Hello World in Rust without the runtime (libcore and libc only)

hello.rs

#![no_std]
extern crate core;
use core::option::{None, Some};
use core::iter::Iterator;
use core::str::StrSlice;

#[lang="stack_exhausted"]
pub extern "C" fn rust_stack_exhausted() {
    unsafe { core::intrinsics::abort() }
}

#[lang="begin_unwind"] pub fn begin_unwind(){ }

#[lang="eh_personality"] pub fn eh_personality() {}

#[link(name="c")]
#[allow(ctypes)]
extern { fn putchar(_:int)->int; }

#[start]
fn start(_:int, _:**u8)->int { 
  for c in "Hello, World!\n".bytes() {
    unsafe {putchar(c as int); }
  }
  0
}