Re: [PATCH] pkl: Re-implement `strace` instruction

[Jose E. Marchesi]

Yes the shuffling of the stack elemnts is ugly.

> diff --git a/libpoke/pvm.jitter b/libpoke/pvm.jitter
> index 6c3a1690..8c943f14 100644
> --- a/libpoke/pvm.jitter
> +++ b/libpoke/pvm.jitter
> @@ -6087,31 +6087,30 @@ end
>  instruction strace (?n)
>    non-relocatable
>    code
> -     pvm_val tmp[1024];
> -     int i = 0, j;
> -     int num_elems = (int) JITTER_ARGN0;
> -
> -     while (((num_elems == 0 || i < num_elems)
> -             && (JITTER_HEIGHT_STACK () !=
> -                 PVM_STATE_BACKING_FIELD (canary))))
> -        {
> -          assert (i < 1024);
> -          pvm_print_val_with_params (PVM_STATE_BACKING_FIELD (vm),
> -                                     JITTER_TOP_STACK (),
> -                                     0 /* depth */,
> -                                     PVM_PRINT_FLAT,
> -                                     16 /* base */,
> -                                     2 /* indent */,
> -                                     0 /* acutoff */,
> -                                     PVM_PRINT_F_MAPS);
> -          pk_puts ("\n");
> -          tmp[i++] = JITTER_TOP_STACK ();
> -          JITTER_DROP_STACK ();
> -        }
> -
> -     /* Restore the stack.  */
> -     for (j = (i - 1); j >= 0; j--)
> -        JITTER_PUSH_STACK (tmp[j]);
> +    int i = 0;
> +    int num_elems_max =
> +      PVM_STATE_BACKING_FIELD (canary) == NULL
> +        ? 1024
> +        :  (pvm_val*)JITTER_HEIGHT_STACK () -
> +           (pvm_val*)PVM_STATE_BACKING_FIELD (canary);

`canary' is supposed to be always set to a meaningful height when strace
is used.  So it would be better to use an assert.  No need for a 1024
default.

Instead of `num_elems_max' I would prefer to use a clearer name, like,
num_elems_in_stack.

OK otherwise, for both master and poke-1.

> +    int num_elems = (int) JITTER_ARGN0;
> +
> +    if (num_elems == 0 || num_elems > num_elems_max)
> +      num_elems = num_elems_max;
> +
> +    while (i < num_elems)
> +      {
> +        pvm_print_val_with_params (PVM_STATE_BACKING_FIELD (vm),
> +                                   JITTER_AT_DEPTH_STACK (i),
> +                                   0 /* depth */,
> +                                   PVM_PRINT_FLAT,
> +                                   16 /* base */,
> +                                   2 /* indent */,
> +                                   0 /* acutoff */,
> +                                   PVM_PRINT_F_MAPS);
> +        pk_puts ("\n");
> +        i++;
> +      }
>    end
>  end