Index: head/sys/arm64/arm64/stack_machdep.c
===================================================================
--- head/sys/arm64/arm64/stack_machdep.c	(revision 281849)
+++ head/sys/arm64/arm64/stack_machdep.c	(revision 281850)
@@ -1,53 +1,60 @@
 /*-
  * Copyright (c) 2015 The FreeBSD Foundation
  * All rights reserved.
  *
  * This software was developed by Andrew Turner under
  * sponsorship from the FreeBSD Foundation.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/proc.h>
 #include <sys/stack.h>
 
 #include <machine/vmparam.h>
 #include <machine/pcb.h>
 #include <machine/stack.h>
 
 void
 stack_save_td(struct stack *st, struct thread *td)
 {
-	panic("stack_save_td");
+
+	if (TD_IS_SWAPPED(td))
+		panic("stack_save_td: swapped");
+	if (TD_IS_RUNNING(td))
+		panic("stack_save_td: running");
+
+	stack_zero(st);
 }
 
 void
 stack_save(struct stack *st)
 {
-	panic("stack_save");
+
+	stack_zero(st);
 }