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Undefined Integer Behaviors in Student Code, Part 1
[This post is based on material from Chad Brubaker, a really smart CS undergrad at Utah who did all the work getting these data. The integer undefined behavior checker was created by my student Peng Li.] Integer undefined behaviors in C/C++, such as INT_MAX+1 or 1<<-1, create interesting opportunities for compiler optimizations and they also…
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Should Software Evolve?
Weimer, Nguyen, Le Goues, and Forrest wrote a paper Automatically Finding Patches Using Genetic Programming that proposes and evaluates this approach for fixing a buggy software system: A failure-inducing test case is found The system code is mutated randomly, but using smart heuristics to increase the probability that the part of the program that is…
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Random Testing Gets No Respect
A funny thing about random testing is that it gets little respect from most computer scientists. Here’s why: Random testing is simple, and peer reviewers hate simple solutions. Random testing does not lend itself to formalization and proofs, which peer reviewers love. Random testing provides no guarantees. Peer reviewers love guarantees — regardless of whether…
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Two Rules for Random Testing
When you run a test case on a piece of software, you’re conducting an experiment where the null hypothesis is “the system under test correctly executes this test.” The problem is that the value of each such experiment is small because there are so many possible inputs. Random testing has a stronger null hypothesis: “the…
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Probabilities in Random Testing
A typical real computer system has an extremely large input space and no testing method can cover more than an infinitesimal part of it. On the other hand, broad regions of the input space will trigger bugs. The problem is that we do not know the shapes or locations of the buggy parts of the…
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Outgunned
Several years ago I published my favorite kind of paper: it took a problem that was hard to solve by hand, and solved it using 20% cleverness and 80% brute force. The details don’t matter here, but the solution had scalability problems. Therefore, the next iteration of the work (done primarily by a very smart…
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The Day I Learned To Love Perl
Following my second year of grad school, I spent the summer of 1997 as an intern for Myricom, a company in the L.A. area that makes really fast local-area networks. It was a great place to work: small, and filled with super-smart ex-Caltech people. One day I was hacking while the important people were in…
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Cryptocontributions, Blogs, and How Science Works
Most people — including many scientists — understand the process of science to be repeated application of the scientific method. In this model, a hypothesis is formulated, experiments are conducted to test the hypothesis, data is analyzed, and the results usually lead to a new hypothesis. This adequately captures the “99% perspiration” aspect of doing…
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Csmith @ PLDI
My group’s paper Finding and Understanding Bugs in C Compilers was accepted to PLDI 2011 (subject to shepherding, which is generally a pretty calm process). I’m excited about this since we’ve put a lot of effort into this project. Thanks to all the people who helped us make this work better!