[llvm-dev] Ubuntu LLVM packages incompatible with clang built projects?

[Reid Kleckner via llvm-dev]

Just be aware that those ifdefs were recommitted and reverted several
times, so I'm not sure what the state is.

On Fri, Sep 28, 2018 at 8:48 AM Alastair Murray via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Kern,
>
> We also had issues with mixing GCC/Clang builds when testing the 7.0
> release branch.
>
> My colleague submitted a patch that fixed the issue for us:
> * https://reviews.llvm.org/D50710
>
> I no longer have a copy of the error we were seeing to see if it was the
> same, but the fix is to llvm::OptionalStorage and your error message
> involves llvm::Optional.  The patch removes a GCC specific ifdef, and
> hopefully fixes the issue that made that necessary in the first place, but
> we never really knew how the GCC miscompilation was expressed.
>
> It would be interesting to know whether this resolves your issue, but
> regardless we should give the patch a prod.
>
> Regards,
> Alastair Murray.
>
> On 27/09/18 08:46, Kern Handa via llvm-dev wrote:
>
> Hi folks,
>
> Not sure if this is the right mailing list target, but I'm trying out the
> new LLVM 7.0 packages found at http://apt.llvm.org by porting over an
> existing LLVM 6.0 project of ours to the new version. In doing so, I found
> that the executable always segfaulted at the same spot with no explanation:
>
> 0x0000000000fefe33 in
> llvm::RegisterTargetMachine<llvm::X86TargetMachine>::Allocator(llvm::Target
> const&, llvm::Triple const&, llvm::StringRef, llvm::StringRef,
> llvm::TargetOptions const&, llvm::Optional<llvm::R
> eloc::Model>, llvm::Optional<llvm::CodeModel::Model>,
> llvm::CodeGenOpt::Level, bool) ()
>
> This happens if I build my project and link it against LLVM 7.0 with
> either clang++ 6.1 or clang++ 7.0. This does not happen if I build my
> project with g++ 8.
>
> I have also confirmed that building LLVM 7.0 with clang++ and then using
> that private build of the libraries fixes the issue.
>
> To summarize, it seems that there's an ABI incompatibility introduced
> somewhere, which means LLVM 7.0 compiled with gcc can only be used by other
> projects also built with gcc. Is this something that's being investigated
> and to be resolved as a fix in 7.1? If not, is there any official release
> note that's remarking on this incompatibility?
>
> Thanks,
> Kern
>
>
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>
> --
> Alastair Murray
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