Ideally, accelerator development should be as easy as software development. Several recent design languages/tools are working toward this goal, but actually testing early designs on real applications end-to-end remains prohibitively difficult due to the costs of building specialized compiler and simulator support. We propose a new first-in-class, mostly automated methodology termed “3LA” to enable end-to-end testing of prototype accelerator designs on unmodified source applications. A key contribution of 3LA is the use of a formal software/hardware interface that specifies an accelerator’s operations and their semantics. Specifically, we leverage the Instruction-level Abstraction (ILA) formal specification for accelerators that has been successfully used thus far for accelerator implementation verification. We show how the ILA for accelerators serves as a software/hardware interface, similar to the Instruction Set Architecture for processors, that can be used for automated development of compilers and instruction-level simulators. Another key contribution of this work is to show how ILA-based accelerator semantics enables extending recent work on equality saturation to auto-generate basic compiler support for prototype accelerators in a technique we term “flexible matching.” By combining flexible matching with simulators auto-generated from ILA specifications, our approach enables end-to-end evaluation with modest engineering effort. We detail several case studies of 3LA, which uncovered an unknown flaw in a recently published accelerator and facilitated its fix.

This paper presents the Instruction-Level Abstraction (ILA) as a formal software/hardware interface for accelerator-rich platforms. The ILA provides a common framework for formal functional specification of processors and accelerator behavior, verifying their implementations, and reasoning about software-hardware interactions of programs with accelerators. The ILA-MCM specification extends the ILA to enable reasoning about interactions of accelerators with other compute engines through shared memory. The 3LA compilation flow for accelerators uses the ILA model to bridge the gap between fine-grain compiler intrinsics and coarse-grain accelerator operations.

Today's Systems-on-Chips (SoCs) comprise general/special purpose programmable processors and specialized hardware modules referred to as accelerators. These accelerators serve as co-processors and are invoked through software or firmware. Thus, verifying SoCs requires co-verification of hardware with software/firmware. Co-verification using cycle-accurate hardware models is often not scalable, and requires hardware abstractions. Among various abstractions, architecture-level abstractions are very effective as they retain only the software visible state. An Instruction-Set Architecture (ISA) serves this role for processors and such ISA-like abstractions are also desirable for accelerators. Manually creating such abstractions for accelerators is tedious and error-prone, and there is a growing need for automation in deriving them from existing Register-Transfer Level (RTL) implementations. An important part of this automation is determining which state variables to retain in the abstract model. For processors and accelerators, this set of variables is naturally the Architectural State Variables (ASVs) - variables that are persistent across instructions. This paper presents the first work to automatically determine ASVs of processors and accelerators from their RTL implementations. We propose three novel algorithms based on different characteristics of ASVs. Each algorithm provides a sound abstraction, i.e., an over-approximate set of ASVs. The quality of the abstraction is measured by the size of the set of ASVs computed. Experiments on several processors and accelerators demonstrate that these algorithms perform best in different cases, and by combining them a high quality set of ASVs can be found in reasonable time.

The cloud runs on REST APIs. In this paper, we study how to intelligently generate data payloads embedded in REST API requests in order to find data-processing bugs in cloud services. We discuss how to leverage REST API specifications, which, by definition, contain data schemas for API request bodies. We then propose and evaluate a range of data fuzzing techniques, including structural schema fuzzing rules, various rule combinations, search heuristics, extracting data values from examples included in REST API specifications, and learning data values on-the-fly from previous service responses. After evaluating these techniques, we identify the top-performing combination and use this algorithm to fuzz several Microsoft Azure cloud services. During our experiments, we found 100s of “Internal Server Error” service crashes, which we triaged into 17 unique bugs and reported to Azure developers. All these bugs are reproducible, confirmed, and fixed or in the process of being fixed.

We present ILAng, a platform for modeling and verification of systems-on-chip (SoCs) using Instruction-Level Abstractions (ILA). The ILA formal model targeting the hardware-software interface enables a clean separation of concerns between software and hardware through a unified model for heterogeneous processors and accelerators. Top-down it provides a specification for functional verification of hardware, and bottom-up it provides an abstraction for software/hardware co-verification. ILAng provides a programming interface for (i) constructing ILA models (ii) synthesizing ILA models from templates using program synthesis techniques (iii) verifying properties on ILA models (iv) behavioral equivalence checking between different ILA models, and between an ILA specification and an implementation. It also provides for translating models and properties into various languages (e.g., Verilog and SMT LIB2) for different verification settings and use of third-party verification tools. This paper demonstrates selected capabilities of the platform through case studies. Data or code related to this paper is available at: [ 9 ].

