#[link_section = ".trap.rust"] #[export_name = "_start_trap_rust"]pub extern "C" fn start_trap_rust(trap_frame: *const TrapFrame)
Trap entry point rust (_start_trap_rust)
mcause is read to determine the cause of the trap. XLEN-1 bit indicates
if it's an interrupt or an exception. The result is examined and ExceptionHandler
or one of the core interrupt handlers is called.