It’s time for another progress report. The last post covered the phases at a high level – please read that first for an overview.
Observing paths To observe paths we associate a bitset with each function, where each bit corresponds to a path. Which bit maps to which path is simply its index in the lexicographically sorted set of paths. When an edge is taken, the a mask is applied to the bitset so the paths not taken are masked out: accu[block] = accu[pred] & paths[block].
After the success of getting MC/DC support into gcc, NASA decided to keep funding the project and focus on (prime) path coverage. I have been working on this problem for a while now and it is about time to write a post on the progress so far.
Prime paths The number of paths in a program grows very fast. Somewhat simplified, a path is a sequence of blocks evaluated for a run.
I have to admit, it feels quite nice to finally write this post. My support for MC/DC in gcc was merged April 4th, followed by a couple of bug fixes. This post is just an announcement - I plan to some time later write a more detailed post on how it works and how to use it, and maybe one on MC/DC itself.
It has been a long project. I started working on it around the start of 2022, so it took a bit more than two calendar years from starting the work to the feature being merged, with mixed activity.