Re: [PATCH] Add line debug info for virtual thunks (PR ipa/97937)

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 1/6/21 12:49 PM, Eric Botcazou wrote:
>> currently there is a problem when debugging a virtual thunk.  That is
>> a decl with DECL_IGNORED_P.  Currently the line information displayed
>> in gdb is completely bogus, thus the last line of whatever function
>> is immediately before the PC of the thunk.
> 
> DECL_IGNORED_P means completely ignored for debug info purposes though and I 
> think that the Ada compiler expects this semantic.
> 
>> This patch improves the debug experience at least a bit by emitting
>> at the line number information where the thunk has been defined.
>> I do not dare to touch anything but dwarf2 debug info, therefore
>> the patch is a bit awkward.
> 
> Please run the GDB testsuite with Ada support on the patch.
> 

Yes, I always do that, and this patch did not affect any Ada tests.
Anyway, I guess this patch will need some rework, to probably attack
the DECL_IGNORED_P without line info.

One thing I remembered from previous testing, and I was not sure if
it is a correctness issue or not, is this:

As I had to call begin_function also for DECL_IGNORED_P,
I noticed that there are a number of Ada functions with
DECL_IGNORED_P, but their  crtl->has_bb_partition is set,
and therefore this block is executed with my patch, but
it is currently not executed:

See dwarf2out_begin_function:

  if (crtl->has_bb_partition && !cold_text_section)
    {
      gcc_assert (current_function_decl == fun);
      cold_text_section = unlikely_text_section ();
      switch_to_section (cold_text_section);
      ASM_OUTPUT_LABEL (asm_out_file, cold_text_section_label);
      switch_to_section (sec);
    }

I had expected that functions with DECL_IGNORED_P should not need
that side effect.  Anyway I had not seen any effect from this.


Bernd.