invo_context

    OpenVMS usage:invo_context_blk
    type:         structure
    access:       modify only
    mechanism:    by reference

    Address of a valid invocation context block. The given invocation
    context block is updated to represent the context of the previous
    (calling) frame.

    The LIBICB$V_BOTTOM_OF_STACK flag of the invocation context block
    is set if the target frame represents the end of the invocation
    call chain or if stack corruption is detected.