Function kernel_path 

pub fn kernel_path(
    out_dir: &str,
    pkg: &str,
    module_path: &str,
    fn_name: &str,
) -> String

Builds the on-disk .bin path for a kernel, from the perspective of the #[device] macro expansion. module_path!() includes the crate name (my_crate::sub::mod), but the plugin’s artifact names use tcx.def_path_str which strips it (sub::mod); this helper drops the leading crate segment and mangles :: → __ so the stem agrees with rustc_plugin::build_one.