Known Limitations of Translation

This document is to track things that we know the translator can't handle, as well as things it probably won't ever handle.

Unimplemented

• variadic function definitions (blocked by Rust language)
• preserving comments (WIP)
• long double and _Complex types (partially blocked by Rust language)
• GNU packed and aligned structs (blocked by Rust language: https://github.com/rust-lang/rust/issues/59154)

Unimplemented, might be implementable but very low priority

• restrict pointers (Rust has references)
• inline assembly
• macros
• SIMD functions with no rust equivalent

Likely won't ever support

• longjmp/setjmp Although there are LLVM intrinsics for these, it is unclear how these interact with Rust (esp. idiomatic Rust).
• jumps into and out of statement expressions We support GNU C statement expressions, but we can not handle jumping into or out of these. Both entry and exit into the expression have to be through the usual fall-through evaluation of the expression.

Nightly Rust Requirements

• The translator itself requires the nightly listed here: https://github.com/immunant/c2rust/blob/master/rust-toolchain
• A subset of translated code requires nightly. This is tracked here: https://github.com/immunant/c2rust/issues/46

Miscellaneous

• LLVM 7 improves support for X86 intrinsics; if you are translating SIMD code, we recommend you use LLVM 7 or later.