runtime.go

// Copyright 2021 The Go Darwin Authors
// SPDX-License-Identifier: BSD-3-Clause

// Copyright 2009 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.

//go:build darwin
// +build darwin

package sys

import (
	_ "unsafe" // for go:linkname
)

// Keep a cached value to make gotraceback fast,
// since we call it on every call to gentraceback.
// The cached value is a uint32 in which the low bits
// are the "crash" and "all" settings and the remaining
// bits are the traceback value (0 off, 1 on, 2 include system).
const (
	TracebackCrash = 1 << iota
	TracebackAll
	TracebackShift = iota
)

//go:noescape
//go:linkname systemstack runtime.systemstack
func systemstack(fn func())

// SystemStack runs fn on a system stack.
// If systemstack is called from the per-OS-thread (g0) stack, or
// if systemstack is called from the signal handling (gsignal) stack,
// systemstack calls fn directly and returns.
// Otherwise, systemstack is being called from the limited stack
// of an ordinary goroutine. In this case, systemstack switches
// to the per-OS-thread stack, calls fn, and switches back.
// It is common to use a func literal as the argument, in order
// to share inputs and outputs with the code around the call
// to system stack:
//
//	... set up y ...
//	systemstack(func() {
//		x = bigcall(y)
//	})
//	... use x ...
func SystemStack(fn func()) {
	systemstack(fn)
}