KDE Purpose build fails only in docker container - docker

Question

We currently encounter a strange issue with the latest KDE / Archlinux releases.
We cannot get KDE's Purpose framework to compile inside a docker container, although it works fine on our host machines. We tried to compile it with GCC and Clang.
The error we receive is:
CMakeFiles/saveasplugin.dir/saveasplugin.cpp.o: In function `SaveAsShare::SaveAsShare()':
saveasplugin.cpp:(.text+0x81): undefined reference to `vtable for SaveAsShare'
CMakeFiles/saveasplugin.dir/saveasplugin.cpp.o: In function `SaveAsShare::~SaveAsShare()':
saveasplugin.cpp:(.text+0x113): undefined reference to `vtable for SaveAsShare'
CMakeFiles/saveasplugin.dir/saveasplugin.cpp.o: In function `SaveAsShare::~SaveAsShare()':
saveasplugin.cpp:(.text+0x133): undefined reference to `vtable for SaveAsShare'
collect2: error: ld returned 1 exit status
make[2]: *** [src/plugins/saveas/CMakeFiles/saveasplugin.dir/build.make:122: bin/kf5/purpose/saveasplugin.so] Error 1
make[1]: *** [CMakeFiles/Makefile2:1149: src/plugins/saveas/CMakeFiles/saveasplugin.dir/all] Error 2
make: *** [Makefile:130: all] Error 2
You can reproduce the docker environment with the following Dockerfile:
FROM archlinux/base
RUN pacman -Syu --noconfirm && pacman --noconfirm -S git base-devel cmake extra-cmake-modules asp sudo
RUN useradd -ms /bin/bash arch
RUN echo 'arch ALL=(ALL) NOPASSWD: ALL' > /etc/sudoers
USER arch
WORKDIR /home/arch
RUN asp checkout purpose
WORKDIR /home/arch/purpose/trunk
RUN gpg --keyserver ipv4.pool.sks-keyservers.net --recv-keys 58D0EE648A48B3BB
(If you only have IPv6 available and no IPv4, you need to edit line 9)
After you build the container run it and execute makepkg -s --noconfirm
It will now build the archlinux package and you will encounter the above mentioned error during the linking phase.
We currently do not even have the slightest clue what the reason for this error could be, as it builds without any problems on our host machines. Any ideas?
We also tested different base archlinux docker images such as pritunl/archlinux.
Environment:
purpose: 5.43.0-1
GCC: 7.3.0
CLang: 5.0.1-2

Answer 1

This is a bug with the statx syscall used by the MOC to generate the appropriate cpp files. In the default confined configuration, docker uses seccomp to prevent or allow certain syscalls, which does not allow the statx syscall. See this for allowed syscalls.
This bug has been reported on the archlinux bugtracker, qt bugtracker and docker bugtracker already, without a (permanent) solution.
Solution 1:
Run your docker container with docker run --security-opt seccomp:unconfined as per this suggestion.
Solution 2:
Patch or downgrade to remove the statx syscall from qt.