14. Debugging

14.1 Introduction

The following code examples are used in this chapter:

14.2 Maemo Debugging Guide

This section is targeted at beginner-level maemo developers needing to know how to perform debugging in the maemo environment.

This section covers the two basic debugging tools available in the maemo environment, and shows how to use them. The tools are:

This section assumes that the developer already knows how to:

14.2.1 Pre-Requisites

To follow the debugging examples the following is needed:

14.2.2 General Notes on Debugging Debugging Issues on ARM Architecture

There are some issues one needs to be aware of when debugging on the ARM architecture. Debugging Issues in Scratchbox

It is recommended to use the native gdb in the target, not the Scratchbox host-gdb.

When debugging threads in an application, gdb needs to be linked against the same thread library that the application is using. For this reason, the Scratchbox-provided gdb is not suitable for threads debugging, but the native gdb needs to be used instead. See instructions in the next section on how to start using the native gdb.

Image dialog-information N.B.

The above-mentioned problem can produce "warning: Cannot initialize thread debugging library: unknown thread_db error '22'" messages in gdb output, and info threads command in gdb will show nothing.

14.2.3 Using Gdb Debugger

The Gnu Project Debugger, or gdb for short, is a general purpose debugger that can be used for various debugging purposes.

This section does not explain how to use the gdb debugger itself, i.e. it does not explain the specific commands in gdb to perform some specific actions. There are other tutorials and documentation readily available in the Internet for that purpose. This section focuses on explaining how to set up and perform the basic debugging steps with the gdb in the maemo environment.

For additional gdb documentation, take a look at the maemo tools documentation for gdb. Setting up Environment

Both the Internet Tablet device, described in section Setting up USB Networking 3.5, and the Scratchbox environment, described in section Installing SDK 3.3, both in chapter Development Environment of the Maemo Reference Manual, need to be set up. Preparing Scratchbox Environment for Debugging

If the maemo SDK is not yet installed, it must be installed before continuing.

After installing maemo SDK, the default target names are armel and x86. These will be used in this example.

Image dialog-information N.B.

The Scratchbox provides a gdb debugger. If just [sbox-x86: ~] > gdb ... is run, then that gdb debugger is used. In this material, the native-gdb (i.e. non-Scratchbox version of gdb) is used.

Next, install gdb to the Scratchbox from the maemo repositories.

[sbox-x86: ~] > fakeroot apt-get install gdb
[sbox-x86: ~] > fakeroot apt-get install maemo-debug-scripts 
[sbox-x86: ~] > fakeroot apt-get install maemo-sdk-debug

Now two gdb programs are installed. The one used can be checked with:

[sbox-x86: ~] > which gdb

If only using the command gdb, then the gdb used is the one provided by Scratchbox.

Start briefly both gdb debuggers to see that they start properly in the Scratchbox environment. First just run gdb:

[sbox-x86: ~] > gdb
GNU gdb 6.4.90
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu".
(gdb) q
[sbox-x86: ~] >

Then run the maemo version of gdb:

[sbox-x86: ~] > native-gdb
GNU gdb 6.6-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
(gdb) q
[sbox-x86: ~] >

To quit from gdb, type 'q' and hit ENTER.

The native-gdb is used here, since it allows also threads to be debugged.

Both gdb versions are available in the Scratchbox X86 environment. The native-gdb should always be run instead of the Scratchbox version. Preparing Internet Tablet for Debugging

Image dialog-information N.B.

Because additional software is going to be installed, and debugging will be performed in the real device that is running the official Sales Image, it is recommended that a full back-up of the device and any important files is made before continuing.

The gdb needs to be installed in the Internet Tablet device. It is recommended that first osso-xterm and then ssh are installed in the device before continuing.

  1. Start osso-xterm.
  2. Gain root access to the device while running osso-xterm.
  3. Edit the /etc/apt/sources.list file in the device so that it contains line:

    deb http://repository.maemo.org/ diablo free non-free

    The /etc/apt/sources.list file can be edited with a text editor (e.g. vi), but the following command given from the osso-xterm is also valid:

    echo "deb http://repository.maemo.org/ diablo free non-free" >> /etc/apt/sources.list

    Important: it is not recommended to perform device software updates from the maemo sdk repositories (for example, 'apt-get upgrade' is not recommended for the device). The reason for this is that there might be some software packages in the SDK repositories that are so-called sdk variants. They might create a problem, if directly installed in the actual device. In this example, only gdb software is used from the repository.

  4. Perform an apt-get update in the device. The update command will refresh the package list database in the device.
  5. Perform an apt-get install gdb

You should now have the gdb and gdbserver (included in the gdb package) installed in the device.

Image dialog-information N.B.

After using the maemo sdk repositories in the device /etc/apt/sources.list file, remove or comment the line out. This way, you will not accidentally get programs from the wrong repository to the device. See notes above. Debugging Use Cases with Gdb Debugging Command Line Application in Scratchbox X86 Environment with Gdb

One of the most common debugging case is performing debugging in the Scratchbox X86 environment.

By now, the gdb is installed in the x86 target. Next, download the gdb_examplesources.

The example apps are:

Next, the small gdb_example.c file should be compiled as shown below, and the gdb debugger should be started. This simple example shows how to set breakpoints, and how to get a backtrace from the program. Backtrace tells what functions have been called and what parameters have been used.

Compile the gdb_example.c application with the -g option like this:

[sbox-x86: ~/src/testing/gdb_example] > gcc gdb_example.c -o gdb_example -g

Next, start the gdb with the gdb_example application as a parameter.

[sbox-x86: ~/src/testing/gdb_example] > native-gdb gdb_example
GNU gdb 6.6-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
Using host libthread_db library "/lib/libthread_db.so.1".

Set the breakpoint (br) to function example_3

(gdb) br example_3
Breakpoint 1 at 0x80483e9: file gdb_example.c, line 48.

Run the application under gdb giving a command line parameter foobar to the application.

(gdb) run foobar
Starting program: /home/user/src/testing/gdb_example/gdb_example foobar
Now in main().
Now in example_1(2) function.
Now in example_2(parameter here) function.

Breakpoint 1, example_3 () at gdb_example.c:48
48        printf("Now in example_3()\n");

The above shows that the running of the application stopped in function example_3. This happened, because the breakpoint (br example_3) was set.

Now the backtrace (bt) can be listed from application to see what functions have been called. The list goes from recent to older. The oldest function was naturally the main() function at the end of the list. It shows also the parameters to the called functions.

