A Conversation about Teaching Software Engineering

For better or worse, my impressions of software engineering as a field were shaped by a course I took as an undergrad that I thought was mostly not very interesting or useful. We spent a lot of time on waterfalls and stuff, while not covering testing in any detail. For the final project in the […]

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 […]

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 […]

Undefined Behavior != Unsafe Programming

Undefined behavior (UB) in C and C++ is a clear and present danger to developers, especially when they are writing code that will execute near a trust boundary. A less well-known kind of undefined behavior exists in the intermediate representation (IR) for most optimizing, ahead-of-time compilers. For example, LLVM IR has undef and poison in […]

Detecting Strict Aliasing Violations in the Wild

Type-based alias analysis, where pointers to different types are assumed to point to distinct objects, gives compilers a simple and effective way to disambiguate memory references in order to generate better code. Unfortunately, C and C++ make it easy for programmers to violate the assumptions upon which type-based alias analysis is built. “Strict aliasing” refers […]

Principles for Undefined Behavior in Programming Language Design

I’ve had a post with this title on the back burner for years but I was never quite convinced that it would say anything I haven’t said before. Last night I watched Chandler Carruth’s talk about undefined behavior at CppCon 2016 and it is good material and he says it better than I think I […]