[PATCH v8 04/10] btrace: Handle stepping and goto for auxiliary instructions.

[Simon Marchi]

On 3/21/23 11:46, Felix Willgerodt via Gdb-patches wrote:
> Print the auxiliary data when stepping. Don't allow to goto an auxiliary
> instruction.
> 
> This patch is in preparation for the new ptwrite feature, which is based on
> auxiliary instructions.

Hi Felix,

Just a few minor comments.  No need to repost just for that.

> @@ -2388,12 +2392,27 @@ record_btrace_single_step_forward (struct thread_info *tp)
>  	 of the execution history.  */
>        steps = btrace_insn_next (replay, 1);
>        if (steps == 0)
> +        {
> +          *replay = start;
> +          return btrace_step_no_history ();
> +        }

These lines just (wrongfully) replaces the indentation with all spaces,
when in reality these lines don't need to be touched.

> +
> +      const struct btrace_insn *insn = btrace_insn_get (replay);
> +      if (insn == nullptr)
> +	continue;
> +
> +      /* If we're stepping a BTRACE_INSN_AUX instruction, print the auxiliary
> +	 data and skip the instruction.  */
> +      if (insn->iclass == BTRACE_INSN_AUX)
>  	{
> -	  *replay = start;
> -	  return btrace_step_no_history ();
> +	  gdb_printf ("[%s]\n",
> +		      btinfo->aux_data.at (insn->aux_data_index).c_str ());

I was a bit thrown off by the use of std::vector::at :P (I think it was
used in the previous patch too).  Did you use it specifically for the
behavior when the access is out of bounds?  If not, using operator[]
would probably be better (and more usual).

> @@ -2859,25 +2895,30 @@ record_btrace_target::goto_record_end ()
>  /* The goto_record method of target record-btrace.  */
>  
>  void
> -record_btrace_target::goto_record (ULONGEST insn)
> +record_btrace_target::goto_record (ULONGEST insn_number)
>  {
>    struct thread_info *tp;
>    struct btrace_insn_iterator it;
>    unsigned int number;
>    int found;
>  
> -  number = insn;
> +  number = insn_number;
>  
>    /* Check for wrap-arounds.  */
> -  if (number != insn)
> +  if (number != insn_number)
>      error (_("Instruction number out of range."));
>  
>    tp = require_btrace_thread ();
>  
>    found = btrace_find_insn_by_number (&it, &tp->btrace, number);
>  
> -  /* Check if the instruction could not be found or is a gap.  */
> -  if (found == 0 || btrace_insn_get (&it) == NULL)
> +  /* Check if the instruction could not be found or is a gap or an
> +     auxilliary instruction.  */
> +  if (found == 0)
> +    error (_("No such instruction."));
> +
> +  const struct btrace_insn *insn = btrace_insn_get (&it);
> +  if ((insn == NULL) || (insn->iclass == BTRACE_INSN_AUX))
>      error (_("No such instruction."));

Just wondering, would it be useful for the user to print a more specific
error message ("Can't go to an auxiliary instruction") if they try to
goto an aux instruction?

Simon