diff --git a/sys/ia64/ia64/vm_machdep.c b/sys/ia64/ia64/vm_machdep.c
index 960cb39589e2..246adeb43e61 100644
--- a/sys/ia64/ia64/vm_machdep.c
+++ b/sys/ia64/ia64/vm_machdep.c
@@ -120,29 +120,29 @@ cpu_thread_setup(struct thread *td)
 }
 
 void
-cpu_set_upcall(struct thread *td, void *pcb)
+cpu_set_upcall(struct thread *td, void *pcb0)
 {
-	struct pcb *pcb2;
+	struct pcb *pcb;
 	struct trapframe *tf;
 
-	pcb2 = td->td_pcb;
-	bcopy(pcb, pcb2, sizeof(*pcb2));
+	pcb = td->td_pcb;
+	KASSERT(pcb != NULL, ("foo"));
+	bcopy(pcb0, pcb, sizeof(*pcb));
 
-	tf = (struct trapframe *)pcb2 - 1;
-	td->td_frame = tf;
-	tf->tf_length = sizeof(struct trapframe);
+	tf = td->td_frame;
+	KASSERT(tf != NULL, ("foo"));
 	tf->tf_flags = FRAME_SYSCALL;
 
+	tf->tf_special.ndirty = 0;
 	tf->tf_scratch.gr8 = 0;
 	tf->tf_scratch.gr9 = 1;
 	tf->tf_scratch.gr10 = 0;
 
-	/* XXX */
-	pcb2->pcb_special.bspstore = td->td_kstack + tf->tf_special.ndirty;
-	pcb2->pcb_special.pfs = 0;
-	pcb2->pcb_current_pmap = vmspace_pmap(td->td_proc->p_vmspace);
-	pcb2->pcb_special.sp = (uintptr_t)tf - 16;
-	pcb2->pcb_special.rp = FDESC_FUNC(fork_trampoline);
+	pcb->pcb_special.bspstore = td->td_kstack;
+	pcb->pcb_special.pfs = 0;
+	pcb->pcb_current_pmap = vmspace_pmap(td->td_proc->p_vmspace);
+	pcb->pcb_special.sp = (uintptr_t)tf - 16;
+	pcb->pcb_special.rp = FDESC_FUNC(fork_trampoline);
 	cpu_set_fork_handler(td, (void (*)(void*))fork_return, td);
 }