Difference between revisions of "Development/Tutorials/Debugging/Debugging IOSlaves"

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This page describes how you can debug an ioslave with gdb.
{{Moved To Community | Guidelines_and_HOWTOs/Debugging }}
==How does an io-slave get started?==
Your application request 'klauncher' via DCOP [FIXME: Isn't that dbus now?] for a slave. If 'klauncher' does
not have an idle slave ready, it will ask kdeinit to start a new one.
kdeinit forks and dlopens the library that contains the io-slave.
Then it calls kdemain() or, if that is not present, main() in the library.
==Attaching gdb to a io-slave==
Due to the above sequence it is rather hard to get an io-slave in your
debugger. But wait there is hope. You can start <tt>klauncher</tt> in such a way
that slaves for a certain protocol (the first parameter of KIO::SlaveBase() constructor of the slave class) are started in debug mode.
E.g. to start all 'http' slaves in debug mode, you type:
        in KDE 3: KDE_SLAVE_DEBUG_WAIT=http kdeinit
        in KDE 4: KDE_SLAVE_DEBUG_WAIT=http kdeinit4
This will restart 'kdeinit' and 'klauncher'.
When your application now requests a http slave, the slave will be started
by kdeinit, but before it calls kdemain() (cq. main()) it will suspend the
slave by sending it a SIGSTOP signal.
In the terminal from which you started kdeinit you will get the following
kdeinit: Suspending process
kdeinit: 'gdb kdeinit 16779' to debug
kdeinit: 'kill -SIGCONT 16779' to continue
You can now debug your slave by typing (or pasting) 'gdb kdeinit 16779' in
a terminal. If you don't want to debug a slave you can let it continue by
sending it a SIGCONT by typing 'kill -SIGCONT 16779'.
Be aware that slaves will not be killed while they are suspended.
Once you have started gdb, you can set e.g. breakpoints and then resume the
slave by typing 'continue'. The debugger will return immediate with a message
that a SIGSTOP has been received so you will have to type 'continue' a second
See also [[Development/Tutorials/Debugging/Debugging_on_MS_Windows#Debugging_kioslaves|Windows-specific notes on debugging io-slaves]].
==Debugging io-slaves with valgrind==
KLauncher can be told to run certain io-slaves through valgrind. The following
command can be used to let klauncher run all https io-slaves via valgrind:
        KDE_SLAVE_VALGRIND=https kdeinit4
The valgrind output will appear as the stderr output of the kdeinit process.
The $VALGRIND_OPTS environment variable can be used to pass options to valgrind.
If you want to use a different skin:
        KDE_SLAVE_VALGRIND_SKIN=calltree      ( for example )
==How to get debug output==
It is useful to redirect the debug output of your particular slave to a file
instead of stderr. E.g. I myself use the following lines in
This redirects all debug info for areas 7103 and 7113 (as used by kio_http)
to the file /tmp/http.
To get debug information from the SMB slave you can add the following to
This will print additional debug info to the stderr of your kdeinit process,
which typically ends up in ~/.X.err or ~/.xsession-errors

Latest revision as of 09:06, 5 August 2016

This page is now on the community wiki.

This page was last edited on 5 August 2016, at 09:06. Content is available under Creative Commons License SA 4.0 unless otherwise noted.