import "unsafe"
  
  const (
  	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
  
  	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
  	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
  	_HWCAP_IDIVA = 1 << 17
  )
  
  var randomNumber uint32
  var armArch uint8 = 6 // we default to ARMv6
  var hwcap uint32      // set by setup_auxv
  var hardDiv bool      // set if a hardware divider is available
  
  func checkgoarm() {
  	// On Android, /proc/self/auxv might be unreadable and hwcap won't
  	// reflect the CPU capabilities. Assume that every Android arm device
  	// has the necessary floating point hardware available.
  	if GOOS == "android" {
  		return
  	}
  	if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
  		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
  		exit(1)
  	}
  	if goarm > 6 && hwcap&_HWCAP_VFPv3 == 0 {
  		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
  		exit(1)
  	}
  }
  
  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_PLATFORM: // v5l, v6l, v7l
  		t := *(*uint8)(unsafe.Pointer(val + 1))
  		if '5' <= t && t <= '7' {
  			armArch = t - '0'
  		}
  
  	case _AT_HWCAP: // CPU capability bit flags
  		hwcap = uint32(val)
  		hardDiv = (hwcap & _HWCAP_IDIVA) != 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)
  }
  

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