func (u *unwinder) cgoCallers(pcBuf []uintptr) int {
	if cgoTraceback == nil || u.frame.fn.funcID != abi.FuncID_cgocallback || u.cgoCtxt < 0 {
		// We don't have a cgo unwinder (typical case), or we do but we're not
		// in a cgo frame or we're out of cgo context.
		return 0
	}

	ctxt := u.g.ptr().cgoCtxt[u.cgoCtxt]
	u.cgoCtxt--
	cgoContextPCs(ctxt, pcBuf)
	for i, pc := range pcBuf {
		if pc == 0 {
			return i
		}
	}

		gp.m.needextram = false
		systemstack(newextram)
	}

	if ctxt != 0 {
		s := append(gp.cgoCtxt, ctxt)

		// Now we need to set gp.cgoCtxt = s, but we could get
		// a SIGPROF signal while manipulating the slice, and
		// the SIGPROF handler could pick up gp.cgoCtxt while
		// tracing up the stack.  We need to ensure that the
		// handler always sees a valid slice, so set the

	startpc       uintptr         // pc of goroutine function
	racectx       uintptr
	waiting       *sudog         // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
	cgoCtxt       []uintptr      // cgo traceback context
	labels        unsafe.Pointer // profiler labels
	timer         *timer         // cached timer for time.Sleep
	sleepWhen     int64          // when to sleep until