Coccinelle: The Linux kernel's source-to-source transformation tool

The best thing Julia Lawall ever did!

Not the hardest, not the thing with the most sophisticated theories behind it, not the thing that helped her academic career the most... but definitely the best and the most useful.

There must be a lot of other academics who could do things that are less theoretical but more useful than what they normally do.

There must be a lot of undervalued academics who in effect are punished for doing things that useful without requiring quite as much deep theory as their fields can muster.

I'm glad she did something that she wasn't really rewarded for and I'm sad that the academic reward functions are so off.

Not the same level of sophistication, but ast-grep allows this for far more languages, since it is based on the tree-sitter parser library. I have used it with some success on C++. Of course it only works on the AST level, and C++ famously need types for correct parsing, so it sometimes fall short (also on macros).

https://ast-grep.github.io/

I think Coccinelle is a really cool tool, but I find its documentation totally incomprehensible for some reason. I've read through it multiple times, but I always end up having to find some preexisting script that does what I want, or else to blunder around trying different variations at random until something works, which is frustrating.

It's a bit of a disservice to call it "The Linux kernel's"; it's its own project that just happens to be used on the Linux kernel quite a bit. It doesn't originate there or belong to the kernel or anything like that.

According to https://coccinelle.gitlabpages.inria.fr/website/ce.html :

> Nevertheless, detecting the holding of locks requires a careful and occasionally interprocedural analysis of the source code, and the other conditions, such as "in a completion handler", are not formally defined and require study of multiple files.

> Due to the complexity of the conditions governing the choice of new argument for usb_submit_urb, 71 of the 158 calls to this function were initially transformed incorrectly to use GFP_KERNEL instead of GFP_ATOMIC.

Okay, but how does Coccinelle help? Is it able to do this careful and not formally defined analysis? Or does it automate the undifferentiated heavy lifting and so make it easier for humans to do it?

I forgot about Coccinelle.

I think semantic patching is an idea whose time has come though. I'm making a more modern set of tools for source-to-source transformation that will work with any desired languages as the input and output.

See also OpenRewrite:

https://github.com/openrewrite/rewrite

And i assume any large organisation running a monorepo has some vaguely equivalent tooling for making mass changes. Have any of them published about that?

coccinelle's one of those tools that's stupid powerful once it clicks, but man the learning curve is steep. i used it to migrate like ~200 call sites when we tweaked an internal API signature in a big C codebase - doing that by hand wouldve been a multi-day slog. the semantic patch language feels kinda weird at first, but it catches edge cases regex stuff just misses, like matching through macro expansions and all that

I thought this was a misspelled article about Kokinelli, the Greek red wine, fairly accurately described here: https://www.arrse.co.uk/wiki/Kokinelli

I used to drink this stuff back in the late 1960s, when my Dad was an RAF pilot based in Cyprus and I was about 15. You had to take it with a Sprite mixer if you wanted to retain your teeth.

It would be a good name for a project, though.