The secret sauce: a new Rust code generator
One key to delivering production-grade Windows software with Rust is a new code generation tool for Rust’s compiler, rustc. rustc is designed to use different code-generation back ends, beyond the default LLVM. There are already variants that work with GCC and with Cranelift. If you’ve not come across Cranelift, it’s the code generator of the Bytecode Alliance, used as part of the wasmtime framework. Adding a new code generator is a matter of building a tool that connects to the Rust compiler’s APIs, takes its bytecode output, generates native code, and passes it on to your choice of build pipeline.
This is the role of Microsoft’s rustc_codegen_utc tooling. It’s designed to work with the existing MSVC stack, giving Rust access to a mature, well-tested, proven part of the Windows development platform without needing any changes to your code (compatibility is baked in). This links it directly to the back end of the Visual C++ compiler, a set of tools marshaled by Microsoft’s build system to work with complex projects that mix code and libraries.
Microsoft calls this back end the UTC, for Universal Tuple Compiler. You won’t see that name anywhere, though; the actual code is a DLL, C2.DLL. Code is generated and delivered as .OBJ files where it can then be passed to the MSVC linker and delivered as a binary executable. This allows Rust tooling to take advantage of the decades of work Microsoft has put into both its compilers and build tooling. There’s no need for Microsoft to duplicate that work, ensuring that existing security and resilience features carry forward to the Rust compiler chain. And the resulting code is compatible with C and C++ code that has been passed through the same back end.
