49 research outputs found
Triggered Clause Pushing for IC3
We propose an improvement of the famous IC3 algorithm for model checking
safety properties of finite state systems. We collect models computed by the
SAT-solver during the clause propagation phase of the algorithm and use them as
witnesses for why the respective clauses could not be pushed forward. It only
makes sense to recheck a particular clause for pushing when its witnessing
model falsifies a newly added clause. Since this trigger test is both
computationally cheap and sufficiently precise, we can afford to keep clauses
pushed as far as possible at all times. Experiments indicate that this strategy
considerably improves IC3's performance.Comment: 4 page
Analyzing Conflict Freedom For Multi-threaded Programs With Time Annotations
Avoiding access conflicts is a major challenge in the design of
multi-threaded programs. In the context of real-time systems, the absence of
conflicts can be guaranteed by ensuring that no two potentially conflicting
accesses are ever scheduled concurrently.In this paper, we analyze programs
that carry time annotations specifying the time for executing each statement.
We propose a technique for verifying that a multi-threaded program with time
annotations is free of access conflicts. In particular, we generate constraints
that reflect the possible schedules for executing the program and the required
properties. We then invoke an SMT solver in order to verify that no execution
gives rise to concurrent conflicting accesses. Otherwise, we obtain a trace
that exhibits the access conflict.Comment: http://journal.ub.tu-berlin.de/eceasst/article/view/97
A Supervisory Control Algorithm Based on Property-Directed Reachability
We present an algorithm for synthesising a controller (supervisor) for a
discrete event system (DES) based on the property-directed reachability (PDR)
model checking algorithm. The discrete event systems framework is useful in
both software, automation and manufacturing, as problems from those domains can
be modelled as discrete supervisory control problems. As a formal framework,
DES is also similar to domains for which the field of formal methods for
computer science has developed techniques and tools. In this paper, we attempt
to marry the two by adapting PDR to the problem of controller synthesis. The
resulting algorithm takes as input a transition system with forbidden states
and uncontrollable transitions, and synthesises a safe and
minimally-restrictive controller, correct-by-design. We also present an
implementation along with experimental results, showing that the algorithm has
potential as a part of the solution to the greater effort of formal supervisory
controller synthesis and verification.Comment: 16 pages; presented at Haifa Verification Conference 2017, the final
publication is available at Springer via
https://doi.org/10.1007/978-3-319-70389-3_
Unbounded safety verification for hardware using software analyzers
Demand for scalable hardware verification is ever-increasing. We propose an unbounded safety verification framework for hardware, at the heart of which is a software verifier. To this end, we synthesize Verilog at register transfer level into a software-netlist, represented as a word-level ANSI-C program. The proposed tool flow allows us to leverage the precision and scalability of state-of-the-art software verification techniques. In particular, we evaluate unbounded proof techniques, such as predicate abstraction, k-induction, interpolation, and IC3/PDR; and we compare the performance of verification tools from the hardware and software domains that use these techniques. To the best of our knowledge, this is the first attempt to perform unbounded verification of hardware using software analyzers
Automatic Abstraction in SMT-Based Unbounded Software Model Checking
Software model checkers based on under-approximations and SMT solvers are
very successful at verifying safety (i.e. reachability) properties. They
combine two key ideas -- (a) "concreteness": a counterexample in an
under-approximation is a counterexample in the original program as well, and
(b) "generalization": a proof of safety of an under-approximation, produced by
an SMT solver, are generalizable to proofs of safety of the original program.
In this paper, we present a combination of "automatic abstraction" with the
under-approximation-driven framework. We explore two iterative approaches for
obtaining and refining abstractions -- "proof based" and "counterexample based"
-- and show how they can be combined into a unified algorithm. To the best of
our knowledge, this is the first application of Proof-Based Abstraction,
primarily used to verify hardware, to Software Verification. We have
implemented a prototype of the framework using Z3, and evaluate it on many
benchmarks from the Software Verification Competition. We show experimentally
that our combination is quite effective on hard instances.Comment: Extended version of a paper in the proceedings of CAV 201
Incremental, Inductive Coverability
We give an incremental, inductive (IC3) procedure to check coverability of
well-structured transition systems. Our procedure generalizes the IC3 procedure
for safety verification that has been successfully applied in finite-state
hardware verification to infinite-state well-structured transition systems. We
show that our procedure is sound, complete, and terminating for downward-finite
well-structured transition systems---where each state has a finite number of
states below it---a class that contains extensions of Petri nets, broadcast
protocols, and lossy channel systems.
We have implemented our algorithm for checking coverability of Petri nets. We
describe how the algorithm can be efficiently implemented without the use of
SMT solvers. Our experiments on standard Petri net benchmarks show that IC3 is
competitive with state-of-the-art implementations for coverability based on
symbolic backward analysis or expand-enlarge-and-check algorithms both in time
taken and space usage.Comment: Non-reviewed version, original version submitted to CAV 2013; this is
a revised version, containing more experimental results and some correction