[PATCH] D110127: [Clang] Support typedef with btf_tag attributes

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


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Comment at: clang/include/clang/Basic/Attr.td:1838-1841
 def BTFTag : DeclOrTypeAttr {
   let Spellings = [Clang<"btf_tag">];
   let Args = [StringArgument<"BTFTag">];
+  let Subjects = SubjectList<[Var, Function, Record, Field, TypedefName],
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What worries me about this is that this is now a decl *or* type attribute and one of the subjects is a typedef name which can be either a type or a decl. However, this attribute has no type semantics currently -- the only reason it's allowed on a type at all is because the Linux kernel seems to use it for cast operations, but we don't support that (we just parse it and ignore it). But then what are the semantics when used on a typedef if we want to actually support that casting case in the future?

(This is one of the reasons why GNU attributes are so incredibly difficult to use in practice -- their ability to "slide" around to whatever makes the most sense based on the name of the attribute means you run into these situations and have to work hard to tease out the desired semantics.)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D110127/new/

https://reviews.llvm.org/D110127