r9xrsrt: rust9x rust runtime

Absolutely minimal runtime for rust9x. Explicitly no C runtime, just the bare minimum to get a pure Rust program running.

Actually, it's less than the bare minimum: Floating point support is not included (yet?), so none of the expected intrincics are available.

Building

cargo +rust9x build --release

Using

.cargo/config.toml:

[target.'cfg(all(target_family = "rust9x", target_env = "msvc"))']
rustflags = [
  '-Ctarget-feature=+crt-static', # link our libcmt.lib
  '-Clink-arg=/LIBPATH:/home/seri/p/rust/rust9x/r9xrsrt/target/i586-rust9x-windows-msvc/release',
  # any platform sdk with kernel32.lib and ws2_32.lib will do
  '-Clink-arg=/LIBPATH:/home/seri/mnt/ext4/msvc-toolchains/vc8/VC/PlatformSDK/Lib',
]

• Unwinding is not supported, use panic = "abort" in your Cargo.toml.
  • Even if unwinding is disabled, you also need to disable it for the standard library (otherwise it'll still ask for symbols like __CxxFrameHandler3) by using -Zbuild-std=panic_abort in the build command.
• memcpy, memmove, memset are the simplest possible implementations. Use -Zbuild-std-features=compiler-builtins-mem to use optimized compiler-builtins instead.
• If you don't need backtraces, don't specify the backtrace feature, saves 5-50KiB.
• You'll need to always build at opt-level = 1 or higher so that dead code elimination can remove unused/unimplemented functions. Otherwise you'll get link errors for missing symbols like _fma, even if you don't use them.

Example build command:

cargo +rust9x build --target i586-rust9x-windows-msvc -Zbuild-std=std,panic_abort -Zbuild-std-features=backtrace,compiler-builtins-mem --release

Alternatively you can add this to your .cargo/config.toml:

[unstable]
build-std = ["std", "panic_abort"]
build-std-features = ["compiler-builtins-mem", "optimize_for_size"]