Macro register_debug_put_char 

macro_rules! register_debug_put_char {
    ($(#[$attrs:meta])* $path:path) => { ... };
}

Registers a function to be used by debug_put_char, debug_print!, and debug_println!.

This macro uses the function $path to define the following symbol:

extern "Rust" {
    fn __sel4_panicking_env__debug_put_char(c: u8);
}