Re: [RFA/DWARF] Add DW_AT_GNAT_descriptive_type support

[Tom Tromey <tromey@redhat.com>]

>>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

Joel> I have taken the time to order the patches to follow the same order
Joel> as if I was to write the patch all over again (gdbtypes updates,
Joel> dwarf2read updates, etc).  Hopefully this will help reading it.

Thanks...  though I don't really want to encourage this sort of thing,
because it will mean people will start expect it from me ;-)

This patch seems pretty reasonable.

Joel> There are still a couple of things that are worth discussing:

Joel>   (a) You'll see that I put a FIXME after modifying the
Joel>   TYPE_CPLUS_SPECIFIC macro.  The comment says it all.  I think
Joel>   that the fix is fine; in fact, we could generalize this approach
Joel>   to all the accessor macros for the type-specific union - I
Joel>   wouldn't see a problem with that, and would make the code more
Joel>   resilient to incorrect field access.  For now, I opted for just
Joel>   fixing this one macro, since C is usually the "universal" "bare"
Joel>   language.  Ada or C++ might be less so: Who would want to use
Joel>   C++ or Ada to display a Fortran array? :-)

The modified macro uses the default if Gnat aux info is available.  It
seem to me that the check should instead be to see if the C++ info is
not available.

Joel>   (b) We need to determine how GCC will tell GDB that it uses the
Joel>   DW_AT_GNAT_descriptive_type attribute.
[...]
Joel>       What's the best way for GCC to tell GDB? At AdaCore, we relied
Joel>       on a hack, where we parsed a special marker in the CU producer
Joel>       attribute.  It's kind of gross, but it served us well.  Any
Joel>       suggestion?
      
How about a new GNU extension attribute in the CU DIE?

Joel> +  if (! HAVE_CPLUS_STRUCT (type))
Joel> +    n_base_classes = 0;
Joel> +  else
Joel> +    n_base_classes = TYPE_N_BASECLASSES (type);

This seems a little weird to me.
Do we need this everywhere we use TYPE_N_BASECLASSES?

Tom