CMAKE Linking dynamic library to module, but not showing as link dependency - c++

Question

Point me in the right direction if this has been asked before. I have lib1 and mod2, which must be linked together. This project is spread to a couple of folders and a couple of CMakeLists.txt files. The cmake commands that I am using are as such:
cmake file 1 (base dir):
# Set C/C++ compile and linking flags
set(GCC_COVERAGE_COMPILE_FLAGS "-fpic -Wno-as-needed")
set(GXX_COVERAGE_COMPILE_FLAGS "-std=c++11")
set(GXX_COVERAGE_LINK_FLAGS "-Wl,--no-undefined -Wno-as-needed")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS} ${GXX_COVERAGE_COMPILE_FLAGS}")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS}")
set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER__FLAGS} ${GCC_COVERAGE_LINK_FLAGS}")
cmake file 2 (lib1 dir):
pybind11_add_module(elka_comm__common
SHARED
pyelka_common.cpp
elka.cpp
elka_comm.cpp
)
set_target_properties(elka_comm__common PROPERTIES
LIBRARY_OUTPUT_DIRECTORY ${ELKA_BINARY_DIR}/python
)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS} ${GXX_COVERAGE_COMPILE_FLAGS}")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS}")
set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER__FLAGS} ${GCC_COVERAGE_LINK_FLAGS}")
add_dependencies(elka_comm__common msg_gen)
cmake file 3 (mod2 dir):
#FIXME ldd not showing elka_comm__common as a link dependency
# -> CommPort undefined symbol upon module import
target_link_libraries(
elka_comm__gnd_station
PUBLIC
elka_comm__common
)
set_target_properties(elka_comm__gnd_station PROPERTIES
LIBRARY_OUTPUT_DIRECTORY ${ELKA_BINARY_DIR}/python
)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS} ${GXX_COVERAGE_COMPILE_FLAGS}")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS}")
set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER__FLAGS} ${GCC_COVERAGE_LINK_FLAGS}")
add_dependencies(elka_comm__gnd_station
elka_comm__common
msg_gen
)
A few of my steps are redundant as sanity checks (e.g. setting flags w/CMAKE variables).
The following is the partial output of ldd -r <path-to-mod2.so>/mod2.so:
linux-vdso.so.1 => (0x00007fff777fe000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fadfe690000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fadfe479000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fadfe0b0000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fadfddaa000)
/lib64/ld-linux-x86-64.so.2 (0x000055f1e6b2c000)
undefined symbol: _ZTIN4elka8CommPortE (build_elka_data_collection/python/elka_comm__gnd_station.so)
lib1 is called elka_comm__common.so, and so it should show up as a library dependency in ldd, right?
Partial output of cmake/make commands:
[100%] Linking CXX shared module ../../../python/elka_comm__gnd_station.so
cd /home/Programs/elka/elka_data_collection/build_elka_data_collection/src/elka_comm/gnd_station && /opt/cmake-3.4.3-Linux-x86_64/bin/cmake -E cmake_link_script CMakeFiles/elka_comm__gnd_station.dir/link.txt --verbose=1
/usr/bin/c++ -fPIC -fpic -Wno-as-needed -std=c++11 -fpic -Wno-as-needed -std=c++11 -g -shared -o ../../../python/elka_comm__gnd_station.so CMakeFiles/elka_comm__gnd_station.dir/pyelka_gnd_station.cpp.o CMakeFiles/elka_comm__gnd_station.dir/elka_devices.cpp.o `CMakeFiles/elka_comm__gnd_station.dir/inet_comm.cpp.o -L/home/Programs/elka/elka_data_collection/build_elka_data_collection/src/elka_comm/common -L/home/Programs/elka/elka_data_collection/build_elka_data_collection/src/elka_comm/gnd_station -L/home/Programs/elka/elka_data_collection/build_elka_data_collection/python -L/home/Programs/elka/elka_data_collection/python ../../../python/elka_comm__common.so -Wl,-rpath,/home/Programs/elka/elka_data_collection/build_elka_data_collection/src/elka_comm/common:/home/Programs/elka/elka_data_collection/build_elka_data_collection/src/elka_comm/gnd_station:/home/Programs/elka/elka_data_collection/build_elka_data_collection/python:/home/Programs/elka/elka_data_collection/python`
From this, it seems to me that linking is done correctly. My best intuition is that the ordering in the cmake generated link command is incorrect, but I can't justify this other than knowing that link commands are particular about ordering.

Answer 1

Solved by adding -Wl,--no-as-needed to CMAKE_CXX_FLAGS. Be mindful that adding to CMAKE_SHARED_LINKER_FLAGS|CMAKE_MODULE_LINKER_FLAGS doesn't work, and neither does adding -Wno-as-needed to CMAKE_CXX_FLAGS.
Other issues persist, though. If anyone is experienced w/binding c++ code to python pm me.