libdl.so missing in impish and jammy

[Steve Langasek]

In impish and later, libc6-dev is missing the libdl.so symlink to the shared library, only shipping libdl.a. Anything trying to link against -ldl will surprisingly get static linkage.

I noticed this because it causes openems to FTBFS, because previously-built libraries have hard-coded references to the libdl.so that causes reverse-dependencies to fail to link:

[ 94%] Building CXX object CMakeFiles/QCSXCAD.dir/qrc_resources.cpp.o
/usr/bin/c++ -DGIT_VERSION=\"v0.6.2\" -DQCSXCAD_EXPORTS -DQT_CORE_LIB -DQT_GUI_LIB -DQT_WIDGETS_LIB -DQT_XML_LIB -DTIXML_USE_STL -DvtkDomainsChemistry_AUTOINIT="1(vtkDomainsChemistryOpenGL2)" -DvtkFiltersCore_AUTOINIT="1(vtkFiltersParallelDIY2)" -DvtkFiltersFlowPaths_AUTOINIT="1(vtkFiltersParallelFlowPaths)" -DvtkIOExodus_AUTOINIT="1(vtkIOParallelExodus)" -DvtkIOGeometry_AUTOINIT="1(vtkIOMPIParallel)" -DvtkIOImage_AUTOINIT="1(vtkIOMPIImage)" -DvtkIOParallel_AUTOINIT="1(vtkIOMPIParallel)" -DvtkIOSQL_AUTOINIT="2(vtkIOMySQL,vtkIOPostgreSQL)" -DvtkRenderingContext2D_AUTOINIT="1(vtkRenderingContextOpenGL2)" -DvtkRenderingCore_AUTOINIT="3(vtkInteractionStyle,vtkRenderingFreeType,vtkRenderingOpenGL2)" -DvtkRenderingFreeType_AUTOINIT="2(vtkRenderingFreeTypeFontConfig,vtkRenderingMatplotlib)" -DvtkRenderingLICOpenGL2_AUTOINIT="1(vtkRenderingParallelLIC)" -DvtkRenderingOpenGL2_AUTOINIT="1(vtkRenderingGL2PSOpenGL2)" -DvtkRenderingVolume_AUTOINIT="1(vtkRenderingVolumeOpenGL2)" -I/<<BUILDDIR>>/openems-0.0.35+git20190103.6a75e98+dfsg.1/QCSXCAD/build/QCSXCAD_autogen/include -I/<<BUILDDIR>>/openems-0.0.35+git20190103.6a75e98+dfsg.1/debian/tmp/usr/include/CSXCAD -I/usr/include/vtk-7.1 -I/usr/include/freetype2 -I/usr/lib/x86_64-linux-gnu/openmpi/include/openmpi -I/usr/lib/x86_64-linux-gnu/openmpi/include -I/usr/include/python3.9 -I/usr/include/hdf5/openmpi -I/usr/include/jsoncpp -I/usr/include/libxml2 -I/usr/include/tcl -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++ -isystem /usr/include/x86_64-linux-gnu/qt5/QtXml -g -fPIC -fPIC -MD -MT CMakeFiles/QCSXCAD.dir/qrc_resources.cpp.o -MF CMakeFiles/QCSXCAD.dir/qrc_resources.cpp.o.d -o CMakeFiles/QCSXCAD.dir/qrc_resources.cpp.o -c /<<BUILDDIR>>/openems-0.0.35+git20190103.6a75e98+dfsg.1/QCSXCAD/build/qrc_resources.cpp
make[4]: *** No rule to make target '/usr/lib/x86_64-linux-gnu/libdl.so', needed by 'libQCSXCAD.so.0.6.2'. Stop.

[Matthias Klose (doko)]

No, nothing gets static linkage. libdl.a is an empty library:

$ ls -l /usr/lib/x86_64-linux-gnu/libdl.a
-rw-r--r-- 1 root root 8 Sep 28 01:38 /usr/lib/x86_64-linux-gnu/libdl.a

There's nothing to fix in glibc itself. What we need to do is to identify references to libdl.so in all Makefiles, and then just rebuild these packages.

It's also questionable that cmake (?) is adding these dependencies instead of just linking with -ldl ...

[Florian Weimer (fweimer)]

libdl.a is empty, it exists only to make -ldl work. This is a curiosity in some Cmake-based build systems. We had to do some rebuilds to make those legacy file references go away, for example:

https://bugzilla.redhat.com/show_bug.cgi?id=1977878

[Steve Langasek (vorlon)]

vtk7 build failure now fixed, so openems is sorted.