Apply by doing:
	cd /usr/src
	patch -p0 < 002_xmm.patch

Then build and install a new kernel.

Index: sys/arch/i386/i386/trap.c
===================================================================
RCS file: /cvs/src/sys/arch/i386/i386/trap.c,v
retrieving revision 1.87
retrieving revision 1.87.8.1
diff -u -p -r1.87 -r1.87.8.1
--- sys/arch/i386/i386/trap.c	9 Apr 2008 16:49:17 -0000	1.87
+++ sys/arch/i386/i386/trap.c	5 Oct 2009 00:37:54 -0000	1.87.8.1
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.87 2008/04/09 16:49:17 thib Exp $	*/
+/*	$OpenBSD: trap.c,v 1.87.8.1 2009/10/05 00:37:54 sthen Exp $	*/
 /*	$NetBSD: trap.c,v 1.95 1996/05/05 06:50:02 mycroft Exp $	*/
 
 /*-
@@ -426,6 +426,10 @@ trap(struct trapframe frame)
 		KERNEL_PROC_LOCK(p);
 		trapsignal(p, SIGFPE, frame.tf_err, FPE_INTOVF, sv);
 		KERNEL_PROC_UNLOCK(p);
+		goto out;
+
+	case T_XFTRAP|T_USER:
+		npxtrap(&frame);
 		goto out;
 
 	case T_PAGEFLT:			/* allow page faults in kernel mode */
Index: sys/arch/i386/include/npx.h
===================================================================
RCS file: /cvs/src/sys/arch/i386/include/npx.h,v
retrieving revision 1.10
retrieving revision 1.10.14.1
diff -u -p -r1.10 -r1.10.14.1
--- sys/arch/i386/include/npx.h	1 Oct 2006 18:07:56 -0000	1.10
+++ sys/arch/i386/include/npx.h	5 Oct 2009 00:37:54 -0000	1.10.14.1
@@ -1,4 +1,4 @@
-/*	$OpenBSD: npx.h,v 1.10 2006/10/01 18:07:56 kettenis Exp $	*/
+/*	$OpenBSD: npx.h,v 1.10.14.1 2009/10/05 00:37:54 sthen Exp $	*/
 /*	$NetBSD: npx.h,v 1.11 1994/10/27 04:16:11 cgd Exp $	*/
 
 /*-
@@ -161,8 +161,11 @@ struct	emcsts {
 
 void    process_xmm_to_s87(const struct savexmm *, struct save87 *);
 void    process_s87_to_xmm(const struct save87 *, struct savexmm *);
+
 struct cpu_info;
+struct trapframe;
 
 void	npxinit(struct cpu_info *);
+void	npxtrap(struct trapframe *);
 
 #endif /* !_I386_NPX_H_ */
Index: sys/arch/i386/isa/npx.c
===================================================================
RCS file: /cvs/src/sys/arch/i386/isa/npx.c,v
retrieving revision 1.44
retrieving revision 1.44.6.1
diff -u -p -r1.44 -r1.44.6.1
--- sys/arch/i386/isa/npx.c	4 Dec 2008 15:48:19 -0000	1.44
+++ sys/arch/i386/isa/npx.c	5 Oct 2009 00:37:54 -0000	1.44.6.1
@@ -1,4 +1,4 @@
-/*	$OpenBSD: npx.c,v 1.44 2008/12/04 15:48:19 weingart Exp $	*/
+/*	$OpenBSD: npx.c,v 1.44.6.1 2009/10/05 00:37:54 sthen Exp $	*/
 /*	$NetBSD: npx.c,v 1.57 1996/05/12 23:12:24 mycroft Exp $	*/
 
 #if 0
@@ -134,8 +134,9 @@ extern int i386_fpu_present;
 extern int i386_fpu_exception;
 extern int i386_fpu_fdivbug;
 
-#define        fxsave(addr)            __asm("fxsave %0" : "=m" (*addr))
-#define        fxrstor(addr)           __asm("fxrstor %0" : : "m" (*addr))
+#define fxsave(addr)		__asm("fxsave %0" : "=m" (*addr))
+#define fxrstor(addr)		__asm("fxrstor %0" : : "m" (*addr))
+#define ldmxcsr(addr)		__asm("ldmxcsr %0" : : "m" (*addr))
 
 static __inline void
 fpu_save(union savefpu *addr)
@@ -533,6 +534,38 @@ npxintr(void *arg)
 	}
 
 	return (1);
+}
+
+void
+npxtrap(struct trapframe *frame)
+{
+	struct proc *p = curcpu()->ci_fpcurproc;
+	union savefpu *addr = &p->p_addr->u_pcb.pcb_savefpu;
+	u_int32_t mxcsr, statbits;
+	int code;
+	union sigval sv;
+
+#ifdef DIAGNOSTIC
+	/*
+	 * At this point, fpcurproc should be curproc.  If it wasn't, the TS
+	 * bit should be set, and we should have gotten a DNA exception.
+	 */
+	if (p != curproc)
+		panic("npxtrap: wrong process");
+#endif
+
+	fxsave(&addr->sv_xmm);
+	mxcsr = addr->sv_xmm.sv_env.en_mxcsr;
+	statbits = mxcsr;
+	mxcsr &= ~0x3f;
+	ldmxcsr(&mxcsr);
+	addr->sv_xmm.sv_ex_sw = addr->sv_xmm.sv_env.en_sw;
+	addr->sv_xmm.sv_ex_tw = addr->sv_xmm.sv_env.en_tw;
+	code = x86fpflags_to_siginfo (statbits);
+	sv.sival_int = frame->tf_eip;
+	KERNEL_PROC_LOCK(p);
+	trapsignal(p, SIGFPE, frame->tf_err, code, sv);
+	KERNEL_PROC_UNLOCK(p);
 }
 
 static int