[llvm-dev] [ThinLTO] static library failure with object files with the same name (original) (raw)

Johan Engelen via llvm-dev llvm-dev at lists.llvm.org
Mon Sep 11 14:21:55 PDT 2017

On Fri, Sep 8, 2017 at 9:04 PM, Johan Engelen <jbc.engelen at gmail.com> wrote:

On Thu, Sep 7, 2017 at 5:44 PM, Mehdi AMINI <joker.eph at gmail.com> wrote:

Hi Johan,

ld64 only calls functions from llvm/include/llvm-c/lto.h (defined in llvm/tools/lto/lto.cpp) For instance ThinLTOCodeGenerator::addModule is called through thinltocodegenaddmodule(). Apple hasn't released the code for ld64 in Xcode 9 yet, did you check if it is fixed in Xcode 9? (I think I remember fixing it in ld64 but I'm not totally sure...). I haven't tried with Xcode 9.

From what I can see with Xcode 8.2, the linker just passes the file name (prefixed with the archive name): https://github.com/michaelweis er/ld64/blob/master/src/ld/parsers/ltofile.cpp#L546 (original here: https://opensource.apple.com/source/ld64/ld64-274.2/ src/ld/parsers/ltofile.cpp.auto.html ) We could workaround this in ThinLTOCodeGenerator by adding a incremental suffix to every new buffer. Something like this diff: I was assuming that we do want to assert/error on calling addModule with the exact same module twice? Otherwise your diff is nice, thanks.

Hi Mehdi, Can you advise me? Is it OK to not error upon the exact same module being added twice? (and thus your patch would be good)

Thanks, Johan

diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp index ffd78dad9228..d6e5d4d0c213 100644 --- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp +++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp @@ -535,7 +535,9 @@ static void initTMBuilder(TargetMachineBuilder &TMBuilder, } // end anonymous namespace void ThinLTOCodeGenerator::addModule(StringRef Identifier, StringRef Data) { - ThinLTOBuffer Buffer(Data, Identifier); + std::string Id = + (Twine(Identifier) + "" + std::tostring(Modules.size())).str(); + ThinLTOBuffer Buffer(Data, std::move(Id)); LLVMContext Context; StringRef TripleStr; ErrorOrstd::string TripleOrErr = expectedToErrorOrAndEmitErrors(

-- Mehdi 2017-09-07 8:18 GMT-07:00 Teresa Johnson <tejohnson at google.com>:

On Wed, Sep 6, 2017 at 1:28 PM, Davide Italiano via llvm-dev <_ _llvm-dev at lists.llvm.org> wrote: On Wed, Sep 6, 2017 at 1:10 PM, Johan Engelen via llvm-dev <llvm-dev at lists.llvm.org> wrote: > On Tue, Sep 5, 2017 at 11:34 PM, Davide Italiano <_ _dccitaliano at gmail.com> > wrote: >> >> 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. See here for the fix. https://reviews.llvm.org/D25495 You pass the the archive name + offset to lto::InputFile::create, assuming your linker uses the new LTO API (and I'm not sure whether ld64 already switched). AFAIK, no. Mehdi started to look at this awhile back but likely has not been able to pick it back up. The linker knows the archive name from which it's fetching the member, as well as its offset (it asks libArchive about it, for lld). I'm not sure how it works ld64, but of course, to get this mechanism working, you need some linker modifications. Right, the linker can compose the new identifier. The proposed fix in ThinLTOCodeGenerator.cpp could be a partial workaround until linkers do this. Agree that it should be documented, at the very least in the header file interfaces to the new/old LTO APIs. Not sure there is a better place to document? Teresa

CC:ed some Mach-O people, they probably know more about this than I do. Thanks, -- Davide

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