[llvm-dev] [ThinLTO] static library failure with object files with the same name

Johan Engelen via llvm-dev llvm-dev at lists.llvm.org
Wed Sep 6 13:10:56 PDT 2017

On Tue, Sep 5, 2017 at 11:34 PM, Davide Italiano <dccitaliano at gmail.com>

> On Tue, Sep 5, 2017 at 2:09 PM, Teresa Johnson <tejohnson at google.com>
> wrote:
> >
> > Hi Johan,
> >
> > Right, per the bug this is fixed in lld (and was already handled in
> gold-plugin), but I guess not in ld64. Note that lld and gold-plugin use
> the new LTO API, while ld64 (and probably other linkers) are still using
> the legacy libLTO (which is what ThinLTOCodeGenerator.cpp is part of).
> Fixing it in the location you propose could work for all legacy libLTO
> users. But I don't think that adding just the size will (always) be enough
> to disambiguate (couldn't the 2 same named members have the same size?) -
> although lld is doing the same thing so this may be as good as what is done
> there. For gold-plugin we add the byte offset into the archive where the
> member starts, which will be unique.
> > +davide for thoughts since he fixed it on the lld side.
> >
> Yes, Teresa is right, this is the correct fix.
> I'm not sure what subset of GNU archives Mach-O supports, but the only
> way of being safe is using offset in the archive + archive name.

ThinLTOCodeGenerator::addModule is called by the linker, right? (I can't
find any callers)
When it is called, we cannot retrieve the offset of the module inside the
archive, because the linker didn't tell us about it.
What we could do is retrieve the module hash from the buffer (although
perhaps it is not always there with ThinLTO?), and use that for

I am assuming that we do want to assert/error on calling addModule with the
exact same module twice? Otherwise, doing a search for the identifier in
Modules vector first and disambiguate if found would work (multithreading
would need to be taken into account too I think?).

- Johan
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