Safe Pointers in SPARK 2014
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In the context of deductive software verification, programs with pointers present a major challenge due to pointer aliasing. In this paper, we introduce pointers to SPARK, a well-defined subset of the Ada language, intended for formal verification of mission-critical software. Our solution is based on static alias analysis inspired by Rust's borrow-checker and affine types, and enforces the Concurrent Read, Exclusive Write principle. This analysis has been implemented in the GNAT Ada compiler and tested against a number of challenging examples including parts of real-life applications. Our tests show that only minor changes in the source code are required to fit the idiomatic Ada code into SPARK extended with pointers, which is a significant improvement upon the previous state of the art. The proposed extension has been approved by the Language Design Committee for SPARK for inclusion in a future version of SPARK, and is being discussed by the Ada Rapporteur Group for inclusion in the next version of Ada. In the report, we give a formal presentation of the analysis rules for a miniature version of SPARK and prove their soundness. We discuss the implementation and the case studies, and compare our solution with Rust.
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