github.com/reiver/go@v0.0.0-20150109200633-1d0c7792f172/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  // Copyright 2009 The Go Authors. All rights reserved.
     6  // Use of this source code is governed by a BSD-style
     7  // license that can be found in the LICENSE file.
     8  
     9  package runtime
    10  
    11  import "unsafe"
    12  
    13  const (
    14  	_AT_NULL     = 0
    15  	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
    16  	_AT_HWCAP    = 16 // introduced in at least 2.6.11
    17  	_AT_RANDOM   = 25 // introduced in 2.6.29
    18  
    19  	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
    20  	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
    21  )
    22  
    23  var randomNumber uint32
    24  var armArch uint8 = 6 // we default to ARMv6
    25  var hwcap uint32      // set by setup_auxv
    26  var goarm uint8       // set by 5l
    27  
    28  func checkgoarm() {
    29  	if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
    30  		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
    31  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    32  		exit(1)
    33  	}
    34  	if goarm > 6 && hwcap&_HWCAP_VFPv3 == 0 {
    35  		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
    36  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    37  		exit(1)
    38  	}
    39  }
    40  
    41  //go:nosplit
    42  func setup_auxv(argc int32, argv **byte) {
    43  	// skip over argv, envv to get to auxv
    44  	n := argc + 1
    45  	for argv_index(argv, n) != nil {
    46  		n++
    47  	}
    48  	n++
    49  	auxv := (*[1 << 28]uint32)(add(unsafe.Pointer(argv), uintptr(n)*ptrSize))
    50  
    51  	for i := 0; auxv[i] != _AT_NULL; i += 2 {
    52  		switch auxv[i] {
    53  		case _AT_RANDOM: // kernel provides a pointer to 16-bytes worth of random data
    54  			startupRandomData = (*[16]byte)(unsafe.Pointer(uintptr(auxv[i+1])))[:]
    55  			// the pointer provided may not be word alined, so we must to treat it
    56  			// as a byte array.
    57  			randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
    58  				uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
    59  
    60  		case _AT_PLATFORM: // v5l, v6l, v7l
    61  			t := *(*uint8)(unsafe.Pointer(uintptr(auxv[i+1] + 1)))
    62  			if '5' <= t && t <= '7' {
    63  				armArch = t - '0'
    64  			}
    65  
    66  		case _AT_HWCAP: // CPU capability bit flags
    67  			hwcap = auxv[i+1]
    68  		}
    69  	}
    70  }
    71  
    72  func cputicks() int64 {
    73  	// Currently cputicks() is used in blocking profiler and to seed fastrand1().
    74  	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
    75  	// randomNumber provides better seeding of fastrand1.
    76  	return nanotime() + int64(randomNumber)
    77  }