(gdb) bt
#0  example_3 () at gdb_example.c:48
#1  0x080483dc in example_2 (a=0x80484f8 "parameter here") at gdb_example.c:39
#2  0x080483b9 in example_1 (x=2) at gdb_example.c:30
#3  0x08048387 in main (argc=2, argv=0xbfc437e4) at gdb_example.c:18

It can be convenient to see what the source code is for a line mentioned in the output:

(gdb) list 39
34       *
35       */
36      int example_2(char* a)
37      {
38        printf("Now in example_2(%s) function.\n",a);
39        example_3();
40        return 0;
41      }
42      /*
43       *

Also the values of the variables can be inspected:

(gdb) br example_2
Breakpoint 1 at 0x80483c4: file gdb_example.c, line 38.
(gdb) run
Starting program: /home/user/src/testing/gdb_example 
Now in main().
Now in example_1(1) function.

Breakpoint 2, example_2 (a=0x80484f8 "parameter here") at gdb_example.c:38
38        printf("Now in example_2(%s) function.\n",a);

To see the value of variable 'a' just type:

(gdb) print a
$1 = 0x80484f8 "parameter here"

Essentially, debugging with gdb in the Scratchbox X86 target is similar to debugging with gdb in any Linux host. In this example, only a small subset of gdb's functionality has been used. Debugging Command Line Application in Internet Tablet Device

It is possible to debug an application in the Internet tablet device itself using gdb. Before starting, log in on the device and install (if you have not done so yet) the gdb debugger to the device:

/home/user # apt-get install gdb
... etc ...
/home/user #

Here it is assumed that ssh and osso-xterm are already installed in the tablet and that it is possible to log in on the device using ssh from a Linux PC. In addition, the maemo repository entries should be set in the /etc/apt/sources.list file as explained previously.

Debugging with the gdb debugger in the device is similar to using gdb in a normal Linux PC environment. The limitations are mostly related to the available free RAM memory, meaning that in the worst case, memory might run out while trying to debug an application in the device.

This example follows the basic logic of the first example, but this time is performed in the device.

  1. Compile the gdb_example.c application in the Scratchbox for armel architecture.

    [sbox-x86: ~] > sb-conf select armel
    Shell restarting...
    [sbox-armel: ~] > pwd
    [sbox-armel: ~] > cd src/testing/gdb_example
    [sbox-armel: ~/src/testing/gdb_example] > gcc gdb_example.c -o gdb_example -g
    [sbox-armel: ~/src/testing/gdb_example] > file gdb_example
    gdb_example: ELF 32-bit LSB executable, ARM, version 1 (SYSV), for GNU/Linux 2.6.8, 
    dynamically linked (uses shared libs), not stripped
    [sbox-armel: ~/src/testing/gdb_example] >
  2. Copy the armel version of the gdb_example to the tablet. You need to have the sshd daemon up and running in the device before you can copy files with scp.

    [sbox-armel: ~/src/testing/gdb_example] > scp gdb_example user@
    user@'s password:  ...........
    gdb_example                                     100% 9135     8.9KB/s   00:00
  3. Log in on the device with ssh with username user. The IP address is an example, and your device IP address can be different.

    [sbox-armel: ~/src/testing/gdb_example] > ssh root@
    root@'s password: ..........
    BusyBox v1.6.1 (2007-09-27 18:08:59 EEST) Built-in shell (ash)
    Enter 'help' for a list of built-in commands.
    ~# cd ~user
  4. Start the gdb debugger with the gdb_example application.

    /home/user# gdb ./gdb_example
    GNU gdb 6.6-debian
    Copyright (C) 2006 Free Software Foundation, Inc.
    GDB is free software, covered by the GNU General Public License, and you are
    welcome to change it and/or distribute copies of it under certain conditions.
    Type "show copying" to see the conditions.
    There is absolutely no warranty for GDB.  Type "show warranty" for details.
    This GDB was configured as "arm-linux-gnueabi"...
    Using host libthread_db library "/lib/libthread_db.so.1".
You should now be able to debug this small example application in a similar way as in the previous example. Debugging Core Files in Device

This section explains how to debug core files in the Internet Tablet.

The kernel does not dump cores of a failing process, unless told where to dump the core files.

The default values for core dumps can be seen by reading the file linuxrc with the more command in the device, and by studying the enable_coredumps() function:

/home/user # more /mnt/initfs/linuxrc 
... snip ...
        echo -n "Enabling core dumps to $coredir/..."
        echo "$coredir/%e-%s-%p.core" > /proc/sys/kernel/core_pattern
        ulimit -c unlimited
        echo "done."
... snip ...

As can be seen, the default location for core dumps is in /media/mmc1/core-dumps directory. The second echo command defines the name of the core dump file. The default name contains the name of the executable (%e), the signal (%s) and the PID number (%p).

If these default settings are satisfactory, it is enough to create the core-dumps directory under the /media/mmc1 directory.

Next, the small example application gdb_example2 will be used to demonstrate how to debug the core file.

  1. Compile the gdb_example2 in the Scratchbox armel target, and just copy the file to the device using scp. Now, unplug the USB cable to get access to memory cards. Then start the gdb_example2 in the device like this:

    /home/user # ./gdb_example2 &
    /home/user # gdb_example2.
    Now in main().
    Now in example_1(1) function.
  2. The gdb_example2 is now running in the background, and it starts to dump its output to the screen. There are some sleep() calls in the gdb_example2, so that you have time to kill it with the SIGSEGV signal. Now just make it to generate a core dump. Assuming that the process is referred to as %1, just use the kill command as below and press the ENTER key a couple of times:

    /home/user # kill -SIGSEGV %1
    /home/user # 
    [1] + Segmentation fault (core dumped) ./gdb_example2
  3. You should now have a compressed core dump data file under the /media/mmc1/core-dumps directory. Its name should include the name of the file and end with the PID number of the gdb_example2 program. Check that you got it (the number shown below, 1390, will naturally be different in your environment):

    /home/user # ls -l /media/mmc1/core-dumps/
    -rw-r--r--    1 user     root       139264 Nov  9 13:09 gdb_example2-11-1390.rcore.lzo
  4. You have to extract the compressed data before you can use it with gdb. You need to install sp-rich-core-postproc package and run the extract command which creates a new directory (given as a second parameter) where to extract data:

    /home/user # apt-get install sp-rich-core-postproc
    ... snip ...
    /home/user # rich-core-extract /media/mmc1/core-dumps/gdb_example2-11-1390.rcore.lzo \

    The newly-created coredir includes lots of information in different files about the system. The file to pass for the gdb is named coredump.

  5. The gdb_example2 is linked against the libc library. If you want to be able to resolve symbols also for the library during debugging, you need to install libc6-dbg package in the device. The same rule applies to other libraries that your application might be linked against. See the further notes about the DBG packages in this material.

    Now install the libc6-dbg package to get symbols for the library.

