Introduction to Cyclone

Cyclone is a language for C programmers who want to write secure, robust programs. It’s a dialect of C designed to be safe: free of crashes, buffer overflows, format string attacks, and so on. Careful C programmers can produce safe C programs, but, in practice, many C programs are unsafe. Our goal is to make all Cyclone programs safe, regardless of how carefully they were written. All Cyclone programs must pass a combination of compile-time, link-time, and run-time checks designed to ensure safety.

There are other safe programming languages, including Java, ML, and Scheme. Cyclone is novel because its syntax, types, and semantics are based closely on C. This makes it easier to interface Cyclone with legacy C code, or port C programs to Cyclone. And writing a new program in Cyclone “feels” like programming in C: Cyclone tries to give programmers the same control over data representations, memory management, and performance that C has.

Cyclone’s combination of performance, control, and safety make it a good language for writing systems and security software. Writing such software in Cyclone will, in turn, motivate new research into safe, low-level languages. For instance, originally, all heap-allocated data in Cyclone were reclaimed via a conservative garbage collector. Though the garbage collector ensures safety by preventing programs from accessing deallocated objects, it also kept Cyclone from being used in latency-critical or space-sensitive applications such as network protocols or device drivers. To address this shortcoming, we have added a region-based memory management system based on the work of Tofte and Talpin. The region-based memory manager allows you some real-time control over memory management and can significantly reduce space overheads when compared to a conventional garbage collector. Furthermore, the region type system ensures the same safety properties as a collector: objects cannot be accessed outside of their lifetimes.

This manual is meant to provide an informal introduction to Cyclone. We have tried to write the manual from the perspective of a C programmer who wishes either to port code from C to Cyclone, or develop a new system using Cyclone. Therefore, we assume a fairly complete understanding of C.

Obviously, Cyclone is a work in progress and we expect to make substantial changes to the design and implementation. Your feedback (and patience) is greatly appreciated.


The people involved in the development of Cyclone are now at Harvard, AT&T, Maryland, and Washington; much work began at Cornell. Dan Grossman, Trevor Jim, and Greg Morrisett worked out the initial design and implementation, basing the language to some degree on Popcorn, a safe-C-like language that was developed at Cornell as part of the Typed Assembly Language (TAL) project. Mike Hicks ported a number of libraries and programs to Cyclone, helped with the configuration and installation procedures, and has been the lead on adding unique and reference-counted pointers to Cyclone, among other things. Mathieu Baudet contributed the bulk of the code for the link-checker. Matthew Harris did much of the hard work needed to wrap and import the necessary libraries. Yanling Wang ported bison and flex to Cyclone. James Cheney has added support for representation types, singleton ints, marshalling support, etc. Nikhil Swamy added support for reaps and the cyclone-inf mode. All of these people have also contributed by finding and fixing various bugs. A number of other people have also helped to find bugs and/or contributed key design ideas including Mujtaba Ali, Fred Smith, Nathan Lutchansky, Rajit Manohar, Bart Samwell, Emmanuel Schanzer, Frances Spalding, Jeff Vinocur, and David Walker.