Re: [Qemu-devel] [PATCH] pl190: fix read of VECTADDR

[Brendan Fennell <bfennell@skynet.ie>]

On Sat, 18 Aug 2012, Peter Maydell wrote:

> On 18 August 2012 03:55, Brendan Fennell <bfennell@skynet.ie> wrote:
>> Signed-off-by: Brendan Fennell <bfennell@skynet.ie>
>> ---
>>  hw/pl190.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/hw/pl190.c b/hw/pl190.c
>> index cb50afb..d69d5be 100644
>> --- a/hw/pl190.c
>> +++ b/hw/pl190.c
>> @@ -133,7 +133,7 @@ static uint64_t pl190_read(void *opaque, target_phys_addr_t offset,
>>              s->priority = i;
>>              pl190_update(s);
>>            }
>> -        return s->vect_addr[s->priority];
>> +        return s->vect_addr[s->priority - 1];
>>      case 13: /* DEFVECTADDR */
>>          return s->vect_addr[16];
>>      default:
>
> This doesn't look right -- if s->priority is zero then we'll read off
> the beginning of the array.
> What's the actual bug you're trying to fix here?

The bug is that when, for example, interrupt 4 triggers the VECTADDR of 
interrupt 5 is returned by pl190_read().

Each s->prio_mask entry contains the interrupt mask for all *higher* 
priority interrupts, see pl190_update_vectors(). This means that 
s->prio_mask[0] is always zero (as zero is the highest priority), 
s->priority can never be  zero as ((s->level | s->soft_level) & 
s->prio_mask[0]) is always zero.

Therefore after the for loop in pl190_read() i is the index of the
current highest priority interrupt + 1.

Brendan.

>
> -- PMM
>
>