Function link_c_function 

pub fn link_c_function<T: CallsC>(
    linker: &mut Linker<T>,
    engine: &Engine,
    function: CFunction,
    func_ptr: usize,
) -> Result<()>

One wrapper for every C function at func_ptr: its arguments go in the integer and float registers by the C calling convention (call_native_function), whatever the signature. sqlite3_column_text(stmt, i) takes a handle and gives a text, sqlite3_open(name) gives the handle its out-pointer received (NULL there is an error naming the C status), a char * result is copied into the module as a warp text (NULL is ø). One of a library that is not thread-safe holds the native call turn while it runs