A few days ago I created CFGBot - a small Bluesky bot that publishes hourly control-flow-graphs.
While technically simple, this bot is something I wanted to create for a few years now. Originally, I wanted to write one that publishes IDA Pro graphs of random functions in system binaries. But due to logistical issues (how to run a bot that uses software I’m only allowed to run on my own PC) and my concerns about copyright (can I freely post the disassembly of copyrighted software?) I never quite got around to it.
Despite those roadblocks, I kept wanting to share the visual wonder of control-flow-graphs with the world.
And a few days ago it dawned on me that now, after writing my control-flow-graph generator, I can finally make this happen. So I glued some pieces together, and here we are.
A bit of internals
The core of the bot is the function-graph-overview project, used to generate the graphs themselves. To choose what function to show every hour - I pre-process a corpus of source-code (currently - CPython’s implementation and standard library, but more to come soon!) to get an index of all the functions in it.
The index contains basic information:
- Location of the function (filepath, location in the file)
- Number of CFG nodes
- The function definition (this accounts for overloads and anonymous functions better than function names)
Then, on every run, I randomly select a function, biased slightly towards higher node-counts, as those are more interesting.
I then render this function to a PNG image, and post to Bluesky.
High-res images
The whole part described above was achieved rather easily (once I had the pieces!) using a bit of Python (to run the scripts and post to Bluesky) and Github-Actions (to “host” the bot and run it hourly). But there is a problem - Bluesky only supports relatively small images. And control-flow-graphs, especially the cool-looking ones, tend to be very large.
To resolve this, I added the /render/ page to function-graph-overview.
It takes a GitHub URL (one that includes a line number) as an argument, and renders the SVG in the browser (this way I don’t need hosting for those images!).
I added basic panning and zooming to make it a tad more useful, and an option to download the SVG. Thus solving the fidelity issue with relative ease.