The crustc repository is C code that you compile with GCC and GNU make into a working Rust compiler. Point make at a matching LLVM build and the binary it produces reports rustc 1.98.0-nightly (c712ea946 2026-06-16) , then goes on to build core, alloc and std. The author built it on ARM64 Linux with GCC 13.3.0 and the LLD 18.1.3 linker. An unoptimized build takes about 78 seconds of wall time (937 seconds of user time with make -j20 ). It still needs LLVM at runtime, because rustc uses LLVM, so the repo asks you to supply libLLVM.so.22.1-rust-1.98.0-nightly from the matching nightly toolchain rather than shipping a binary.

That is rustc itself, translated to C and built by a C compiler. The repo is a demo for cilly, the author's Rust-to-C toolchain and, by their count, the 14th attempt at the problem over three years (rustc_codegen_clr was an earlier public one). cilly is a Rust library that generates C plus a rustc backend plugin.…