Re: BTF tag support in DWARF (notes for today's BPF Office Hours)

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2023-02-22 at 10:11 -0800, Alexei Starovoitov wrote:
[...]
> > > > What do you think about something like "debug_type_tag" or
> > > > "debug_type_annotation" (and a similar update for the decl tags)?
> > > > The translation into BTF records would be the same, but the DWARF info
> > > > would stand on its own without being tied to BTF.
> > > > 
> > > > (Naming is a bit tricky since terms like 'tag' are already in use by
> > > > DWARF, e.g. "type tag" in the context of DWARF DIEs makes me think of
> > > > DW_TAG_xxxx_type...)
> > > > 
> > > > As far as I understand, early proposals for the tags were more generic
> > > > but the LLVM reviewers wished for something more specific due to the
> > > > relatively limited use of the tags at the time. Now that the tags and
> > > > their DWARF format have matured I think a good case can be made to
> > > > make these generic. We'd be happy to help push for such change.
> > > 
> > > On the other hand, BTF is a thing we are using this annotation for.
> > > Any other tool can reuse DW_TAG_LLVM_annotation, but it will need a
> > > way to distinguish it's annotations from BTF annotations. And this can
> > > be done by using a different DW_AT_name. So, it seems logical to
> > > retain "btf" in the DW_AT_name. What do you think?
> > 
> > OK I can understand keeping it BTF specific.
> > 
> > Other than that, I don't come up with any significantly different idea
> > than to use the ":v2" suffix, so let's go with "btf_type_tag:v2"?
> 
> I don't like v2 suffix either.
> Please come up with something else.

Nothing particularly good comes to mind:
- btf_type_tag:wrapper
- btf_type_tag:outer
- btf_type_tag:own
- exterior_btf_type_tag
- outer_btf_tag
- btf_type_prefix
- btf_type_qualifier (as in const/volatile)

Or might as well use btf_type_tag:gcc, as you suggested earlier,
but it is as confusing as the others.