[llvm-dev] [RFC] Fail early on unimplementable append linkage uses

[Rafael Espíndola via llvm-dev]

Append linkage is magical. It doesn't correspond to anything available
in real object files (ELF/COFF/MachO). In those files sections are
appended, but symbols are just resolved.

That means that appending linkage can only be used with llvm special
symbols that never hit a real .o.

Long term I think we should delete it an replace with explicit use of section.

But for now I would like to just error early if we try to actually put
one in an object file. That is what http://reviews.llvm.org/D20179
does. Is everyone OK with that with a langref update?

Cheers,
Rafael