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

[Brendan Fennell]

On Sat, 18 Aug 2012, Peter Maydell wrote:

> On 18 August 2012 03:55, Brendan Fennell <address@hidden> wrote:
> > Signed-off-by: Brendan Fennell <address@hidden>
> > ---
> >  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