Re: [Qemu-devel] [PATCH 3/5] tcg: always keep jump target and tb->jmp_next consistent

[Richard Henderson <rth@twiddle.net>]

On 03/17/2016 06:46 AM, sergey.fedorov@linaro.org wrote:
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> Simple code simplification.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
> ---
>  translate-all.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/translate-all.c b/translate-all.c
> index f17ace1ae899..a1ac9841de48 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -927,6 +927,14 @@ static inline void tb_page_remove(TranslationBlock **ptb, TranslationBlock *tb)
>      }
>  }
>  
> +/* reset the jump entry 'n' of a TB so that it is not chained to
> +   another TB */
> +static inline void tb_reset_jump(TranslationBlock *tb, int n)
> +{
> +    tb_set_jmp_target(tb, n, (uintptr_t)(tb->tc_ptr + tb->tb_next_offset[n]));
> +    tb->jmp_next[n] = NULL;
> +}
> +
>  static inline void tb_jmp_remove(TranslationBlock *tb, int n)
>  {
>      TranslationBlock *tb1, **ptb;
> @@ -951,18 +959,10 @@ static inline void tb_jmp_remove(TranslationBlock *tb, int n)
>          }
>          /* now we can suppress tb(n) from the list */
>          *ptb = tb->jmp_next[n];
> -
> -        tb->jmp_next[n] = NULL;
> +        tb_reset_jump(tb, n);

What's the motivation here?  This implies an extra cache flush.
Where were we resetting the jump previously?  Or is this a bug
in that we *weren't* resetting the jump previously?


r~