github.com/geraldss/go/src@v0.0.0-20210511222824-ac7d0ebfc235/runtime/vdso_freebsd_x86.go (about)

     1  // Copyright 2018 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 freebsd
     6  // +build 386 amd64
     7  
     8  package runtime
     9  
    10  import (
    11  	"runtime/internal/atomic"
    12  	"unsafe"
    13  )
    14  
    15  const (
    16  	_VDSO_TH_ALGO_X86_TSC  = 1
    17  	_VDSO_TH_ALGO_X86_HPET = 2
    18  )
    19  
    20  const (
    21  	_HPET_DEV_MAP_MAX  = 10
    22  	_HPET_MAIN_COUNTER = 0xf0 /* Main counter register */
    23  
    24  	hpetDevPath = "/dev/hpetX\x00"
    25  )
    26  
    27  var hpetDevMap [_HPET_DEV_MAP_MAX]uintptr
    28  
    29  //go:nosplit
    30  func (th *vdsoTimehands) getTSCTimecounter() uint32 {
    31  	tsc := cputicks()
    32  	if th.x86_shift > 0 {
    33  		tsc >>= th.x86_shift
    34  	}
    35  	return uint32(tsc)
    36  }
    37  
    38  //go:systemstack
    39  func (th *vdsoTimehands) getHPETTimecounter() (uint32, bool) {
    40  	const digits = "0123456789"
    41  
    42  	idx := int(th.x86_hpet_idx)
    43  	if idx >= len(hpetDevMap) {
    44  		return 0, false
    45  	}
    46  
    47  	p := atomic.Loaduintptr(&hpetDevMap[idx])
    48  	if p == 0 {
    49  		var devPath [len(hpetDevPath)]byte
    50  		copy(devPath[:], hpetDevPath)
    51  		devPath[9] = digits[idx]
    52  
    53  		fd := open(&devPath[0], 0 /* O_RDONLY */, 0)
    54  		if fd < 0 {
    55  			atomic.Casuintptr(&hpetDevMap[idx], 0, ^uintptr(0))
    56  			return 0, false
    57  		}
    58  
    59  		addr, mmapErr := mmap(nil, physPageSize, _PROT_READ, _MAP_SHARED, fd, 0)
    60  		closefd(fd)
    61  		newP := uintptr(addr)
    62  		if mmapErr != 0 {
    63  			newP = ^uintptr(0)
    64  		}
    65  		if !atomic.Casuintptr(&hpetDevMap[idx], 0, newP) && mmapErr == 0 {
    66  			munmap(addr, physPageSize)
    67  		}
    68  		p = atomic.Loaduintptr(&hpetDevMap[idx])
    69  	}
    70  	if p == ^uintptr(0) {
    71  		return 0, false
    72  	}
    73  	return *(*uint32)(unsafe.Pointer(p + _HPET_MAIN_COUNTER)), true
    74  }
    75  
    76  //go:nosplit
    77  func (th *vdsoTimehands) getTimecounter() (uint32, bool) {
    78  	switch th.algo {
    79  	case _VDSO_TH_ALGO_X86_TSC:
    80  		return th.getTSCTimecounter(), true
    81  	case _VDSO_TH_ALGO_X86_HPET:
    82  		var (
    83  			tc uint32
    84  			ok bool
    85  		)
    86  		systemstack(func() {
    87  			tc, ok = th.getHPETTimecounter()
    88  		})
    89  		return tc, ok
    90  	default:
    91  		return 0, false
    92  	}
    93  }