Implementation of the Metal Privileged Architecture

Abstract

The privileged architecture of modern computer architectures is expanded through new architectural features that are implemented in hardware or through instruction set extensions. These extensions are tied to particular architecture and operating system developers are not able to customize the privileged mechanisms. As a result, they have to work around fixed abstractions provided by processor vendors to implement desired functionalities. Programmable approaches such as PALcode also remain heavily tied to the hardware and modifying the privileged architecture has to be done by the processor manufacturer. To accelerate operating system development and enable rapid prototyping of new operating system designs and features, we need to rethink the privileged architecture design.

We present a new abstraction called Metal that enables extensions to the architecture by the operating system. It provides system developers with a general-purpose and easy-to-use interface to build a variety of facilities that range from performance measurements to novel privilege models. We implement a simplified version of the Alpha architecture which we call μAlpha and build a prototype of Metal on this architecture. μAlpha is a five-stage pipelined processor with a multi-level cache hierarchy. Lastly, we implement a few facilities in Metal including system calls and transactional memory to show the practicality of Metal.