    /home/user #  apt-get install libc6-dbg
    Reading Package Lists... Done
    Building Dependency Tree... Done
    The following NEW packages will be installed:
    .... snip ...
    /home/user #
  6. Now you can debug the core file together with the gdb_example2 binary that you compiled with the -g flag. Try and see where the execution of the gdb_example2 was when you used the -SIGSEGV signal. Start the gdb and give the gdb_example2 as the first parameter, and the core file as the second parameter:

    /home/user # gdb ./gdb_example2 coredir/coredump 
    GNU gdb 6.6-debian
    Copyright (C) 2006 Free Software Foundation, Inc.
    GDB is free software, covered by the GNU General Public License, and you are
    welcome to change it and/or distribute copies of it under certain conditions.
    Type "show copying" to see the conditions.
    There is absolutely no warranty for GDB.  Type "show warranty" for details.
    This GDB was configured as "arm-linux-gnueabi"...
    Using host libthread_db library "/lib/libthread_db.so.1".
    Reading symbols from /lib/libc.so.6...BFD: /usr/lib/debug/lib/libc-2.5.so: 
    warning: sh_link not set for section `.ARM.exidx'
    Reading symbols from /usr/lib/debug/lib/libc-2.5.so...done.
    Loaded symbols for /lib/libc.so.6
    Reading symbols from /lib/ld-linux.so.3...BFD: /usr/lib/debug/lib/ld-2.5.so: 
    warning: sh_link not set for section `.ARM.exidx'
    Reading symbols from /usr/lib/debug/lib/ld-2.5.so...done.
    Loaded symbols for /lib/ld-linux.so.3
    Core was generated by `./gdb_example2'.
    Program terminated with signal 11, Segmentation fault.
    #0  0x410adcec in nanosleep () from /lib/libc.so.6

    The example above shows that now gdb is using debug symbols from /usr/lib/debug/lib/libc-2.5.so. Had the libc6-dbg package not been installed, the gdb would not have information available about the libraries' debug symbols.

    Now, the gdb is waiting for a command, so just give the bt (backtrace) command. You should see something similar to this:

    (gdb) bt
    #0  0x410adcec in nanosleep () from /lib/libc.so.6
    #1  0x410ada54 in sleep () from /lib/libc.so.6
    #2  0x0000846c in example_2 (a=0x8570 "parameter here") at gdb_example2.c:41
    #3  0x0000842c in example_1 (x=1) at gdb_example2.c:32
    #4  0x000083e0 in main (argc=1, argv=0xbee57e24) at gdb_example2.c:19

    Image dialog-information N.B.

    For this simple example, the available libc6-dbg package was installed before starting to debug the gdb_example2 application. If the dbg packages for various libraries were not installed, it would mean that the backtrace information coming from the non-debug version of the library could not be trusted.

    Depending on at what point the kill -SIGSEGV command was given, the output may be different. In this example, the process was hit when it was calling the sleep function inside the example_1 function in file gdb_example2.c. It can also be seen that the sleep() function has further called the nanosleep() function, and that is when it got the -SIGSEGV signal (see the note above). Debugging Core File from Device Inside Scratchbox

Because the binaries and libraries in the device are prelinked, successful debugging inside the Scratchbox environment using the programs core file (from the device) would require that:

After copying the /lib/libc6 library from the device and setting the native gdb to be used, the application can be debugged normally.

Image dialog-information N.B.

Keep in mind that generally the Scratchbox tools override the target tools. Debugging UI Applications in Scratchbox X86

Many maemo applications use the graphical UI, and debugging these applications differs slightly from debugging simple command line applications.

Here the maemopad will be used as an example application to debug in the X86 target with gdb.

If the Scratchbox environment is set up correctly as explained above, these steps should be easy to follow to perform UI debugging with maemopad application.

  1. Activate the X86 target, go to the testing directory and download the source package of maemopad application.

    [sbox-armel] sb-conf select x86
    [sbox-x86] cd ~/src/
    [sbox-x86 ~/src] mkdir maemopad 
    [sbox-x86 ~/src/maemopad] cd maemopad 
    [sbox-x86 ~/src/maemopad] apt-get source maemopad
    Reading package lists... Done
    Building dependency tree... Done
    Need to get 384kB of source archives.
    Get:1 http://juri.research.nokia.com diablo/free maemopad 2.3 (dsc) [476B]
    Get:2 http://juri.research.nokia.com diablo/free maemopad 2.3 (tar) [384kB]
    Fetched 384kB in 0s (4637kB/s)
    dpkg-source: warning: extracting unsigned source package (./maemopad_2.3.dsc)
    dpkg-source: extracting maemopad in maemopad-2.3
    dpkg-source: unpacking maemopad_2.3.tar.gz
  2. Check that you have the correct files.

    [sbox-x86: ~/src/maemopad] > ls -l 
    total 388
    drwxrwxr-x  6 maemo maemo   4096 Sep 26 15:00 maemopad-2.3
    -rw-rw-r--  1 maemo maemo    476 Nov  8 17:26 maemopad_2.3.dsc
    -rw-rw-r--  1 maemo maemo 383834 Nov  8 17:26 maemopad_2.3.tar.gz
  3. Go to the maemopad-2.3 source directory, and set the DEB_BUILD_OPTIONS environment variable, so that the generated binaries are not stripped. Then build the maemopad package with dpkg-buildpackage command as shown here:

    [sbox-x86: ~/src/maemopad] > cd maemopad-2.3
    [sbox-x86: ~/src/maemopad/maemopad-2.3] > export DEB_BUILD_OPTIONS=debug,\
    [sbox-x86: ~/src/maemopad/maemopad-2.3] > dpkg-buildpackage -rfakeroot -d
    dpkg-buildpackage: source package is maemopad
    dpkg-buildpackage: source version is 2.3
    dpkg-buildpackage: source changed by Maemo Integration <integration@maemo.org>
    dpkg-buildpackage: host architecture i386
    dpkg-buildpackage: source version without epoch 2.3
    : Using Scratchbox tools to satisfy builddeps
    .... etc ....

    Image dialog-information N.B.

