Re: [Qemu-devel] [PATCH 3/3] target-i386: make it clearer that op table accesses don't overrun

[Stefan Weil <sw@weilnetz.de>]

Please see comments below.

Am 05.07.2012 23:29, schrieb Peter Maydell:
> Rephrase some of the expressions used to select an entry
> in the SSE op table arrays so that it's clearer that they
> don't overrun the op table array size.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   target-i386/translate.c |   12 ++++++------
>   1 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/target-i386/translate.c b/target-i386/translate.c
> index 5899e09..1988dae 100644
> --- a/target-i386/translate.c
> +++ b/target-i386/translate.c
> @@ -2964,16 +2964,16 @@ static const SSEFunc_0_pl sse_op_table3aq[] = {
>   
>   static const SSEFunc_i_p sse_op_table3bi[] = {
>       gen_helper_cvttss2si,
> -    gen_helper_cvttsd2si,
>       gen_helper_cvtss2si,
> +    gen_helper_cvttsd2si,
>       gen_helper_cvtsd2si
>   };
>   
>   #ifdef TARGET_X86_64
>   static const SSEFunc_l_p sse_op_table3bq[] = {
>       gen_helper_cvttss2sq,
> -    gen_helper_cvttsd2sq,
>       gen_helper_cvtss2sq,
> +    gen_helper_cvttsd2sq,
>       gen_helper_cvtsd2sq
>   };
>   #endif
> @@ -3571,12 +3571,12 @@ static void gen_sse(DisasContext *s, int b, target_ulong pc_start, int rex_r)
>               op1_offset = offsetof(CPUX86State,xmm_regs[reg]);
>               tcg_gen_addi_ptr(cpu_ptr0, cpu_env, op1_offset);
>               if (ot == OT_LONG) {
> -                SSEFunc_0_pi sse_fn_pi = sse_op_table3ai[(b >> 8) - 2];
> +                SSEFunc_0_pi sse_fn_pi = sse_op_table3ai[(b >> 8) & 1];
>                   tcg_gen_trunc_tl_i32(cpu_tmp2_i32, cpu_T[0]);
>                   sse_fn_pi(cpu_ptr0, cpu_tmp2_i32);
>               } else {
>   #ifdef TARGET_X86_64
> -                SSEFunc_0_pl sse_fn_pl = sse_op_table3aq[(b >> 8) - 2];
> +                SSEFunc_0_pl sse_fn_pl = sse_op_table3aq[(b >> 8) & 1];
>                   sse_fn_pl(cpu_ptr0, cpu_T[0]);
>   #else
>                   goto illegal_op;
> @@ -3635,13 +3635,13 @@ static void gen_sse(DisasContext *s, int b, target_ulong pc_start, int rex_r)

Here I suggest to reorder the case statements:

         case 0x22c: /* cvttss2si */
         case 0x22d: /* cvtss2si */
         case 0x32c: /* cvttsd2si */
         case 0x32d: /* cvtsd2si */

That's the numeric order, and it matches the order in the modified
array again.

>
>               tcg_gen_addi_ptr(cpu_ptr0, cpu_env, op2_offset);
>               if (ot == OT_LONG) {
>                   SSEFunc_i_p sse_fn_i_p =
> -                    sse_op_table3bi[(b >> 8) - 2 + (b & 1) * 2];
> +                    sse_op_table3bi[((b >> 7) & 2) | (b & 1)];
>                   sse_fn_i_p(cpu_tmp2_i32, cpu_ptr0);
>                   tcg_gen_extu_i32_tl(cpu_T[0], cpu_tmp2_i32);
>               } else {
>   #ifdef TARGET_X86_64
>                   SSEFunc_l_p sse_fn_l_p =
> -                    sse_op_table3bq[(b >> 8) - 2 + (b & 1) * 2];
> +                    sse_op_table3bq[((b >> 7) & 2) | (b & 1)];
>                   sse_fn_l_p(cpu_T[0], cpu_ptr0);
>   #else
>                   goto illegal_op;

Maybe a 2-dimensional array would make that code even
more readable:

sse_op_table3bq[(b >> 8) & 1][b & 1];


Anyway, you may add a

Reviewed-by: Stefan Weil <sw@weilnetz.de>

Regards,

Stefan W.