Frequently, VAX MACRO source code must save and restore register
    values, because that is part of the defined interface or because
    the code requires work registers.

    On OpenVMS VAX, code can invoke any number of macros to do
    this. On OpenVMS Alpha and OpenVMS I64, you cannot simply
    replace these macros with 64-bit pushes and pops to and from
    the stack, because there is no guarantee that the macro caller
    has a quadword-aligned stack. Instead, you should replace such
    macro invocations with $PUSH64 and $POP64 macros. These macros,
    located in STARLET.MLB, preserve all 64 bits of a register but
    use longword references to do so.

1  –  $POP64

    Pops the 64-bit value on the top of the stack into a register.

    Format

      $POP64  reg

1.1  –  Parameters

 reg

    Register into which the macro places the 64-bit value from the
    top of the stack.

1.2  –  Description

    $POP64 takes the 64-bit value at the top of the stack and places
    it in a register using longword instructions. This is to avoid
    using quadword instructions when an alignment fault should be
    avoided, but restoring all 64 bits is necessary.

2  –  $PUSH64

    Pushes the contents of a 64-bit register onto the stack.

    Format

      $PUSH64  reg

2.1  –  Parameters

 reg

    Register to be pushed onto the stack.

2.2  –  Description

    $PUSH64 takes a 64-bit register and puts it on the stack
    using longword instructions. This is to avoid using quadword
    instructions when an alignment fault should be avoided, but
    saving all 64 bits is necessary.