VMS Help MACRO, /MIGRATION, Compiler Directives, .JSB32 ENTRY, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The .JSB32_ENTRY directive is an alternative way of declaring a
    JSB entry point. It is designed to streamline the declaration of
    VAX MACRO routines that operate within a well-defined, bounded
    application environment, such as that of a single application
    or a self-contained subsystem. For any routine declared with the
    .JSB32_ENTRY directive, the compiler does not automatically save
    or restore any VAX registers (R2 through R12), therefore leaving
    the current 32-bit operation untouched. When you use the .JSB32_
    ENTRY directive to declare a JSB entry point, you are responsible
    for declaring and saving registers which must be preserved.

    If the externally visible entry points of a subsystem can be
    called from the 64-bit environment, those entry points should
    not be declared with .JSB32_ENTRY. Instead, .JSB_ENTRY (or .CALL_
    ENTRY) should be used so that the full 64-bit register values are
    saved, if necessary.