On Wed, Apr 26, 2017 at 10:40:45 +0200, Richard Henderson wrote:
> On 04/26/2017 08:23 AM, Emilio G. Cota wrote:
> >This paves the way for upcoming work.
> >
> >Reviewed-by: Richard Henderson <[email protected]>
> >Signed-off-by: Emilio G. Cota <[email protected]>
> >---
> > tcg-runtime.c | 21 +++++++++++++++++++++
> > tcg/tcg-runtime.h | 2 ++
> > tcg/tcg.h | 1 +
> > 3 files changed, 24 insertions(+)
> >
> >diff --git a/tcg-runtime.c b/tcg-runtime.c
> >index 4c60c96..90d2d4b 100644
> >--- a/tcg-runtime.c
> >+++ b/tcg-runtime.c
> >@@ -27,6 +27,7 @@
> > #include "exec/helper-proto.h"
> > #include "exec/cpu_ldst.h"
> > #include "exec/exec-all.h"
> >+#include "exec/tb-hash.h"
> > /* 32-bit helpers */
> >@@ -141,6 +142,26 @@ uint64_t HELPER(ctpop_i64)(uint64_t arg)
> > return ctpop64(arg);
> > }
> >+ 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;
>
> where you don't even load the cpu state if there isn't a preliminary hit in
> the cache.
Yes, I like this.
> (Note to self: That minor optimization would also apply to tb_find.)
FWIW I looked at tb_find -- you need the pc though, which comes from
loading the CPU state:
cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
^^
tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
^^
If we wanted to really avoid getting all the state I guess we'd have to add
another function that returned just the pc.
E.
