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

[Emilio G. Cota]

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?

                E.