github.com/flowerwrong/netstack@v0.0.0-20191009141956-e5848263af28/tcpip/link/rawfile/blockingpoll_yield_unsafe.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // +build linux,amd64 linux,arm64
    16  // +build go1.12
    17  // +build !go1.14
    18  
    19  // Check go:linkname function signatures when updating Go version.
    20  
    21  package rawfile
    22  
    23  import (
    24  	"syscall"
    25  	_ "unsafe" // for go:linkname
    26  )
    27  
    28  // BlockingPoll on amd64/arm64 makes the ppoll() syscall while calling the
    29  // version of entersyscall that relinquishes the P so that other Gs can
    30  // run. This is meant to be called in cases when the syscall is expected to
    31  // block. On non amd64/arm64 platforms it just forwards to the ppoll() system
    32  // call.
    33  //
    34  //go:noescape
    35  func BlockingPoll(fds *PollEvent, nfds int, timeout *syscall.Timespec) (int, syscall.Errno)
    36  
    37  // Use go:linkname to call into the runtime. As of Go 1.12 this has to
    38  // be done from Go code so that we make an ABIInternal call to an
    39  // ABIInternal function; see https://golang.org/issue/27539.
    40  
    41  // We need to call both entersyscallblock and exitsyscall this way so
    42  // that the runtime's check on the stack pointer lines up.
    43  
    44  // Note that calling an unexported function in the runtime package is
    45  // unsafe and this hack is likely to break in future Go releases.
    46  
    47  //go:linkname entersyscallblock runtime.entersyscallblock
    48  func entersyscallblock()
    49  
    50  //go:linkname exitsyscall runtime.exitsyscall
    51  func exitsyscall()
    52  
    53  // These forwarding functions must be nosplit because 1) we must
    54  // disallow preemption between entersyscallblock and exitsyscall, and
    55  // 2) we have an untyped assembly frame on the stack which can not be
    56  // grown or moved.
    57  
    58  //go:nosplit
    59  func callEntersyscallblock() {
    60  	entersyscallblock()
    61  }
    62  
    63  //go:nosplit
    64  func callExitsyscall() {
    65  	exitsyscall()
    66  }