Towards Porting Operating Systems with Program Synthesis

The end of Moore's Law has ushered in a diversity of hardware not seen in decades. Operating system (and system software) portability is accordingly becoming increasingly critical. Simultaneously, there has been tremendous progress in program synthesis. We set out to explore the feasibility of using modern program synthesis to generate the machine-dependent parts of an operating system. Our ultimate goal is to generate new ports automatically from descriptions of new machines. One of the issues involved is writing specifications, both for machine-dependent operating system functionality and for instruction set architectures. We designed two domain-specific languages: Alewife for machine-independent specifications of machine-dependent operating system functionality and Cassiopea for describing instruction set architecture semantics. Automated porting also requires an implementation. We developed a toolchain that, given an Alewife specification and a Cassiopea machine description, specializes the machine-independent specification to the target instruction set architecture and synthesizes an implementation in assembly language with a customized symbolic execution engine. Using this approach, we demonstrate successful synthesis of a total of 140 OS components from two pre-existing OSes for four real hardware platforms. We also developed several optimization methods for OS-related assembly synthesis to improve scalability. The effectiveness of our languages and ability to synthesize code for all 140 specifications is evidence of the feasibility of program synthesis for machine-dependent OS code. However, many research challenges remain; we also discuss the benefits and limitations of our synthesis-based approach to automated OS porting.Comment: ACM Transactions on Programming Languages and Systems. Accepted on August 202

Bit-precise Verification of Numerical Properties in Fixed-point Programs

Numerical software is prone to inaccuracies due to the finite representation of numbers. These inaccuracies propagate, possibly non-linearly, throughout the statements of a program, making it hard to predict the accumulated errors. Moreover, in programs that contain control structures, numerical errors can affect the control flow. As a result of these inaccuracies, reachability, and thus safety, may be altered with respect to the intended infinite-precision computation. This thesis considers programs that use fixed-point arithmetic to compute over non-integer quantities in finite precision. We first define a semantics of fixed-point operations in terms of operations over bit-vectors. The proposed semantics generalizes current attempts to a standardization of fixedpoint arithmetic. We then consider the problem of bit-precise numerical accuracy certification of fixed-point programs with control structures and arithmetic over variables of arbitrary, mixed precision and possibly non-deterministic value. By applying a set of parametrized transformation rules based on computable expressions for the errors incurred by single program statements, we reduce the problem of assessing whether a fixed-point program can exceed a given error bound to a reachability problem in a bit-vector program. We present an experimental evaluation of the certification technique, implemented in a prototype analyzer in a bounded model checking-based verification workflow. Our experiments on a set of fixed-point arithmetic routines commonly used in the industry show that the proposed technique can successfully certify numerical errors and can do so bitprecisely, making it the only such verification technique

Theory and Implementation of Software Bounded Model Checking

This thesis provides a detailed overview of the theory of software bounded model checking (SBMC) and its implementation in LLBMC, which is based on the LLVM compiler framework. The whole process from a C program to an SMT formula is described in detail. Furthermore, a theory of dynamic memory allocation is introduced which allows modelling C\u27s memory model with high precision. Finally, it is shown that LLBMC\u27s approach to software bounded model checking performs well compared to competing tools

Synthesis from multi-paradigm specifications

This work proposes a language for describing reactive synthesis problems that integrates imperative and declarative elements. The semantics is defined in terms of two-player turn-based infinite games with full information. Currently, synthesis tools accept linear temporal logic (LTL) as input, but this description is less structured and does not facilitate the expression of sequential constraints. This motivates the use of a structured programming language to specify synthesis problems. Transition systems and guarded commands serve as imperative constructs, expressed in a syntax based on that of the modeling language Promela. The syntax allows defining which player controls data and control flow, and separating a program into assumptions and guarantees. These notions are necessary for input to game solvers. The integration of imperative and declarative paradigms allows using the paradigm that is most appropriate for expressing each requirement. The declarative part is expressed in the LTL fragment of generalized reactivity(1), which admits efficient synthesis algorithms. The implementation translates Promela to input for the Slugs synthesizer and is written in Python

Formal Verification of Industrial Software and Neural Networks

Software ist ein wichtiger Bestandteil unsere heutige Gesellschaft. Da Software vermehrt in sicherheitskritischen Bereichen angewandt wird, müssen wir uns auf eine korrekte und sichere Ausführung verlassen können. Besonders eingebettete Software, zum Beispiel in medizinischen Geräten, Autos oder Flugzeugen, muss gründlich und formal geprüft werden. Die Software solcher eingebetteten Systeme kann man in zwei Komponenten aufgeteilt. In klassische (deterministische) Steuerungssoftware und maschinelle Lernverfahren zum Beispiel für die Bilderkennung oder Kollisionsvermeidung angewandt werden. Das Ziel dieser Dissertation ist es den Stand der Technik bei der Verifikation von zwei Hauptkomponenten moderner eingebetteter Systeme zu verbessern: in C/C++ geschriebene Software und neuronalen Netze. Für beide Komponenten wird das Verifikationsproblem formal definiert und neue Verifikationsansätze werden vorgestellt

Programming Languages and Systems

This open access book constitutes the proceedings of the 30th European Symposium on Programming, ESOP 2021, which was held during March 27 until April 1, 2021, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg and changed to an online format due to the COVID-19 pandemic. The 24 papers included in this volume were carefully reviewed and selected from 79 submissions. They deal with fundamental issues in the specification, design, analysis, and implementation of programming languages and systems

Computer Aided Verification

This open access two-volume set LNCS 10980 and 10981 constitutes the refereed proceedings of the 30th International Conference on Computer Aided Verification, CAV 2018, held in Oxford, UK, in July 2018. The 52 full and 13 tool papers presented together with 3 invited papers and 2 tutorials were carefully reviewed and selected from 215 submissions. The papers cover a wide range of topics and techniques, from algorithmic and logical foundations of verification to practical applications in distributed, networked, cyber-physical, and autonomous systems. They are organized in topical sections on model checking, program analysis using polyhedra, synthesis, learning, runtime verification, hybrid and timed systems, tools, probabilistic systems, static analysis, theory and security, SAT, SMT and decisions procedures, concurrency, and CPS, hardware, industrial applications