704 research outputs found
Algorithmic Verification of Asynchronous Programs
Asynchronous programming is a ubiquitous systems programming idiom to manage
concurrent interactions with the environment. In this style, instead of waiting
for time-consuming operations to complete, the programmer makes a non-blocking
call to the operation and posts a callback task to a task buffer that is
executed later when the time-consuming operation completes. A co-operative
scheduler mediates the interaction by picking and executing callback tasks from
the task buffer to completion (and these callbacks can post further callbacks
to be executed later). Writing correct asynchronous programs is hard because
the use of callbacks, while efficient, obscures program control flow.
We provide a formal model underlying asynchronous programs and study
verification problems for this model. We show that the safety verification
problem for finite-data asynchronous programs is expspace-complete. We show
that liveness verification for finite-data asynchronous programs is decidable
and polynomial-time equivalent to Petri Net reachability. Decidability is not
obvious, since even if the data is finite-state, asynchronous programs
constitute infinite-state transition systems: both the program stack and the
task buffer of pending asynchronous calls can be potentially unbounded.
Our main technical construction is a polynomial-time semantics-preserving
reduction from asynchronous programs to Petri Nets and conversely. The
reduction allows the use of algorithmic techniques on Petri Nets to the
verification of asynchronous programs.
We also study several extensions to the basic models of asynchronous programs
that are inspired by additional capabilities provided by implementations of
asynchronous libraries, and classify the decidability and undecidability of
verification questions on these extensions.Comment: 46 pages, 9 figure
Automatic Verification of Message-Based Device Drivers
We develop a practical solution to the problem of automatic verification of
the interface between device drivers and the OS. Our solution relies on a
combination of improved driver architecture and verification tools. It supports
drivers written in C and can be implemented in any existing OS, which sets it
apart from previous proposals for verification-friendly drivers. Our
Linux-based evaluation shows that this methodology amplifies the power of
existing verification tools in detecting driver bugs, making it possible to
verify properties beyond the reach of traditional techniques.Comment: In Proceedings SSV 2012, arXiv:1211.587
Divide and Scale: Formalization of Distributed Ledger Sharding Protocols
Sharding distributed ledgers is the most promising on-chain solution for
scaling blockchain technology. In this work, we define and analyze the
properties a sharded distributed ledger should fulfill. More specifically, we
show that a sharded blockchain cannot be scalable under a fully adaptive
adversary, but it can scale up to under an epoch-adaptive
adversary. This is possible only if the distributed ledger creates succinct
proofs of the valid state updates at the end of each epoch. Our model builds
upon and extends the Bitcoin backbone protocol by defining consistency and
scalability. Consistency encompasses the need for atomic execution of
cross-shard transactions to preserve safety, whereas scalability encapsulates
the speedup a sharded system can gain in comparison to a non-sharded system. We
introduce a protocol abstraction and highlight the sufficient components for
secure and efficient sharding in our model. In order to show the power of our
framework, we analyze the most prominent shared blockchains (Elastico,
Monoxide, OmniLedger, RapidChain) and pinpoint where they fail to meet the
desired properties
Choreography automata
Automata models are well-established in many areas of computer science and are supported by a wealth of theoretical results including a wide range of algorithms and techniques to specify and analyse systems. We introduce choreography automata for the choreographic modelling of communicating systems. The projection of a choreography automaton yields a system of communicating finite-state machines. We consider both the standard asynchronous semantics of communicating systems and a synchronous variant of it. For both, the projections of well-formed automata are proved to be live as well as lock- and deadlock-free
Parameterized Synthesis Case Study: AMBA AHB (extended version)
We revisit the AMBA AHB case study that has been used as a benchmark for
several reactive syn- thesis tools. Synthesizing AMBA AHB implementations that
can serve a large number of masters is still a difficult problem. We
demonstrate how to use parameterized synthesis in token rings to obtain an
implementation for a component that serves a single master, and can be arranged
in a ring of arbitrarily many components. We describe new tricks -- property
decompositional synthesis, and direct encoding of simple GR(1) -- that together
with previously described optimizations allowed us to synthesize the model with
14 states in 30 minutes.Comment: Moved to appendix some not very important proofs. To section
'optimizations: added the model for 0-process. Extended version of the paper
submitted to SYNT 201
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