Heads-up: Major issue in Qt 5.4 branch (will be 5.4.1)

Luca Beltrame lbeltrame at kde.org
Tue Dec 2 23:10:46 UTC 2014


TL; DR: beware of commit c91c05b056c769c3df0d7634aed7d9bf2c0e550d in qtbase, 
which is in the 5.4 branch and will be in Qt 5.4.1. 

I spent most of this evening fighting a nasty bug that occurred with KF5 apps. 
Basically most apps would crash instantly (the moment they displayed 
something) if launched from inside X11, but run perfectly if ran with 
DISPLAY=:0 foo.

Notice that it seems system-dependent: I tried to debug this with a couple of 
openSUSE KDE team members  and they were unable to reproduce.

Backtraces pointed at the Qt XCB plugin, but there weren't any recent changes 
there. Strace however indicated that libcomposeplatforminputcontextplugin.so 
was the last library loaded before the crash.

And it turned out that  c91c05b056c769c3df0d7634aed7d9bf2c0e550d touched 
exactly that plugin. Reverting it fixed all crashes.

My level of skill with C++ is limited and I doubt I'd be able to make a Qt bug 
report with a Qt-only case. However I'm writing this to inform everyone, 
packagers included, to keep an eye on this. People with X11 knowledge (Martin, 
Thomas? ;) might be able to help.

Luca Beltrame - KDE Forums team
KDE Science supporter
GPG key ID: 6E1A4E79
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