Re: [Qemu-devel] [PATCH v1 1/5] target-microblaze: Respect MSR.PVR as read-only

["Edgar E. Iglesias" <edgar.iglesias@xilinx.com>]

On Thu, Apr 19, 2018 at 11:17:58AM -1000, Richard Henderson wrote:
> On 04/19/2018 10:33 AM, Edgar E. Iglesias wrote:
> > On Thu, Apr 19, 2018 at 09:56:40AM -1000, Richard Henderson wrote:
> >> On 04/19/2018 01:21 AM, Edgar E. Iglesias wrote:
> >>>  static inline void msr_write(DisasContext *dc, TCGv v)
> >>>  {
> >>> -    TCGv t;
> >>> -
> >>> -    t = tcg_temp_new();
> >>>      dc->cpustate_changed = 1;
> >>>      /* PVR bit is not writable.  */
> >>> -    tcg_gen_andi_tl(t, v, ~MSR_PVR);
> >>> -    tcg_gen_andi_tl(cpu_SR[SR_MSR], cpu_SR[SR_MSR], MSR_PVR);
> >>> -    tcg_gen_or_tl(cpu_SR[SR_MSR], cpu_SR[SR_MSR], v);
> >>> -    tcg_temp_free(t);
> >>> +    tcg_gen_deposit_tl(cpu_SR[SR_MSR], v, cpu_SR[SR_MSR], MSR_PVR_SHIFT, 1);
> >>>  }
> >>
> >> Um... the old code was correct, but the new code isn't.
> >>
> >> The new code sets msr to v, with bit 10 set to the old msr bit 0.
> >>
> >> Why do you believe the old code to be wrong?
> > 
> > The old code was incorrectly ORing v instead of t...
> 
> Ah, yes.
> 
> > What about the following?
> >     tcg_gen_shri_tl(cpu_SR[SR_MSR], cpu_SR[SR_MSR], MSR_PVR_SHIFT);
> >     tcg_gen_deposit_tl(cpu_SR[SR_MSR], v, cpu_SR[SR_MSR], MSR_PVR_SHIFT, 1);
> 
> *shrug* While that would be functional, I don't think it's any better than just
> fixing the typo in the OR.

Allright, I'll fix the typo and send out a v2.

Thanks for catching this.

Cheers,
Edgar