Cython build failed during migration GCC 9.3.0 --> GCC 10.2.0

[alkalinin]

I use this wonderful MingGW package in my Cython projects to build C extensions. But during the migration from GCC 9.3.0 to the GCC 10.2.0 I get the problem during the static build.

See details in https://github.com/cython/cython/issues/3851

In GCC 9.3.0 we have the following dependencies:

• libgcc_s_seh-1.dll
• libgomp-1.dll
• libwinpthread-1.dll

In GCC 10.20 we have one more dependence:

• libgcc_s_seh-1.dll
• libgomp-1.dll
• libwinpthread-1.dll
• libdl.dll

However there is no libdl.a in the mingw folder. Is it possible to include "libdl.a" into the mingw build?

[brechtsanders]

For the new release https://github.com/brechtsanders/winlibs_mingw/releases/tag/10.2.0-11.0.0-8.0.0-r6 I have tried to minimize dependancies on libdl, but I'm afraid gcc.exe itself still depends on it. Can you check if this release works better for you?

[alkalinin]

I checked the latest release "GCC 10.3.0 + LLVM/Clang 11.1.0 + MinGW-w64 8.0.0 (release 2)" and this release also depends on libdl in Cython compilations.

However I added manually the libdl library into the distributive and everything works good in my environment.

[brechtsanders]

libdl.dll is present in that distribution If any software that you build has it's own libdl dependancy then you should indeed build libdl (from https://github.com/dlfcn-win32/dlfcn-win32) and have it available to build your source.

[brechtsanders]

Can you clarify what exactly you mean with "depends on libdl in Cython compilations"?

[alkalinin]

I am a Python developer. Cython is the special language and the special tool for writing binary extension for the Python.

The Cython workflow is following: .pyx python extension source file --> .pyx to .c cython conversion --> compiling .c to the binary. For the last step we need C compiler. I use the gcc.

The compilation string looks like

gcc -mdll -O -Wall -IC:\Dev\Python\python-3.9\lib\site-packages\numpy\core\include -IC:\Dev\Python\python-3.9\include -IC:\Dev\Python\python-3.9\include -c src-py/nuance/algs\linalg_ext.c -o build\temp.win-amd64-3.9\Release\src-py\nuance\algs\linalg_ext.o -O3 -fopenmp -fvisibility=hidden -flto -fno-fat-lto-objects -DMS_WIN64
gcc -shared -s build\temp.win-amd64-3.9\Release\src-py\nuance\algs\linalg_ext.o build\temp.win-amd64-3.9\Release\src-py\nuance\algs\linalg_ext.cp39-win_amd64.def -LC:\Dev\Python\python-3.9\libs -LC:\Dev\Python\python-3.9\PCbuild\amd64 -lpython39 -o C:\WST-Stage\nuance\src-py\nuance\algs\linalg_ext.cp39-win_amd64.pyd -fopenmp -static-libgcc -static-libstdc++ -Wl,-Bstatic,--whole-archive -lwinpthread -Wl,--no-whole-archive

and errors look like

c:/dev/mingw/x86_64-10.3.0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe: c:/dev/mingw/x86_64-10.3.0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../lib\libgomp.a(target.o):(.text+0x39f): undefined reference to `dlopen'
c:/dev/mingw/x86_64-10.3.0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe: c:/dev/mingw/x86_64-10.3.0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../lib\libgomp.a(target.o):(.text+0x3ba): undefined reference to `dlsym'
c:/dev/mingw/x86_64-10.3.0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe: c:/dev/mingw/x86_64-10.3.0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../lib\libgomp.a(target.o):(.text+0x3ef): undefined reference to `dlclose'

Here I use the -static-libgcc flag because I need the static assembling, the reason is the Python 3.8+ rule of the dll resolution process.

My solution is:

1. Download and copy libdl package into the mingw64 folder.
2. Add -ldl linking flag.

[imba-tjd]

It seems that Cython discourage you to use mingw-w64: https://github.com/cython/cython/wiki/CythonExtensionsOnWindows#less-useful-information

[brechtsanders]

I understand why they are saying that, as mixing runtimes should be avoided at all cost. I would like to be able to build Python or CPython and all of the dependancies with MinGW-w64. Then there would be no mix of runtimes. Unfortunately I'm stuck at building Python with MinGW-w64: static build works, but shared build still won't link.