github.com/zxy12/golang151_with_comment@v0.0.0-20190507085033-721809559d3c/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_NULL     = 0
    11  	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
    12  	_AT_HWCAP    = 16 // introduced in at least 2.6.11
    13  	_AT_RANDOM   = 25 // introduced in 2.6.29
    14  
    15  	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
    16  	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
    17  )
    18  
    19  var randomNumber uint32
    20  var armArch uint8 = 6 // we default to ARMv6
    21  var hwcap uint32      // set by setup_auxv
    22  
    23  func checkgoarm() {
    24  	if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
    25  		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
    26  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    27  		exit(1)
    28  	}
    29  	if goarm > 6 && hwcap&_HWCAP_VFPv3 == 0 {
    30  		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
    31  		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
    32  		exit(1)
    33  	}
    34  }
    35  
    36  func sysargs(argc int32, argv **byte) {
    37  	// skip over argv, envv to get to auxv
    38  	n := argc + 1
    39  	for argv_index(argv, n) != nil {
    40  		n++
    41  	}
    42  	n++
    43  	auxv := (*[1 << 28]uint32)(add(unsafe.Pointer(argv), uintptr(n)*ptrSize))
    44  
    45  	for i := 0; auxv[i] != _AT_NULL; i += 2 {
    46  		switch auxv[i] {
    47  		case _AT_RANDOM: // kernel provides a pointer to 16-bytes worth of random data
    48  			startupRandomData = (*[16]byte)(unsafe.Pointer(uintptr(auxv[i+1])))[:]
    49  			// the pointer provided may not be word aligned, so we must treat it
    50  			// as a byte array.
    51  			randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
    52  				uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
    53  
    54  		case _AT_PLATFORM: // v5l, v6l, v7l
    55  			t := *(*uint8)(unsafe.Pointer(uintptr(auxv[i+1] + 1)))
    56  			if '5' <= t && t <= '7' {
    57  				armArch = t - '0'
    58  			}
    59  
    60  		case _AT_HWCAP: // CPU capability bit flags
    61  			hwcap = auxv[i+1]
    62  		}
    63  	}
    64  }
    65  
    66  //go:nosplit
    67  func cputicks() int64 {
    68  	// Currently cputicks() is used in blocking profiler and to seed fastrand1().
    69  	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
    70  	// randomNumber provides better seeding of fastrand1.
    71  	return nanotime() + int64(randomNumber)
    72  }