Friday, October 29, 2021

[SOLVED] CMake linking error (undefined reference to)

Issue

I am working with the SSL-Vision software. It has an example client that I've been trying to separate from the whole project. I found the sources needed to edit a client myself, so I just copied them from the software and used CMake to build my client.

The project structure below is simplified, narrowing to the issue (I believe!).

.
├── CMakeLists.txt 
├── main.cc
├── build
│   ├── CMakeLists.txt
│   └── messages_ssl_... (.cc/.h, 4 each)
└── src
    ├── CMakeLists.txt
    └── (Other subdirs and sources/headers)

./CMakeLists.txt:

cmake_minimum_required(VERSION 2.6)
project( TestClient )

find_package( PkgConfig REQUIRED )
pkg_check_modules( QTCORE_PKG QtCore )
include_directories( ${QTCORE_PKG_INCLUDE_DIRS} )

include(FindProtobuf)
find_package( Protobuf REQUIRED )
include_directories( ${PROTOBUF_INCLUDE_DIRS} )

find_package( PkgConfig REQUIRED )
pkg_check_modules( GLIB_PKG glib-2.0 ) 
include_directories( ${GLIB_PKG_INCLUDE_DIRS} )

include_directories( "src" ) 
add_subdirectory( src )

include_directories( "build" ) 
add_subdirectory( build )


add_executable( clientTest clientTest.cc )

target_link_libraries( clientTest robocup_ssl_client messages_robocup_ssl_detection.pb messages_robocup_ssl_geometry.pb messages_robocup_ssl_wrapper.pb messages_robocup_ssl_refbox_log.pb netraw robocup_ssl_client protobuf QtCore )

./build/CMakeLists.txt:

add_library( messages_robocup_ssl_detection.pb SHARED messages_robocup_ssl_detection.pb.cc )

add_library( messages_robocup_ssl_refbox_log.pb SHARED messages_robocup_ssl_refbox_log.pb.cc )

add_library( messages_robocup_ssl_geometry.pb SHARED messages_robocup_ssl_geometry.pb.cc )

add_library( messages_robocup_ssl_wrapper.pb SHARED messages_robocup_ssl_wrapper.pb.cc )

It could be a missing #include in the messages_ssl_... files, but they all are auto-generated and seems to be correct.

In messages_robocup_ssl_detection.pb.h and messages_robocup_ssl_detection.pb.h there are only protobuf includes.

In messages_robocup_ssl_refbox_log.pb.h:

#include "messages_robocup_ssl_detection.pb.h"
// Other protobuf includes

In messages_robocup_ssl_wrapper.h:

#include "messages_robocup_ssl_detection.pb.h"
#include "messages_robocup_ssl_geometry.pb.h"
// Other protobuf includes

In each .cc file is included only its header and other protobuf libs.

Finally, when I do make, the following error is generated:

Linking CXX executable clientTest
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::ByteSize() const'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::MergeFrom(SSL_GeometryData const&)'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `protobuf_AddDesc_messages_5frobocup_5fssl_5fgeometry_2eproto()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::Clear()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::SSL_GeometryData()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::default_instance()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::SerializeWithCachedSizesToArray(unsigned char*) const'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::MergePartialFromCodedStream(google::protobuf::io::CodedInputStream*)'
collect2: ld returned 1 exit status
make[2]: ** [clientTest] Erro 1
make[1]: ** [CMakeFiles/clientTest.dir/all] Erro 2
make: ** [all] Erro 2

I've been trying to fix this for some time. Why is the libmessages_robocup_ssl_wrapper.pb.so showing errors if it has already been built before the linkage?


Solution

It could well be the linking order.

It looks like messages_robocup_ssl_wrapper.pb depends on messages_robocup_ssl_geometry.pb. If so, wrapper should come before geometry in the link line.

target_link_libraries( clientTest robocup_ssl_client
                       messages_robocup_ssl_detection.pb
                       messages_robocup_ssl_wrapper.pb
                       messages_robocup_ssl_geometry.pb
                       messages_robocup_ssl_refbox_log.pb
                       netraw
                       robocup_ssl_client
                       protobuf
                       QtCore )

Even better, let CMake take care of dependencies like this.

If you add...

target_link_libraries( messages_robocup_ssl_wrapper.pb
                       messages_robocup_ssl_geometry.pb )

then CMake will automatically retain that dependency when messages_robocup_ssl_wrapper.pb is specified as a dependency of another target. If you do this, then you can choose to omit messages_robocup_ssl_geometry.pb from the target_link_libraries( clientTest ... ) call.



Answered By - Fraser
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