Program analysis for safety guarantees in a Java virtual machine written in Java

In this paper, we report on our experiences with guaranteeing GC-pointer sa fety when using unsafe low-level language extensions to implement a JVM in Java. We give an overview of the original unsafe language extensions that w ere defined for use by Jalapeno implementers, and introduce sanitized repla cements that capture common idioms while also guaranteeing GO-pointer safet y. We also outline some simple static and dynamic checks for correct usage of low-level operations, and examine how code containing low-level operatio ns can be optimized correctly and effectively.