[cfe-dev] Link error in clang but not g++

[Eli Friedman]

On Wed, Sep 14, 2011 at 9:55 AM, Holger Brandsmeier
<holger.brandsmeier at sam.math.ethz.ch> wrote:
> Dear clang list,
>
> first thank you a lot for providing clang, clang is really so much
> better for error messages (especially templates) than gcc!
>
> I build a shared library essentialy with the CMake part
>
> add_library(integration quadraturePy.cpp quadratureRulesPy.cpp)
>
> In the file `quadratureRulesPy.cpp` the constructor for the template
> QuadratureRules<double, 0> is define. It is also part of the object
> file:
>
>> nm -C CMakeFiles/integration.dir/quadratureRulesPy.cpp.o | grep "parfem::QuadratureRules<double, 0>::QuadratureRules"
> 00000000 W parfem::QuadratureRules<double, 0>::QuadratureRules(unsigned int)
>
> In the file `quadraturePy.cpp` this symbol is not defined, and thus
> also not part of the object file:
>
>> nm -C CMakeFiles/integration.dir/quadraturePy.cpp.o | grep "parfem::QuadratureRules<double, 0>::QuadratureRules"
>         U parfem::QuadratureRules<double, 0>::QuadratureRules(unsigned int)
>
> In the final library both object files are combined and the symbol
> appears twice:
>
>> nm -C libintegration.so | grep "parfem::QuadratureRules<double, 0>::QuadratureRules"
>         U parfem::QuadratureRules<double, 0>::QuadratureRules(unsigned int)
> 000ad400 W parfem::QuadratureRules<double, 0>::QuadratureRules(unsigned int)

Something very strange is happening in your link step; if I'm reading
this right, it should not be possible...

Have you tried building the code with clang, and linking with gcc?

-Eli

> Once this library is loaded from python, I get the following linker error:
>
> ImportError: libintegration.so: undefined symbol:
> _ZN6parfem15QuadratureRulesIdLi0EEC1Ej
> (where c++filt shows that the problem is exactly this symbol.
>
> -----------------------------------
>
> On the other hand, if I do exactly the same thing with g++ the symbol
> is only contained once in the shared library. And there is no problem
> when loading the library from python.
>
>>  nm -C libintegration.so | grep "parfem::QuadratureRules<double, 0>::QuadratureRules"
> 00091d60 W parfem::QuadratureRules<double, 0>::QuadratureRules(unsigned int)
> 0009fe40 r parfem::QuadratureRules<double,
> 0>::QuadratureRules(unsigned int)::__PRETTY_FUNCTION__
>
> (I am not sure about the __PRETTY_FUNCTION__ part but I assume this
> has nothing to do with the function itself.)
>
> Am I using clang in a wrong way? Is there a special compiler flag that
> I should be adding?
>
> The compiler flags I'm using are: -O3 -g -fPIC
> The linker flags are additionally: -Wl,-E -shared
> For the `-Wl,-E` I followed the guide in `http://gcc.gnu.org/faq.html#dso`.
>
> Given that I don't know better I pass the same flags to clang and g++.
>
> Thanks for any help,
> Holger
>
> --
> Holger Brandsmeier, SAM, ETH Zürich
> http://www.sam.math.ethz.ch/people/bholger
>
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