Archive for November, 2006

Session-wide valgrind

Now that we know that even Evolution runs under Valgrind, we need a bigger challenge. So, how about the entire GNOME session?

I’ve written a couple of tiny scripts that lower the threshold to doing this. They take care of properly launching your session in Valgrind, collecting (and filtering slightly) the resulting logs and cleaning up (important, since you can get lots of lingering valgrind processes if you don’t).

I made an OpenSuSE package (for the 10.2 beta, possibly 10.1) that integrates this functionality as a pair of standard GDM sessions that you can select on login. Just click “Session” in the login screen and select one of the GNOME Valgrind ones, then log in using that. When you log out, it’ll generate a log file in “$HOME/valgrind-session.$N”.

The generated reports from a typical session say something about our code quality. Especially the leak report is interesting - the log file, after everything but “definite leaks” (i.e. allocated blocks to which no pointers exist, neither to the beginning nor to an internal offset) is removed, is about 2MB for a login + immediate logout here. Even though there are many repetitions and fairly harmless leaks, there are some serious-looking ones in there:

[~] grep “definitely” valgrind-session.0 | wc -l

Just install and restart GDM. At least one billion bytes of RAM recommended to run.

Not everything works in an instrumented session (su, sudo definitely don’t, and I’ve had problems with “recent items” and logging out using the slab - remedied by adding a logout button to your panel), but overall it’s not bad. You can browse the web, read mail, use Nautilus, customize your desktop, launch applications (which will themselves be instrumented) etc.

If you like proactive bug fixing (and have fairly powerful hardware), I encourage you to check it out and maybe even improve on the concept (there’s a lot that could be done).

El Laberinto del Fauno

Yesterday, Maru and I saw El Laberinto del Fauno at the cinema. Highly recommended. Although the movie has fantasy elements and the main character is a child, I would say it’s definitely not for children. I.e. it’s not in the “Harry Potter” category which can be enjoyed by both children and adults. This is for adults only, and it contains plenty of graphic violence to underscore that fact.

I won’t say any more. If you - unlike IMDB trolls - can come to terms with it a) not being in English and b) being “leftist-liberal” for portraying fascists as, er, fascists, go see it.

Write your own Valgrind tool

The Building Workload Characterization Tools with Valgrind talk slides, published just a couple of days ago, make it look easy.

Evolution is da logic bomb

You know the story. Random crashes preventing you from reading your mail all morning. This time, though, there’s a twist (and a moral).

The twist is that instead of complaining on IRC - ok, I mean in addition to complaining on IRC - I actually ran the crashy bugger through valgrind, much like you would run a zombie head through a blender. Sifting through the resulting goop provided me with enough information to file patches for buffer overrun 1, buffer overrun 2 and bug of the theoretical variety. All three bugs have been around for a really long time (several years).

As for the moral:

1) Valgrind works extremely well these days, even on large and complex programs like Evolution. It is nothing short of a masterpiece. It did not interfere with operation apart from the expected slowdown, and pinpointed the bug I was looking for (and then some) in a matter of minutes. It is highly recommended that programs be valground regularly with a “typical use” regimen, even if they appear to work fine. At the very least, this should be on all maintainers’ pre-release checklists.

2) If you’re a programmer, and a particular program is misbehaving for you, take the time to actually look for the bug. Valgrind makes it easy, and you’ll find trivial bugs even in large and complex programs. So there’s no reason to be intimidated. Even if you can’t immediately say what’s causing the problem, valgrind logs make for valuable bugzilla attachments.

3) Valgrind’s performance isn’t too bad, but it’s still the best excuse today for getting a faster computer. Start using it so you can justify the expense.

4) With a little time investment, Evolution is totally salvageable. If you were thinking of giving up on it, don’t. Version 2.8 has a tri-pane mail view and global search, making it an awesome mailer.