github.com/megatontech/mynoteforgo@v0.0.0-20200507084910-5d0c6ea6e890/源码/runtime/os_linux_arm.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import "internal/cpu"
     8  
     9  const (
    10  	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
    11  	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
    12  )
    13  
    14  var randomNumber uint32
    15  
    16  func checkgoarm() {
    17  	// On Android, /proc/self/auxv might be unreadable and hwcap won't
    18  	// reflect the CPU capabilities. Assume that every Android arm device
    19  	// has the necessary floating point hardware available.
    20  	if GOOS == "android" {
    21  		return
    22  	}
    23  	if goarm > 5 && cpu.HWCap&_HWCAP_VFP == 0 {
    24  		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
    25  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    26  		exit(1)
    27  	}
    28  	if goarm > 6 && cpu.HWCap&_HWCAP_VFPv3 == 0 {
    29  		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
    30  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5 or GOARM=6.\n")
    31  		exit(1)
    32  	}
    33  }
    34  
    35  func archauxv(tag, val uintptr) {
    36  	switch tag {
    37  	case _AT_RANDOM:
    38  		// sysargs filled in startupRandomData, but that
    39  		// pointer may not be word aligned, so we must treat
    40  		// it as a byte array.
    41  		randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
    42  			uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
    43  
    44  	case _AT_HWCAP:
    45  		cpu.HWCap = uint(val)
    46  	case _AT_HWCAP2:
    47  		cpu.HWCap2 = uint(val)
    48  	}
    49  }
    50  
    51  //go:nosplit
    52  func cputicks() int64 {
    53  	// Currently cputicks() is used in blocking profiler and to seed fastrand().
    54  	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
    55  	// randomNumber provides better seeding of fastrand.
    56  	return nanotime() + int64(randomNumber)
    57  }