    In this example, the standard export DEB_BUILD_OPTIONS=debug,nostrip environment variable is used, but there might be source packages that do not support these debug,nostrip options. In that case, one must make sure that the source is compiled with -g flag (usually this option can be added to the CFLAGS variable in the debian/rules file), and that the produced binaries will not be stripped. In the long run, it is better to modify the source package to generate a separate debug symbol (-dbg) package. This requires modifying both the debian/rules and debian/control files.
  4. You should now have maemopad binaries generated so that they have the debug symbols in them. Check that you get a not stripped flag from the maemopad binary:

    [sbox-x86: ~/src/maemopad/maemopad-2.3] > file debian/maemopad/usr/bin/maemopad 
    debian/tmp/usr/bin/maemopad: ELF 32-bit LSB executable, Intel 80386, version 1 
    (SYSV), for GNU/Linux 2.6.0, dynamically linked (uses shared libs), not stripped
  5. You should now have a maemopad_2.3_i386.deb file in the ~/src/maemopad directory. Check that you have it:

    [sbox-x86: ~/src/maemopad] > ls -l 
    total 440
    drwxrwxr-x  6 maemo maemo   4096 Nov  9 13:37 maemopad-2.3
    -rw-rw-r--  1 maemo maemo    476 Nov  9 13:36 maemopad_2.3.dsc
    -rw-rw-r--  1 maemo maemo 388593 Nov  9 13:36 maemopad_2.3.tar.gz
    -rw-rw-r--  1 maemo maemo    675 Nov  9 13:37 maemopad_2.3_i386.changes
    -rw-r--r--  1 maemo maemo  42632 Nov  9 13:37 maemopad_2.3_i386.deb
  6. Install the newly compiled maemopad_2.3_i386.deb file inside the Scratchbox environment:

    [sbox-x86: ~/src/maemopad] > dpkg -i maemopad_2.3_i386.deb
    ... output from dpkg ...
  7. Start the Xephyr server outside the Scratchbox:

    Linux-PC$ Xephyr :2 -host-cursor -screen 800x480x16 -dpi 96 -ac -extension Composite &
  8. Start the Application Framework from inside the Scratchbox X86 target:

    [sbox-x86: ~/src/maemopad/maemopad-2.1] > export DISPLAY=:2
    [sbox-x86: ~/src/maemopad/maemopad-2.1] > af-sb-init.sh start
    ... lots of output from various programs ...

    You should now have the application framework up and running and the Xephyr window should contain the normal SDK UI.

  9. Move to the source directory:

    [sbox-x86: ~/src/maemopad/maemopad-2.1] > cd src/ui
  10. In the ui directory, you should have the files:

    [sbox-x86: ~/src/maemopad/maemopad-2.1/src/ui] ls -l 
    total 40
    -rw-r--r--  1 maemo maemo 12404 Sep 26 14:13 callbacks.c
    -rw-r--r--  1 maemo maemo  2250 Sep 26 14:11 callbacks.h
    -rw-r--r--  1 maemo maemo 15562 Jun 20 10:42 interface.c
    -rw-r--r--  1 maemo maemo  3282 Jun 20 10:42 interface.h
  11. In this example, a debugging breakpoint will be set at the callback function callback_help() located in the callbacks.c file. This function is called when the user clicks the HELP button from the maemopad menu. Set the debugging breakpoint like this:

    [sbox-x86: ~/src/maemopad/maemopad-2.1/src/ui] > run-standalone.sh gdb \
    (gdb) br callback_help
    Breakpoint 1 at 0x804bf56: file ui/callbacks.c, line 296.
  12. Start the maemopad application from the gdb.

    (gdb) run
    Starting program: /targets/x86/usr/bin/maemopad
    [Thread debugging using libthread_db enabled]
    [New Thread -1222154560 (LWP 22944)]
    /home/maemo/.osso/current-gtk-key-theme:1: Unable to find include file: 
    maemopad[22944]: GLIB WARNING ** GLib-GObject - invalid cast from 'HildonProgram' 
    to 'GtkWidget'
    maemopad[22944]: GLIB CRITICAL ** Gtk - gtk_widget_show: assertion 
    'GTK_IS_WIDGET (widget)' failed
    Audio File Library: could not open file '/usr/share/sounds/ui-window_open.wav' 
    [error 3]
    Audio File Library: could not open file '/usr/share/sounds/ui-window_close.wav' 
    [error 3]
    hello-world background

    Image dialog-information N.B.

    Thread-debugging: Now the native gdb program is used. If you need to debug threads in the application, you need to use the native gdb linked against the same thread library that your application is using. Remember that the Scratchbox gdb is not suitable for this purpose. To use the native gdb, native-gdb needs to be used, as mentioned earlier in this material.
  13. Now you should be able to see the maemopad application inside the Xephyr window, and you should be able to use it normally. Next, click the upper menu and select the item HELP. In your gdb terminal window you should now see :

    Breakpoint 1, callback_help (action=0x80bda40, data=0x806eca8) at ui/callbacks.c:296
    296     {
  14. The breakpoint that you set above is now reached, and execution of maemopad application is stopped. The gdb debugger waits for your command now. Try something simple, like using the list command to see where the execution of the application is going. You should get:

    (gdb) list
    291         }
    292     }
    294     /* help */
    295     void callback_help( GtkAction * action, gpointer data )
    296     {
    297         osso_return_t retval;
    299         /* connect pointer to our AppUIData struct */
    300         AppUIData *mainview = NULL;
  15. You can now debug the maemopad normally. Try and see, if you can execute the maemopad step by step so that you can get the help window on screen. Enter the s command like this:

    (gdb) s
    302         g_assert(mainview != NULL && mainview->data != NULL );
    (gdb) s
    304         retval = hildon_help_show(
    (gdb) s
    hildon_help_show (osso=0x80bda40, help_id=0x804cb08 "Example_MaemoPad_Content", 
                      flags=1) at osso-helplib.c:636
    636     osso-helplib.c: No such file or directory.
            in osso-helplib.c
  16. You can also try the bt (backtrace) command to see what functions were called. You should see a list of functions that have been called, similar to the following:

