Index: sys/kern/kern_synch.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_synch.c,v
retrieving revision 1.309
diff -p -u -r1.309 kern_synch.c
--- sys/kern/kern_synch.c	13 Oct 2015 00:25:51 -0000	1.309
+++ sys/kern/kern_synch.c	8 Nov 2015 23:16:19 -0000
@@ -453,6 +453,31 @@ updatertime(lwp_t *l, const struct binti
 	if (__predict_false(l->l_flag & LW_IDLE))
 		return;
 
+#if defined(__sparc__)
+    {
+	/*
+	 * "now - stime" becomes negative sometimes, which it shouldn't.
+	 * try to figure out where it comes from, because we don't ever
+	 * add a negative value from the timecounter side.
+	 */
+	struct bintime delta = *now;
+	bintime_sub(&delta, &l->l_stime);
+        if (delta.sec < 0) {
+		log(LOG_DEBUG, "cpu%u: (%u.%u:%s) "
+			       "delta.sec = %lld, delta.frac = %llu, "
+			       "now.sec = %lld, now.frac = %llu, "
+			       "l_stime.sec = %lld, l_stime.frac = %llu, "
+			       "RA = %p\n",
+			       cpu_number(), l->l_proc->p_pid, l->l_lid,
+			       l->l_name ? l->l_name : l->l_proc->p_comm,
+			       (long long)delta.sec, (unsigned long long)delta.frac,
+			       (long long)now->sec, (unsigned long long)now->frac,
+			       (long long)l->l_stime.sec,
+			       (unsigned long long)l->l_stime.frac,
+			       __builtin_return_address(0));
+	}
+    }
+#endif
 	/* rtime += now - stime */
 	bintime_add(&l->l_rtime, now);
 	bintime_sub(&l->l_rtime, &l->l_stime);
Index: sys/kern/kern_tc.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_tc.c,v
retrieving revision 1.46
diff -p -u -r1.46 kern_tc.c
--- sys/kern/kern_tc.c	14 Sep 2013 20:52:43 -0000	1.46
+++ sys/kern/kern_tc.c	8 Nov 2015 23:16:19 -0000
@@ -739,6 +739,12 @@ tc_windup(void)
 		ncount = 0;
 	th->th_offset_count += delta;
 	bintime_addx(&th->th_offset, th->th_scale * delta);
+#ifdef __sparc__
+if (delta & 0x80000000)
+  log(LOG_DEBUG, "cpu%u: (%u.%u:%s) tc_delta() gave: %x (th_offset_count now %llx)\n",
+    cpu_number(), curlwp->l_proc->p_pid, curlwp->l_lid, curlwp->l_name ? curlwp->l_name : curlwp->l_proc->p_comm,
+    delta, (unsigned long long)th->th_offset_count);
+#endif
 
 	/*
 	 * Hardware latching timecounters may not generate interrupts on