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This document describes how you can debug an io-slave with gdb.
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How does an io-slave get started?
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=================================
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Your application request 'klauncher' via DCOP for a slave. If 'klauncher' does
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not have an idle slave ready, it will ask kdeinit to start a new one.
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kdeinit forks and dlopens the library that tqcontains the io-slave.
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Then it calls kdemain() or, if that is not present, main() in the library.
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Attaching gdb to a io-slave
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===========================
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Due to the above sequence it is rather hard to get an io-slave in your
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debugger. But wait there is hope. You can start klauncher in such a way
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that slaves for a certain protocol are started in debug mode.
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E.g. to start all 'http' slaves in debug mode, you type:
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KDE_SLAVE_DEBUG_WAIT=http kdeinit
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This will restart 'kdeinit' and 'klauncher'.
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When your application now requests a http slave, the slave will be started
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by kdeinit, but before it calls kdemain() (cq. main()) it will suspend the
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slave by sending it a SIGSTOP signal.
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In the terminal from which you started kdeinit you will get the following
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message:
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kdeinit: Suspending process
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kdeinit: 'gdb kdeinit 16779' to debug
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kdeinit: 'kill -SIGCONT 16779' to continue
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You can now debug your slave by typing (or pasting) 'gdb kdeinit 16779' in
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a terminal. If you don't want to debug a slave you can let it continue by
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sending it a SIGCONT by typing 'kill -SIGCONT 16779'.
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Be aware that slaves will not be killed while they are suspended.
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Once you have started gdb, you can set e.g. breakpoints and then resume the
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slave by typing 'continue'. The debugger will return immediate with a message
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that a SIGSTOP has been received so you will have to type 'continue' a second
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time.
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Debugging io-slaves with valgrind
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=================================
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KLauncher can be told to run certain io-slaves through valgrind. The following
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command can be used to let klauncher run all https io-slaves via valgrind:
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KDE_SLAVE_VALGRIND=https kdeinit
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The valgrind output will appear as the stderr output of the kdeinit process.
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The $VALGRIND_OPTS environment variable can be used to pass options to valgrind.
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If you want to use a different skin:
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KDE_SLAVE_VALGRIND_SKIN=calltree ( for example )
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How to get debug output
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=======================
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It is useful to redirect the debug output of your particular slave to a file
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instead of stderr. E.g. I myself use the following lines in
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$KDEDIR/share/config/kdebugrc.
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[7113]
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InfoOutput=0
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InfoFilename=/tmp/http
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[7103]
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InfoOutput=0
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InfoFilename=/tmp/http
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This redirects all debug info for areas 7103 and 7113 (as used by kio_http)
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to the file /tmp/http.
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To get debug information from the SMB slave you can add the following to
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kioslaverc:
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[SMB]
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DebugLevel=100
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This will print additional debug info to the stderr of your kdeinit process,
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which typically ends up in ~/.X.err or ~/.xsession-errors
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Happy debugging.
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