[PATCH] hw/ptimer: Assert next_event is newer than last_event

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

If the period is too big, the 'delta * period' product result
might overflow, resulting in a negative number, then the
next_event ends before the last_event. This is buggy, as there
is no forward progress. Assert this can not happen.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/core/ptimer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
index d58e2dfdb0..88085d4c81 100644
--- a/hw/core/ptimer.c
+++ b/hw/core/ptimer.c
@@ -125,6 +125,9 @@ static void ptimer_reload(ptimer_state *s, int delta_adjust)
 
     s->last_event = s->next_event;
     s->next_event = s->last_event + delta * period;
+    /* Verify forward progress */
+    g_assert(s->next_event > s->last_event);
+
     if (period_frac) {
         s->next_event += ((int64_t)period_frac * delta) >> 32;
     }
-- 
2.20.1