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Marchesi wrote: > > Of the two problems discussed: > > 1. DW_TAG_LLVM_annotation not being able to denote annotations to > non-pointed based types. clang currently ignores these instances. > > We discussed two possible options to deal with this: > 1.1 To continue ignoring these cases in the front-end, keep the dwarf > expressiveness limitation, and document it. > 1.2 To change DW_TAG_LLVM_annotation so it behaves like a qualifier > DIE (like const, volatile, etc.) so it can apply to any type. Thanks for the detailed update. Yes, we do want to __tag behaving like a qualifier. Today clang only support 'base_type *' style of code. But we are open to support non-pointer style of tagging like 'base_type global_var'. Because of this, the following dwarf output should be adopted: C: int __tag1 * __tag2 * p; dwarf: ptr -> __tag2 --> ptr -> __tag1 -> int or C: int __tag1 g; dwarf: var_g -> __tag1 --> int The above format *might* require particular dwarf tools to add support for __tag attribute. But I think it is a good thing in the long run esp. if we might add support to non-pointer types. In current implementation, dwarf tools can simply ignore the children of ptr which they may already do it. > > 2. The ordering problem: sparse annotations order differently than > GNU/C99 compiler attributes. Therefore translating 1-to-1 from > sparse annotations to compiler attributes results in attributes with > different syntax than normal compiler attributes. > > This was accepted in clang. > But found resistance in GCC when we sent the first patch series. > > During the meeting we went thru several possible ways of dealing with > this problem, but we didn't reach any conclusion on what to do, since > the time ran out. > > We agreed to continue the discussion at the BPF office hours next 5 > January 2023. > > In the meanwhile, below in this email is a slightly updated version of > the material used to go thru the topics during the discussion. If there > is any mistake or if you see that our understanding of the > problem/situation is not correct, please point it out. If you want to > add more information, please do so by replying to this thread. > > Finally, it was agreed that we (GCC BPF hackers) would send Yonghong our > github accounts so he can subscribe us to notifications in the llvm > phabricator, so we can be aware of potentially ABI/breaking changes at > the time they are discussed, and not afterwards scanning bpf@vger. I > alredy sent him the information. > > Thank you for your time today. It is appreciated. > [...]