The .EXCEPTION_ENTRY directive indicates the entry point of an
    exception service routine. At routine entry, R3 must contain the
    address of the procedure descriptor. The routine must exit with
    an REI instruction.

    You should declare with the .EXCEPTION_ENTRY directive all of the
    following interrupt service routines:

    o  Interval clock

    o  Interprocessor interrupt

    o  System/processor correctable error

    o  Power failure

    o  System/processor machine abort

    o  Software interrupt