Clang-extdef-mapping : Any documentation for it? What does it actually do?

Clang Frontend Static Analyzer
1

And what it’s output format is?

I can run it without error from the command line, but codechecker seems to do something strange with it and it then fails to find header files.

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the extdefmap (aka. external definition mapping) is supposed to list all external linkage symbols (decls) to a file path where it gets defined.
Decls are identified by USRs - which you can think of as a special name mangling to get unique but deterministic “hashes” or “names” for the external symbols (They are mostly free of whitespaces, but actually they can contain spaces.)

Inside the clang/include/clang/Basic/DiagnosticCrossTUKinds.td file you can see the error diagnostics for CTU stuff, including if a line of the extdefmapping file could not be parsed:

def err_extdefmap_parsing : Error<
  "error parsing index file: '%0' line: %1 '<USR-Length>:<USR> <File-Path>' "
  "format expected">;

USRs are generated for decls, by bool clang::index::generateUSRForDecl(const Decl *D, SmallVectorImpl<char> &Buf);, declared in clang/include/clang/Index/USRGeneration.h.

For the CTU analysis logic, I’d suggest reading clang/lib/CrossTU/CrossTranslationUnit.cpp, ensureCTUIndexLoaded(), and parseCrossTUIndex() functions.

And to answer your question, well we probably don’t have documentation for it.

1 Like
3

Thanks, I note that it doesn’t (as at clang-extdef-mapping-14) emit any information about whether the symbol is weak or strong.

Which I think is causing my problems downstream with CTU spewing lots “error: multiple definitions are found for the same key in index” messages.

Do you know if this is a known bug or limitation? My google fu failed to mention of it.