rustup target list
rustc +nightly -Z unstable-options --print target-features --target=riscv64gc-unknown-none-elf
rustc +nightly -Z unstable-options --print target-spec-json
zig targets > zig_targets.json
zig build-exe -target riscv64-linux -ODebug -fsingle-threaded zig_hello.zig
zig build-exe -target riscv64-freestanding -ODebug hello.s --name hello.rv