Hi,
Following BLFS dev, I built latest KDE plasma and sddm with QT-5.6.0.
The build was OK.
However starting sddm or kde plasma failed (segmentation fault).
Using gdb on sddm, I finally found the culprit: the crash occured in
QV4::ExecutionEngine::newArrayObject(int) () from /usr/lib/libQt5Qml.so.5
Googling the problem, I found this issue in Qt bugreports:
https://bugreports.qt.io/browse/QTBUG-52057
The description explains exactly what happens :
"Upcoming gcc-6 has much more aggressive dead-store elimination.
See: http://gcc.gnu.org/gcc-6/porting_to.html (-flifetime-dse section).
Due to undefined behavior in QV4::ExecutionEngine::newArrayObject(int)
this will lead to segfaults"
There is no patch currently available however, the author suggests
compiling Qt-5.6.0 with gcc-6 adding "-flifetime-dse=1" to
QMAKE_CXXFLAGS (addition in
qt-everywhere-opensource-src-5.6.0/qtbase/mkspecs/linux-g++/qmake.conf).
And it works ! I now can start sddm / kde plasma without crash.
Hope this can help if anyone encounters the same problem.
Pierre
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