This paper reports on the development and formal verification (proof of semantic preservation) of CompCert, a compiler from Clight (a large subset of the C programming language) to PowerPC assembly code, using the Coq proof assistant both for programming the compiler and for proving its correctness. Such a verified compiler is useful in the context of critical software and its formal verification: the verification of the compiler guarantees that the safety properties proved on the source code hold for the executable compiled code as well. 1.

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Software pipelining is a loop optimization that overlaps the execution of several iterations of a loop to expose more instruction-level parallelism. It can result in first-class performances characteristics, but at the cost of significant obfuscation of the code, making this optimization difficult to test and debug. In this paper, we present a translation validation algorithm that uses symbolic evaluation to detect semantics discrepancies between a loop and its pipelined version. Our algorithm can be implemented simply and efficiently, is provably sound, and appears to be complete with respect to most modulo scheduling algorithms. A conclusion of this case study is that it is possible and effective to use symbolic evaluation to reason about loop transformations. Categories and Subject Descriptors D.2.4 [Software Engineering]:

We describe the design, implementation, and use of a machinecertified framework for correct compilation and execution of programs in garbage-collected languages. Our framework extends Leroy’s Coq-certified Compcert compiler and Cminor intermediate language. We add: (i) a new intermediate language, GCminor, that includes primitives for allocating memory in a garbage-collected heap and for specifying GC roots; (ii) a precise, low-level specification for a Cminor library for garbage collection; and (iii) a proven semantics-preserving translation from GCminor to Cminor plus the GC library. GCminor neatly encapsulates the interface between mutator and collector code, while remaining simple and flexible enough to be used with a wide variety of source languages and collector styles. Front ends targeting GCminor can be implemented using any compiler technology and any desired degree of verification, including full semantics preservation, type preservation, or informal trust. As an example application of our framework, we describe a compiler for Haskell that translates the Glasgow Haskell Compiler’s Core intermediate language to GCminor. To support a simple but useful memory safety argument for this compiler, the front end uses a novel combination of type preservation and runtime checks, which is of independent interest.

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Soundness proofs of program logics such as Hoare logics and type systems are often made easier by decorating the operational semantics with information that is useful in the proof. However, modifying the operational semantics to carry around such information can make it more difficult to show that the operational semantics corresponds to what actually occurs on a real machine. In this work we present a program logic framework targeting operational semantics in Curry-style—that is, operational semantics without proof decorations such as separation algebras, share models, and step indexes. Although we target Curry-style operational semantics, our framework permits local reasoning via the frame rule and retains expressive assertions in the program logic. Soundness of the program logic is derived mechanically from simple properties of primitive commands and expressions. We demonstrate our framework by deriving a separation logic for the model of a core imperative programming language with external function calls. We also apply our framework in a more realistic setting in the soundness proof of a separation logic for CompCert’s Cminor. Our proofs are machine-checked in Coq.

Abstract This article presents the formal semantics of a large subset of the C language called Clight. Clight includes pointer arithmetic, struct and union types, C loops and structured switch statements. Clight is the source language of the CompCert verified compiler. The formal semantics of Clight is a big-step operational semantics that observes both terminating and diverging executions and produces traces of input/output events. The formal semantics of Clight is mechanized using the Coq proof assistant. In addition to the semantics of Clight, this article describes its integration in the CompCert verified compiler and several ways by which the semantics was validated.

Abstract. Through foreign function interfaces (FFIs), software components in different programming languages interact with each other in the same address space. Recent years have witnessed a number of systems that analyze FFIs for safety and reliability. However, lack of formal specifications of FFIs hampers progress in this endeavor. We present a formal operational model, JNI Light (JNIL), for a subset of a widely used FFI—the Java Native Interface (JNI). JNIL focuses on the core issues when a high-level garbage-collected language interacts with a low-level language. It proposes abstractions for handling a shared heap, crosslanguage method calls, cross-language exception handling, and garbage collection. JNIL can directly serve as a formal basis for JNI tools and systems. The abstractions in JNIL are also useful when modeling other FFIs, such as the Python/C interface and the OCaml/C interface. 1

Abstract. The simulation of Systems-on-Chip (SoC) is nowadays a hot topic because, beyond providing many debugging facilities, it allows the development of dedicated software before the hardware is available. Lowconsumption CPUs such as ARM play a central role in SoC. However, the effectiveness of simulation depends on the faithfulness of the simulator. To this effect, we propose here to prove significant parts of such a simulator, SimSoC. Basically, on one hand, we develop a Coq formal model of the ARM architecture while on the other hand, we consider a version of the simulator including components written in Compcert-C. Then we prove that the simulation of ARM operations, according to Compcert-C formal semantics, conforms to the expected formal model of ARM. Size issues are partly dealt with using automatic generation of significant parts of the Coq model and of SimSoC from the official textual definition of ARM. However, this is still a long-term project. We report here the current stage of our efforts and discuss in particular the use of Compcert-C in this framework. 1