Debugging session and effective bug reporting session notes.

Software debugging & effective bug reprting

Bug reporting,

• How to report an annoying feature and/or requesting a new feature in an application.
  • BE NICE!
  • Talking to the developer and/or explaining why this feature is annoying or why this missing feature is important is a big plus "When I explained why the libwxgtk should be compiled with unicode/gtk2 support is important for Arabic language, The package maintainer got interested".

Debugging

• What is debugging, What's a debugger ?
• The GNU debugger "gdb"
• Compiling applications with debugging symbols.

  -ggdb

  • Removing the debugging symbols

     "strip -S" 

    • Obtaining a meaningful back trace.
      • What's a back trace ?

    A list of steps by the application or a list of function calls lead to this situation.

    • What is a core file ? What's a core dump ?

    Simply the memory of the application is being dumped to a file!

    • Getting a useful back trace:
      • we must compile with debugging symbols

        -ggdb

        • from a core file

          gdb <application> <core file>
          where
          

          • Attaching to another process

            gdb <application> <pid>
            where
            

            This is useful if the application is started via a script as openoffice and mozilla.

            • Directly from gdb

              gdb foo
              set args bar zot
              r
              "When the crash happens: go back to the terminal, You might need to press C-C"
              where
              quit
              

              • How to set break points.

                break file.c:#

                Diffs and patches

                * How to generate a unified diff:

                diff -Naur <orig> <modified>
                -N - Treat absent files as empty.
                -a - treat all files as text
                -u - Unified diff:
                -r - recursive
                

                • How to exclude:

                    -X <file>
                  

                  • How to apply a patch:

                    patch --dry-run -p# < patch
                    --dry-run: Don't really modify files.
                    -p#: strip # leading slashes from the files.
                    

                    • How to remove "unapply" a patch:

                      patch -R
                      -R: Reverse.
                      

                      CVS:

                      • Using my CVS server as an example.
                      • How to login.

                        cvs -d:pserver:anonymous@uniball.dyndns.org:/var/lib/cvs login
                        export CVSROOT=":pserver:anonymous@uniball.dyndns.org:/var/lib/cvs"
                        cvs login
                        

                        • How to checkout.

                          cvs -d:pserver:anonymous@uniball.dyndns.org:/var/lib/cvs co projects/illigal
                          or
                          export CVSROOT=":pserver:anonymous@uniball.dyndns.org:/var/lib/cvs"
                          cvs -z3 co projects/illigal
                          

                          • How to update.

                            cvs -z3 update
                            

                            • How to request a diff

                              cvs diff -u or cvs diff -u <file>
                              

                              Demonstration of some crashes using my "illigal operation" application

                              • 1: Integer by zero (Random value) - Our code crashed.
                              • 6: strcpy crash! (Copy to a NULL pointer) - here our application caused an external function to crash.

                              Bugzilla:

                              • Bugzilla is one of the most widely spreaded bug tracking systems.
                              • Registration:
                              • Submitting a bug:
                                • Gnome bugzilla: http://bugzilla.gnome.org
                                • Mozilla bugzilla: http://bugzilla.mozilla.org
                                • KDE bug tracking system: http://bugs.kde.org
                                • OpenOffice IssueZilla.
                              • We might have a wizard.
                              • We might have the old complicated method.
                              • Severety "If found": The effect of the bug on the user.
                                • Blocker: Non usable application.
                                • Critical: Crashes, causes loss of data, or is a severe memory leak.
                                • Major: Major loss of functionality
                              • Priority "If found": The importance of the bug
                                • Immediate: Can't test or use the application or it's a security issue.
                                • Urgent: I can't use an important features of the application because of it.
                                • High: Something is broken but the application is still usable.
                              • We have more bug tracking systems like gnats and the debian bug tracking system.

                              strace & ltrace: trace system calls, signals & library calls

                              Notes about interacting with the developers:

                              • Generally be nice and remember that the guy is a volunteer.
                              • Generally don't hijack a thread to include your patch, The patch is a trivial thing, This means that you attach it to the same thread if related, Otherwise start a new thread.
                              • Most people prefere the unified diff format.
                              • Try to stick to the coding standard used by the developer, This is not that important unless you are emailing a kernel patch ;-)
                              • Don't feel angry if the developer tell you that the software is under the GPL and you can do whatever you can.
                              • When reporting a bug, Report either a reproducable bug or the exact steps you followed with a backtrace if you can't reproduce it.

                              Links:

                              • Capturing Stack Traces http://bugzilla.gnome.org/getting-traces.cgi
                              • Emacs!: http://www.emacswiki.org ;-)
                              • GDB, The GNU Debugger: http://www.gnu.org/software/gdb/gdb.html
                              • Unified diff format and example: http://www.gnu.org/software/diffutils/manual/html_node/Detailed-Unified.html