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

[Emilio G. Cota]

On Thu, Apr 27, 2017 at 00:29:49 +0200, Richard Henderson wrote:
> 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

I see, thanks!

                Emilio