extern "C" { fn call_guest_fn(f: u32) -> u32; fn call_guest_fn2(f: u32) -> u32; fn host_callback() -> u32; } #[no_mangle] fn test_callback() -> u32 { 42 } #[no_mangle] fn test_callback2() -> u32 { 45 } fn main() { unsafe { call_guest_fn(test_callback as usize as u32) }; unsafe { call_guest_fn(host_callback as usize as u32) }; unsafe { call_guest_fn(test_callback2 as usize as u32) }; unsafe { call_guest_fn2(test_callback2 as usize as u32) }; unsafe { call_guest_fn2(test_callback as usize as u32) }; unsafe { call_guest_fn2(host_callback as usize as u32) }; }