    (gdb) bt
    #0  hildon_help_show (osso=0x80bda40, help_id=0x804cb08 "Example_MaemoPad_Content", 
        flags=1) at osso-helplib.c:636
    #1  0x0804bfb0 in callback_help (action=0x80bda40, data=0x1) at ui/callbacks.c:304
    #2  0xb78bc688 in IA__g_cclosure_marshal_VOID__VOID (closure=0x8106ae0, 
        return_value=0x0, n_param_values=1, param_values=0xfffffffe, 
        invocation_hint=0xbfac6798, marshal_data=0x0) at gmarshal.c:77
    #3  0xb78a563b in IA__g_closure_invoke (closure=0x8106ae0, return_value=0x1, 
        n_param_values=1, param_values=0x1, invocation_hint=0x1) at gclosure.c:490
    #4  0xb78bb058 in signal_emit_unlocked_R (node=0x80f2bb8, detail=0, 
        instance=0x80bda40, emission_return=0x0,instance_and_params=0xbfac68c0) 
        at gsignal.c:2440
    #5  0xb78bbfa8 in IA__g_signal_emit_valist (instance=0x80bda40, signal_id=1, 
        detail=0, var_args=0xbfac6a4c "\001\020") at gsignal.c:2199
    #6  0xb78bc296 in IA__g_signal_emit (instance=0x1, signal_id=1, detail=1) 
        at gsignal.c:2243
    #7  0xb7def78b in IA__gtk_widget_activate (widget=0x80bda40) at gtkwidget.c:4273
    #8  0xb7cd9c62 in IA__gtk_menu_shell_activate_item (menu_shell=0x8103030, 
        menu_item=0x80bda40, force_deactivate=1) at gtkmenushell.c:1230
    #9  0xb7cda009 in gtk_menu_shell_button_release (widget=0x8103030, event=0x810c060) 
        at gtkmenushell.c:748
    #10 0xb7cd0f78 in gtk_menu_button_release (widget=0x8103030, event=0x810c060) 
        at gtkmenu.c:2978
    #11 0xb7cc67d0 in _gtk_marshal_BOOLEAN__BOXED (closure=0x8071028, 
        return_value=0xbfac6c90, n_param_values=2, param_values=0xbfac6de0, 
        invocation_hint=0xbfac6cb8, marshal_data=0xb7cd0e40) at gtkmarshalers.c:84
    #12 0xb78a5979 in g_type_class_meta_marshal (closure=0x8071028, return_value=0x1, 
        n_param_values=1, param_values=0xbfac6de0, invocation_hint=0x1, marshal_data=0x1) 
        at gclosure.c:567
    #13 0xb78a563b in IA__g_closure_invoke (closure=0x8071028, return_value=0x1, 
        n_param_values=1, param_values=0x1, invocation_hint=0x1) at gclosure.c:490
    #14 0xb78babcb in signal_emit_unlocked_R (node=0x80708c0, detail=0, 
        instance=0x8103030, emission_return=0xbfac6d70, instance_and_params=0xbfac6de0) 
        at gsignal.c:2478
    #15 0xb78bbcfd in IA__g_signal_emit_valist (instance=0x8103030, signal_id=0, detail=0,
        var_args=0xbfac6f70 "xo %G       %@00\020\b") at gsignal.c:2209
    #16 0xb78bc296 in IA__g_signal_emit (instance=0x1, signal_id=1, detail=1) 
        at gsignal.c:2243
    #17 0xb7def914 in gtk_widget_event_internal (widget=0x8103030, event=0x810c060) 
        at gtkwidget.c:4242
    #18 0xb7cc4bd7 in IA__gtk_propagate_event (widget=0x8103030, event=0x810c060) 
        at gtkmain.c:2348
    #19 0xb7cc4f2f in IA__gtk_main_do_event (event=0x810c060) at gtkmain.c:1582
    #20 0xb7b40551 in gdk_event_dispatch (source=0x1, callback=0, user_data=0x0) 
        at gdkevents-x11.c:2318
    #21 0xb78341fc in IA__g_main_context_dispatch (context=0x8066cc8) at gmain.c:2045
    #22 0xb7835bb5 in g_main_context_iterate (context=0x8066cc8, block=1, dispatch=1, 
        self=0x80690e0) at gmain.c:2677
    #23 0xb7835eda in IA__g_main_loop_run (loop=0x8062200) at gmain.c:2881
    #24 0xb7cc41b3 in IA__gtk_main () at gtkmain.c:1155
    #25 0x0804a669 in main (argc=1, argv=0xbfac7224) at main.c:108

    At the top of the backtrace list are functions that were called last, and at the bottom of the list are the applications main() function and then the gtk_main(), etc.

  17. If you now continued debugging with s (step) command, you would end up looping the gtk main event loop. However, it is better to just give the c (continue) command:

    (gdb) c
  18. Now the maemopad application is running. If you select the HELP menu item again, the breakpoint is still set. So if you click HELP you would get again:

    Breakpoint 1, callback_help (action=0x80bda40, data=0x806ec78) at ui/callbacks.c:296
    296     {
  19. You can clear a specific breakpoint using the clear command. Remove the breakpoint in callback_help() function:

    (gdb) clear callback_help
    Deleted breakpoint 1 
    (gdb) c
  20. Because the breakpoint is now cleared, you can use the application normally under the Xephyr.

14.2.4 Debugging Hildon Desktop Plug-ins

This section explains how to debug Hildon Desktop plug-ins in maemo environment.

Desktop and Control Panel applications are both launched by the maemo-launcher daemon. Their plug-ins are all shared libraries (i.e. .so files). Writing these plug-ins is explained in maemo.org documentation [62]. Downloading and Compiling the Example Apps

For this example, you need to first download, compile and install the hello-world-app package.

  1. Download the source package of hello-world-app:

    [sbox-x86: ~/src] > apt-get source hello-world-app
    Reading package lists... Done
    Building dependency tree... Done
    Need to get 235kB of source archives.
    Get:1 http://repository.maemo.org diablo/free hello-world-app 2.1 (dsc) [363B]
    Get:2 http://repository.maemo.org diablo/free hello-world-app 2.1 (tar) [235kB]
    Fetched 235kB in 0s (264kB/s)
    dpkg-source: warning: extracting unsigned source package (./hello-world-app_2.1.dsc)
    dpkg-source: extracting hello-world-app in hello-world-app-2.1
    dpkg-source: unpacking hello-world-app_2.1.tar.gz
  2. Go to the sources directory ...

    [sbox-x86: ~/src] > cd hello-world-app-2.1
    [sbox-x86: ~/src/hello-world-app-2.1] >
  3. ... and compile it like this:

    [sbox-x86: ~/src/hello-world-app-2.1] > export DEB_BUILD_OPTIONS=debug,\
    [sbox-x86: ~/src/hello-world-app-2.1] > ./autogen.sh
    ... etc ...
    [sbox-x86: ~/src/hello-world-app-2.1] > dpkg-buildpackage -rfakeroot
    dpkg-buildpackage: source package is hello-world-app
    dpkg-buildpackage: source version is 2.1
    dpkg-buildpackage: source changed by Maemo Integration <integration@maemo.org>
    dpkg-buildpackage: host architecture i386
    dpkg-buildpackage: source version without epoch 2.1
    dpkg-checkbuilddeps: Using Scratchbox tools to satisfy builddeps
     fakeroot debian/rules clean
    rm -f build-stamp configure-stamp
    # Add here commands to clean up after the build process.
    /scratchbox/tools/bin/make clean
    ... snip, output from compilation ...
    dpkg-genchanges: including full source code in upload
    dpkg-buildpackage: full upload; Debian-native package (full source is included)
    [sbox-x86: ~/src/hello-world-app-2.1] >
  4. You should now have:

    [sbox-x86: ~/src/hello-world-app-2.1] > cd ..
    [sbox-x86: ~/src] > ls -lt 
    total 312
    -rw-rw-r--  1 maemo maemo    738 Nov 14 08:27 hello-world-app_2.1_i386.changes
    -rw-r--r--  1 maemo maemo  58402 Nov 14 08:27 hello-world-app_2.1_i386.deb
    drwxr-xr-x  5 maemo maemo   4096 Nov 14 08:27 hello-world-app-2.1
    -rw-rw-r--  1 maemo maemo    363 Nov 14 08:26 hello-world-app_2.1.dsc
    -rw-rw-r--  1 maemo maemo 234825 Nov 14 08:26 hello-world-app_2.1.tar.gz
  5. Install the newly compiled debug version of the package hello-world-app_2.1_i386.deb:

    [sbox-x86: ~/src] > fakeroot dpkg -i hello-world-app_2.1_i386.deb
    (Reading database ... 15186 files and directories currently installed.)
    Unpacking hello-world-app (from hello-world-app_2.1_i386.deb) ...
    ... snip ...
Now the Hildon desktop plug-ins example applications should be installed in the Scratchbox X86 target. How to Debug Applications Started by Maemo-Launcher

Basically, these applications can be debugged by: Attaching to Maemo-Launched Application with Gdb

With maemo-launched applications, it is necessary to give maemo-launcher binary to gdb and attach to the already running process.

