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
where
Attaching to another process
gdb
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
-N - Treat absent files as empty.
-a - treat all files as text
-u - Unified diff:
-r - recursive
How to exclude:
-X
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 iff -u
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.
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