C++ Linking Static Library against Shared Library

Question

I am trying to build a plugin based application in C++.

I have two targets - base and plugin.

This is a portion of my CMakeLists.txt that does the main work

# Executables
# build plugin
file (GLOB SRCP "plugin/*.?pp")
include_directories(plugin/)
MESSAGE ( STATUS "SRC: " "${SRCP}" )
add_library(testplugin MODULE ${SRCP} )
add_dependencies( testplugin ${DEPS_TARGETS})
#target_link_libraries( testplugin dlib::dlib )
#build main
file( GLOB SRC "*.?pp" )
message( STATUS "SRC: " "${SRC}" )
add_executable( exec ${SRC} )
add_dependencies( exec ${DEPS_TARGETS})
target_link_libraries( exec dlib::dlib )

It builds successfully but when I try to load the plugin, it fails with this error

Error: Cannot load library: libtestplugin.so: undefined symbol: _ZN4dlib6loggerD1Ev

That symbol corresponds to a statement in the plugin dlib::logger dlog("main.abstract_cnn");

dlib is a static library which I am using in both the base and the plugin. I link this library to the base application but I don't know how to link it to a library/module? Won't the base application pass on the symbols to the plugin? What can I do in this situation?

I would also like a cross-platform solution. Mainly linux+windows.

Can anyone advise? Please?

How I am Loading I am using a library called Libsourcey which has a module called pluga for easy loading. My program is the basic test program given here pluga. It works for me, but when I try to include a 3rd party library I am stuck.

If anyone could point to resources that explain how to use 3rd party libraries in plugins, it would be great!

You link shared libraries just like you link executable programs. That target_link_libraries that you commented out for the shared library, what happens if you actually let CMake run it? — Some programmer dude
i tried that, but I get this error /usr/bin/ld: deps_build/dlib_build/libdlib.a(logger_kernel_1.cpp.o): relocation R_X86_64_32 against '.bss' can not be used when making a shared object; recompile with -fPIC — azmath
Okay, that's a problem. Then you need to tell us how you load the "plugin"? Please create a Minimal, Complete, and Verifiable Example and show us. — Some programmer dude
Try linking your executable with -rdynamic flag, that might export the missing symbol. — Maxim Egorushkin
@MaximEgorushkin do you mean compile the base with that flag? how to specify that in cmake? — azmath

azmath azmath · Accepted Answer · 2017-10-17T11:54:15

SOLVED!

I added this to my cmake file set(CMAKE_POSITION_INDEPENDENT_CODE ON) which is what the error message was trying to tell me (compile with -fPIC).
I did that and now I am able to link my plugin against the static library.

C++ Linking Static Library against Shared Library

1 Answers