pl190: fix read of VECTADDR

Reading VECTADDR was causing us to set the current priority to
the wrong value, the most obvious effect of which was that we
would return the vector for the wrong interrupt as the result
of the read.

Signed-off-by: Brendan Fennell <bfennell@skynet.ie>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 12 insertions, 6 deletions

diff --git a/hw/pl190.c b/hw/pl190.c
index cb50afb9f4..7332f4dbae 100644
--- a/hw/pl190.c
+++ b/hw/pl190.c
@@ -117,12 +117,18 @@ static uint64_t pl190_read(void *opaque, target_phys_addr_t offset,
         return s->protected;
     case 12: /* VECTADDR */
         /* Read vector address at the start of an ISR.  Increases the
-           current priority level to that of the current interrupt.  */
-        for (i = 0; i < s->priority; i++)
-          {
-            if ((s->level | s->soft_level) & s->prio_mask[i])
-              break;
-          }
+         * current priority level to that of the current interrupt.
+         *
+         * Since an enabled interrupt X at priority P causes prio_mask[Y]
+         * to have bit X set for all Y > P, this loop will stop with
+         * i == the priority of the highest priority set interrupt.
+         */
+        for (i = 0; i < s->priority; i++) {
+            if ((s->level | s->soft_level) & s->prio_mask[i + 1]) {
+                break;
+            }
+        }
+
         /* Reading this value with no pending interrupts is undefined.
            We return the default address.  */
         if (i == PL190_NUM_PRIO)