cc_library failed to merge multiple static libraries into one on Linux

[Xreki]

To create a single c-api static library, we need to merge all the needed libraries, including

• paddle_capi
• paddle_utils
• paddle_parameter
• paddle_math
• paddle_cuda
• paddle_function
• paddle_gserver
• paddle_proto
• paddle_pserver
• paddle_network

It was originally implemented by following codes:

# combine all paddle static libraries together, into libpaddle_capi_whole.a
# user should use PaddleCAPI as -lpaddle_capi_whole
set(capi_whole_library libpaddle_capi_whole.a)
add_custom_target(paddle_capi_whole ALL
        COMMAND mkdir -p o_files/capi && cd o_files/capi/ && ar -x $<TARGET_FILE:paddle_capi>
        COMMAND mkdir -p o_files/utils && cd o_files/utils/ && ar -x $<TARGET_FILE:paddle_utils>
        COMMAND mkdir -p o_files/parameter && cd o_files/parameter/ && ar -x $<TARGET_FILE:paddle_parameter>
        COMMAND mkdir -p o_files/math && cd o_files/math/  && ar -x $<TARGET_FILE:paddle_math>
        COMMAND mkdir -p o_files/cuda && cd o_files/cuda/ && ar -x $<TARGET_FILE:paddle_cuda>
        COMMAND mkdir -p o_files/function && cd o_files/function/ && ar -x $<TARGET_FILE:paddle_function>
        COMMAND mkdir -p o_files/gserver && cd o_files/gserver/ && ar -x $<TARGET_FILE:paddle_gserver>
        COMMAND mkdir -p o_files/proto && cd o_files/proto/ && ar -x $<TARGET_FILE:paddle_proto>
        COMMAND mkdir -p o_files/network && cd o_files/network/ && ar -x $<TARGET_FILE:paddle_network>
        COMMAND mkdir -p o_files/pserver && cd o_files/pserver/ && ar -x $<TARGET_FILE:paddle_pserver>
        COMMAND ar crs ${capi_whole_library} `find ./o_files -name '*.o'`
        COMMAND rm -rf o_files
        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
        DEPENDS paddle_capi paddle_utils paddle_parameter paddle_math
                paddle_cuda paddle_function paddle_gserver
                paddle_proto paddle_pserver paddle_network
        )
set_target_properties(paddle_capi_whole
  PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_BINARY_DIR}/${capi_whole_library})

However, the codes failed on Mac. Since the function cc_library also supports to merge static libraries, we chose to use cc_library instead. The codes were changed to

# combine all paddle static libraries together, into libpaddle_capi_whole.a
# user should use PaddleCAPI as -lpaddle_capi_whole
set(PADDLE_CAPI_INFER_LIBS
    paddle_utils
    paddle_parameter
    paddle_math
    paddle_cuda
    paddle_function
    paddle_gserver
    paddle_proto
    paddle_pserver
    paddle_network)

cc_library(paddle_capi_whole DEPS paddle_capi ${PADDLE_CAPI_INFER_LIBS})

However, when trying to link libpaddle_capi_whole.a in external applications, we are tracked by following errors

error: undefined reference to `paddle_matrix_create`
error: undefined reference to `paddle_matrix_get_row`
error: undefined reference to `paddle_matrix_create_none`
error: undefined reference to `paddle_matrix_get_shape`
error: undefined reference to `paddle_matrix_get_destroy`
...

Overal, cc_library failed to merge multiple static libraries into one on Linux.