if gp.lockedm == 0 {
		return nil, plainError("goroutine not locked to thread")
	}

	tid := int(gp.lockedm.ptr().procid)
	if tid == 0 {
		return nil, plainError("missing tid")
	}

	f := efaceOf(&fn)
	if f._type == nil || f._type.Kind_&abi.KindMask != abi.Func {
		return nil, plainError("fn must be a function")
	}
	fv := (*funcval)(f.data)

	a := efaceOf(&stackArgs)

	ctxt.set_pc(ctxt.pc() + 4)
}

// case 8
func (h *debugCallHandler) debugCallUnsafe(ctxt *sigctxt) {
	sp := ctxt.sp()
	reason := *(*string)(unsafe.Pointer(uintptr(sp) + 8))
	h.err = plainError(reason)
	ctxt.set_pc(ctxt.pc() + 4)
}

// case 16
func (h *debugCallHandler) restoreSigContext(ctxt *sigctxt) {
	// Restore all registers except for pc and sp
	pc, sp := ctxt.pc(), ctxt.sp()

	ctxt.set_pc(ctxt.pc() + 4)
}

// case 8
func (h *debugCallHandler) debugCallUnsafe(ctxt *sigctxt) {
	sp := ctxt.sp()
	reason := *(*string)(unsafe.Pointer(uintptr(sp) + 40))
	h.err = plainError(reason)
	ctxt.set_pc(ctxt.pc() + 4)
}

// case 16
func (h *debugCallHandler) restoreSigContext(ctxt *sigctxt) {
	// Restore all registers except for pc and sp
	pc, sp := ctxt.pc(), ctxt.sp()

}

// case 8
func (h *debugCallHandler) debugCallUnsafe(ctxt *sigctxt) {
	rsp := ctxt.rsp()
	reason := *(*string)(unsafe.Pointer(uintptr(rsp)))
	h.err = plainError(reason)
}

// case 16
func (h *debugCallHandler) restoreSigContext(ctxt *sigctxt) {
	// Restore all registers except RIP and RSP.
	rip, rsp := ctxt.rip(), ctxt.rsp()
	fp := ctxt.regs().fpstate