Why two targets linking differently using cmake? - c++

Question

I have this target that compiles ok.
#
file(GLOB SOURCE_FILES
8021QBG/*.h
8021QBG/*.cpp
)
add_library(8021qbg SHARED
${SOURCE_FILES}
)
set_target_properties(8021qbg PROPERTIES LINKER_LANGUAGE CXX)
set(CMAKE_CXX_FLAGS_CUSTOM " ")
set_target_properties(8021qbg PROPERTIES COMPILE_FLAGS " ${CMAKE_CXX_FLAGS_CUSTOM} ${CMAKE_CXX_FLAGS_COMMON}")
add_dependencies(8021qbg core )
target_link_libraries(8021qbg -L${PROJECT_BINARY_DIR})
target_link_libraries(8021qbg -L/home/user/protocol_so )
target_link_libraries(8021qbg -L${PROJECT_SOURCE_DIR}/lib64 )
target_link_libraries(8021qbg -L${PROJECT_SOURCE_DIR})
target_link_libraries(8021qbg protocol_common thread vip core m xml2)
target_include_directories(8021qbg PUBLIC
8021QBG
nte-encap
)
and this that fails.
#
file(GLOB SOURCE_FILES
Agent/*.h
Agent/*.cpp
)
add_library(agent SHARED
${SOURCE_FILES}
)
set_target_properties(agent PROPERTIES LINKER_LANGUAGE CXX)
set(CMAKE_CXX_FLAGS_CUSTOM " ")
set_target_properties(agent PROPERTIES COMPILE_FLAGS " ${CMAKE_CXX_FLAGS_CUSTOM} ${CMAKE_CXX_FLAGS_COMMON}")
add_dependencies(agent core)
target_link_libraries(agent -L${PROJECT_BINARY_DIR})
target_link_libraries(agent -L/home/user/protocol_so )
target_link_libraries(agent -L${PROJECT_SOURCE_DIR}/lib64 )
target_link_libraries(agent -L${PROJECT_SOURCE_DIR})
target_link_libraries(agent protocol_common thread vip core xml2 pthread)
target_include_directories(agent PUBLIC
Agent
nte-encap
)
Also these targets have the same flags:
set (CMAKE_CXX_FLAGS_COMMON "-g -fpermissive -std=gnu89 -Wall -O0 -m64 -fPIC -DLINUX -DCPU_64 -DXSTREAM ")
set (CMAKE_SHARED_LINKER_FLAGS "-Wl,--unresolved-symbols=ignore-in-shared-libs -shared -Wl,-rpath,/home/user/protocol_so:/home/user/cmake_libs/lib64:libwifi")
if(NOT CMAKE_CXX_CREATE_SHARED_LIBRARY)
set(CMAKE_CXX_CREATE_SHARED_LIBRARY
"<CMAKE_CXX_COMPILER> <CMAKE_SHARED_LIBRARY_CXX_FLAGS> <LANGUAGE_COMPILE_FLAGS> <LINK_FLAGS> <CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS> <SONAME_FLAG><TARGET_SONAME> -o <TARGET> <OBJECTS> <LINK_LIBRARIES>")
endif()
This is linker stage
/usr/bin/g++ -fPIC -g -Wl,--unresolved-symbols=ignore-in-shared-libs -shared -Wl,-rpath,/home/user/protocol_so:/home/user/cmake_libs/lib64:libwifi -shared -Wl,-soname,libagent.so -o libagent.so CMakeFiles/agent.dir/Agent/agent_common.cpp.o CMakeFiles/agent.dir/Agent/agent_main.cpp.o CMakeFiles/agent.dir/Agent/agent_client.cpp.o CMakeFiles/agent.dir/Agent/agent_cmd.cpp.o CMakeFiles/agent.dir/Agent/agent_go.cpp.o -L/home/user/cmake_libs/cmake-build-debug-rurem -L/home/user/protocol_so -L/home/user/cmake_libs/lib64 -L/home/user/cmake_libs -lprotocol_common -lthread -lvip libcore.so -lxml2 -lpthread -L/home/user/cmake_libs/lib64 -lprotocol_common -lthread -lvip -lcrypto -lglib-2.0 -lm -lxml2 -lpthread -Wl,-rpath,/home/user/cmake_libs/cmake-build-debug-rurem
This is error codes
/home/user/cmake_libs/Agent/agent_main.cpp:47: undefined reference to `agent_client_register'
/home/user/cmake_libs/Agent/agent_main.cpp:48: undefined reference to `agent_client_unregister'
/home/user/cmake_libs/Agent/agent_main.cpp:49: undefined reference to `agent_client_register_task'
/home/user/cmake_libs/Agent/agent_main.cpp:50: undefined reference to `agent_client_unregister_task'
Cmake compiles each *.cpp file to *.o object and than linker combine them in one *.so lib -> in the linker stage I got this error.
Sources located in "Agent" folder and I add it to the target 'agent'.
UDP>
simple makefile and GCC build this library.
makefile part:
libagent.so: ${wildcard Agent/*.[c,h]} libcore.so
$(CC) $(CFLAGS) -fPIC -shared -o $# $(filter %.c,$^) $(IPATH) $(RPATH) $(TE_VIP) -lcore -lxml2 -lpthread
gcc command
gcc -g -Wall -O0 -m64 -Wl,--unresolved-symbols=ignore-in-shared-libs -fPIC -shared -o libagent.so -Inte-include -Ixst_inc -Ixst_tls -L./lib64 -L./cmake-build-debug-rurem -Wl,-rpath,/home/user/protocol_so:/home/user/lib64:libwifi -DLINUX -DCPU_64 -DXSTREAM -lprotocol_common -lthread -lvip -lcore -lxml2 -lpthread
UDP#2.
on arm machine with gcc v9.1.0 it builds successfully via makefile.
on x86 machine with gcc v4.3.4 I have such undefined referencies.
this is compiling command
g++ -g -Wall -O0 -m64 -Wl,--unresolved-symbols=ignore-in-shared-libs -fPIC -shared -o 0libagent.so -Inte-include -Iinc -Itls -L/home/user/cmake_libs/lib64 -L/home/user/cmake_libs -Wl,-rpath,/home/user/protocol_so:/home/user/cmake_libs/lib64:libwifi -DLINUX -DCPU_64 -DXSTREAM -lprotocol_common -lthread -lvip -lcore -lxml2 -lpthread Agent/agent_main.cpp Agent/agent_cmd.cpp Agent/agent_client.cpp Agent/agent_go.cpp Agent/agent_common.cpp
This is piece of agent_main.cpp that causes errors:
This is function that defined in agent_client.cpp that causes undefined reference
UPD#3
nm says that definitions are in objects.
> nm CMakeFiles/agent.dir/Agent/agent_client.cpp.o
...
00000000000007e2 T _Z21agent_client_registeriP20_protocol_callback_t
0000000000000000 T _Z21agent_client_run_taskiPv
0000000000000033 T _Z22agent_client_do_actionPviS_S_
...
x86 machine - SUSE 11 sp3 x64
Why it fails?
How to fix it?

Answer 1

The main point was not in cmake, and even not in make commands. I think this is about gcc versions support. On x86 I have gcc v4.3.4.
As #AlexCohn said in the comments
I would try to declare agent_client_register() and the rest of them as
extern "C" in agent_client.h and make sure this header is included in
both agent_client.cpp and agent_main.cpp