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Marchesi wrote: > > Hi Yonghong. > >> On 12/15/22 10:43 AM, Jose E. 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. > > I wonder, since these annotations are atomic, is there a reason for not > using an attribute instead of a DIE tag? Something like DW_AT_annotation. Yes, we can. My suggestion is to facilitate gcc implementation. Currently clang uses an attribute instead of a DIE tag. I am totally fine if gcc uses the same dwarf representation mechanism as clang. > > The attribute could then be used by any DIE (declaration, type, ...) and > existing DWARF consumers that don't support the new attribute would > happily just ignore it. clang already use attributes to represent btf_type_tag and btf_decl_tag. One of early considerations to use attribute in clang indeed is to avoid existing tool changes as much as possible.