github.com/fenixara/go@v0.0.0-20170127160404-96ea0918e670/src/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 "unsafe"
     8  
     9  const (
    10  	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
    11  
    12  	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
    13  	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
    14  )
    15  
    16  var randomNumber uint32
    17  var armArch uint8 = 6 // we default to ARMv6
    18  var hwcap uint32      // set by setup_auxv
    19  
    20  func checkgoarm() {
    21  	// On Android, /proc/self/auxv might be unreadable and hwcap won't
    22  	// reflect the CPU capabilities. Assume that every Android arm device
    23  	// has the necessary floating point hardware available.
    24  	if GOOS == "android" {
    25  		return
    26  	}
    27  	if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
    28  		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
    29  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    30  		exit(1)
    31  	}
    32  	if goarm > 6 && hwcap&_HWCAP_VFPv3 == 0 {
    33  		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
    34  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    35  		exit(1)
    36  	}
    37  }
    38  
    39  func archauxv(tag, val uintptr) {
    40  	switch tag {
    41  	case _AT_RANDOM:
    42  		// sysargs filled in startupRandomData, but that
    43  		// pointer may not be word aligned, so we must treat
    44  		// it as a byte array.
    45  		randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
    46  			uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
    47  
    48  	case _AT_PLATFORM: // v5l, v6l, v7l
    49  		t := *(*uint8)(unsafe.Pointer(val + 1))
    50  		if '5' <= t && t <= '7' {
    51  			armArch = t - '0'
    52  		}
    53  
    54  	case _AT_HWCAP: // CPU capability bit flags
    55  		hwcap = uint32(val)
    56  	}
    57  }
    58  
    59  //go:nosplit
    60  func cputicks() int64 {
    61  	// Currently cputicks() is used in blocking profiler and to seed fastrand().
    62  	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
    63  	// randomNumber provides better seeding of fastrand.
    64  	return nanotime() + int64(randomNumber)
    65  }