Re: [PATCH][v2] Always default to DWARF2_DEBUG if not specified, warn about deprecated STABS

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/13/2021 10:52 AM, Koning, Paul wrote:
>
>> On Sep 13, 2021, at 3:31 AM, Richard Biener <rguenther@suse.de> wrote:
>>
>> This makes defaults.h choose DWARF2_DEBUG if PREFERRED_DEBUGGING_TYPE
>> is not specified by the target and NO_DEBUG if DWARF is not supported.
>>
>> It also makes us warn when STABS is enabled and removes the corresponding
>> diagnostic from the Ada frontend.  The warnings are pruned from the
>> testsuite output via prune_gcc_output.
>>
>> This leaves the following targets without debug support:
>>
>> pdp11-*-*   pdp11 is a.out, dwarf support is difficult
> I'll admit that I don't know much about debug formats.  It is definitely the case that pdp11 output is a.out (it may be BSD 2.x style a.out -- which I think is somewhat different though it's been many years since I looked at that, and then only briefly).  I guess that constrains which debug formats can be used, but I don't know any details.
My recollection of aout stabs is mostly lost.  IIRC we'd emit .stabs 
directives to the assembler which would turn into symbol table entries.

Embedded stabs used the same underlying stab strings, but instead put 
the information into a special section.  That requires an object format 
that supports named sections, so it's a non-starter for a.out.

dwarf also requires named sections.  While in theory one could probably 
do something hackish like dwarf embedded in .stab directives, that just 
seems just awful.

>
> pdp11-elf was done as an experiment by someone else, in binutils.  I'll ask about the status of that.  If it's possible to deliver that, it would presumably enable DWARF support.  Is that all common code so it's a matter of enabling it, or would "DWARF machine details for pdp11" have to be defined?
That's going to be the best path forward.  Get the pdp11-elf bits 
working and the dwarf2 debugging stuff should come along for free.

Jeff