Index: lib/libc/i386/sys/Makefile.inc
===================================================================
--- lib/libc/i386/sys/Makefile.inc	(revision 249580)
+++ lib/libc/i386/sys/Makefile.inc	(working copy)
@@ -9,7 +9,7 @@
 	__vdso_gettc.c
 
 MDASM=	Ovfork.S brk.S cerror.S exect.S getcontext.S pipe.S ptrace.S \
-	reboot.S sbrk.S setlogin.S sigreturn.S syscall.S
+	reboot.S sbrk.S setlogin.S sigreturn.S syscall.S swapcontext.S
 
 # Don't generate default code for these syscalls:
 NOASM=	break.o exit.o getlogin.o openbsd_poll.o sstk.o vfork.o yield.o
@@ -25,3 +25,13 @@
 MLINKS+=i386_get_ioperm.2 i386_set_ioperm.2
 MLINKS+=i386_get_ldt.2 i386_set_ldt.2
 MLINKS+=i386_set_watch.3 i386_clr_watch.3
+
+
+# This rule stops ./assym.s in .depend from causing problems.
+./assym.s: assym.s
+
+assym.s: ${.CURDIR}/../../sys/kern/genassym.sh genassym.o
+	NM='${NM}' sh ${.CURDIR}/../../sys/kern/genassym.sh genassym.o > ${.TARGET}
+
+genassym.o: ${.CURDIR}/${LIBC_ARCH}/sys/genassym.c
+	${CC} -c ${CFLAGS:N-fno-common} ${.CURDIR}/${LIBC_ARCH}/sys/genassym.c
Index: lib/libc/i386/sys/genassym.c
===================================================================
--- lib/libc/i386/sys/genassym.c	(revision 0)
+++ lib/libc/i386/sys/genassym.c	(working copy)
@@ -0,0 +1,6 @@
+#include <sys/stddef.h>
+#include <sys/assym.h>
+#include <sys/ucontext.h>
+
+ASSYM(UC_ESP, offsetof(struct __ucontext,  uc_mcontext.mc_esp));
+ASSYM(UC_EIP, offsetof(struct __ucontext,  uc_mcontext.mc_eip));
Index: lib/libc/i386/sys/swapcontext.S
===================================================================
--- lib/libc/i386/sys/swapcontext.S	(revision 0)
+++ lib/libc/i386/sys/swapcontext.S	(working copy)
@@ -0,0 +1,62 @@
+/*-
+ * Copyright (c) 2013 David Xu <davidxu@FreeBSD.org>
+ * All rights reserved.
+ *
+ * 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 <machine/asm.h>
+__FBSDID("$FreeBSD$");
+
+#include <SYS.h>
+#include "../../assym.s"
+
+	.weak	_swapcontext
+	.set	_swapcontext,__sys_swapcontext
+	.weak	swapcontext
+	.set	swapcontext,__sys__swapcontext
+
+ENTRY(__sys_swapcontext)
+	mov	$SYS_getcontext,%eax
+	KERNCALL
+	jb	HIDENAME(cerror)
+	movl    4(%esp),%eax		/* get oucp, see manual */
+	movl	(%esp),%ecx		/* get return address */
+	leal	4(%esp),%edx		/* the %esp needs to be restored */
+	movl    %ecx,UC_EIP(%eax)
+	movl	%edx,UC_ESP(%eax)
+	movl    8(%esp),%ecx		/* get ucp */
+#ifdef PIC
+	PIC_PROLOGUE
+	pushl	%ecx
+	call	PIC_PLT(CNAME(_setcontext))
+	addl	$4, %esp
+	PIC_EPILOGUE
+#else
+	pushl	%ecx
+	call	CNAME(_setcontext)
+	addl	$4, %esp
+#endif
+	ret
+END(__sys_swapcontext)
+
+	.section .note.GNU-stack,"",%progbits