[sbox-x86: ~/ ] > export DISPLAY=:2
[sbox-x86: ~/ ] > af-sb-init.sh start
... snip ...
[sbox-x86: ~/ ] > pidof hildon-desktop | cut -d' ' -f1
# this would take the first (largest) PID value from the returned list. The number 22961 is 
just an example.
# smallest PID value is maemo-invoker which had requested maemo-launcher to start 
[sbox-x86: ~/ ] > native-gdb maemo-launcher
... snip ...
(gdb) attach 22961
Attaching to program: /targets/x86/usr/bin/maemo-launcher, process 22961
... snip...

Now it should be possible to debug the application normally with the gdb. Starting Maemo-Launched Application with Maemo-Summoner

The following will start the Control Panel under (native) gdb, and the newly installed Control Panel applet called hello-world-app will be debugged. The breakpoint will be set to function hello_world_dialog_show(). Pay attention to the question about the "pending shared library load".

[sbox-x86: ~/ ] > export DISPLAY=:2
[sbox-x86: ~/ ] > af-sb-init.sh start
... snip ...
[sbox-x86: ~/ ] > run-standalone.sh native-gdb maemo-summoner
... snip ...
(gdb) br hello_world_dialog_show
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (hello_world_dialog_show) pending.
(gdb) run /usr/bin/controlpanel.launch
Starting program: /targets/x86/usr/bin/maemo-summoner /usr/bin/controlpanel.launch
... snip ...

This should start the Control Panel in the Xephyr screen. When clicking the hello world plug-in in the Control Panel, the execution should stop at the given breakpoint. Try, for example, to get a backtrace:

Breakpoint 2, hello_world_dialog_show () at libhelloworld.c:68
68        GtkWidget *dialog = hello_world_dialog_new ();
(gdb) bt
#0  hello_world_dialog_show () at libhelloworld.c:68
#1  0xb70b05f7 in execute (osso=0x8075948, data=0x8084088, user_activated=1) 
    at hello-world-applet.c:11
#2  0xb7ea4a71 in hcp_app_idle_launch (d=0x810ad08) at hcp-app.c:200
#3  0xb776c4d1 in g_idle_dispatch (source=0x810ac98, callback=0x806ac70, 
    user_data=0x8075948) at gmain.c:3928
#4  0xb77691fc in IA__g_main_context_dispatch (context=0x806dbc0) at gmain.c:2045
#5  0xb776abb5 in g_main_context_iterate (context=0x806dbc0, block=1, dispatch=1, 
    self=0x806f228) at gmain.c:2677
#6  0xb776aeda in IA__g_main_loop_run (loop=0x80deb40) at gmain.c:2881
#7  0xb7bec1b3 in IA__gtk_main () at gtkmain.c:1155
#8  0xb7ea1e37 in main (argc=1, argv=0xbfa7d184) at hcp-main.c:64
#9  0x08048a8b in main (argc=2, argv=0xbfc15bb4) at summoner.c:45
#10 0xb7e667e5 in __libc_start_main () from /lib/libc.so.6
#11 0x08048791 in _start ()
(gdb) list
63      }
65      void
66      hello_world_dialog_show ()
67      {
68        GtkWidget *dialog = hello_world_dialog_new ();
69        gtk_dialog_run (dialog);
70        gtk_widget_destroy (dialog);
71      }
(gdb) c

The backtrace tells what functions were called before the breakpoint was reached at hello_world_dialog_show(). Now the plug-in can be debugged normally with gdb.

Because the hello world plug-in was compiled with the -g option, the source code listing can be viewed with the list command.

To do this same for desktop, the hildon-desktop process needs to be killed first. The desktop can be killed with the command:

[sbox-x86: ~] > kill $(pidof hildon-desktop)
# after this you could start the hildon-desktop under gdb like this:
[sbox-x86: ~] > run-standalone.sh gdb maemo-summoner
... snip ...
(gdb) run /usr/bin/hildon-desktop.launch
... snip ...

Image dialog-information N.B.

Doing this on the device would require first disabling the software lifeguard with the flasher tool. If this is not done, the device will reboot. The flag is:

14.2.5 Running Out of Memory During Debugging in Device

If running out of RAM memory during debugging in the device, there are a couple of options:

  1. Add (more) swap to the device using the Memory applet from the Control Panel.

    If there is enough memory, but gdb is still abruptly terminated, you can try setting it OOM-protected as root:

          /home/user # echo -17 > /proc/[PID of your gdb]/oom_adj

    By default, processes have OOM (i.e. Out-of-Memory) adjustment value of zero. The value -17 disables the kernel OOM killing for the given process. N.B. As a result of this, some other processes might be killed by the kernel.

  2. Use gdbserver to debug. Notes on Using Gdbserver

gdbserver is a debugging tool that can be started and run in the Internet Tablet device. Then a connection can be made to this running instance of gdbserver program from a Linux PC with a gdb program. Gdbserver uses a lot less memory than a full scale gdb program, thus making it possible to perform debugging in devices that have a limited RAM memory, such as PDAs.

The gdbserver does not care about symbols in the binary, but instead the Linux PC side gdb expects to have a local copy of the binary being debugged so that the binaries in the device can be stripped.

Image dialog-information N.B.

Debugging core files from the device in Scratchbox with gdbserver has the same issues. In practice, it is easier to perform the debugging in the device itself. See the section above about prelinked binaries and libraries.

For further information about using gdbserver, gdb and DDD, see:

14.2.6 Valgrind Debugger

Valgrind is a CPU simulator with different debugging and analyzing plug-ins. The Valgrind plug-ins are:

Image dialog-information N.B.

In the maemo environment, you can use the Valgrind debugger only in the Scratchbox X86 target.

Valgrind has many options, but only the basic ones are covered here with examples. The link to the full Valgrind manual is given at the end of this section. Installing Valgrind Tool

Installing Valgrind is simple. Log in on Scratchbox and run the following commands:

  1. Get Valgrind from the repository:

    [sbox-armel: ~] > sb-conf select x86
    [sbox-x86: ~] > apt-get install valgrind
    Setting up valgrind (3.3.0-1.osso1) ...
    [sbox-x86: ~] >

    Image dialog-information N.B.

