6,762 research outputs found
Formal Verification of an SSA-based Middle-end for CompCert
CompCert is a formally verified compiler that generates compact and efficient PowerPC, ARM and x86 code for a large and realistic subset of the C language. However, CompCert foregoes using Static Single Assignment (SSA), an intermediate representation that allows for writing simpler and faster optimizers, and that is used by many compilers. In fact, it has remained an open problem to verify formally an SSA-based compiler middle-end. We report on a formally verified, SSA-based, middle-end for CompCert. Our middle-end performs conversion from CompCert intermediate form to SSA form, optimization of SSA programs, including Global Value Numbering, and transforming out of SSA to intermediate form. In addition to provide the first formally verified SSA-based middle-end, we address two problems raised by Leroy in 2009: giving a simple and intuitive formal semantics to SSA, and leveraging the global properties of SSA to reason locally about program optimizations
Embedded Program Annotations for WCET Analysis
We present __builtin_ais_annot(), a user-friendly, versatile way to transfer annotations (also known as flow facts) written on the source code level to the machine code level. To do so, we couple two tools often used during the development of safety-critical hard real-time systems, the formally verified C compiler CompCert and the static WCET analyzer aiT. CompCert stores the AIS annotations given via __builtin_ais_annot() in a special section of the ELF binary, which can later be extracted automatically by aiT
A formally verified compiler back-end
This article describes the development and formal verification (proof of
semantic preservation) of a compiler back-end from Cminor (a simple imperative
intermediate 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 formal methods applied to the
certification of critical software: the verification of the compiler guarantees
that the safety properties proved on the source code hold for the executable
compiled code as well
Compiler verification for fun and profit
International audienceFormal verification of software or hardware systems — be it by model checking, deductive verification, abstract interpretation, type checking, or any other kind of static analysis — is generally conducted over high-level programming or description languages, quite remote from the actual machine code and circuits that execute in the system. To bridge this particular gap, we all rely on compilers and other code generators to automatically produce the executable artifact. Compilers are, however, vulnerable to miscompilation: bugs in the compiler that cause incorrect code to be generated from a correct source code, possibly invalidating the guarantees so painfully obtained by source-level formal verification. Recent experimental studies show that many widely-used production-quality compilers suffer from miscompilation.The formal verification of compilers and related code generators is a radical, mathematically-grounded answer to the miscompilation issue. By applying formal verification (typically, interactive theorem proving) to the compiler itself, it is possible to guarantee that the compiler preserves the semantics of the source programs it transforms, or at least preserves the properties of interest that were formally verified over the source programs. Proving the correctness of compilers is an old idea that took a long time to scale all the way to realistic compilers. In the talk, I give an overview of CompCert C, a moderately-optimizing compiler for almost all of the ISO C 99 language that has been formally verified using the Coq proof assistant.The CompCert project is one point in a space of code generators whose verification deserves attention. For example, functional languages and object-oriented languages raise the issue of jointly verifying the compiler and the run-time system (memory management, exception handling, etc) that the generated code depends on. At the other end of the expressiveness spectrum, synchronous languages and hardware description languages also raise interesting verified generation issues, as exemplified by Pnueli’s seminal work on translation validation for Signal and Braibant and Chlipala’s recent work on verified hardware synthesis.Orthogonally, the integration of verification tools and compilers that are both verified against a shared formal semantics opens fascinating opportunities for “super-optimizations” that generate better code by exploiting the properties of the source code that were formally verified
Mechanized semantics
The goal of this lecture is to show how modern theorem provers---in this
case, the Coq proof assistant---can be used to mechanize the specification of
programming languages and their semantics, and to reason over individual
programs and over generic program transformations, as typically found in
compilers. The topics covered include: operational semantics (small-step,
big-step, definitional interpreters); a simple form of denotational semantics;
axiomatic semantics and Hoare logic; generation of verification conditions,
with application to program proof; compilation to virtual machine code and its
proof of correctness; an example of an optimizing program transformation (dead
code elimination) and its proof of correctness
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