Given an invocation context block and general-purpose register
    index such that 0 <= index < 16, copy the register value to
    gr_copy, for example, index 4 fetches the invocation context
    block IREG[4] value, which represents the contents of %rsi for
    the context. LIB$X86_GET_GR fails if the index represents a
    scratch register whose contents have not been realized.

    Format
      LIB$X86_GET_GR (invo_context, index, gr_copy)

1  –  Returns

 status

    A value of 1 indicates success. A value of 0 indicates failure.

2  –  Arguments

 invo_context

    OpenVMS usage: invo_context_blk
    type:          structure
    access:        read
    mechanism:     by reference

    Address of a valid invocation context block.

 index

    OpenVMS usage: index
    type:          longword
    access:        read
    mechanism:     by value

    Index into the IREG array of the invocation context block.

 gr_copy

    OpenVMS usage: integer value
    type:          quadword
    access:        write
    mechanism:     by reference

    Address of a quadword to receive the value from the invocation
    context block.