$NetBSD$

--- src/arch/netbsd/mcontext/context.c.orig	2017-11-02 06:34:51.953668414 +0000
+++ src/arch/netbsd/mcontext/context.c
@@ -0,0 +1,63 @@
+/* This code is taken from libtask library.
+ * Rip-off done by stsp for dosemu2 project.
+ * Original copyrights below. */
+
+/* Copyright (c) 2005-2006 Russ Cox, MIT; see COPYRIGHT */
+
+#include <ucontext.h>
+#include <stdarg.h>
+#include <string.h>
+#include <inttypes.h>
+#include <assert.h>
+#include "mcontext.h"
+
+#if defined(__i386__)
+void
+makemcontext(m_ucontext_t *ucp, void (*func)(void), int argc, ...)
+{
+	int *sp;
+
+	sp = (int*)ucp->uc_stack.ss_sp+ucp->uc_stack.ss_size/4;
+	sp -= argc;
+	sp = (void*)((uintptr_t)sp - (uintptr_t)sp%16);	/* 16-align for OS X */
+	memmove(sp, &argc+1, argc*sizeof(int));
+
+	*--sp = 0;		/* return address */
+	ucp->uc_mcontext.mc_eip = (long)func;
+	ucp->uc_mcontext.mc_esp = (int)sp;
+}
+#endif
+
+#if defined(__x86_64__)
+void
+makemcontext(m_ucontext_t *ucp, void (*func)(void), int argc, ...)
+{
+	long *sp;
+	va_list va;
+
+	memset(&ucp->uc_mcontext, 0, sizeof ucp->uc_mcontext);
+	if (argc) {
+		assert(argc <= 2);	// oops
+		va_start(va, argc);
+		if (argc >= 1)
+			ucp->uc_mcontext.mc_rdi = va_arg(va, long);
+		if (argc >= 2)
+			ucp->uc_mcontext.mc_rsi = va_arg(va, long);
+		va_end(va);
+	}
+	sp = (long*)ucp->uc_stack.ss_sp+ucp->uc_stack.ss_size/sizeof(long);
+	sp -= argc;
+	sp = (void*)((uintptr_t)sp - (uintptr_t)sp%16);	/* 16-align for OS X */
+	*--sp = 0;	/* return address */
+	ucp->uc_mcontext.mc_rip = (long)func;
+	ucp->uc_mcontext.mc_rsp = (long)sp;
+}
+#endif
+
+int
+swapmcontext(m_ucontext_t *oucp, const m_ucontext_t *ucp)
+{
+	if(getmcontext(oucp) == 0)
+		setmcontext(ucp);
+	return 0;
+}