Rust programs

grease has experimental support for analyzing Rust programs, both when compiled to executables and when compiled to LLVM bitcode. From a grease perspective, the average Rust program is significantly more complicated than, say, an average C program for a variety of reasons, including:

• Rust has a large standard library, and much of the standard library will be included in a typical Rust program. As such, grease has to simulate more code on average.
• Some library functions (e.g., Rust functions related to string formatting or panicking) have rather complex implementations that are difficult to symbolically execute. As such, it is often necessary to override tricky library functions to replace them with simpler implementations.
• The code that rustc produces often looks quite different from the code that a typical C compiler would produce. grease's memory model is designed to work well with C compiler idioms, but perhaps not as much with rustc idioms.

As a general rule, it is wise to invoke grease with the --rust flag when simulating Rust programs. Doing so changes some of grease's simulator settings to be more permissive when analyzing code so that it does not mistakenly flag common rustc idioms as undefined behavior. This is especially important for dealing with Rust enums, as grease will often flag enum-related code as reading from uninitialized memory unless --rust is enabled.