    The maemo Valgrind version depends on the libc6-dbg. On the desktop Linux, some of the debug symbols are included in the libc6 library itself. If the debug symbols are missing from the libraries, Valgrind cannot match the error suppressions to the internal library functions. In the maemo libc6 case, it would show lots of errors for the dynamic linker.
    If using a non-maemo version of Valgrind, the following environment variable needs to be set before valgrinding programs using Glib:
    [sbox-x86: ~] > export \
    Without this, Valgrind will report bogus leaks from Glib.
  2. Get the two small example applications written in C language to demonstrate the basic usage of valgrind tool. You can download these from maemo.org: valgrind_example.tar.gz.

    [sbox-x86: ~] > mkdir src
    [sbox-x86: ~] > cd src
    [sbox-x86: ~/src] >

    After downloading, just copy the valgrind_example.tar.gz file to the ~/src/ directory and perform the following:

    [sbox-x86: ~/src] > tar xvzf valgrind_example.tar.gz
    [sbox-x86: ~/src] > cd valgrind_example
    [sbox-x86: ~/src/valgrind_example] >
  3. Compile the two small example applications in the following way:

    [sbox-x86: ~/src/valgrind_example] > gcc valgrind_example.c -o \
    valgrind_example -g 
    [sbox-x86: ~/src/valgrind_example] > gcc valgrind_example2.c -o \
    valgrind_example2 -g Using Valgrind Memory Debugger Tool

After compiling the small example application, it can be run under valgrind with the command:

[sbox-x86: ~/src/valgrind_example] > valgrind --tool=memcheck --leak-check=yes \
--show-reachable=yes --num-callers=20 --track-fds=yes ./valgrind_example

Explanation of the parameters and their meanings:

The output of the example application should look like:

==4493== Memcheck, a memory error detector.
==4493== Copyright (C) 2002-2007, and GNU GPL'd, by Julian Seward et al.
==4493== Using LibVEX rev 1732, a library for dynamic binary translation.
==4493== Copyright (C) 2004-2007, and GNU GPL'd, by OpenWorks LLP.
==4493== Using valgrind-3.2.3-Debian, a dynamic binary instrumentation framework.
==4493== Copyright (C) 2000-2007, and GNU GPL'd, by Julian Seward et al.
==4493== For more details, rerun with: -v
==4493== Conditional jump or move depends on uninitialised value(s)
==4493==    at 0x400A970: _dl_relocate_object (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x40033B3: dl_main (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4012C29: _dl_sysdep_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x400193F: _dl_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4000846: (within /targets/x86/lib/ld-2.5.so)
==4493== Conditional jump or move depends on uninitialised value(s)
==4493==    at 0x400A99C: _dl_relocate_object (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x40033B3: dl_main (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4012C29: _dl_sysdep_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x400193F: _dl_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4000846: (within /targets/x86/lib/ld-2.5.so)
==4493== Conditional jump or move depends on uninitialised value(s)
==4493==    at 0x400AFF3: _dl_relocate_object (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x40033B3: dl_main (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4012C29: _dl_sysdep_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x400193F: _dl_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4000846: (within /targets/x86/lib/ld-2.5.so)
==4493== Conditional jump or move depends on uninitialised value(s)
==4493==    at 0x400A825: _dl_relocate_object (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4003448: dl_main (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4012C29: _dl_sysdep_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x400193F: _dl_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4000846: (within /targets/x86/lib/ld-2.5.so)
==4493== Conditional jump or move depends on uninitialised value(s)
==4493==    at 0x400A86C: _dl_relocate_object (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4003448: dl_main (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4012C29: _dl_sysdep_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x400193F: _dl_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4000846: (within /targets/x86/lib/ld-2.5.so)
==4493== Conditional jump or move depends on uninitialised value(s)
==4493==    at 0x400A99C: _dl_relocate_object (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4003448: dl_main (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4012C29: _dl_sysdep_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x400193F: _dl_start (in /targets/x86/lib/ld-2.5.so)
==4493==    by 0x4000846: (within /targets/x86/lib/ld-2.5.so)
==4493== FILE DESCRIPTORS: 3 open at exit.
==4493== Open file descriptor 2: /dev/pts/2
==4493==    <inherited from parent>
==4493== Open file descriptor 1: /dev/pts/2
==4493==    <inherited from parent>
==4493== Open file descriptor 0: /dev/pts/2
==4493==    <inherited from parent>
==4493== ERROR SUMMARY: 11 errors from 6 contexts (suppressed: 0 from 0)
==4493== malloc/free: in use at exit: 40 bytes in 2 blocks.
==4493== malloc/free: 3 allocs, 1 frees, 60 bytes allocated.
==4493== For counts of detected errors, rerun with: -v
==4493== searching for pointers to 2 not-freed blocks.
==4493== checked 56,760 bytes.
==4493== 10 bytes in 1 blocks are definitely lost in loss record 1 of 2
==4493==    at 0x4020626: malloc (vg_replace_malloc.c:149)
==4493==    by 0x804841B: main (valgrind_example.c:26)
==4493== 30 bytes in 1 blocks are definitely lost in loss record 2 of 2
==4493==    at 0x4020626: malloc (vg_replace_malloc.c:149)
==4493==    by 0x8048482: main (valgrind_example.c:48)
==4493== LEAK SUMMARY:
==4493==    definitely lost: 40 bytes in 2 blocks.
==4493==      possibly lost: 0 bytes in 0 blocks.
==4493==    still reachable: 0 bytes in 0 blocks.
==4493==         suppressed: 0 bytes in 0 blocks.
[sbox-x86: ~/src/valgrind_example] >

The output of the Valgrind tells that there were 40 unallocated bytes for the application ("definitely lost"). This means that the example application is leaking memory, and cannot free it anymore. This means that the code should be studied closely.

Valgrind also tells the lines in the code where these allocations that are not freed are performed. In this example, the lines in question are 41 and 19. Official Valgrind Manual

Valgrind.org has an official Valgrind manual available in the Internet, explaining the many options and debugging practices that Valgrind can support. For full coverage of Valgrind see Valgrind User Manual [100].

14.2.7 Other Debugging Tools

The SDK provides a number of other tools that are useful in debugging. See the linked documentation pages to learn more about them.

Please also have a look at the tools main page Maemo SDK tools [73] for even more tools that could be useful for you.

14.3 Making a Debian Debug Package

Application developers should provide debug packages corresponding to their application packages. This section shows how to do that.

Debian debug packages contain debug symbol files that debuggers (like gdb) will automatically load when the application is debugged.

On ARM environment, the debugger cannot do backtracing or show correct function names without debugging symbols making it thus impossible to debug optimized binaries or libraries. All libraries in the device are optimized.

In X86 target, debugging can be done without debug symbols.

