github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/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 !go1.18
    18  
    19  // Check go:linkname function signatures when updating Go version.
    20  
    21  package rawfile
    22  
    23  import (
    24  	_ "unsafe" // for go:linkname
    25  
    26  	"golang.org/x/sys/unix"
    27  )
    28  
    29  // BlockingPoll on amd64/arm64 makes the ppoll() syscall while calling the
    30  // version of entersyscall that relinquishes the P so that other Gs can
    31  // run. This is meant to be called in cases when the syscall is expected to
    32  // block. On non amd64/arm64 platforms it just forwards to the ppoll() system
    33  // call.
    34  //
    35  //go:noescape
    36  func BlockingPoll(fds *PollEvent, nfds int, timeout *unix.Timespec) (int, unix.Errno)
    37  
    38  // Use go:linkname to call into the runtime. As of Go 1.12 this has to
    39  // be done from Go code so that we make an ABIInternal call to an
    40  // ABIInternal function; see https://golang.org/issue/27539.
    41  
    42  // We need to call both entersyscallblock and exitsyscall this way so
    43  // that the runtime's check on the stack pointer lines up.
    44  
    45  // Note that calling an unexported function in the runtime package is
    46  // unsafe and this hack is likely to break in future Go releases.
    47  
    48  //go:linkname entersyscallblock runtime.entersyscallblock
    49  func entersyscallblock()
    50  
    51  //go:linkname exitsyscall runtime.exitsyscall
    52  func exitsyscall()
    53  
    54  // These forwarding functions must be nosplit because 1) we must
    55  // disallow preemption between entersyscallblock and exitsyscall, and
    56  // 2) we have an untyped assembly frame on the stack which can not be
    57  // grown or moved.
    58  
    59  //go:nosplit
    60  func callEntersyscallblock() {
    61  	entersyscallblock()
    62  }
    63  
    64  //go:nosplit
    65  func callExitsyscall() {
    66  	exitsyscall()
    67  }