libcore.c

#include <stdio.h>

int hello(char args[])
{
        printf("%s\n", args);
        return 0;
}

main.rs

extern crate libc;

#[link(name="libcore")]
extern {
	fn hello(args: &str) -> i32;
}

fn main(){
	let input = "hello, cffi!";
	unsafe{
		hello(&input);
		}
}