Re: [Qemu-devel] Sparc32: Mask writes to the WIM register

[Blue Swirl]

On 8/20/08, Luis Pureza <address@hidden> wrote:
> OK, the following patch works for me:
>
>  ---
>   target-sparc/translate.c |    7 +++++++
>   1 files changed, 7 insertions(+), 0 deletions(-)
>
>  diff --git a/target-sparc/translate.c b/target-sparc/translate.c
>  index 8286d36..02e497f 100644
>
> --- a/target-sparc/translate.c
>  +++ b/target-sparc/translate.c
>
> @@ -73,6 +73,7 @@ typedef struct DisasContext {
>      struct TranslationBlock *tb;
>      uint32_t features;
>      int extra_cpu_cycles;
>  +    uint32_t wim_mask;
>   } DisasContext;
>
>   // This function uses non-native bit order
>  @@ -3485,6 +3486,7 @@ static void disas_sparc_insn(DisasContext * dc)
>
>                              }
>   #else
>                              tcg_gen_trunc_tl_i32(cpu_tmp32, cpu_tmp0);
>
> +                            tcg_gen_andi_tl(cpu_tmp32, cpu_tmp32,
>  dc->wim_mask);
>
>                              tcg_gen_st_i32(cpu_tmp32, cpu_env,
>                                             offsetof(CPUSPARCState, wim));
>
>  #endif
>  @@ -4848,6 +4850,11 @@ static inline void
>  gen_intermediate_code_internal(TranslationBlock * tb,
>   #ifdef TARGET_SPARC64
>      dc->address_mask_32bit = env->pstate & PS_AM;
>   #endif
>  +    if (env->nwindows == 32) {
>  +        dc->wim_mask = 0xFFFFFFFF;
>  +    } else {
>  +        dc->wim_mask = (1 << env->nwindows) - 1;
>  +    }
>      gen_opc_end = gen_opc_buf + OPC_MAX_SIZE;
>
>      cpu_tmp0 = tcg_temp_new(TCG_TYPE_TL);

Thanks. But now every translation would be slowed down by a tiny
amount because the wim mask is calculated, even if it will never be
used. More optimally, the mask should be calculated as needed and only
nwindows should be copied to dc.

A more complex solution would be to avoid most of the copying
entirely, so that env would have a pointer to sparc_def_t structure
and dc could copy only this "def" pointer. Then instead of
dc->features and dc->nwindows, dc->def->features and dc->def->nwindows
would be used. This would be more useful in the future, if I add code
to select the ASI helper at translation time.