Question

I am trying to create a shared library (really a Python module) that links against a static library. Both libraries are part of the same project and built using cmake.

Now, the shared library is built like this:

add_library(MyLibPython SHARED ${PYTHON_WRAPPERS_SRC})
set_target_properties(MyLibPython PROPERTIES PREFIX "")
target_link_libraries(MyLibPython MyLibStatic ${LIBS})

This builds without error, but when I try to import the Python module, I get:

ImportError:
lib/python/MyLibPython.so: undefined symbol: _Zone_of_my_MyLibStatic_functions

I also have a number of executables (unit tests) that are built in a similar way, and they work perfectly.

I should add, this is using gcc on Linux.

Answer 1

Check your linker command line. Is it passing something like -Wl,--as-needed? If so, it might not be including everything required by the static library.

I don’t think your technique is portable in general. Can you get a shared library to link against? I think that there are some platforms where everything that goes into a shared library needs to be compiled as PIC.

Anyway, to link an entire archive with GNU ld (look up man ld):

gcc -o foo foo.o bar.o baz.o -Wl,--whole-archive libfoo.a -Wl,--no-whole-archive [rest-of-linker-args]