diff --git a/libc/Makefile b/libc/Makefile
index 6a49d20..77d15c6 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -35,8 +35,10 @@ CFLAGS += -nobuiltininc -isystem ../include/freebsd
 CFLAGS += -fvisibility-nodllstorageclass=default
 CFLAGS += -O1
 
+ASFLAGS := $(CFLAGS)
+
 SRCS := $(wildcard *.c)
-OBJS := $(SRCS:.c=.o)
+OBJS := $(SRCS:.c=.o) _setjmp.o
 
 ARCHIVE := libc.a
 
diff --git a/libc/_setjmp.S b/libc/_setjmp.S
new file mode 100644
index 0000000..57079a1
--- /dev/null
+++ b/libc/_setjmp.S
@@ -0,0 +1,95 @@
+/*-
+ * Copyright (c) 1990 The Regents of the University of California.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * William Jolitz.
+ *
+ * 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.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
+ */
+
+#if defined(LIBC_SCCS) && !defined(lint)
+	.asciz "@(#)_setjmp.s	5.1 (Berkeley) 4/23/90"
+#endif /* LIBC_SCCS and not lint */
+#include <machine/asm.h>
+__FBSDID("$FreeBSD$");
+
+/*
+ * C library -- _setjmp, _longjmp
+ *
+ *	_longjmp(a,v)
+ * will generate a "return(v)" from the last call to
+ *	_setjmp(a)
+ * by restoring registers from the environment 'a'.
+ * The previous signal state is NOT restored.
+ */
+
+ENTRY(_setjmp)
+	movq	%rdi,%rax
+	movq	0(%rsp),%rdx		/* retval */
+	movq	%rdx, 0(%rax)		/* 0; retval */
+	movq	%rbx, 8(%rax)		/* 1; rbx */
+	movq	%rsp,16(%rax)		/* 2; rsp */
+	movq	%rbp,24(%rax)		/* 3; rbp */
+	movq	%r12,32(%rax)		/* 4; r12 */
+	movq	%r13,40(%rax)		/* 5; r13 */
+	movq	%r14,48(%rax)		/* 6; r14 */
+	movq	%r15,56(%rax)		/* 7; r15 */
+	fnstcw	64(%rax)		/* 8; fpu cw */
+	stmxcsr	68(%rax)		/*    and mxcsr */
+	xorq	%rax,%rax
+	ret
+END(_setjmp)
+
+	WEAK_REFERENCE(___longjmp, _longjmp)
+ENTRY(___longjmp)
+	movq	%rdi,%rdx
+	/* Restore the mxcsr, but leave exception flags intact. */
+	stmxcsr	-4(%rsp)
+	movl	68(%rdx),%eax
+	andl	$0xffffffc0,%eax
+	movl	-4(%rsp),%edi
+	andl	$0x3f,%edi
+	xorl	%eax,%edi
+	movl	%edi,-4(%rsp)
+	ldmxcsr -4(%rsp)
+	movq	%rsi,%rax		/* retval */
+	movq	0(%rdx),%rcx
+	movq	8(%rdx),%rbx
+	movq	16(%rdx),%rsp
+	movq	24(%rdx),%rbp
+	movq	32(%rdx),%r12
+	movq	40(%rdx),%r13
+	movq	48(%rdx),%r14
+	movq	56(%rdx),%r15
+	fldcw	64(%rdx)
+	testq	%rax,%rax
+	jnz	1f
+	incq	%rax
+1:	movq	%rcx,0(%rsp)
+	ret
+END(___longjmp)
+
+	.section .note.GNU-stack,"",%progbits