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

    Declares the entry point of a called routine to the compiler.
    This entry declaration will save and restore the full 64 bits of
    any registers (except R0 and R1) that are modified by the routine
    and are not declared as scratch or output.

    Format

      .CALL_ENTRY  [max_args] [,home_args=TRUE|FALSE]

                   [,quad_args=TRUE|FALSE] [,input] [,output]

                   [,scratch] [,preserve] [,label]

1 - Parameters

 max_args

    Maximum number of arguments the called procedure expects. The
    compiler uses this value as the number of longwords it allocates
    in the fixed temporary region of the stack frame, if the argument
    list must be homed. If homing is not necessary, the max_args
    count is not required. The compiler flags procedure entry
    points, where max_args has not been specified, that require homed
    argument lists.

    Note that, for .CALL_ENTRY routines in which max_args exceeds
    14, the compiler uses the received argument count, or max_args,
    whichever is smaller, when homing the argument list.

 home_args=TRUE|FALSE

    Indication to the compiler that the called procedure's argument
    list should or should not be homed. The home_args argument
    overrides the compiler's default logicfor determining the
    circumstances under which an argument list must be homed.

 quad_args=TRUE|FALSE

    Indication to the compiler that the called procedure's argument
    list will have quadword references.

 input=<>

    Register set that indicates those registers from which the
    routine receives input values.

    This register set informs the compiler that the registers
    specified have meaningful values at routine entry and are
    unavailable for use as temporary registers even before the first
    compiler-detected use of the registers. Specifying registers in
    this register set affects compiler temporary register usage in
    two cases:

    o  If you are using the VAXREGS optimization switch. This
       optimization allows the compiler to use as temporary registers
       any of the VAX registers which are not explicitly being used
       by the VAX MACRO code.

    o  If you are explicitly using any of the Alpha registers (R13
       and above).

    In either of these cases, if you do not specify a register that
    is being used as input in the input argument, the compiler may
    use the register as a temporary register, corrupting the input
    value.

    This register set has no effect on the compiler's default
    register preservation behavior. If you are not using the VAXREGS
    optimization switch or any of the Alpha registers, the input mask
    is used only to document your routine.

 output=<>

    Register set that indicates those registers to which the routine
    assigns values that are returned to the routine's caller.
    Registers included in this register set are not saved and
    restored by the compiler, even if they are modified by the
    routine.

    This register set also informs the compiler that the registers
    specified have meaningful values at routine exit and are
    unavailable for use as temporary registers even after the last
    compiler-detected use of the registers. Specifying registers in
    this register set affects compiler temporary register usage in
    two cases:

    o  If you are using the VAXREGS optimization switch. This
       optimization allows the compiler to use as temporary registers
       any of the VAX registers which are not explicitly being used
       by the VAX MACRO code.

    o  If you are explicitly using any of the Alpha registers (R13
       and above).

    In either of these cases, if you do not specify a register that
    is being used as output in the output argument, the compiler may
    use the register as a temporary register, corrupting the output
    value.

 scratch=<>

    Register set that indicates registers that are used within the
    routine but which should not be saved and restored at routine
    entry and exit. The caller of the routine does not expect to
    receive output values nor does it expect the registers to be
    preserved. Registers included in this register set are not saved
    and restored by the compiler, even if they are modified by the
    routine.

    This also pertains to the compiler's temporary register usage.
    The compiler may use registers R13 and above as temporary
    registers if they are unused in the routine source code. Because
    R13 through R15 must be preserved, if modified, according to
    the OpenVMS Alpha calling standard, the compiler preserves those
    registers if it uses them.

    However, if they appear in the scratch register set declaration,
    the compiler will not preserve them if it uses them as temporary
    registers. As a result, these registers may be scratched at
    routine exit, even if they were not used in the routine source
    but are in the scratch set. If the VAXREGS optimization is used,
    this applies to registers R2 through R12, as well.

 preserve=<>

    Register set that indicates those registers that should be
    preserved over the routine call. This should include only those
    registers that are modified and whose full 64-bit contents should
    be saved and restored.

    This register set causes registers to be preserved whether or
    not they would have been preserved automatically by the compiler.
    Note that because R0 and R1 are scratch registers, by calling
    standard definition, the compiler never saves and restores them
    unless you specify them in this register set.

    This register set overrides the output and scratch register sets.
    If you specify a register both in the preserve register set and
    in the output or scratch register sets, the compiler will report
    the warning:

    %AMAC-W-REGDECCON, register declaration conflict in routine A

 label=name

    Optionally specify a label as in a VAX MACRO .ENTRY directive.
    This can be used if a module is to be common between VAX and
    Alpha, the VAX version needs to reference the entry with a .MASK
    directive, and the Alpha version needs to use one or more of
    the special .CALL_ENTRY parameters. When the label parameter
    is specified and the symbol VAX is defined, an .ENTRY directive
    is used. If the symbol VAX is not defined, it creates the label
    and does a normal .CALL_ENTRY. Note that label is not the first
    parameter. Therefore, you cannot simply replace .ENTRY with
    .CALL_ENTRY. You must use the label parameter declaration.