Cython : C++ shared library and undefined symbols using pure virtual methods from a base class

Question

I build a .so C++ library using g++ and -fPIC (using eclipse).

Still using eclipse, I linked this library and used it in another C++ project without any problem.

But, When I build a Cython project with that same lib to generate a python extension, using :

from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext

setup(
    cmdclass = {'build_ext': build_ext},
    ext_modules = [
    Extension("cyelp", 
              sources=["cyelp.pyx", \
                       "adapter/ATestClass.cpp", \
                       "adapter/ALabSimulatorTime.cpp", \
                       ],
              libraries=["elp"],
              language="c++",
              )
    ]
)

"libelp.so" being the mentioned library, the build is fine too : I get my cyelp.so library.

The problem occurs when I get a specific class from the library at runtime from python side script :

Here is my cython class (that inherits from a ALabSimulationTime:LabSimulationTime class implementing the method FireEvent() - method which is declared as "pure virtual" in LabSimulationTime) :

cimport cpython.ref as cpy_ref

cdef extern from "adapter/ALabSimulatorTime.h" namespace "elps" :
    cdef cppclass ALabSimulatorTime:
        ALabSimulatorTime(cpy_ref.PyObject *obj)
        # Virtual overridable
        void ResetTime()
        double TimeStep()
        void FireEvent()
        void StepSimulation()
        int EndSimulation()
        void RunSimulation()
        # Others
        void UpdateEventsRate(double rate)
        void SetEndTime(double end_time)
        void SetOutputTimeStep(double out_time_step)
        double GetTime()
        int GetNbFiredEvents()
        void SetTime(double time)


cdef class PyLabSimulatorTime:
    cdef ALabSimulatorTime* thisptr

    def __cinit__(self):
       self.thisptr = new ALabSimulatorTime(<cpy_ref.PyObject*>self)

    def __dealloc__(self):
       if self.thisptr:
           del self.thisptr

    cpdef ResetTime(self):
        self.thisptr.ResetTime()

    cpdef double TimeStep(self):
        return self.thisptr.TimeStep()

And here, my python loading attempt :

from cyelp import PyLabSimulatorTime;

Finally, here's the error message :

Traceback (most recent call last):
  File "src/Spacial/BdmLsim2.py", line 1, in <module>
    from cyelp import PyLabSimulatorTime;
ImportError: setup/cyelp.so: undefined symbol: _ZN4elps16LabSimulatorTime9FireEventEv

The fact is that it doesn't happen if I redefine the "FireEvent()" method in ALabSimulatorTime class from the header file :

virtual void FireEvent() {};

But does happen if I redefine the method from the ".cpp" file :

void ALabSimulatorTime::FireEvent()
{
    //...
}

Note : Everything works well if I turn FireEvent to "non-pure" from the base class "LabSimulatorTime".

I could, of course, try to be more specific, but may be some of you already has an idea about what is going on.

Thanks a lot