If the package maintainer provides no debug package, then the other developers in the community need to spend extra time and effort to recompile the application (or the library) with the debugging symbols. This extra (time-consuming) step can be simply eliminated by the package maintainer by providing a ready compiled debug package.

This section covers creating a Debian debug package from the
maemo/Scratchbox point of view.

It is the package maintainers role and decision to create and provide a debug package for their application or library. This means that you as the package owner are responsible to modify the debian package configurations, so that the dpkg-buildpackage tool will produce the additional dbg-package.

If you are a maintainer of a library or binary package, it is strongly recommended to create a corresponding debug package. This is needed by anybody wanting to either debug or profile your software or something using it.

14.3.1 Creating DBG Packages

Steps to create a debian DBG package are:

  1. Clean up any previous dbg configurations from your package

    If your package already provides the debugging symbols the "hard, old way" then you should clean these configurations first.

    If you use dh_strip --dbg-package option in debian/rules file, then it is not necessary to build or copy anything to the -dbg package build directory anymore. Check your packages debian/rules file and remove all lines that have statements to create dbg packages.

    If you have any files named debian/*-dbg.* then just remove these files. These were required with the old way to use dh_strip.

    The following steps are the only ones needed to create the debug packages with newer versions of dh_strip.

    After you have cleaned up any previous dbg configurations from your debian files move to the next step.

  2. Define DBG package(s)

    For every package listed in your debian/control file that contains libraries or binaries, you need to add corresponding <package>-dbg entry. If you have debian/control.in then modify that instead.

    Make the debug package(s) to depend from the corresponding binary/library package. Here is an example:

    . other package definitions above
    Package: libgtk2.0-0-dbg
    Section: libdevel
    Architecture: any
    Depends: libgtk2.0-0 (= ${binary-Version})
    Description: Debug symbols for the Gtk library

    Image dialog-information N.B.

    If the package contains binaries instead of libraries, the Section should be devel. N.B. The new -dbg package may have a different name from the old style debug package (for example libgtk2.0-0-dbg, not libgtk2.0-dbg). If there are earlier (old style) debug packages in the repositories the new debug package should replace/conflict with the old one.
  3. Add option -g to CFLAGS

    Make sure you have set option -g in CFLAGS in the debian/rules file, and that this option is effective and always enabled. Otherwise the debug package will not contain the required debug symbols.

    For example, use a line like this for CFLAGS

    CFLAGS = -Wall -g
  4. Use dh_strip

    You can either provide all debugging information for your package, or just a minimal debugging information required to debug something else using your library.

    You want to select the latter option only if you want to reveal as little of your code as possible (for example) for contract reasons.

    1. Providing all debug information in your dbg package.

      Debian/compat levels smaller than 3 should not be used (1 is default!). If your package sets debian/compat level below 5, give the following arguments to dh_strip in debian/rules file:

      dh_strip --dbg-package=<package1> [--dbg-package=<package2> ...]

      For example:

      dh_strip --dbg-package=libgtk2.0-0

      If compat level is 5 or higher, use syntax:

      dh_strip --dbg-package=<package1>-dbg [--dbg-package=<package2>-dbg ...]

      For example:

      dh_strip --dbg-package=libgtk2.0-0-dbg

      If you're using cdbs instead of debhelper (i.e. dh_* commands) in your debian/rules file, use this instead:

      DEB_DH_STRIP_ARGS := <dh_strip arguments>

      For example (for compat levels below 5):

      DEB_DH_STRIP_ARGS := --dbg-package=<package1> ...

    2. Providing just minimal debug information

      In case you do not want to reveal all information about your binary (e.g. for contract reasons), you can provide a debug symbol file just with the .debug_frame section (which is the minimal information needed by gdb to show working backtraces in ARM environment). In addition to information provided by the binary file, it will reveal only static function names and the number of function arguments.

      To do this, replace the above dh_strip line in debian/rules file binary-arch target with:

      chmod +x $(shell pwd)/debian/wrapper
      export PATH=$(shell pwd)/debian/wrapper:$$PATH; \
      dh_strip  --dbg-package=<package1> [--dbg-package=<package2> ...]

      Notice that the wrapper script is set executable because the dpkg-source does not preserve the exec permissions.

      Store the following wrapper script as debian/wrapper/objcopy:

      case " $* " in
        *" --only-keep-debug "*)
          exec /usr/bin/objcopy -R .debug_info -R .debug_aranges \
               -R .debug_pubnames -R .debug_abbrev -R .debug_line \
               -R .debug_str -R .debug_ranges -R .comment -R .note "$@"
      exec /usr/bin/objcopy "$@"

      With this dh_strip will use objcopy through this wrapper (i.e. remove the other debug sections).

  5. Verify the package(s)

    Update the Debian changelog with dch -i and build the package with dpkg-buildpackage -rfakeroot. This will create new Debian source package (dsc + diff) and binary package(s) which you can install on the target for additional testing.

See also dh_strip (1) and debhelper (7) manual pages for details about the helper scripts.

Image dialog-information N.B.

If the package has any function(s) that have the noreturn GCC attribute, you need to make sure that the object(s) containing those are compiled with -fno-omit-frame-pointer (or remove the noreturn attribute). This is needed for backtraces containing them to be debuggable when the binaries are optimized, the debug symbols are not enough for them. By default GCC omits frame pointer when code is optimized.

14.3.2 Using and Installing DBG Packages

The debug packages are easy to use, just apt-get install them and on target gdb will load the new style debug symbol files (installed to subdirectories under /usr/lib/debug/) automatically.

Inside Scratchbox, debuggers and profilers will search for the debug symbol files under scratchbox target directory under /usr/lib/debug, so a target directory needs to be linked under it.

mkdir /usr/lib/debug
cd /usr/lib/debug
mkdir targets
ln -s /usr/lib/debug \
 targets/$(sh -c '. /targets/links/scratchbox.config;echo $SBOX_TARGET_NAME')

The reason for this is that realpath on libraries and binaries inside Scratchbox returns /scratchbox/targets/.../usr/lib/... instead of just normal /usr/lib/....

Installing the maemo-debug-scripts package does this link automatically.

And for thread debugging to work, you need to install libc6-dbg package and gdb package, the Scratchbox provided host gdb doesn't work with threads (or ARM core dumps). To use the native gdb in Scratchbox, you need to start gdb the following way:

SBOX_REDIRECT_IGNORE=/usr/bin/gdb /usr/bin/gdb /usr/bin/my-binary

maemo-debug-scripts package provides native-gdb script for this.

For gdb to find old style debug symbol files (installed directly into /usr/lib/debug/) you need to use LD_LIBRARY_PATH or load them manually in gdb.

Files in these old style debug symbol files contain both the binary and debug symbol sections, so they are also larger than the new style debug symbols that dh_strip instructions above will create.

14.3.3 For Further Reading

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