Getting a stack trace with debug symbols out of a flatpak

This article was originally published at in October 2019 and this is an updated version.

The Flatpak application you use just crashed.

How do you report it? If you file a bug just saying it crashed, the developers will probably wish and ask for a stack trace. On Fedora 30, for example, abrt, the crash reporting system, doesn’t provide any useful information. Let’s see if we can extract that information.

We are gonna have to use the terminal to use some command line tools. Flatpak has a tool flatpak-coredumpctl to use the core dump in the flatpak sandbox. The core dump is an image of the program memory when it crashed, image that will contain a lot of information about the crash. By default the tool will not be able to provide much useful information. There is some initial setup needed to be able to have a better output.

First you must make sure that you have the right debug package for the right version of the Flatpak runtime. Well, actually, for the corresponding SDK.

Check the runtime and version associated to the application:

$ flatpak info org.gnome.MyApp

In the output of that command, check the line that starts with Sdk. It could be:

Sdk: org.gnome.Sdk/x86_64/3.34

What is after Sdk: could be a different value, and that is the information we are looking for. org.gnome.Sdk is the SDK identifier, x86_64 is the architecture, and 3.34 is the version.

First, you need to install the SDK: flatpak install --user org.gnome.Sdk/x86_64/3.34. The debug package has the same name with a suffix of .Debug. So in that case you can use the command flatpak install --user org.gnome.Sdk.Debug/x86_64/3.34 to install it. The is the one in our example, you probably to adjust to your own case. WARNING: it is likely a big download. For example the debug package for GNOME 3.34 on x86_64 is 3.4GB. I recommend installing it for the user, as, unless you have a lot of space on your system filesystem (if separate), it will fail.

Then you need to install the debug info for the app. It is the application identifier suffixed with .Debug. In that case org.gnome.MyApp.Debug.

Both will provide the debugging information that is necessary to be able to see where things crashed in the code.

Now you can run:

$ flatpak-coredumpctl org.gnome.MyApp

This is launching gdb inside the flatpak sandbox. It will take a while to process, and use quite a good chunk of memory. What follows is mostly for people that are not familiar with gdb ; if you are, just go ahead, you know what to do.

When it is ready, something like this will be printed in the terminal:

Program terminated with signal SIGSEGV, Segmentation fault.

And then at the end, the prompt: (gdb)

You can type where and press “Enter”. This prints the stack trace: lines starting with #NNN where NNN is an increasing number. You can copy that output and provide it to the developers in the bug report.

Then you can type quit followed by “Enter” when you are done.

I hope that has been useful to you.