Re: [Qemu-devel] [PATCH RFC 3/8] target-arm: Add support for S2 page-table protection bits

[Edgar E. Iglesias]

On Thu, Oct 01, 2015 at 08:48:17PM +0100, Peter Maydell wrote:
> On 1 October 2015 at 19:44, Edgar E. Iglesias <address@hidden> wrote:
> > On Wed, Sep 23, 2015 at 09:55:05AM -0700, Peter Maydell wrote:
> >> This isn't right -- the XN bit controls executability and the
> >> S2AP bits don't affect it at all. I think you want:
> >>
> >>     int prot_rw = 0;
> >>     if (s2ap & 1) {
> >>         prot_rw |= PAGE_READ;
> >>     }
> >>     if (s2ap & 2) {
> >>         prot_rw |= PAGE_WRITE;
> >>     }
> >>     if (!xn) {
> >>         prot_rw |= PAGE_EXEC;
> >>     }
> >
> >
> > Thanks, this was the stuff I was worried about when we talked about it
> > last time. I've got the following now which seems to be the same as
> > you suggest:
> >
> > static int get_S2prot(CPUARMState *env, int s2ap, int xn)
> > {
> >     int prot;
> >
> >     prot = s2ap & 1 ? PAGE_READ : 0;
> >     prot |= s2ap & 2 ? PAGE_WRITE : 0;
> >     if (!xn) {
> >         prot |= PAGE_EXEC;
> >     }
> >     return prot;
> > }
> 
> Yep, that's the right logic, though it seems a bit odd not
> to consistently use either 'if' or '?:' for all 3 bits.

OK, that's true, I'll change it to all ifs.

Thanks,
Edgar