pc_value

    OpenVMS usage:PC value
    type:         quadword
    access:       read
    mechanism:    by reference

    Address of a location that contains the PC value. pc_value
    is used to find the unwind information block and the unwind
    information block operating system-specific data area address.

 unwind_ossd_p

    OpenVMS usage:address
    type:         quadword
    access:       write
    mechanism:    by reference

    Address of a quadword to receive the address of the operating
    system-specific data area.