Re: [PATCH 1/7] xen/arm: fix rank calculation in vgic_vcpu_inject_irq

[Tim Deegan <tim@xen.org>]

At 21:47 +0100 on 26 Oct (1351288040), Ian Campbell wrote:
> On Fri, 2012-10-26 at 19:42 +0100, Stefano Stabellini wrote:
> > I think that the problem is the usage of vgic_irq_rank with registers
> > that have 1 bit per interrupt.
> 
> That's very plausible indeed.
> 
> > diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
> > index 3c3983f..92731b6 100644
> > --- a/xen/arch/arm/vgic.c
> > +++ b/xen/arch/arm/vgic.c
> > @@ -42,13 +42,7 @@
> >   */
> >  static inline int REG_RANK_NR(int b, uint32_t n)
> >  {
> > -    switch ( b )
> > -    {
> > -    case 8: return n >> 3;
> > -    case 4: return n >> 2;
> > -    case 2: return n >> 1;
> > -    default: BUG();
> > -    }
> > +    return n / b;
> 
> All the infrastructure will fall apart if b isn't a power of two, that's
> why I used the switch. Can you just add the appropriate case 1 instead?
> Probably the bug should be a call to an undefined function to make this
> a compile time rather than runtime failure too.

BUILD_BUG_ON((b & -b) != b); ?

Tim.