Static analysis – the automatic determination of simple properties of a program – is the basis both for optimizing compilation and for verification of safety properties such as absence of run-time errors. To support the use of static analyses in verified compilers and in high-confidence verification environments, the analyses must be proved to be sound. In this invited talk, I will review some ongoing work in this direction in the CompCert and Verasco projects, in particular the construction and formal verification of a modular static analyzer based on abstract interpretation.