[This piece is co-authored with Vsevolod Livinskii.] Formal verification isn’t some sort of magic pixie dust that we sprinkle over a computer system to make it better. Real formal verification involves a lot of the same kind of difficult, nasty, grungy engineering work that any other systems-level job involves. Furthermore, the verification tools themselves are…

Compilers can be improved over time, but this is a slow process. “Proebsting’s Law” is an old joke which suggested that advances in compiler optimization will double the speed of a computation every 18 years — but if anything this is optimistic. Slow compiler evolution is never a good thing, but this is particularly problematic…

In its original form, a peephole optimization applied to a collection of instructions located close together in a program. For example, in a register transfer language we might find this sequence of instructions: r0 = xor r8, -1 r1 = xor r9, -1 r0 = and r0, r1 Here, assuming the two’s complement representation, -1…

[This piece is coauthored by Yuyou Fan and John Regehr] Mutation-based fuzzing is based on the idea that new, bug-triggering inputs can often be created by randomly modifying existing, non-bug-triggering inputs. For example, if we wanted to find bugs in a PDF reader, we could grab a bunch of PDF files off the web, mutate…

The spinlock is the most basic mutual exclusion primitive provided by a multiprocessor operating system. Spinlocks need to protect against preemption on the current CPU (typically by disabling interrupts, but we’ll ignore that aspect in this post) and also against attempts by other cores to concurrently access the critical section (by using atomic memory operations).…

Test-case reduction is more or less a necessity when debugging failures of complex programs such as compilers. Automated test-case reduction is useful not only because it allows developers to avoid wasting time reducing inputs by hand, but also because it supports new techniques such as automatically triaging bulk failures seen in the field or during…

People tend to be visual: we use pictures to understand problems. Mainstream programming languages, on the other hand, operate in an almost completely different kind of abstract space, leaving a big gap between programs and pictures. This piece is about pictures drawn using a text character set and then embedded in source code. I love…