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Abstract-We illustrate how to employ metacircular assume/guarantee reasoning to reduce the verification complexity of finite instances of protocols for safety, using nothing more than an explicit state model checker. The formal underpinnings of our method are based on establishing a simulation relation between the given protocol M , and several overapproximations thereof, M1, . . . ,M k . EachMi simulates M , and represents one "view" of it. TheMis depend on each other both to define the abstractions as well as to justify them. We show that in case of our hierarchical coherence protocol, its designer could easily construct each of theMi in a counterexample guided manner. This approach is practical, considerably reduces the verification complexity, and has been successfully applied to a complex hierarchical multicore cache coherence protocol which could not be verified through traditional model checking.

An efficient way to synchronize an asynchronous network with a bounded delay message delivery is presented. Two types of synchronlzaiioo algorithms are presented. Both types require an initializing phase that costs IEl messages (where IEl is the number of links). The first requires an additional hit in every message and increases the time complexily by a factor of 2. The second does not require any additional hits but increases the time complexity by a factor of 3. We also explain how to overcome differences in nodal timer raies.

Mechanical theorem proving and model checking are the two mMn methods of formal verification, each with its own strengths and weaknesses. While mechanical theorem proving is more general, it requires intensive human guidance, model checking is automatic, but is applicable to a more restricted class of problems. It is appealing to combine these two methods in order to take advantage of their different strengths. Prior research in this direction has focused on how to decompose a verification problem into parts each of which is manageable by one of the two methods. In this paper we explore another possibility: we use mechanical theorem proving to formally verify a meta-theory of model checking. As a case study, we use the mechanical theorem prover HOL to verify the correctness of a partial-order reduction technique for cutting down the amount of state search performed by model checkers. We choose this example for two reasons. First, this reduction technique has been implemented in the protocol analysis tool SPIN to significantly speed up the analysis of many practical protocols; hence its correctness has important practical consequences. Second, the correctness arguments involve nontrivial mathematics, the formalization of which we hope will become the basis of a formal meta-theory of many model checking algorithms and techniques. Our formalization led to a nontrivial generalization of the original informal theory. We also discuss the lessons, both encouraging and discouraging, learned from this exercise.