A Modular Formalization of Reversibility for Concurrent Models and Languages

Causal-consistent reversibility is the reference notion of reversibility for concurrency. We introduce a modular framework for defining causal-consistent reversible extensions of concurrent models and languages. We show how our framework can be used to define reversible extensions of formalisms as different as CCS and concurrent X-machines. The generality of the approach allows for the reuse of theories and techniques in different settings.Comment: In Proceedings ICE 2016, arXiv:1608.0313

Automated Debugging for Arbitrarily Long Executions

One of the most energy-draining and frustrating parts of software development is playing detective with elu-sive bugs. In this paper we argue that automated post-mortem debugging of failures is feasible for real, in-production systems with no runtime recording. We pro-pose reverse execution synthesis (RES), a technique that takes a coredump obtained after a failure and automat-ically computes the suffix of an execution that leads to that coredump. RES provides a way to then play back this suffix in a debugger deterministically, over and over again. We argue that the RES approach could be used to (1) automatically classify bug reports based on their root cause, (2) automatically identify coredumps for which hardware errors (e.g., bad memory), not software bugs are to blame, and (3) ultimately help developers repro-duce the root cause of the failure in order to debug it.

Programming with Undo

This thesis is about objects that can undo their state changes. Based on an earlier work on data structure persistence, we propose generating undo methods for classes from annotated classes automatically. As opposed to ephemeral data structures, persistent data structures carry their older versions, and undo for a persistent structure is just returning to a previous version. Undoable objects simplify programming in a number of areas such as backtracking in constraint programming, and undo for interactive applications. Using the undo methods of individual objects, larger application level undo functionality can be built in an easier way

Validating Software States Using Reverse Execution

A key feature of software analysis is determining whether it is possible for a program to reach a certain state. Various methods have been devised to accomplish this including directed fuzzing and dynamic execution. In this thesis we present a reverse execution engine to validate states, the Complex Emulator. The Complex Emulator seeks to validate a program state by emulating it in reverse to discover if a contradiction exists. When unknown variables are found during execution, the emulator is designed to use constraint solving to compute their values. The Complex Emulator has been tested on small assembly programs and is able to detect contradictions in program states. If developed further the Complex Emulator could be used to validate program states on larger and more elaborate software

The Backstroke framework for source level reverse computation applied to parallel discrete event simulation

This report introduces Backstroke, a new open source framework for the automatic generation of reverse code for functions written in C++. Backstroke enables reverse computation for optimistic parallel discrete event simulations. It is built over the ROSE open- source compiler infrastructure, and handles complex C++ features including pointers and pointer types, arrays, function and method calls, class types. inheritance, polymorphism, virtual functions, abstract classes, templated classes and containers. Backstroke also introduces new program inversion techniques based on advanced compiler analysis tools built into ROSE. We explore and illustrate some of the complex language and semantic issues that arise in generating correct reverse code for C++ functions

A Modular Formalization of Reversibility for Concurrent Models and Languages

International audienceCausal-consistent reversibility is the reference notion of reversibility for concurrency. We introduce a modular framework for defining causal-consistent reversible extensions of concurrent models and languages. We show how our framework can be used to define reversible extensions of formalisms as different as CCS and concurrent X-machines. The generality of the approach allows for the reuse of theories and techniques in different settings

A new approach to reversible computing with applications to speculative parallel simulation

In this thesis, we propose an innovative approach to reversible computing that shifts the focus from the operations to the memory outcome of a generic program. This choice allows us to overcome some typical challenges of "plain" reversible computing. Our methodology is to instrument a generic application with the help of an instrumentation tool, namely Hijacker, which we have redesigned and developed for the purpose. Through compile-time instrumentation, we enhance the program's code to keep track of the memory trace it produces until the end. Regardless of the complexity behind the generation of each computational step of the program, we can build inverse machine instructions just by inspecting the instruction that is attempting to write some value to memory. Therefore from this information, we craft an ad-hoc instruction that conveys this old value and the knowledge of where to replace it. This instruction will become part of a more comprehensive structure, namely the reverse window. Through this structure, we have sufficient information to cancel all the updates done by the generic program during its execution. In this writing, we will discuss the structure of the reverse window, as the building block for the whole reversing framework we designed and finally realized. Albeit we settle our solution in the specific context of the parallel discrete event simulation (PDES) adopting the Time Warp synchronization protocol, this framework paves the way for further general-purpose development and employment. We also present two additional innovative contributions coming from our innovative reversibility approach, both of them still embrace traditional state saving-based rollback strategy. The first contribution aims to harness the advantages of both the possible approaches. We implement the rollback operation combining state saving together with our reversible support through a mathematical model. This model enables the system to choose in autonomicity the best rollback strategy, by the mutable runtime dynamics of programs. The second contribution explores an orthogonal direction, still related to reversible computing aspects. In particular, we will address the problem of reversing shared libraries. Indeed, leading from their nature, shared objects are visible to the whole system and so does every possible external modification of their code. As a consequence, it is not possible to instrument them without affecting other unaware applications. We propose a different method to deal with the instrumentation of shared objects. All our innovative proposals have been assessed using the last generation of the open source ROOT-Sim PDES platform, where we integrated our solutions. ROOT-Sim is a C-based package implementing a general purpose simulation environment based on the Time Warp synchronization protocol

Assembly Instruction Level Reverse Execution for Debugging

Reverse execution can be defined as a method which recovers the states that a program attains during its execution. Therefore, reverse execution eliminates the need for repetitive program restarts every time a bug location is missed. This potentially shortens debug time considerably. This thesis presents a new approach which, for the first time ever (to the best of the author's knowledge), achieves reverse execution at the assembly instruction level on general purpose processors via execution of a reverse program. A reverse program almost always regenerates destroyed states rather than restoring them from a record. Furthermore, a reverse program provides assembly instruction by assembly instruction execution in the backward direction. This significantly reduces state saving and thus decreases the associated memory and time costs of reverse execution support. Furthermore, this thesis presents a new dynamic slicing algorithm that is built on top of assembly instruction level reverse execution. Dynamic slicing is a technique which isolates the code parts that influence an erroneous variable at a program point. The algorithm presented in this thesis achieves dynamic slicing via execution of a reduced reverse program. A reduced reverse program is obtained from a full reverse program by omitting the instructions that recover states irrelevant to the dynamic slice under consideration. This provides a reverse execution capability along a designated dynamic slice only. The use of a reduced reverse program for dynamic slicing removes the need for runtime execution trajectories. The methodology of this thesis has been implemented on a PowerPC processor with a custom made debugger. As compared to previous work, all of which heavily use state saving techniques, the experimental results show up to 2206X reduction in runtime memory usage, up to 403X reduction in forward execution time overhead and up to 2.32X reduction in forward execution time for the tested benchmarks. Measurements on the selected benchmarks also indicate that the dynamic slicing method presented in this thesis can achieve up to six orders of magnitude (1,928,500X) speedups in reverse execution along the dynamic slice as compared to full-scale reverse execution.Ph.D.Committee Chair: Mooney, Vincent J.; Committee Member: LeBlanc, Richard J.; Committee Member: Madisetti, Vijay K.; Committee Member: Pande, Santosh; Committee Member: Sivakumar, Raghupath