Java虚拟机动态类加载的形式化模型

Java虚拟机支持一种功能很强的动态加戡类的机制．它具有惰性加戡、类型安全连接、用户自定义加戡策略、以及劝态名字空间等特性。但是，在Java的早期实现(JDK1．0和1．1)中，这种机制包含了一种称为类型欺骗的严重设计错误．尽管JDK1．2通过引入一种类加戡约束策略修正了这个错误，但是由动态加戡引起的其它形式的类型欺骗仍然存在于JDK1．2和1．3中。本文详细讨论了与动态类加戡相关的类型欺骗问题，提出了一个严格定义Java虚拟机操作语义和静态语义的形式化模型。其中，操作语义描述了类加戡约束策略、字段及方法解析算法等类加戡的主要特性；静态语义采用类型规修正了JDK1．2和1．3中的类型欺骗。

A Formal Model for Dynamic Class Loading in the Java Virtual Machine

The Java Virtual Machine(JVM)supports a novel and powerful class loading mechanism which incorporates all of the following features: lazy loading, type-safety linkage, user-definable class loading policy and multiple names- paces. However, that class loading methanism contained a seerious type-spoofing bug in earlier implementations (JDK 1.0 and 1.1), which leads to type safety violations. Although JDK 1.2 introduces a class loading constraint scheme to fix the bug, subtle type spoofing related to class loaders still exists in JDK 1.2 and 1.3. We develop a formal model to specity the operational semantics and static semantics of the Java virtual machine, rigorously. In the model, the opera- tional semantics describes the main features of class loading such as class loading constraints scheme, field and method resolutions etc. The static semantics uses typing rules to fix the type-spoofing bug in JDK 1.2 and 1.3.