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== Debugging with RR

[https://rr-project.org/ rr]  is a lightweight tool for recording, replaying and debugging execution of applications (trees of processes and threads). Debugging extends gdb with very efficient reverse-execution, which in combination with standard gdb/x86 features like hardware data watchpoints, makes debugging much more fun.

=== Using RR with the SDK

The Flatpak SDK already provides RR. You don't need to install it on your host machine. To record a trace, use this command:

{{{
#!sh
$ WEBKIT_MINI_BROWSER_PREFIX=rr Tools/Scripts/run-minibrowser --gtk ...
}}}

You don't necessarily need a debug build, but it's better to have one.

To replay a trace or simply run rr:

{{{
#!sh
$ Tools/Scripts/webkit-flatpak -c rr <rr arguments here>
...
$ Tools/Scripts/webkit-flatpak -c rr ps                                                                                                                                                            14:32:37
PID	PPID	EXIT	CMD
35	--	0	/app/webkit/WebKitBuild/Debug/bin/MiniBrowser http://192.168.1.44/test.html
43	35	-5	/app/webkit/WebKitBuild/Debug/bin/WebKitWebProcess 7 24
44	35	0	/app/webkit/WebKitBuild/Debug/bin/WebKitNetworkProcess 8 24
}}}

Alternatively, you can run rr from the flatpak shell:


{{{
#!sh
$ Tools/Scripts/webkit-flatpak --gtk --debug
[📦🌐🐱 org.webkit.Sdk WebKit]$ rr record /app/webkit/WebKitBuild/Debug/bin/MiniBrowser ...
...
[📦🌐🐱 org.webkit.Sdk WebKit]$ rr ps
...
[📦🌐🐱 org.webkit.Sdk WebKit]$ TEST_RUNNER_TEST_PLUGIN_PATH= rr record /app/webkit/WebKitBuild/Debug/bin/WebKitTestRunner ...
...
[📦🌐🐱 org.webkit.Sdk WebKit]$ rr replay
...
}}}

If you want to clear old unused traces, they're stored in `~/.local/share/rr/`.