AnICA: Analyzing Inconsistencies in Microarchitectural Code Analyzers

Microarchitectural code analyzers, i.e., tools that estimate the throughput of machine code basic blocks, are important utensils in the tool belt of performance engineers. Recent tools like llvm-mca, uiCA, and Ithemal use a variety of techniques and different models for their throughput predictions. When put to the test, it is common to see these state-of-the-art tools give very different results. These inconsistencies are either errors, or they point to different and rarely documented assumptions made by the tool designers. In this paper, we present AnICA, a tool taking inspiration from differential testing and abstract interpretation to systematically analyze inconsistencies among these code analyzers. Our evaluation shows that AnICA can summarize thousands of inconsistencies in a few dozen descriptions that directly lead to high-level insights into the different behavior of the tools. In several case studies, we further demonstrate how AnICA automatically finds and characterizes known and unknown bugs in llvm-mca, as well as a quirk in AMD's Zen microarchitectures.Comment: To appear in Proceedings of the ACM on Programming Languages (PACMPL), Vol. 6, No. OOPSLA

Synthesizing Hardware-Software Leakage Contracts for RISC-V Open-Source Processors

Microarchitectural attacks compromise security by exploiting software-visible artifacts of microarchitectural optimizations such as caches and speculative execution. Defending against such attacks at the software level requires an appropriate abstraction at the instruction set architecture (ISA) level that captures microarchitectural leakage. Hardware-software leakage contracts have recently been proposed as such an abstraction. In this paper, we propose a semi-automatic methodology for synthesizing hardware-software leakage contracts for open-source microarchitectures. For a given ISA, our approach relies on human experts to (a) capture the space of possible contracts in the form of contract templates and (b) devise a test-case generation strategy to explore a microarchitecture's potential leakage. For a given implementation of an ISA, these two ingredients are then used to automatically synthesize the most precise leakage contract that is satisfied by the microarchitecture. We have instantiated this methodology for the RISC-V ISA and applied it to the Ibex and CVA6 open-source processors. Our experiments demonstrate the practical applicability of the methodology and uncover subtle and unexpected leaks

An approach for automatic design of application specific instruction set processors (ASIP)

Today‟s hectic world is primarily dominated by electronics. The use of large and hard electronic devices is rapidly being replaced with simple, light and easy-to-carry ones. The past was primarily filled with the notion of performing varied tasks under one roof and the gadgets were built to serve that purpose through the introduction of General Purpose Processors (GPPs) into them. On the contrary, the present tendency is towards devices that are able to perform specific tasks. In the line of this modern concept, the world of embedded system is chiefly dominated by Application Specific Instruction set Processors (ASIPs) because they are geared to perform specific tasks without placing heavy burdens in many respects on the part of the users. Application Specific Instruction set Processors (ASIP), also known as customized processorsare processors designed for particular applications or, for a set of applications.They can be optimized for speed, chip area, and power consumption taking advantage of the flexibility of a synthesized semi-custom implementation. The development of application-specific instruction- set processors is currently the exclusive domain of the semiconductor houses and core vendors. This is due to the fact that building such an architecture is a difficult task that requires expertise in different domains. The main aim of this paper is to propose an approach that will automatically design an ASIP based on the application requirement, which is given as the input to the system. We propose to achieve the same by analyzing different types of RISCMIPS assembly instructions to map the corresponding target VHDL processor to customize maximize the memory access and components of the central processing unit and count the occurrences for the 32-bit RISC CPU based on MIPS. In this work, we also analyze MIPS instruction format, instruction data path, RISC CPU instruction set

Proactive Aging Mitigation in CGRAs through Utilization-Aware Allocation

Resource balancing has been effectively used to mitigate the long-term aging effects of Negative Bias Temperature Instability (NBTI) in multi-core and Graphics Processing Unit (GPU) architectures. In this work, we investigate this strategy in Coarse-Grained Reconfigurable Arrays (CGRAs) with a novel application-to-CGRA allocation approach. By introducing important extensions to the reconfiguration logic and the datapath, we enable the dynamic movement of configurations throughout the fabric and allow overutilized Functional Units (FUs) to recover from stress-induced NBTI aging. Implementing the approach in a resource-constrained state-of-the-art CGRA reveals $2.2\times$ lifetime improvement with negligible performance overheads and less than $10\%$ increase in area.Comment: Please cite this as: M. Brandalero, B. N. Lignati, A. Carlos Schneider Beck, M. Shafique and M. H\"ubner, "Proactive Aging Mitigation in CGRAs through Utilization-Aware Allocation," 2020 57th ACM/IEEE Design Automation Conference (DAC), San Francisco, CA, USA, 2020, pp. 1-6, doi: 10.1109/DAC18072.2020.921858

New Techniques for On-line Testing and Fault Mitigation in GPUs

L'abstract è presente nell'allegato / the abstract is in the attachmen