[LLVMdev] MCJIT handling of linkonce_odr

[Keno Fischer]

Hi Axel.

I put up a patch at http://reviews.llvm.org/D6950. Have a look and see if
it works for you.

Thanks,
Keno

On Tue, Jan 13, 2015 at 9:44 AM, Axel Naumann <Axel.Naumann at cern.ch> wrote:

> Hi Keno,
>
> The part that scares me a bit is
>
> > and then adjust the other methods to not
> > bail out two quickly when encountering a weak symbol.
>
> I would very much appreciate if you could implement this; I don't have
> enough knowledge of the MCJIT nor llvm CodeGen internals... I will
> happily try it out and provide you with feedback, though! :-)
>
> Thank you *so* much for your fast reaction!
>
> Cheers, Axel
>
>
>
> On 13.01.2015 00:30, Keno Fischer wrote:
> > Hi Axel,
> >
> > the problem is that weak symbols are not handled in RuntimeDyld at all.
> > The proper solution is probably to add a separate case for weak symbols
> > (where we're already taking care of common symbols) in
> > RuntimeDyld::loadObjectImpl and then adjust the other methods to not
> > bail out two quickly when encountering a weak symbol.
> >
> > Please let me know if you're planning to work on a patch for this,
> > otherwise I'll have a go tomorrow.
> >
> > Thanks,
> > Keno
> >
> > On Mon, Jan 12, 2015 at 11:45 AM, Axel Naumann <Axel.Naumann at cern.ch
> > <mailto:Axel.Naumann at cern.ch>> wrote:
> >
> >     Hi,
> >
> >     I'm finally moving cling to MCJIT - and MCJIT is wonderful! So far I
> >     only ran into this issue:
> >
> >     $ cat linkonceodr.cxx
> >     extern "C" int printf(const char*,...);
> >
> >     template <class T> struct StaticStuff {
> >       static T s_data;
> >     };
> >     template <class T> T StaticStuff<T>::s_data = 42;
> >
> >     int compareAddr(int* mcjit);
> >
> >     #ifdef BUILD_SHARED
> >     int compareAddr(int* mcjit) {
> >       if (mcjit != &StaticStuff<int>::s_data) {
> >         printf("Wrong address, %ld in shared lib, %ld in mcjit!\n",
> >                (long)&StaticStuff<int>::s_data, (long)mcjit);
> >         return 1;
> >       }
> >       return 0;
> >     }
> >     #else
> >     int main(int, char**) {
> >       return compareAddr(&StaticStuff<int>::s_data);
> >     }
> >     #endif
> >
> >
> >     $ clang++ -fPIC -shared -DBUILD_SHARED -o liblinkonceodr.so
> >     linkonceodr.cxx
> >     $ clang++ -emit-llvm -c linkonceodr.cxx -o - |
> >     LD_PRELOAD=./liblinkonceodr.so lli -
> >     Wrong address, 140449908087496 in shared lib, 140449908076544 in
> mcjit!
> >
> >
> >     I.e. while compareAddr is resolved from the dylib, this:
> >
> >     @_ZN11StaticStuffIiE6s_dataE = linkonce_odr global i32 42, align 4
> >
> >     is not: it is re-emitted by the MCJIT. When building a binary and
> >     linking against that dylib, _ZN11StaticStuffIiE6s is correctly
> picked up
> >     from the dylib. I would expect MCJIT to behave the same.
> >
> >     I'll try to fix that myself, but I'd appreciate a hint where to do
> that.
> >     Should I collect linkonce_odr-s and "replace" their emitted code as
> part
> >     of llvm::RuntimeDyldImpl::resolveRelocations()? Or is this just a
> >     missing case somewhere?
> >
> >     That's e.g. with
> >
> >     $ lli --version
> >     LLVM (http://llvm.org/):
> >       LLVM version 3.6.0svn
> >       Optimized build.
> >       Built Jan 12 2015 (10:52:59).
> >       Default target: x86_64-unknown-linux-gnu
> >       Host CPU: corei7-avx
> >
> >
> >     Cheers, Axel.
> >
> >
> >     _______________________________________________
> >     LLVM Developers mailing list
> >     LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
> >      http://llvm.cs.uiuc.edu
> >     http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> >
>
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