Re: [PATCH v14 02/10] accel/tcg: introduce TBStatistics structure

[Richard Henderson]

On 5/31/23 18:30, Wu, Fei wrote:
> On 6/1/2023 7:59 AM, Richard Henderson wrote:
> > On 5/30/23 01:35, Fei Wu wrote:
> > > +    /*
> > > +     * We want to fetch the stats structure before we start code
> > > +     * generation so we can count interesting things about this
> > > +     * generation.
> > > +     */
> > > +    if (tb_stats_collection_enabled()) {
> > > +        tb->tb_stats = tb_get_stats(phys_pc, pc, cs_base, flags);
> >
> > If cflags & CF_PCREL, then 'pc' should not be cached or matched.
> > Using 'phys_pc' will suffice, so pass 0 in that case.
> OK, tb_get_stats(phys_pc, (cflags & CF_PCREL ? 0 : pc), cs_base, flags);
>
> btw, is it possible to drop 'pc' even w/o CF_PCREL setting in cflags?
> Two TBs with different 'pc' but same 'phys_pc', are they the same?

For the purpose of statistics, yes, plausibly.

Knowing how many different translations of the same bit of libc.so, for a guest that does 
not support CF_PCREL, could be revealing.  In any case, you can get back to the virtual 
addresses via tb_stats->tbs[i]->pc, so long as tb_stats->tb[i].cflags & CF_PCREL is not set.


r~