Re: [PATCH 2/2] gdb: more infrun debug from breakpoint.c

[Simon Marchi <simark@simark.ca>]

On 2022-10-05 05:34, Andrew Burgess via Gdb-patches wrote:
> This commit adds additional infrun debug from the breakpoint.c file.
> The new debug output all relates to breakpoint condition evaluation.
> 
> There is already some infrun debug emitted from the breakpoint.c file,
> so hopefully, adding more will not be contentious.  I think the
> functions being instrumented make sense as part of the infrun process,
> the inferior stops, evaluates the condition, and then either stops or
> continues.  This new debug gives more insight into that process.
> 
> I had to make the bp_location* argument to find_loc_num_by_location
> const, and add a declaration for find_loc_num_by_location.
> 
> There should be no user visible changes unless they turn on debug
> output.
> ---
>  gdb/breakpoint.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index 002f4a935b1..38546ea44ba 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -165,6 +165,8 @@ static std::vector<symtab_and_line> bkpt_probe_decode_location_spec
>  
>  static bool bl_address_is_meaningful (bp_location *loc);
>  
> +static int find_loc_num_by_location (const bp_location *loc);
> +
>  /* update_global_location_list's modes of operation wrt to whether to
>     insert locations now.  */
>  enum ugll_insert_mode
> @@ -5302,6 +5304,8 @@ bpstat_check_watchpoint (bpstat *bs)
>  static void
>  bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
>  {
> +  INFRUN_SCOPED_DEBUG_ENTER_EXIT;
> +
>    const struct bp_location *bl;
>    struct breakpoint *b;
>    /* Assume stop.  */
> @@ -5316,6 +5320,10 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
>    b = bs->breakpoint_at;
>    gdb_assert (b != NULL);
>  
> +  infrun_debug_printf ("thread = %s, breakpoint %d.%d",
> +		       thread->ptid.to_string ().c_str (),
> +		       b->number, find_loc_num_by_location (bl));
> +
>    /* Even if the target evaluated the condition on its end and notified GDB, we
>       need to do so again since GDB does not know if we stopped due to a
>       breakpoint or a single step breakpoint.  */
> @@ -5323,6 +5331,9 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
>    if (frame_id_p (b->frame_id)
>        && !frame_id_eq (b->frame_id, get_stack_frame_id (get_current_frame ())))
>      {
> +      infrun_debug_printf ("incorrect frame %s not %s, not stopping",
> +			   get_stack_frame_id (get_current_frame ()).to_string ().c_str (),
> +			   b->frame_id.to_string ().c_str ());
>        bs->stop = 0;
>        return;
>      }
> @@ -5333,6 +5344,7 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
>    if ((b->thread != -1 && b->thread != thread->global_num)
>        || (b->task != 0 && b->task != ada_get_task_number (thread)))
>      {
> +      infrun_debug_printf ("incorrect thread or task, not stopping");
>        bs->stop = 0;
>        return;
>      }
> @@ -5424,16 +5436,22 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
>  
>    if (cond && !condition_result)
>      {
> +      infrun_debug_printf ("condition_result = false, not stopping");
>        bs->stop = 0;
>      }
>    else if (b->ignore_count > 0)
>      {
> +      infrun_debug_printf ("ignore count %d, not stopping",
> +			   b->ignore_count);
>        b->ignore_count--;
>        bs->stop = 0;
>        /* Increase the hit count even though we don't stop.  */
>        ++(b->hit_count);
>        gdb::observers::breakpoint_modified.notify (b);
> -    }	
> +    }
> +
> +  if (bs->stop)
> +    infrun_debug_printf ("stopping at this breakpoint");
>  }

I'd suggest a little change just for readability:

  if (cond != nullptr && !condition_result)
    {
      ...
      return;
    }

  if (b->ignore_count > 0)
    {
      ...
      return;
    }

  infrun_debug_printf ("stopping at this breakpoint");

This way, all cases where we decided not to stop are handled as early
returns (there are more above in the function).  And if we reach the
very end of the function, it means we decided to stop.

Other than that, this patch and the previous one LGTM.

Simon