Protobuf version conflicts with Qt

Question

I'm trying to use protobufs v 3.3.2 with Qt 5.9.1. This works with some Qt applications, but only if they are command line programs. Once I create a GUI application with Qt and protobufs, I get this error:

[libprotobuf FATAL /home/mkraus/Documents/dev/star385/build/linux-desktop-debug-libs/protobuf/src/src/google/protobuf/stubs/common.cc:78] This program was compiled against version 2.6.1 of the Protocol Buffer runtime library, which is not compatible with the installed version (3.3.2). Contact the program author for an update. If you compiled the program yourself, make sure that your headers are from the same version of Protocol Buffers as your link-time library. (Version verification failed in "/build/mir-ui6vjS/mir-0.26.3+16.04.20170605/obj-x86_64-linux-gnu/src/protobuf/mir_protobuf.pb.cc".)

I should clarify that my part of the code is certainly using version 3.3.2 (I'm downloading and compiling protobufs from the git sources and statically linking). Look at the stack trace below to see that something that Qt is referencing is causing a protobuf version mismatch.

I'm developing on Ubuntu 16.04 and using the default desktop environment (Unity).

Work-Arounds

My troubleshooting has revealed these symptoms and work-arounds:

• Use KDE / KUbuntu. Changing the desktop environment when logging in completely avoids the version mismatch issue.

• Run the Qt application with -platform eglfs. This runs the application in full-screen mode using OpenGL. The program runs, but the window size is incorrect. When using the -platform eglfs option, it works even in Unity, but without this option, it gives me the above error.

• Any Qt application that is a command-line only application (using QCoreApplication instead of QGuiApplication) can use protobufs 3.3.2. Changing the same app to use a GUI causes the version mismatch issue.

Questions

How can I use protobufs 3.3.2 with Qt GUI applications, and also not be dependent on what desktop environment is in use? Is it Qt that is using the version 2.6.1 of protobufs, and if so, is it feasible to compile Qt to use protobufs 3.3.2?

Debug Info

Here is a stack trace (the program crashes almost immediately upon starting):

terminate called after throwing an instance of 'google::protobuf::FatalException'
  what():  This program was compiled against version 2.6.1 of the Protocol Buffer runtime library, which is not compatible with the installed version (3.3.2).  Contact the program author for an update.  If you compiled the program yourself, make sure that your headers are from the same version of Protocol Buffers as your link-time library.  (Version verification failed in "/build/mir-ui6vjS/mir-0.26.3+16.04.20170605/obj-x86_64-linux-gnu/src/protobuf/mir_protobuf.pb.cc".)

