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Debugging Qt Extended Applications


This document describes useful techniques for debugging Qt Extended and Qt Extended applications. These techniques include:

Debugging Qt Extended using gdb

This section provides instructions on how to debug desktop builds of Qt Extended using gdb in a Linux environment.

Build the Application with Debug Symbols

To build an application with debug symbols:

Run the Debugging Environment

The runqtopia script supports running Qt Extended in several different debugging environments. To run Qt Extended in using gdb:

    $QPEDIR/bin/runqtopia -runmode gdb

Once the gdb command prompt is displayed enter the following command to run Qt Extended:

    (gdb) run

Alternatively to debug an application outside of the Qt Extended environment:

    runqtopia -qpe theProgram -runmode gdb

Once the gdb command prompt is displayed enter the following command to run the application

    (gdb) set args -qws
    (gdb) run

Examining Application Crashes

If an application crashes, a core file is produced. Use the following commands to examine the core file contents:

    $ runqtopia -qpe theProgram -runmode gdb
    (gdb) core <core file>
    (gdb) backtrace full

Note: If no core file is generated run: ulimit -c 64000.

Remote Debugging

Remote debugging using the GNU Debugger is possible between machines of the same or different architecture. In both instances the procedure is the same. However, when cross-debugging you must ensure that gdb finds and loads the correct shared libraries for the remote architecture.

On the remote machine run:

    gdbserver :22222 qpe

On the host machine run:

  1. Create symlink from /opt/Qtopia to the directory containing the Qt Extended image.
        ln -s /path/to/Qtopia/image /opt/Qtopia
  2. Run gdb and connect to the remote debugging session
        $ /opt/toolchains/.../bin/gdb /opt/Qtopia/bin/qpe
        (gdb) target remote REMOTE_IP_ADDRESS:22222
        (gdb) handle SIG32 nostop noprint
        (gdb) handle SIGTRAP nostop noprint
        (gdb) handle SIGPIPE nostop noprint
        (gdb) break main
        (gdb) cont

qLog - Categorized Logging

Qt Extended provides the qLog(CategoryIdentifier) function for categorized logging, built on top of the QDebug class in Qt for Embedded Linux.

The following is an example of using a log message in the source code:

    #include <qtopialog.h>

    qLog(Type) << "Test";
    qLog(Type) << "string=" << str << ", int=" << i;

where Type is a category as defined in qtopialog-config.h.

The categories are declared by using one of the following macros:

The CategoryIdentifier has _QLog appended within the macros, so it can be any identifier you choose. The associated type name might be a useful choice:

    qLog(QWidget) << "Created" << name;

For categories declared with QTOPIA_LOG_OPTION, the output of logging depends on the Log settings. As with all Qt Extended settings files, the defaults are found in:


and these are overridden by settings in:


For example, the following enables logging messages related to the user interface:

    Enabled = 1
    Name[] = User interface
    Help[] = Anything to do with the user interface.

Note: Changes to Log.conf are not reflected in running applications immediately. A QCop message (QPE/System LogConfChanged()) can be sent which will cause all applications to re-read Log.conf and re-process the categories created with QTOPIA_LOG_OPTION.

To assist field testing, there is a Logging Settings application that uses the logread program to interface with the BusyBox syslogd output. To forward the output to syslogd, use the logger program:

  1. Start the syslog daemon in circular buffer mode. With the command:
        syslogd -C <buffersize>

    For example, to start syslogd with a 512 byte circular buffer use:

        syslogd -C 512
  2. Start Qt Extended with logging output redirected to the system log using:
        qpe 2>&1 | logger -t Qtopia
  3. Start Logging Settings to view log messages.
  4. Select Categories... from the context menu to select the log messages to enable/disable. The effects are immediate for all categories created with QTOPIA_LOG_OPTION.
  5. Log messages can be viewed on the console by running:
        logread -f

For an example of a script that uses syslogd when starting Qt Extended see <source>/devices/greenphone/src/devtools/startup/qpe.sh

Customizing Log Output

The formatting of log messages can be modified globally by setting MessageHandler/Format in the Log2 settings file. This can be used to add additional information to all logged messages suitable for log analysis tools. A C-style format string determines the output format to be used, with the following specifiers being supported:

For example, if $HOME/Settings/Trolltech/Log2.conf contains the following text:

    Format = %t %p %n: %s

Log messages will be formatted as in the following example:

qLog(UI) << "Creating main user interface";212 18755 myapp: UI : Creating main user interface
MainWindow win;
qLog(UI) << "Done creating main user interface";320 18755 myapp: UI : Done creating main user interface

As with changes to the qLog categories, sending the QPE/System LogConfChanged() QCop message is necessary for changes to log formatting to take effect in running applications.


Copyright © 2009 Trolltech Trademarks
Qt Extended 4.4.3