[fpc-devel] RECENT Commit breaking FpDebug - Dwarf / and not even fully fixing the original issue

[Pierre Muller]

Le 29/04/2026 à 22:45, Martin Frb via fpc-devel a écrit :
> The below mention commit removes writing of class constants.
>

  I did commit this indeed.


> It also breaks this for FpDebug, which was able to show them. (btw, gdb
> can too)
> Though, it is still correct.... (more or less).
> I agree, we do need DWARF that works with GDB...
>

  GDB is generating an assertion error when trying to dispaly the value of these constants.


> Which leads to an interesting question
> - Why wasn't it fixed?
> It now works for classes, but is left broken for advanced records (see
> example at the end)....

   I do not understand what you mean by saying that it is now fixed,
before my commit, I wasn't able to debug the Free Pascal trunk compiler using GDB.


> It breaks GDB. But not because GDB doesn't deal with "incorrect dwarf"
> It breaks GDB because GDB's Pascal mode is severely broken, and declining.
> GDB has comments "we haven't seen that by any producer, so we don't
> support it yet" (that may include: just not seen, because not tried hard
> enough).
>

  I still have not enough knowledge about Dwarf internal to understand all those issues.
For that reason, I would prefer that Jonas or Florian would look at you MR concerning
DWarf improvement and FpDebug specifics.

> And yes its the Pascal part of GDB:
> When compiled with -godwarfcpp then this incorrect dwarf works => so
> maybe that could have been kept?
> Yes, its still wrong Dwarf, so ok, still correct to remove.



> But then, why not: REPLACE?
> Wouldn't that be better?
> There is correct and valid DWARF to implement this.
> In DWARF-5 => but I made an MR for DWARF-5, and then can easily make one
> for the "class const" as follow up.
> 
> Only problem: gdb is broken if the language is set to Pascal.
> The valid DWARF-5 works if the language is c++. But of course not, if it
> is Pascal.

I am still the official Pascal maintainer of GDB, but I didn't do anything
to improve GDB for a looonng time.

I would maybe make more sense if you would directly step up to volunteer
as Pascal maintainer of GDB?


> Given that we have a switch -godwarfcpp => should we not then also have
> one for -godwarffpdebug ?
> 
> If we go by the minimum between gdb and lldb => given that gdb is
> shrinking its minimum (the string tag worked in gdb 12 but no longer in
> gdb 17 at least not for pascal) there wont be much left.


   Adding support for Dwarf-5 is certainly a good move, but again, I do not feel competent in that area, sorry.

> ---------------------------------------
> 
> Out of sheer curiosity:
> 
> Why is there a (reverted) commit that attempts to fix this by removing
> the constant from TObject (and leaving the dwarf info as is)?

   This is how I did on several test machines to be able to use GDB to debug Free Pascal compiler.
I pushed this local change by accident, that is why I reverted it.
We had a discussion on core when I raised the issue about the fact that adding a constant
field to the system TObject (which is the base class of all classes)
completely broke the usage of GDB, as any inspection of a class instance
led to a internal assertion error inside GDB.

Pierre