Assistance to diagnose crashes in Qt 5.9.0 default web examples

eureka

Recently I migrated from Ubuntu 14.04 (32bit) to Ubuntu 16.04 (64bit). My earlier limited experimenting with Qt was on 32bit and with this new setup I installed Qt 5.9.0 via online installer.

I intend to develop a hybrid web application and so started in Qt Creator (Community) by testing a couple of examples from Qt (unchanged).

contentmanipulator
markdowneditor

Each example launches but in each case the launched window soon crashes with segmentation fault reported.

I can inspect build by running ..

QT_DEBUG_PLUGINS=1 ./contentmanipulation

and at the point of crash I see this in terminal ...

loaded library "/opt/Qt/5.9/gcc_64/plugins/iconengines/libqsvgicon.so"
Segmentation fault (core dumped)

...

Running the second example ..
QT_DEBUG_PLUGINS=1 ./markdowneditor

markdowneditor: ../../nouveau/pushbuf.c:727: nouveau_pushbuf_data: Assertion `kref' failed.
Aborted (core dumped)

That path looks rather odd so I searched and did not find it anywhere in my file system.

sudo updatedb
sudo locate /nouveau/pushbuf.c

...

For good measure I tried building a third web example with debugging unselected.

I built demobrowser.

A window was launched as expected and I could browse tabs.
However the app soon crashed.

7f8ec2488000-7f8ec2489000 rw-p 00000000 00:00 0
7fffc57ce000-7fffc57ee000 rwxp 00000000 00:00 0 [stack]
7fffc57ee000-7fffc57ef000 rw-p 00000000 00:00 0
7fffc57f7000-7fffc57f9000 r--p 00000000 00:00 0 [vvar]
7fffc57f9000-7fffc57fb000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
The program has unexpectedly finished.

Again I tried running this in terminal ...

QT_DEBUG_PLUGINS=1 ./demobrowser

and the app launches but soon crashes.

This is the tail of output to terminal:

7fd47407a000-7fd47407c000 rw-s 00000000 08:12 2635975 /home/<user>/.local/share/Qt/demobrowser/QtWebEngine/Default/GPUCache/data_3
7fd47407c000-7fd47407e000 rw-s 00000000 08:12 2635974 /home/<user>/.local/share/Qt/demobrowser/QtWebEngine/Default/GPUCache/data_2
7fd47407e000-7fd474080000 rw-s 00000000 08:12 2635973 /home/<user>/.local/share/Qt/demobrowser/QtWebEngine/Default/GPUCache/dAborted (core dumped)

...

Trying again the app crashed and this was the tail of output ...

loaded library "/opt/Qt/5.9/gcc_64/plugins/iconengines/libqsvgicon.so"
Xlib: sequence lost (0x10273 > 0x276) in reply type 0x0!
Xlib: sequence lost (0x10294 > 0x297) in reply type 0x0!
Segmentation fault (core dumped)

...

Crash appears on several apps to occur at this point ..

loaded library "/opt/Qt/5.9/gcc_64/plugins/iconengines/libqsvgicon.so"

...

Can you recommend a structured debugging process for tracking down cause(s) of these crashes?

jsulm

@eureka said in Assistance to diagnose crashes in Qt 5.9.0 default web examples:

nouveau

this is the open source driver for NVidia graphics cards.
Can you try a simple Qt widget application? Is it crashing?
You could try to install NVidia driver (Ubuntu can do it for you) and see whether it helps.

eureka

@jsulm
Your diagnosis was correct. Thanks.

To summarise my workflow in case other Ubuntu developers have this problem. I'm developing on an old Dell laptop. I read advice here ..

http://www.webupd8.org/2016/06/how-to-install-latest-nvidia-drivers-in.html

I could narrow down search by running this command ..

apt-cache search nvidia | grep nvidia-

In Ubuntu I launched System Settings > Software & Updates >

Additional Drivers

Driver Installed version ..

NVIDIA Corporation: [G86M 8400M GS]
this device is using an alternative driver

There are three options and I had the third driver selected ..

Using XOrg server - Nouveau display driver from xserver-org-video-nouveau (open source)

I unticked this option and selected another option ...

Using NVIDIA binary driver - version 340.102 from nvidia-340 (proprietary, tested)
...

After rebooting and then running demobrowser again I experience no crashes.