bar.c

void foo();
void factory();

struct {
  int version;
  void *entry_data;
  int entry_len;
  void *children_data;
  int children_len;
  void *f;
} _rust_crate_map_toplevel = {
  2, 
  0, 0,
  0, 0,
  factory
};

int main() {
  foo();
  return 0;
}

foo.rs

extern mod rustuv;

use std::rt;
use std::rt::rtio::EventLoop;
use std::ptr;

#[no_mangle]
pub extern "C" fn factory() -> ~EventLoop {
  rustuv::uvio::new_loop()
}

#[no_mangle]
pub extern "C" fn foo() {
  do rt::start(0, ptr::null()) {
    println!("hello");
  };
}

Makefile

all: libfoo.dylib bar.c
	clang bar.c -o bar -L. -lfoo -Wl,-rpath,`pwd`

libfoo.dylib: foo.rs
	rustc --lib foo.rs 
	ln -nsf libfoo-*.dylib libfoo.dylib