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

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On Wed, Feb 22, 2023 at 11:51 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> 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.

btf.type_tag or btf:type_tag or btf/type_tag (you get the idea, it's
"BTF scoped")?



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