Michael Hicks
Scott Nettles
Abstract
Many important applications must run continuously and without interruption, and yet also must be changed to fix bugs or upgrade functionality. No prior general-purpose methodology for dynamic updating achieves a practical balance between flexibility, robustness, low overhead, ease of use, and low cost.We present an approach for C-like languages that provides type-safe dynamic updating of native code in an extremely flexible manner---code, data, and types may be updated, at programmer-determined times---and permits the use of automated tools to aid the programmer in the updating process. Our system is based on dynamic patches that contain both the updated code and the code needed to transition from the old version to the new. A novel aspect of our patches is that they consist of verifiable native code (e.g. Proof-Carrying Code or Typed Assembly Language), which is native code accompanied by annotations that allow online verification of the code's safety. We discuss how patches are generated mostly automatically, how they are applied using dynamic-linking technology, and how code is compiled to make it updateable.To concretely illustrate our system, we have implemented a dynamically updateable web server, FlashEd. We discuss our experience building and maintaining FlashEd, and generalize to present observations about updateable software development. Performance experiments show that for FlashEd, the overhead due to updating is low: typically less than 1 percent.
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Index Terms
- Dynamic software updating
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Reviews
Maulik A Dave
Many software applications must run continuously, this presents problems when these applications need to be updated or upgraded. This paper proposes a methodology for updating software, using dynamic patch technology. After a brief introduction, the authors' approach is discussed in the second section. The goals are flexibility, robustness, ease of use, and low overhead. Section 3 is devoted to a detailed conceptual description of dynamic patches. The term "dynamic patch" describes dynamic changes between two program modules. It consists of new code, a state transformer function, and a set of stubs. The fourth section contains implementation details. A patch is dynamically linked to the running program. The function calls and data of the running program are redirected to new function stubs and new data definitions. The prototype implementation targets typed assembly language (TAL). Section 5 discusses the automatic generation of patches. The effect of patches on program timing is discussed in the sixth section. The authors propose specifying these timings statically. The next two sections describe a case study done on a Web server, and a corresponding performance analysis. Before concluding, the previously set goals are discussed. This work attempts to choose the best alternatives in the methodology. Related approaches are compared throughout. A programmer new to the field of dynamic patches will be able to easily understand the paper. Online Computing Reviews Service
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