vdso_freebsd_x86.go

Documentation: runtime

     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  //go:build freebsd && (386 || amd64)
     6  // +build freebsd
     7  // +build 386 amd64
     8  
     9  package runtime
    10  
    11  import (
    12  	"runtime/internal/atomic"
    13  	"unsafe"
    14  )
    15  
    16  const (
    17  	_VDSO_TH_ALGO_X86_TSC  = 1
    18  	_VDSO_TH_ALGO_X86_HPET = 2
    19  )
    20  
    21  const (
    22  	_HPET_DEV_MAP_MAX  = 10
    23  	_HPET_MAIN_COUNTER = 0xf0 /* Main counter register */
    24  
    25  	hpetDevPath = "/dev/hpetX\x00"
    26  )
    27  
    28  var hpetDevMap [_HPET_DEV_MAP_MAX]uintptr
    29  
    30  //go:nosplit
    31  func (th *vdsoTimehands) getTSCTimecounter() uint32 {
    32  	tsc := cputicks()
    33  	if th.x86_shift > 0 {
    34  		tsc >>= th.x86_shift
    35  	}
    36  	return uint32(tsc)
    37  }
    38  
    39  //go:systemstack
    40  func (th *vdsoTimehands) getHPETTimecounter() (uint32, bool) {
    41  	const digits = "0123456789"
    42  
    43  	idx := int(th.x86_hpet_idx)
    44  	if idx >= len(hpetDevMap) {
    45  		return 0, false
    46  	}
    47  
    48  	p := atomic.Loaduintptr(&hpetDevMap[idx])
    49  	if p == 0 {
    50  		var devPath [len(hpetDevPath)]byte
    51  		copy(devPath[:], hpetDevPath)
    52  		devPath[9] = digits[idx]
    53  
    54  		fd := open(&devPath[0], 0 /* O_RDONLY */, 0)
    55  		if fd < 0 {
    56  			atomic.Casuintptr(&hpetDevMap[idx], 0, ^uintptr(0))
    57  			return 0, false
    58  		}
    59  
    60  		addr, mmapErr := mmap(nil, physPageSize, _PROT_READ, _MAP_SHARED, fd, 0)
    61  		closefd(fd)
    62  		newP := uintptr(addr)
    63  		if mmapErr != 0 {
    64  			newP = ^uintptr(0)
    65  		}
    66  		if !atomic.Casuintptr(&hpetDevMap[idx], 0, newP) && mmapErr == 0 {
    67  			munmap(addr, physPageSize)
    68  		}
    69  		p = atomic.Loaduintptr(&hpetDevMap[idx])
    70  	}
    71  	if p == ^uintptr(0) {
    72  		return 0, false
    73  	}
    74  	return *(*uint32)(unsafe.Pointer(p + _HPET_MAIN_COUNTER)), true
    75  }
    76  
    77  //go:nosplit
    78  func (th *vdsoTimehands) getTimecounter() (uint32, bool) {
    79  	switch th.algo {
    80  	case _VDSO_TH_ALGO_X86_TSC:
    81  		return th.getTSCTimecounter(), true
    82  	case _VDSO_TH_ALGO_X86_HPET:
    83  		var (
    84  			tc uint32
    85  			ok bool
    86  		)
    87  		systemstack(func() {
    88  			tc, ok = th.getHPETTimecounter()
    89  		})
    90  		return tc, ok
    91  	default:
    92  		return 0, false
    93  	}
    94  }
    95
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