[kragen]

this sort of exists at https://github.com/cksystemsteaching/selfie (http://selfie.cs.uni-salzburg.at/)

> Selfie is a self-contained 64-bit, 12KLOC C implementation of: (...) a tiny (...) subset of C called C Star (C*) (...) to a tiny (...) subset of RISC-V called RISC-U[;] a[n] (...) emulator (...) that executes RISC-U code[;] (...) a (...) hypervisor (...) that provides RISC-U virtual machines

so they have a self-hosted instruction set architecture, compiler, and operating system, though the operating system is much simpler than xv6. because the instruction set is a subset of risc-v you can run its code on actual risc-v hardware (or qemu-system-riscv), but presumably you could also design risc-u hardware in verilog that was simpler than a full implementation of rv64i with whatever extensions the hypervisor needs