Cyclone (programming language)

The Cyclone programming language was intended to be a safe dialect of the C language. It avoids buffer overflows and other vulnerabilities that are possible in C programs by design, without losing the power and convenience of C as a tool for system programming. It is no longer supported by its original developers, with the reference tooling not supporting 64-bit platforms. The Rust language is mentioned by the original developers for having integrated many of the same ideas Cyclone had.

Cyclone development was started as a joint project of AT&T Labs Research and Greg Morrisett's group at Cornell University in 2001. Version 1.0 was released on May 8, 2006.

Language features
Cyclone attempts to avoid some of the common pitfalls of C, while still maintaining its look and performance. To this end, Cyclone places the following limits on programs:
 * checks are inserted to prevent segmentation faults
 * Pointer arithmetic is limited
 * Pointers must be initialized before use (this is enforced by definite assignment analysis)
 * Dangling pointers are prevented through region analysis and limits on
 * Only "safe" casts and unions are allowed
 * into scopes is disallowed
 * labels in different scopes are disallowed
 * Pointer-returning functions must execute
 * and  are not supported

To maintain the tool set that C programmers are used to, Cyclone provides the following extensions:
 * Never- pointers do not require   checks
 * "Fat" pointers support pointer arithmetic with run-time bounds checking
 * Growable regions support a form of safe manual memory management
 * Garbage collection for heap-allocated values
 * Tagged unions support type-varying arguments
 * Injections help automate the use of tagged unions for programmers
 * Polymorphism replaces some uses of
 * varargs are implemented as fat pointers
 * Exceptions replace some uses of  and

For a better high-level introduction to Cyclone, the reasoning behind Cyclone and the source of these lists, see this paper.

Cyclone looks, in general, much like C, but it should be viewed as a C-like language.

Pointer types
Cyclone implements three kinds of pointer: The purpose of introducing these new pointer types is to avoid common problems when using pointers. Take for instance a function, called  that takes a pointer to an int: Although the person who wrote the function  could have inserted   checks, let us assume that for performance reasons they did not. Calling  will result in undefined behavior (typically, although not necessarily, a SIGSEGV signal being sent to the application). To avoid such problems, Cyclone introduces the  pointer type, which can never be. Thus, the "safe" version of  would be: This tells the Cyclone compiler that the argument to  should never be , avoiding the aforementioned undefined behavior. The simple change of  to   saves the programmer from having to write   checks and the operating system from having to trap   pointer dereferences. This extra limit, however, can be a rather large stumbling block for most C programmers, who are used to being able to manipulate their pointers directly with arithmetic. Although this is desirable, it can lead to buffer overflows and other "off-by-one"-style mistakes. To avoid this, the  pointer type is delimited by a known bound, the size of the array. Although this adds overhead due to the extra information stored about the pointer, it improves safety and security. Take for instance a simple (and naïve)  function, written in C: This function assumes that the string being passed in is terminated by NULL. However, what would happen if char buf[6] = {'h','e','l','l','o','!'}; were passed to this string? This is perfectly legal in C, yet would cause  to iterate through memory not necessarily associated with the string. There are functions, such as  which can be used to avoid such problems, but these functions are not standard with every implementation of ANSI C. The Cyclone version of  is not so different from the C version: Here,  bounds itself by the length of the array passed to it, thus not going over the actual length. Each of the kinds of pointer type can be safely cast to each of the others, and arrays and strings are automatically cast to  by the compiler. (Casting from  to   invokes a bounds check, and casting from   to   invokes both a   check and a bounds check. Casting from   to   results in no checks whatsoever; the resulting   pointer has a size of 1.)
 * (the normal type)
 * (the never- pointer), and
 * (the only type with pointer arithmetic allowed, "fat" pointers).

Dangling pointers and region analysis
Consider the following code, in C: The function  allocates an array of chars   on the stack and returns a pointer to the start of. However, the memory used on the stack for  is deallocated when the function returns, so the returned value cannot be used safely outside of the function. While GNU Compiler Collection and other compilers will warn about such code, the following will typically compile without warnings: GNU Compiler Collection can produce warnings for such code as a side-effect of option -O2 or -O3, but there are no guarantees that all such errors will be detected. Cyclone does regional analysis of each segment of code, preventing dangling pointers, such as the one returned from this version of. All of the local variables in a given scope are considered to be part of the same region, separate from the heap or any other local region. Thus, when analyzing, the Cyclone compiler would see that   is a pointer into the local stack, and would report an error.