The ISCR.ISRPENDING bit is set when an external interrupt is pending.
This is true whether that external interrupt is enabled or not.
This means that we can't use 's->vectpending == 0' as a shortcut to
"ISRPENDING is zero", because s->vectpending indicates only the
highest priority pending enabled interrupt.

Remove the incorrect optimization so that if there is no pending
enabled interrupt we fall through to scanning through the whole
interrupt array.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/intc/armv7m_nvic.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
index 94fe00235af..2aba2136822 100644
--- a/hw/intc/armv7m_nvic.c
+++ b/hw/intc/armv7m_nvic.c
@@ -127,15 +127,14 @@ static bool nvic_isrpending(NVICState *s)
 {
     int irq;
 
-    /* We can shortcut if the highest priority pending interrupt
-     * happens to be external or if there is nothing pending.
+    /*
+     * We can shortcut if the highest priority pending interrupt
+     * happens to be external; if not we need to check the whole
+     * vectors[] array.
      */
     if (s->vectpending > NVIC_FIRST_IRQ) {
         return true;
     }
-    if (s->vectpending == 0) {
-        return false;
-    }
 
     for (irq = NVIC_FIRST_IRQ; irq < s->num_irq; irq++) {
         if (s->vectors[irq].pending) {
-- 
2.20.1

On 7/23/21 6:21 AM, Peter Maydell wrote:
> The ISCR.ISRPENDING bit is set when an external interrupt is pending.
> This is true whether that external interrupt is enabled or not.
> This means that we can't use 's->vectpending == 0' as a shortcut to
> "ISRPENDING is zero", because s->vectpending indicates only the
> highest priority pending enabled interrupt.
> 
> Remove the incorrect optimization so that if there is no pending
> enabled interrupt we fall through to scanning through the whole
> interrupt array.
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   hw/intc/armv7m_nvic.c | 9 ++++-----
>   1 file changed, 4 insertions(+), 5 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~