known-limitations.md

Known Limitations of Translation

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

Partially implemented, experimental

• variadic function definitions and macros that operate on va_lists
• preserving comments
• GNU inline assembly
• long double type (Linux only)

Unimplemented

• _Complex type (partially blocked by Rust language)
• C11 _Atomic type-specifier and type-qualifier (see https://en.cppreference.com/w/c/language/atomic)
• Using long double type in variadic functions (blocked on Rust language; see immunant#154)
• Non-x86/64 SIMD function/types and x86/64 SIMD function/types which have no Rust equivalent
• Certain compiler builtins (see e.g. immunant#88)
• Exposing functions with different names and linkage types (blocked on Rust language. Example: https://github.com/ConradIrwin/libxml2/blob/master/elfgcchack.h)

Unimplemented, might be implementable

• GNU packed structs (Rust has #[repr(packed)] compatible with #[repr(C)])
• restrict pointers (Rust has references)
• macros
• GNU labels-as-values (immunant#221)

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.