Re: [Qemu-arm] [PATCH v3 01/10] tcg-runtime: add lookup_tb_ptr helper

[Richard Henderson]

On 04/26/2017 11:56 PM, Emilio G. Cota wrote:
> On Wed, Apr 26, 2017 at 10:40:45 +0200, Richard Henderson wrote:
> > On 04/26/2017 08:23 AM, Emilio G. Cota wrote:
> (snip)
> > > +    cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> > > +    tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)]);
> > > +    if (likely(tb && tb->pc == addr && tb->cs_base == cs_base &&
> > > +               tb->flags == flags)) {
> >
> > This comparison is wrong.  It will incorrectly reject a TB for i386 guest
> > when CS_BASE != 0.  You really want
> >
> >    tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)]);
> >    if (tb) {
> >      cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> >      if (tb->pc == pc && tb->cs_base == cs_base && tb->flags == flags) {
> >        return tb->tc_ptr;
> >      }
> >    }
> >    return tcg_ctx.code_gen_epilogue;
>
> wrt the comparison, the only change I notice in your suggested change is
>    tb->pc == pc
>
> instead of
>    tb->pc == addr
>
> , which seems innocuous to me (since tb->pc == addr).
>
> I fail to see how this relates to your "CS_BASE != 0" comment.
> What am I missing?

Recall how you computed vaddr for target/i386:

  addr = pc + cs_base


r~