Anatomy of a graphics driver bug

 debugging, x-plane

X-Plane's plugin systems allows authors to load models in two ways: Asynchronously and Synchronously. Most plugins tend to use synchronous loading, but since all plugins run on the main thread there is a need and desire for some to use asynchronous loading. Up until now, the latter was broken however, and plugin authors complained about invisible models. From what I understand Pilot Edge were the first to complain, but they want to use async loading to dynamically load in models of planes that flew in via multiplayer, which makes it non-trivial to debug. Luckily, the author of the fantastic Better Pushback also ran into the issue and his plugin is completely local, so it's no problem to stop at a

Investigating a X-Plane plugin's crash to desktop

 debugging, x-plane

This post is about a crash to desktop that I investigated in a popular plugin for X-Plane, X-Assign. This happened in my free time, although I had the advantage of having the X-Plane source code at hand. Git bisect My new favourite tool on earth is git bisect, which I used to find the offending commit rather quickly. At this point I wasn't sure who was at fault for the crash, X-Plane or X-Assign, since the issue only showed up with the update to X-Plane 11.02 and it was working fine in previous versions. The offending commit however turned out to be rather boring, it simply changed the capacity of a couple of datarefs from 100 to 250. Two

Firedrake memory corruption bug

 programming, firedrake, debugging

There was a bug that I couldn’t figure out for the life of me. It was somewhere deep in my hobby kernel Firedrake and it made zero sense. It manifests as memory corruption, more specifically, at some point a pointer suddenly becomes zero. I tried to narrow it down with printf() debugging, but that didn’t get me very far because at that point the scheduler is already running and regular task switches occur, which have the side effect of the kernel not running in consecutive order any longer. Luckily, QEMU, my go to emulator, has support for GDB. The easy solution is therefore to fire up GDB, attach it to the remote debugger exposed by QEMU and set