[PATCH] D91426: [PowerPC] Fix issue where binary uses a .got but is missing a .TOC.

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp added a comment.



> I'll need to go over this again to refresh my memory. As a quick recap though:
>
> - On PPC, if we create a .got, then the first entry must be the tocbase.
> - If `.TOC.` is not defined by one of the input objects, then we do not increment the number of .got entries here <https://github.com/llvm/llvm-project/blob/3fd7d0d281a9b1dc7a8352cbd29178cbfacc73f1/lld/ELF/SyntheticSections.cpp#L653>
> - If we synthetically define `.TOC.` in the linker, then we end up with a .got section in some cases where we would otherwise not need one.

Yes, you got it!

> Is it possible to change the .got section to always add `gotHeaderEntriesNum` in its constructor for PPC64, and remove the section late if all it contains is the single entry and `.TOC.` is not defined?

I see what you mean. An option might be to modify this function:

  bool GotSection::isNeeded() const {
    // We need to emit a GOT even if it's empty if there's a relocation that is
    // relative to GOT(such as GOTOFFREL).
    return numEntries || hasGotOffRel;
  }

On power PC we can say that we don't need the GOT if the number of entries is one and if the `.TOC.` is not defined. We now always add the GOT header but if we only have a GOT header at the end then we can say that we don't need the GOT. Does does that sound ok?

I can try to rework the patch to have it do this.


Repository:
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