We offer a solution to the type inference problem for an extension of Hindley and Milner's type system with generalized algebraic data types. Our approach is in two strata. The bottom stratum is a core language that marries type inference in the style of Hindley and Milner with type checking for generalized algebraic data types. This results in an extremely simple specification, where case constructs must carry an explicit type annotation and type conversions must be made explicit. The top stratum consists of (two variants of) an independent shape inference algorithm. This algorithm accepts a source term that contains some explicit type information, propagates this information in a local, predictable way, and produces a new source term that carries more explicit type information. It can be viewed as a preprocessor that helps produce some of the type annotations required by the bottom stratum. It is proven sound in the sense that it never inserts annotations that could contradict the type derivation that the programmer has in mind.
We present a so-called labelling method to enrich a compiler in order to turn it into a "cost annotating compiler", that is, a compiler which can lift pieces of information on the execution cost of the object code as cost annotations on the source code. These cost annotations characterize the execution costs of code fragments of constant complexity. The first contribution of this paper is a proof methodology that extends standard simulation proofs of compiler correctness to ensure that the cost annotations on the source code are sound and precise with respect to an execution cost model of the object code. As a second contribution, we demonstrate that our label-based instrumentation is scalable because it consists in a modular extension of the compilation chain. To that end, we report our successful experience in implementing and testing the labelling approach on top of a prototype compiler written in ocaml for (a large fragment of) the C language. As a third and last contribution, we provide evidence for the usability of the generated cost annotations as a mean to reason on the concrete complexity of programs written in C. For this purpose, we present a Frama-C plugin that uses our cost annotating compiler to automatically infer trustworthy logic assertions about the concrete worst case execution cost of programs written in a fragment of the C language. These logic assertions are synthetic in the sense that they characterize the cost of executing the entire program, not only constant-time fragments. (These bounds may depend on the size of the input data.) We report our experimentations on some C programs, especially programs generated by a compiler for the synchronous programming language Lustre used in critical embedded software.
Modern computing systems have grown in complexity, and the attack surface has increased accordingly. Even though system components are generally carefully designed and even verified by different groups of people, the composition of these components is often regarded with less attention. This paves the way for "architectural attacks", a class of security vulnerabilities where the attacker is able to threaten the security of the system even if each of its components continues to act as expected. In this article, we introduce FreeSpec, a formalism built upon the key idea that components can be modelled as programs with algebraic effects to be realized by other components. FreeSpec allows for the modular modelling of a complex system, by defining idealized components connected together, and the modular verification of the properties of their composition. In addition, we have implemented a framework for the Coq proof assistant based on FreeSpec. OSApp Execution Unit MMU Cache APIC IOMMU MCH Management Engine DRAM Controller VGA Controller SENTER Sandman [6], SpeedRacer [5] SMRAM cache poisoning [2,3] DMA Attacks [7] Sinkhole [4]
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