SMT-based verification of low-level code requires modeling and reasoning about memory operations. Prior work has shown that optimizing memory representations is beneficial for scaling verification—pointer analysis, for example can be used to split memory into disjoint regions leading to faster SMT solving. However, these techniques are mostly designed for C and C++ programs with explicit operations for memory allocation which are not present in all languages. For instance, on the Ethereum virtual machine, memory is simply a monolithic array of bytes which can be freely accessed by Ethereum bytecode, and there is no allocation primitive. In this paper, we present a memory splitting transformation guided by a conservative memory analysis for Ethereum bytecode generated by the Solidity compiler. The analysis consists of two phases: recovering memory allocation and memory regions, followed by a pointer analysis. The goal of the analysis is to enable memory splitting which in turn speeds up verification. We have implemented both the analysis and the memory splitting transformation as part of a verification tool, CertoraProver, and show that the transformation speeds up SMT solving by up to 120× and additionally mitigates 16 timeouts when used on 229 real-world smart contract verification tasks.

We present pretend synchrony , a new approach to verifying distributed systems, based on the observation that while distributed programs must execute asynchronously, we can often soundly treat them as if they were synchronous when verifying their correctness. To do so, we compute a synchronization , a semantically equivalent program where all sends, receives, and message buffers, have been replaced by simple assignments, yielding a program that can be verified using Floyd-Hoare style Verification Conditions and SMT. We implement our approach as a framework for writing verified distributed programs in Go and evaluate it with four challenging case studies— the classic two-phase commit protocol, the Raft leader election protocol, single-decree Paxos protocol, and a Multi-Paxos based distributed key-value store. We find that pretend synchrony allows us to develop performant systems while making verification of functional correctness simpler by reducing manually specified invariants by a factor of 6, and faster , by reducing checking time by three orders of magnitude.

We introduce canonical sequentialization, a new approach to verifying unbounded, asynchronous, message-passing programs at compile-time. Our approach builds upon the following observation: due the combinatorial explosion in complexity, programmers do not reason about their systems by case-splitting over all the possible execution orders. Instead, correct programs tend to be well-structured so that the programmer can reason about a small number of representative executions, which we call the program’s canonical sequentialization. We have implemented our approach in a tool called Brisk that synthesizes canonical sequentializations for programs written in Haskell, and evaluated it on a wide variety of distributed systems including benchmarks from the literature and implementations of MapReduce, two-phase commit, and a version of the Disco distributed file-system. We show that unlike model checking, which gets prohibitively slow with just 10 processes Brisk verifies the unbounded versions of the benchmarks in tens of milliseconds, yielding the first concurrency verification tool that is fast enough to be integrated into a design-implement-check cycle.

We present a notion of bounded quantification for refinement types and show how it expands the expressiveness of refinement typing by using it to develop typed combinators for: (1) relational algebra and safe database access, (2) Floyd-Hoare logic within a state transformer monad equipped with combinators for branching and looping, and (3) using the above to implement a refined IO monad that tracks capabilities and resource usage. This leap in expressiveness comes via a translation to ``ghost" functions, which lets us retain the automated and decidable SMT based checking and inference that makes refinement typing effective in practice.

Shared memory multithreading is a popular approach to parallel programming, but also fiendishly hard to get right. We present Liquid Effects, a type-and-effect system based on refinement types which allows for fine-grained, low-level, shared memory multi-threading while statically guaranteeing that a program is deterministic. Liquid Effects records the effect of an expression as a for- mula in first-order logic, making our type-and-effect system highly expressive. Further, effects like Read and Write are recorded in Liquid Effects as ordinary uninterpreted predicates, leaving the effect system open to extension by the user. By building our system as an extension to an existing dependent refinement type system, our system gains precise value- and branch-sensitive reasoning about effects. Finally, our system exploits the Liquid Types refinement type inference technique to automatically infer refinement types and effects. We have implemented our type-and-effect checking techniques in CSOLVE, a refinement type inference system for C programs. We demonstrate how CSOLVE uses Liquid Effects to prove the determinism of a variety of benchmarks.