github.com/miolini/go@v0.0.0-20160405192216-fca68c8cb408/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 (
     8  	"runtime/internal/sys"
     9  	"unsafe"
    10  )
    11  
    12  const (
    13  	_AT_NULL     = 0
    14  	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
    15  	_AT_HWCAP    = 16 // introduced in at least 2.6.11
    16  	_AT_RANDOM   = 25 // introduced in 2.6.29
    17  
    18  	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
    19  	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
    20  )
    21  
    22  var randomNumber uint32
    23  var armArch uint8 = 6 // we default to ARMv6
    24  var hwcap uint32      // set by setup_auxv
    25  
    26  func checkgoarm() {
    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 sysargs(argc int32, argv **byte) {
    40  	// skip over argv, envv to get to auxv
    41  	n := argc + 1
    42  	for argv_index(argv, n) != nil {
    43  		n++
    44  	}
    45  	n++
    46  	auxv := (*[1 << 28]uint32)(add(unsafe.Pointer(argv), uintptr(n)*sys.PtrSize))
    47  
    48  	for i := 0; auxv[i] != _AT_NULL; i += 2 {
    49  		switch auxv[i] {
    50  		case _AT_RANDOM: // kernel provides a pointer to 16-bytes worth of random data
    51  			startupRandomData = (*[16]byte)(unsafe.Pointer(uintptr(auxv[i+1])))[:]
    52  			// the pointer provided may not be word aligned, so we must treat it
    53  			// as a byte array.
    54  			randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
    55  				uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
    56  
    57  		case _AT_PLATFORM: // v5l, v6l, v7l
    58  			t := *(*uint8)(unsafe.Pointer(uintptr(auxv[i+1] + 1)))
    59  			if '5' <= t && t <= '7' {
    60  				armArch = t - '0'
    61  			}
    62  
    63  		case _AT_HWCAP: // CPU capability bit flags
    64  			hwcap = auxv[i+1]
    65  		}
    66  	}
    67  }
    68  
    69  //go:nosplit
    70  func cputicks() int64 {
    71  	// Currently cputicks() is used in blocking profiler and to seed fastrand1().
    72  	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
    73  	// randomNumber provides better seeding of fastrand1.
    74  	return nanotime() + int64(randomNumber)
    75  }