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