Previous attempts at garbage collection in uncooperative environments have generally used conservative or mostly conservative approaches. We describe a technique for doing fully type-accurate garbage collection in an uncooperative environment, using a "shadow stack" to link structs of pointer-containing variables, together with the data or code needed to trace them. We have implemented this in the Mercury compiler, which generates C code, and present preliminary performance data on the overheads of this technique. We also show how this technique can be extended to handle multithreaded applications.

This article presents Cool, a freely available, portable compiler project. Cool has been used for the past two years in compiler courses at Berkeley and the project is quite mature. Cool is being distributed in the hope that instructors at other institutions can benefit from the efforts of the project developers and the many students who have written Cool compilers. Cool will not suit everyone's needs or tastes; another purpose of this article is to encourage others to make compiler projects publicly available. This article concludes with a few comments about desirable features for a portable compiler project.