//go:nowritebarrierrec
func setsigstack(i uint32) {
	var osa usigactiont
	sigaction(i, nil, &osa)
	handler := *(*uintptr)(unsafe.Pointer(&osa.__sigaction_u))
	if osa.sa_flags&_SA_ONSTACK != 0 {
		return
	}
	var sa usigactiont
	*(*uintptr)(unsafe.Pointer(&sa.__sigaction_u)) = handler
	sa.sa_mask = osa.sa_mask
	sa.sa_flags = osa.sa_flags | _SA_ONSTACK
	sigaction(i, &sa, nil)
}

//go:nosplit
//go:nowritebarrierrec