$NetBSD: README,v 1.7 2017/02/08 03:44:41 kamil Exp $

Due to limitations in the current pthread implementation, makecontext(3)
and sigaltstack(2) should not be used in programs which link against
libpthread (whether threads are used or not). This has been noted in the
makecontext(3), sigaltstack(2), and pthread(3) man pages.