On 2/21/23 14:57, Eduard Zingerman wrote: > On Tue, 2023-02-21 at 11:38 -0800, David Faust wrote: > [...] >> Very nice. >> Keeping the 0x6000 tag and instead changing the name sounds good to us. >> >> From the GCC side, support for BTF tags will be new either way but >> conserving DWARF tag numbers is a good idea. > > Great, thank you! > >>> Both [1] and [2] are in a workable state, but [2] lacks support for >>> subroutine types and "void *" for now. If you are onboard with this change >>> I'll proceed with finalizing [1] and [2]. (Also, ":v2" suffix might be not >>> the best, I'm open to naming suggestions). >> >> As for the name, I am not sure the ":v2" suffix is a good idea. >> >> If we need a new name anyway, this could be a good opportunity to use >> something more generic. The annotation DIEs, especially with the new >> format, could be more widely useful than exclusively for producing BTF. >> >> For example, some other tool may want to process these same user >> annotations which are now recorded in DWARF, but may not involve BPF/BTF >> at all. Tying "btf" into the name seems to unnecessarily discourage >> those use cases. >> >> 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"? Thanks > >>> As a somewhat orthogonal question, would it be possible for you to use the >>> same 0x6000 tag on GCC side? I looked at master branch of [3] but can't >>> find any mentions of btf_type_tag. >> >> Yes, we plan to use the same 0x6000 in GCC. Support for btf_type_tag isn't >> committed in master yet; I originally worked on patches [1] last spring but >> they were not committed due to some of the issues we've now worked out >> (notably the attribute ordering/association problem). But 0x6000 is not >> currently in use in GCC and didn't come up as a problem for those patches, >> so I don't think it should be an issue. > > Understood, thank you for the clarification. > > Thanks, > Eduard
