CMake + MSys2 对所有内容的未定义引用（包括 c++ 运行时）

Question

I'm playing around with developing a cross-platform C++ project. Things build fine on Linux, but on Windows (10) + MSys2 I've run into a strange issue. Compile works fine (picks up my include dirs, etc.), but linking fails with all sorts of undefined reference errors to a static imported library I have, and even the C++ runtime.

I've tried setting CMAKE_C[XX]_COMPILER, CMAKE_MAKE_PROGRAM, but the output from the configuration step is always the same:

$ cmake ..
-- The C compiler identification is GNU 10.2.0
-- The CXX compiler identification is GNU 10.2.0
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting C compiler ABI info
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /mingw64/bin/cc.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /mingw64/bin/CC.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: <....>

As mentioned earlier the compile works, but linking the executable fails spectacularly. Here is my minimal working example:

$ cat ../CMakeLists.txt
project(example)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED True)

add_executable(example
        main.cpp
)

Here is an sample of the output (the rest is omitted for brevity):

C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.cpp.obj:main.cpp:(.text+0x51): undefined reference to `std::ios_base::Init::~Init()'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.cpp.obj:main.cpp:(.text+0x81): undefined reference to `std::ios_base::Init::Init()'

Adding -v to cmake produces the following commands.

Compile:

/mingw64/bin/CC.exe   -std=gnu++17 -o CMakeFiles/example.dir/main.cpp.obj -c /home/.../Development/minex/main.cpp

Link:

/mingw64/bin/CC.exe CMakeFiles/example.dir/main.cpp.obj -o example

CC.exe seems off... and it's used if I set the CXX compiler flag or not...

I also tried generating "MSYS2 Makefiles" but that also fails (doesn't know the generator).

I can reproduce the output by running

$ CC main.cpp -o example

while

$ g++ main.cpp -o example

works fine.

CMake version is 3.18.4.

Edit: This is the entire output of running make VERBOSE=1 (using mingw64-cmake seems to produce the same output, except the 'entering directory' and 'leaving directory' paths are absolute windows paths):

    $ cat log
/usr/bin/cmake.exe -S/home/<...>/Development/minex -B/home/<...>/Development/minex/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake.exe -E cmake_progress_start /home/<...>/Development/minex/build/CMakeFiles /home/<...>/Development/minex/build//CMakeFiles/progress.marks
make  -f CMakeFiles/Makefile2 all
make[1]: Entering directory '/home/<...>/Development/minex/build'
make  -f CMakeFiles/example.dir/build.make CMakeFiles/example.dir/depend
make[2]: Entering directory '/home/<...>/Development/minex/build'
cd /home/<...>/Development/minex/build && /usr/bin/cmake.exe -E cmake_depends "Unix Makefiles" /home/<...>/Development/minex /home/<...>/Development/minex /home/<...>/Development/minex/build /home/<...>/Development/minex/build /home/<...>/Development/minex/build/CMakeFiles/example.dir/DependInfo.cmake --color=
Dependee "/home/<...>/Development/minex/build/CMakeFiles/example.dir/DependInfo.cmake" is newer than depender "/home/<...>/Development/minex/build/CMakeFiles/example.dir/depend.internal".
Dependee "/home/<...>/Development/minex/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/home/<...>/Development/minex/build/CMakeFiles/example.dir/depend.internal".
Scanning dependencies of target example
make[2]: Leaving directory '/home/<...>/Development/minex/build'
make  -f CMakeFiles/example.dir/build.make CMakeFiles/example.dir/build
make[2]: Entering directory '/home/<...>/Development/minex/build'
[ 50%] Building CXX object CMakeFiles/example.dir/main.obj
/mingw64/bin/CC.exe   -std=gnu++17 -o CMakeFiles/example.dir/main.obj -c /home/<...>/Development/minex/main.cpp
[100%] Linking CXX executable example
/usr/bin/cmake.exe -E cmake_link_script CMakeFiles/example.dir/link.txt --verbose=1
/mingw64/bin/CC.exe CMakeFiles/example.dir/main.obj -o example
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x23): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x32): undefined reference to `std::ostream::operator<<(std::ostream& (*)(std::ostream&))'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x51): undefined reference to `std::ios_base::Init::~Init()'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.text+0x81): undefined reference to `std::ios_base::Init::Init()'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.rdata$.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_[.refptr._ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_]+0x0): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/example.dir/main.obj:main.cpp:(.rdata$.refptr._ZSt4cout[.refptr._ZSt4cout]+0x0): undefined reference to `std::cout'
collect2.exe: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/example.dir/build.make:103: example] Error 1
make[2]: Leaving directory '/home/<...>/Development/minex/build'
make[1]: *** [CMakeFiles/Makefile2:95: CMakeFiles/example.dir/all] Error 2
make[1]: Leaving directory '/home/<...>/Development/minex/build'
make: *** [Makefile:103: all] Error 2

Solution:

I was setting CMAKE_CXX_COMPILER wrong:/. I was doing it from memory, and I just did

CMAKE_CXX_COMPILER=... cmake ..

not

cmake .. -DCMAKE_CXX_COMPILER=...

However! It's still weird that CC is used to successfully compile cpp files, but it can't link the object files.

Answer 1

If you are using mingw64 compiler in MSYS2 make sure you are using mingw64 version of cmake too.

Using cmake not aligned with gcc eg:

MINGW64
# which gcc
/mingw64/bin/gcc

MINGW64
# which cmake
/usr/bin/cmake

Will led to following error when running cmake:

...
-- The CXX compiler identification is GNU 10.2.0
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19041 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
...

and linker error in build step.

So make sure you install mingw64 version of cmake:

MINGW64
pacman -S mingw-w64-x86_64-cmake

You need to close terminal and open it again after cmake is installed. Then make sure you have aligned versions of gcc and cmake installed:

MINGW64
# which gcc
/mingw64/bin/gcc

MINGW64
# which cmake
/mingw64/bin/cmake

Now cmake should work properly.

Answer 2

You have these errors because you are trying to compile/link c++ program with a c compiler. For example the two undefined references you are mentioning are part of libstdc++. It is used by default when using g++ but not with CC . If you want to use CC you have to add it manually -lstdc++ .

The easiest way is to compile and link c++ programs by using g++.

For some reason the /mingw64/bin/CC.exe is considered as the CXX compiler and the working detection is skipped. to avoid the skipp of the working detection you can add set(CMAKE_CXX_COMPILER_WORKS 1) . to modify the compiler it self you can set CMAKE_CXX_COMPILER as explained in CMAKE_CXX_COMPILER or set CXX as explained in CXX . be careful to clean the cache.