Thread 1 "scan" received signal SIGABRT, Aborted.
0x00007ffff4dff428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
54  ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007ffff4dff428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#1  0x00007ffff4e0102a in __GI_abort () at abort.c:89
#2  0x00007ffff543984d in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x00007ffff54376b6 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#4  0x00007ffff5437701 in std::terminate() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#5  0x00007ffff5437919 in __cxa_throw () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#6  0x0000000000603e0a in google::protobuf::internal::LogMessage::Finish (this=0x7fffffffc250)
    at /home/mkraus/Documents/dev/star385/build/linux-desktop-debug-libs/protobuf/src/src/google/protobuf/stubs/common.cc:268
#7  0x0000000000603e5a in google::protobuf::internal::LogFinisher::operator= (this=0x7fffffffc20f, other=...)
    at /home/mkraus/Documents/dev/star385/build/linux-desktop-debug-libs/protobuf/src/src/google/protobuf/stubs/common.cc:276
#8  0x0000000000603171 in google::protobuf::internal::VerifyVersion (headerVersion=2006001, minLibraryVersion=2006000, 
    filename=0x7fffde80aec0 "/build/mir-ui6vjS/mir-0.26.3+16.04.20170605/obj-x86_64-linux-gnu/src/protobuf/mir_protobuf.pb.cc")
    at /home/mkraus/Documents/dev/star385/build/linux-desktop-debug-libs/protobuf/src/src/google/protobuf/stubs/common.cc:86
#9  0x00007fffde7d490b in mir::protobuf::protobuf_AddDesc_mir_5fprotobuf_2eproto() ()
   from /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3
#10 0x00007fffde7d2409 in ?? () from /usr/lib/x86_64-linux-gnu/libmirprotobuf.so.3
#11 0x00007ffff7de76ba in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffd5d8, 
    env=env@entry=0x7fffffffd5e8) at dl-init.c:72
#12 0x00007ffff7de77cb in call_init (env=0x7fffffffd5e8, argv=0x7fffffffd5d8, argc=1, l=<optimized out>) at dl-init.c:30
#13 _dl_init (main_map=main_map@entry=0xa2f450, argc=1, argv=0x7fffffffd5d8, env=0x7fffffffd5e8) at dl-init.c:120
#14 0x00007ffff7dec8e2 in dl_open_worker (a=a@entry=0x7fffffffc6e0) at dl-open.c:575
#15 0x00007ffff7de7564 in _dl_catch_error (objname=objname@entry=0x7fffffffc6d0, errstring=errstring@entry=0x7fffffffc6d8, 
    mallocedp=mallocedp@entry=0x7fffffffc6cf, operate=operate@entry=0x7ffff7dec4d0 <dl_open_worker>, args=args@entry=0x7fffffffc6e0)
    at dl-error.c:187
#16 0x00007ffff7debda9 in _dl_open (file=0xa2f048 "/opt/Qt5.8.0/5.8/gcc_64/plugins/platformthemes/libqgtk3.so", mode=-2147479551, 
    caller_dlopen=0x7ffff599b7a8, nsid=-2, argc=<optimized out>, argv=<optimized out>, env=0x7fffffffd5e8) at dl-open.c:660
#17 0x00007ffff1806f09 in dlopen_doit (a=a@entry=0x7fffffffc910) at dlopen.c:66
#18 0x00007ffff7de7564 in _dl_catch_error (objname=0xa02b80, errstring=0xa02b88, mallocedp=0xa02b78, 
    operate=0x7ffff1806eb0 <dlopen_doit>, args=0x7fffffffc910) at dl-error.c:187
#19 0x00007ffff1807571 in _dlerror_run (operate=operate@entry=0x7ffff1806eb0 <dlopen_doit>, args=args@entry=0x7fffffffc910)
    at dlerror.c:163
#20 0x00007ffff1806fa1 in __dlopen (file=<optimized out>, mode=<optimized out>) at dlopen.c:87
#21 0x00007ffff599b7a8 in ?? () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Core.so.5
#22 0x00007ffff5994fd5 in ?? () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Core.so.5
#23 0x00007ffff598a647 in QFactoryLoader::instance(int) const () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Core.so.5
#24 0x00007ffff6b392f1 in ?? () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Gui.so.5
#25 0x00007ffff6b43538 in QGuiApplicationPrivate::createPlatformIntegration() () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Gui.so.5
#26 0x00007ffff6b43edd in QGuiApplicationPrivate::createEventDispatcher() () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Gui.so.5
#27 0x00007ffff59a57d6 in QCoreApplicationPrivate::init() () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Core.so.5
#28 0x00007ffff6b456ab in QGuiApplicationPrivate::init() () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Gui.so.5
#29 0x00007ffff6b46364 in QGuiApplication::QGuiApplication(int&, char**, int) () from /opt/Qt5.8.0/5.8/gcc_64/lib/libQt5Gui.so.5
#30 0x00000000005c55bd in main (argc=1, argv=0x7fffffffd5d8) at /home/mkraus/Documents/dev/star385/src/linux/ui/scan/main.cpp:35

Answer 1

As Blabdouze said, this error is caused by the libqgtk3 plugin which is used to set the GUI style. libqgtk3 uses the libmir system library, which uses protobuf 2.6.1. This leads to conflicts when the application starts.

I found a workaround that allows you to avoid editing of Qt files:

1. You need to copy the "plugins" folder from ".../Qt/5.хх.хх/gcc_64/" to some other location (for example, next to the project build folder).
2. Then you must remove "platformthemes/libqgtk3.so" and "platformthemes/libqgtk3.so.debug" from the copied folder.
3. In main(), before creating a QApplication instance, call the static function "QApplication::setLibraryPaths("path/to/copied/plugins/folder")".
4. Finally, you must add variable "LD_LIBRARY_PATH" with the value ".../Qt/5.хх.хх/gcc_64/lib" (correct path will depend on your Qt version) in a project's "environment settings" in Qt Creator. You also may add a "QT_DEBUG_PLUGINS" variable with a value of "1". It will allow you to check which plugins are used by your project and remove unnecessary plugins from the release version.

In conclusion I would like to note that this error occurred when running the project in Ubuntu 16.04, but it disappeared when I switched to version 18.04. It seems that in version 18.04 app uses the default Qt style instead of the GTK style.