Detecting strict aliasing violations in the wild

Abstract

Type-based alias analyses allow C compilers to infer that memory locations of distinct types do not alias. Idiomatic reliance on pointers on the one hand, and separate compilation on the other hand, together make it impossible to get this aliasing information any other way. As a consequence, most modern optimizing C compilers implement some sort of type-based alias analysis. Unfortunately, pointer conversions, another pervasive idiom to achieve code reuse in C, can interact badly with type-based alias analyses. This article investigate the fine line between the allowable uses of low-level constructs (pointer conversions, unions) that should never cause the predictions of a standard-compliant type-based alias analysis to be wrong, and the dangerous uses that can result in bugs in the generated binary. A sound and precise analyzer for “strict aliasing” violations is briefly described.