spdlog 1.14.0: undefined reference to `spdlog::get(char const*)' about spdlog

[gabime]

It is not intended. Please provide steps to reproduce.

[FlorianReimold]

Hi @gabime,

This is the actual project (Eclipse eCAL) that fails building. The long CMake Options mostly turn everything off while still building enough to trigger the issue.
I know that this still isn't really a minimal setup. Creating one will cost me some time, so please tell me if you require one.

The commands target Ubuntu 22.04 but should work on other Ubuntu versions as well.

sudo apt-get -y update
sudo apt-get -y install git cmake  build-essential libprotobuf-dev libprotoc-dev protobuf-compiler libyaml-cpp-dev
 
git clone https://github.com/eclipse-ecal/ecal.git
 
cd ecal
 
git submodule init
git submodule update
 
git -C thirdparty/spdlog/spdlog/ checkout v1.14.0
 
mkdir _build
cd _build
 
cmake ..  -DCMAKE_EXPORT_COMPILE_COMMANDS=ON  -DHAS_HDF5=OFF  -DHAS_QT=OFF  -DHAS_CURL=OFF  -DHAS_CAPNPROTO=OFF  -DHAS_FTXUI=OFF  -DBUILD_DOCS=OFF  -DBUILD_APPS=ON  -DBUILD_SAMPLES=OFF  -DBUILD_TIME=OFF  -DBUILD_PY_BINDING=OFF  -DBUILD_STANDALONE_PY_WHEEL=OFF  -DBUILD_CSHARP_BINDING=OFF  -DBUILD_ECAL_TESTS=OFF  -DECAL_INCLUDE_PY_SAMPLES=OFF  -DECAL_INSTALL_SAMPLE_SOURCES=OFF  -DECAL_JOIN_MULTICAST_TWICE=OFF  -DECAL_NPCAP_SUPPORT=OFF  -DECAL_THIRDPARTY_BUILD_CMAKE_FUNCTIONS=ON  -DECAL_THIRDPARTY_BUILD_PROTOBUF=OFF  -DECAL_THIRDPARTY_BUILD_SPDLOG=ON  -DECAL_THIRDPARTY_BUILD_TINYXML2=ON  -DECAL_THIRDPARTY_BUILD_FINEFTP=ON  -DECAL_THIRDPARTY_BUILD_CURL=OFF  -DECAL_THIRDPARTY_BUILD_GTEST=OFF  -DECAL_THIRDPARTY_BUILD_HDF5=OFF  -DECAL_THIRDPARTY_BUILD_RECYCLE=ON  -DECAL_THIRDPARTY_BUILD_TCP_PUBSUB=ON  -DECAL_THIRDPARTY_BUILD_QWT=OFF  -DECAL_THIRDPARTY_BUILD_YAML-CPP=OFF  -DCMAKE_BUILD_TYPE=Debug

make -j8

The error printed by this is:

[ 85%] Linking CXX executable ../../../bin/ecal_sys_client
/usr/bin/ld: CMakeFiles/sys_client.dir/src/ecal_sys_client_cli.cpp.o: in function `eCAL::sys_client::EcalSysClientLogger::EcalSysClientLogger()':
/home/florian/ecal/app/sys/sys_client_core/include/sys_client_core/ecal_sys_client_logger.h:80: undefined reference to `spdlog::get(char const*)'
/usr/bin/ld: /home/florian/ecal/app/sys/sys_client_core/include/sys_client_core/ecal_sys_client_logger.h:96: undefined reference to `spdlog::get(char const*)'
collect2: error: ld returned 1 exit status

Checking out spdlog 1.13.0 instead of 1.14.0 resolves the issue.

[tt4g]

This commit (5532231) adds overloads to spdlog::get() if C++17 or later is specified.
ABI is broken after C++17.

[gabime]

This could be something in the project setup(e.g. linking to wrong spdlog version). Pleas provide minimal reproducible example. The steps you provided are time consuming and project specific.

[FlorianReimold]

@tt4g: Thanks for pointing that out. As I see it, that header takes the C++ version of the library consumer into account and not the C++ version used for compiling spdlog. So consuming a C++14 compatible spdlog binary with a C++ 17 project will break.

The proper solution I guess would for example be to configure a header file while building spdlog and saving whether the lib was built with / without C++17 API. This header file can then be included later by the public API headers, so the existence of the overloads depend on the actual library and not on the C++ standard of the consumer.
Another solution would be to set public preprocessor defines via cmake (so no configured header file is needed) that then activate those overloads for the consumer.

I checked the build logs and found the following:

spdlog is built with C++11

[  0%] Building CXX object thirdparty/spdlog/spdlog/CMakeFiles/spdlog.dir/src/spdlog.cpp.o
cd /home/florian/ecal/_build/thirdparty/spdlog/spdlog && /usr/bin/c++ -DSPDLOG_COMPILED_LIB -I/home/florian/ecal/thirdparty/spdlog/spdlog/include -g   -Wall -Wextra -std=c++11 -MD -MT thirdparty/spdlog/spdlog/CMakeFiles/spdlog.dir/src/spdlog.cpp.o -MF CMakeFiles/spdlog.dir/src/spdlog.cpp.o.d -o CMakeFiles/spdlog.dir/src/spdlog.cpp.o -c /home/florian/ecal/thirdparty/spdlog/spdlog/src/spdlog.cpp
[  0%] Building CXX object thirdparty/spdlog/spdlog/CMakeFiles/spdlog.dir/src/stdout_sinks.cpp.o
cd /home/florian/ecal/_build/thirdparty/spdlog/spdlog && /usr/bin/c++ -DSPDLOG_COMPILED_LIB -I/home/florian/ecal/thirdparty/spdlog/spdlog/include -g   -Wall -Wextra -std=c++11 -MD -MT thirdparty/spdlog/spdlog/CMakeFiles/spdlog.dir/src/stdout_sinks.cpp.o -MF CMakeFiles/spdlog.dir/src/stdout_sinks.cpp.o.d -o CMakeFiles/spdlog.dir/src/stdout_sinks.cpp.o -c /home/florian/ecal/thirdparty/spdlog/spdlog/src/stdout_sinks.cpp

