src/runtime/internal/syscall/syscall_linux.go

// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package syscall provides the syscall primitives required for the runtime.
package syscall

import (
	"unsafe"
)

// TODO(https://go.dev/issue/51087): This package is incomplete and currently
// only contains very minimal support for Linux.

// Syscall6 calls system call number 'num' with arguments a1-6.
func Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr)

// syscall_RawSyscall6 is a push linkname to export Syscall6 as
// syscall.RawSyscall6.
//
// //go:uintptrkeepalive because the uintptr argument may be converted pointers
// that need to be kept alive in the caller (this is implied for Syscall6 since
// it has no body).
//
// //go:nosplit because stack copying does not account for uintptrkeepalive, so
// the stack must not grow. Stack copying cannot blindly assume that all
// uintptr arguments are pointers, because some values may look like pointers,
// but not really be pointers, and adjusting their value would break the call.
//
// This is a separate wrapper because we can't export one function as two
// names. The assembly implementations name themselves Syscall6 would not be
// affected by a linkname.
//
//go:uintptrkeepalive
//go:nosplit
//go:linkname syscall_RawSyscall6 syscall.RawSyscall6
func syscall_RawSyscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr) {
	return Syscall6(num, a1, a2, a3, a4, a5, a6)
}

func EpollCreate1(flags int32) (fd int32, errno uintptr) {
	r1, _, e := Syscall6(SYS_EPOLL_CREATE1, uintptr(flags), 0, 0, 0, 0, 0)
	return int32(r1), e
}

var _zero uintptr

func EpollWait(epfd int32, events []EpollEvent, maxev, waitms int32) (n int32, errno uintptr) {
	var ev unsafe.Pointer
	if len(events) > 0 {
		ev = unsafe.Pointer(&events[0])
	} else {
		ev = unsafe.Pointer(&_zero)
	}
	r1, _, e := Syscall6(SYS_EPOLL_PWAIT, uintptr(epfd), uintptr(ev), uintptr(maxev), uintptr(waitms), 0, 0)
	return int32(r1), e
}

func EpollCtl(epfd, op, fd int32, event *EpollEvent) (errno uintptr) {
	_, _, e := Syscall6(SYS_EPOLL_CTL, uintptr(epfd), uintptr(op), uintptr(fd), uintptr(unsafe.Pointer(event)), 0, 0)
	return e
}

func CloseOnExec(fd int32) {
	Syscall6(SYS_FCNTL, uintptr(fd), F_SETFD, FD_CLOEXEC, 0, 0, 0)
}