Category: Computer Science

  • The Real Problem with the US News Rankings

    The latest list of Best Global Universities for Computer Science from US News has not been well received. For example, the Computing Research Association issued a statement saying that “Anyone with knowledge of CS research will see these rankings for what they are – nonsense – and ignore them. But others may be seriously misled.” […]

  • The Dreaded Practice Talk

    [I wrote a post with the same title in 2010; this is an updated version.] In a week you’ll be giving a talk about your work to 600 people at a conference, or perhaps to five people who will sign off (or not) on your thesis. Depending on your area and the type of talk, […]

  • Undefined Behavior in 2017

    This post is jointly authored by Pascal Cuoq and John Regehr. Recently we’ve heard a few people imply that problems stemming from undefined behaviors (UB) in C and C++ are largely solved due to ubiquitous availability of dynamic checking tools such as ASan, UBSan, MSan, and TSan. We are here to state the obvious — […]

  • Pointer Overflow Checking is in LLVM

    Production-grade memory safety for legacy C and C++ code has proven to be a frustratingly elusive goal: plenty of research solutions exist but none of them appear to be deployable as-is. So instead, we have a patchwork of partial solutions such as CFI, ASLR, stack canaries, hardened allocators, and NX. Today’s quick post is about […]

  • Compiler Optimizations are Awesome

    This piece, which I hadn’t gotten around to writing until now since I thought it was all pretty obvious, explains why Daniel J. Bernstein’s talk, The death of optimizing compilers (audio) is wrong, and in fact compiler optimizations are extremely wonderful and aren’t going anywhere. First, the thesis of the talk is that almost all […]

  • Translation Validation of Bounded Exhaustive Test Cases

    This piece is jointly authored by Nuno Lopes and John Regehr. Compilers should be correct, but it is not straightforward to formally verify a production-quality compiler implementation. It is just too difficult to recover the high-level algorithms by looking at an enormous mess of arithmetic, loops, and memory side effects. One solution is to write […]

  • Taming Undefined Behavior in LLVM

    Earlier I wrote that Undefined Behavior != Unsafe Programming, a piece intended to convince you that there’s nothing inherently wrong with undefined behavior as long as it isn’t in developer-facing parts of the system. Today I want to talk about a new paper about undefined behavior in LLVM that’s going to be presented in June […]

  • Fun at the UNIX Terminal Part 1

    This post is aimed at kids, like the 6th graders who I was recently teaching about programming in Python. It is more about having fun than about learning, but I hope that if you enjoy playing around at the UNIX terminal, you’ll eventually learn to use this kind of system for real. Keep in mind […]

  • Do Expressive Programming Languages Always Have Undefined Behavior?

    In the Hacker News comments on one of my previous posts about undefined behavior, someone said this: AFAIK Gödel’s incompleteness theorems imply that _any_ language will have at least some undefined behaviour. Let’s take a quick look at this statement, keeping in mind that incompleteness and undecidability can be remarkably tricky topics. Some years ago […]

  • Mapping Mountains on Exoplanets

    Snow in the mountains evolves in predictable ways that are strongly influenced by the terrain. For example, warmish snowstorms leave a characteristic snow line that looks very much like a contour on a topographic map: (source) (source) On the other hand, when snow melts the effect is very different, and is often dominated by aspect. […]