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The original ANSI C standard, C89, introduced the concept of “undefined behavior,” which was used both to describe the effect of outright bugs like accessing memory in a freed object and also to capture the fact that existing implementations differed about handling certain aspects of the language, including use of…
My last post described how user-level CPU profilers work, and specifically how Google’s pprof profiler gathers its CPU profiles with the help of the operating system. The specific feature needed from the operating system is the profiling timer provided by setitimer (2) and the SIGPROF signals that it delivers.
A decision that arises over and over when designing concurrent programs is whether to represent program state in control flow or as data. This post is about what that decision means and how to approach it. Done well, taking program state stored in data and storing it instead in control flow can make programs much…
This is the story of a clever trick that's been around for at least 35 years, in which array values can be left uninitialized and then read during normal operations, yet the code behaves correctly no matter what garbage is sitting in the array. Like the best programming tricks, this one is the right tool for the job…
[ I wrote this post in mid-2014 for debuggers.co, which seems to have gone at least partly defunct, so I am reproducing it here. That site collected answers from programmers to the prompt “What’s the most interesting bug you’ve encountered?” ]
A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room…