github.com/megatontech/mynoteforgo@v0.0.0-20200507084910-5d0c6ea6e890/源码/runtime/os_linux_arm64.go (about)

     1  // Copyright 2015 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  // +build arm64
     6  
     7  package runtime
     8  
     9  import "internal/cpu"
    10  
    11  var randomNumber uint32
    12  
    13  func archauxv(tag, val uintptr) {
    14  	switch tag {
    15  	case _AT_RANDOM:
    16  		// sysargs filled in startupRandomData, but that
    17  		// pointer may not be word aligned, so we must treat
    18  		// it as a byte array.
    19  		randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
    20  			uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
    21  
    22  	case _AT_HWCAP:
    23  		// arm64 doesn't have a 'cpuid' instruction equivalent and relies on
    24  		// HWCAP/HWCAP2 bits for hardware capabilities.
    25  		hwcap := uint(val)
    26  		if GOOS == "android" {
    27  			// The Samsung S9+ kernel reports support for atomics, but not all cores
    28  			// actually support them, resulting in SIGILL. See issue #28431.
    29  			// TODO(elias.naur): Only disable the optimization on bad chipsets.
    30  			const hwcap_ATOMICS = 1 << 8
    31  			hwcap &= ^uint(hwcap_ATOMICS)
    32  		}
    33  		cpu.HWCap = hwcap
    34  	case _AT_HWCAP2:
    35  		cpu.HWCap2 = uint(val)
    36  	}
    37  }
    38  
    39  //go:nosplit
    40  func cputicks() int64 {
    41  	// Currently cputicks() is used in blocking profiler and to seed fastrand().
    42  	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
    43  	// randomNumber provides better seeding of fastrand.
    44  	return nanotime() + int64(randomNumber)
    45  }