ecal_sys_client is built with C++17 (gcc 11 default)

cd /home/florian/ecal/_build/app/sys/sys_client_cli && /usr/bin/cmake -E cmake_link_script CMakeFiles/sys_client.dir/link.txt --verbose=1
/usr/bin/c++ -g CMakeFiles/sys_client.dir/src/ecal_sys_client_cli.cpp.o CMakeFiles/sys_client.dir/src/ecal_sys_client_service.cpp.o -o ../../../bin/ecal_sys_client-5.13.0  -Wl,-rpath,/home/florian/ecal/_build/lib: ../../../thirdparty/spdlog/spdlog/libspdlogd.a /usr/lib/x86_64-linux-gnu/libprotobuf.so ../sys_client_core/libsys_client_core.a ../../../lib/CustomTclap/libecal_CustomTclap.a ../../../lib/ecal_utils/libecal_ecal-utils.a ../../../thirdparty/spdlog/spdlog/libspdlogd.a ../../../lib/libecal_core.so.5.13.0 ../../../contrib/ecalproto/libecal_proto.a /usr/lib/x86_64-linux-gnu/libprotobuf.so ../../../lib/libecal_core_pb.so.5.13.0 /usr/lib/x86_64-linux-gnu/libprotobuf.so ../../../lib/libecal_app_pb.so.5.13.0 /usr/lib/x86_64-linux-gnu/libprotobuf.so /usr/lib/x86_64-linux-gnu/libprotobuf.so ../../../lib/EcalParser/libEcalParser.a ../../../lib/ecal_utils/libecal_ecal-utils.a 

Later it breaks when linking the binaries:

/usr/bin/ld: CMakeFiles/sys_client.dir/src/ecal_sys_client_cli.cpp.o: in function `eCAL::sys_client::EcalSysClientLogger::EcalSysClientLogger()':
/home/florian/ecal/app/sys/sys_client_core/include/sys_client_core/ecal_sys_client_logger.h:80: undefined reference to `spdlog::get(char const*)'
/usr/bin/ld: /home/florian/ecal/app/sys/sys_client_core/include/sys_client_core/ecal_sys_client_logger.h:96: undefined reference to `spdlog::get(char const*)'

[gabime]

If I understand the issue correctly, any C++17 (or later) project that uses spdlog, which was compiled with C++11, will fail. This is indeed problematic and should be addressed in the next release of spdlog.

[tt4g]

C++ version is a tricky issue.
The C++ standard specification does not guarantee behavior when linking with libraries of different C++ versions.
So, even if spdlog thinks it has a workaround for different C++ versions, the workaround may not work as expected due to compiler incompatibility.

The best workaround I can think of is to use the same C++ version in the project with build tools such as autotools and CMake.

[gabime]

The C++ standard specification does not guarantee behavior when linking with libraries of different C++ versions.

Thanks for pointing this out @tt4g , I wasn’t aware of this. But even so, I am thunking about reverting this commit if it causes a problem that didn’t exist before.

[FlorianReimold]

@gabime Yes, that is the case.

spdlog downgrades itself to C++11 by default, which also isn't the nicest behavior:

spdlog/CMakeLists.txt

Lines 31 to 34 in 238c9ff

	elseif(NOT CMAKE_CXX_STANDARD)
	set(CMAKE_CXX_STANDARD 11)
	set(CMAKE_CXX_STANDARD_REQUIRED ON)
	endif()

We don't use CMAKE_CXX_STANDARD in our projects but rather set a minimum Cxx standard via target_compile_features. Thus, spdlog downgraded itself to C++11, even though gcc11 defaults to C++17.

@tt4g: at least on gcc and msvc it is quite common to use different cxx standards. As long as the API doesn't use unsupported features, there is no issue with linking a library that was built with a different cxx standard.

[tt4g]

@FlorianReimold In fact, I have never encountered the problem of C++ standard features being broken by different C++ versions.
However, there have been cases of ABI breakage due to the migration from libstdc++ to libstdc++11 to comply with the C++11 standard.
Developers must understand that STL can also be added and deprecated by C++ versions, so the memory layout of STL objects can be changed and broken.

[yurivict]

Please make a release that corrects this problem.
Many depending ports might be affected.

[tt4g]

@yurivict Reverted 37b8476

[gabime]

Fixed in version 1.14.1

[KerstinKeller]

In general, you need to make sure that at both build and consumption time, the user sees the same features.
If you still want to integrate this, I would recommend to introduce a define SPDLOG_USE_STRING_VIEW and guard the availability of the functions with this define:

#if SPDLOG_USE_STRING_VIEW 

#endif

In CMake you can then do something like

if () # tbd, check the active cxx standard
set(SPDLOG_USE_STRING_VIEW 1)
else()
set(SPDLOG_USE_STRING_VIEW 0)
endif()

target_compile_definition(spdlog PUBLIC SPDLOG_USE_STRING_VIEW=${SPDLOG_USE_STRING_VIEW})