The L4 microkernel has undergone 20 years of use and evolution. It has an active user and developer community, and there are commercial versions that are deployed on a large scale and in safety-critical systems. In this article we examine the lessons learnt in those 20 years about microkernel design and implementation. We revisit the L4 design articles and examine the evolution of design and implementation from the original L4 to the latest generation of L4 kernels. We specifically look at seL4, which has pushed the L4 model furthest and was the first OS kernel to undergo a complete formal verification of its implementation as well as a sound analysis of worst-case execution times. We demonstrate that while much has changed, the fundamental principles of minimality, generality, and high inter-process communication (IPC) performance remain the main drivers of design and implementation decisions.

中文翻译：

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L4 微内核

L4 微内核经历了 20 年的使用和演变。它有一个活跃的用户和开发者社区，并且有大规模部署在安全关键系统中的商业版本。在本文中，我们研究了这 20 年来关于微内核设计和实现的经验教训。我们重温了 L4 设计文章，研究了从最初的 L4 到最新一代 L4 内核的设计和实现的演变。我们特别关注 seL4，它把 L4 模型推得最远，是第一个对其实现进行完整形式验证以及对最坏情况执行时间进行合理分析的 OS 内核。我们证明，虽然发生了很大变化，但最小化、通用性、