Point UBSan at your existing test suite

I have a bit of an obsession with undefined behaviour in C, and this year, some time on my hands due to paternity leave. So I spent a stretch of it finding easy bugs in mature C codebases — CPython, glibc, the Linux kernel. The method takes much less cleverness than the results suggest: build the project with sanitisers turned on, and run the test suite it already has. That really is all of it. No…