Modern Systems-on-Chip (SoC) designs are increasingly heterogeneous and contain specialized semi-programmable accelerators in addition to programmable processors. In contrast to the pre-accelerator era, when the ISA played an important role in verification by enabling a clean separation of concerns between software and hardware, verification of these “accelerator-rich” SoCs presents new challenges. From the perspective of hardware designers, there is a lack of a common framework for formal functional specification of accelerator behavior. From the perspective of software developers, there exists no unified framework for reasoning about software/hardware interactions of programs that interact with accelerators. This article addresses these challenges by providing a formal specification and high-level abstraction for accelerator functional behavior. It formalizes the concept of an Instruction Level Abstraction (ILA), developed informally in our previous work, and shows its application in modeling and verification of accelerators. This formal ILA extends the familiar notion of instructions to accelerators and provides a uniform, modular, and hierarchical abstraction for modeling software-visible behavior of both accelerators and programmable processors. We demonstrate the applicability of the ILA through several case studies of accelerators (for image processing, machine learning, and cryptography), and a general-purpose processor (RISC-V). We show how the ILA model facilitates equivalence checking between two ILAs, and between an ILA and its hardware finite-state machine (FSM) implementation. Further, this equivalence checking supports accelerator upgrades using the notion of ILA compatibility, similar to processor upgrades using ISA compatibility.

Formal security verification of firmware interacting with hardware in modern Systems-on-Chip (SoCs) is a critical research problem. This faces the following challenges: (1) design complexity and heterogeneity, (2) semantics gaps between software and hardware, (3) concurrency between firmware/hardware and between Intellectual Property Blocks (IPs), and (4) expensive bit-precise reasoning. In this paper, we present a co-verification methodology to address these challenges. We model hardware using the Instruction-Level Abstraction (ILA), capturing firmware-visible behavior at the architecture level. This enables integrating hardware behavior with firmware in each IP into a single thread. The co-verification with multiple firmware across IPs is formulated as a multi-threaded program verification problem, for which we leverage software verification techniques. We also propose an optimization using abstraction to prevent expensive bit-precise reasoning. The evaluation of our methodology on an industry SoC Secure Boot design demonstrates its applicability in SoC security verification.

GPUs have been widely used to accelerate big-data inference applications and scientific computing through their parallelized hardware resources and programming model. Their extreme parallelism increases the possibility of bugs such as data races and un-coalesced memory accesses, and thus verifying program correctness is critical. State-of-the-art GPU program verification efforts mainly focus on analyzing application-level programs, e.g., in C, and suffer from the following limitations: (1) high false-positive rate due to coarse-grained abstraction of synchronization primitives, (2) high complexity of reasoning about pointer arithmetic, and (3) keeping up with an evolving API for developing application-level programs. In this paper, we address these limitations by modeling GPUs and reasoning about programs at the instruction level. We formally model the Nvidia GPU at the parallel execution thread (PTX) level using the recently proposed Instruction-Level Abstraction (ILA) model for accelerators. PTX is analogous to the Instruction-Set Architecture (ISA) of a general-purpose processor. Our formal ILA model of the GPU includes non-synchronization instructions as well as all synchronization primitives, enabling us to verify multithreaded programs. We demonstrate the applicability of our ILA model in scalable GPU program verification of data-race checking. The evaluation shows that our checker outperforms state-of-the-art GPU data race checkers with fewer false-positives and improved scalability.

Modern system-on-chip (SoC) designs comprise programmable cores, application-specific accelerators, and I/O devices. Accelerators are controlled by software/firmware and functionality is implemented by this combination of programmable cores, firmware, and accelerators. Verification of such SoCs is challenging, especially for system-level properties maintained by a combination of firmware and hardware. Attempting to formally verify the full SoC design with both firmware and hardware is not scalable, while separate verification can miss bugs. A general technique for scalable system-level verification is to construct an abstraction of SoC hardware and verify firmware/software using it. There are two challenges in applying this technique in practice. Constructing the abstraction to capture required details and interactions is error-prone and time-consuming. The second is ensuring abstraction correctness so that properties proven with it are valid. This paper introduces a methodology for SoC design and verification based on the synthesis of instruction-level abstractions (ILAs). The ILA is an abstraction of SoC hardware which models updates to firmware-visible state at the granularity of instructions. For hardware accelerators, the ILA is analogous to the instruction-set architecture definition for programmable processors and enables scalable verification of firmware interacting with hardware accelerators. To alleviate the disadvantages of manual construction of abstractions, we introduce two algorithms for synthesis of ILAs from partial description called templates. We then show how the ILA can be verified to be correct. We evaluate the methodology using a small SoC design consisting of the 8051 microcontroller and two cryptographic accelerators. The methodology uncovered 15 bugs.

Asynchronous circuits are promising in resolving the emerging issue of process variation and high synchronization power consumption. Among various asynchronous delay models, quasi-delay insensitive (QDI) model is the most robust and yet practical one due to its relaxed timing assumption. However, automatic synthesis of QDI circuits from signal transition graph (STG) protocol specification has not yet been proposed, despite the fact that algorithms synthesizing circuits under other delay models do exist. In this paper we propose the first algorithm synthesizing protocols specified in STGs into QDI circuits by analyzing STG structures without utilizing state graph assignment techniques. Furthermore, an optimization technique is proposed to simplify QDI circuits. In our synthesis algorithm, the state explosion issue is avoided, and restrictions on STGs are relaxed. Case studies on Advanced Microcontroller Bus Architecture (AMBA) and other protocols indicate the feasibility of our method.