119 lines
4.3 KiB
NASM
119 lines
4.3 KiB
NASM
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TITLE ABSOLUTE - helper for assembly routines
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;***
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; ABSOLUTE - Helper for calling BASIC interpreter assembly routines
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;
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; Copyright <C> 1986, Microsoft Corporation
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;
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;Purpose:
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; Allow a BASIC program to call a routine which is located at an
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; absolute memory address in the DEF SEG.
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;
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; The form of the call is:
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;
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; CALL ABSOLUTE(<param>,...,<loc>)
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;
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; where
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; <param>,... - zero or more parameters for the assembly routine
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; <loc> - an Integer variable that contains the
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; location in the DEF SEG of the start of
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; the assembly routine
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;
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; The location parameter will be removed, and the routine at DEF SEG:<loc>
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; will be called with the remaining parameters.
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;
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; Notes:
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; - The parameters are not checked or verified before being passed
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; to the assembly routine.
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; - CALL must be used. CALLS will cause execution to jump to a
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; random location.
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; - The DOSSEG, .MODEL, .CODE, and .DATA? directives are part of
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; the simplified segment system of MASM 5.0. If you have an
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; earlier version of MASM, you must modify the source to define
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; the segments required by Microsoft high-level languages. These
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; segments are discussed in Appendix C of "Learning and Using
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; QuickBASIC."
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;
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;******************************************************************************
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;
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DOSSEG ;requires MASM 5.0 or higher
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.MODEL medium
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; Define the routine as public.
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PUBLIC ABSOLUTE
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; Define the seg segment
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.DATA?
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EXTRN b$seg:WORD ;seg segment
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;***
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; ABSOLUTE - Call absolute address
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;
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;Purpose:
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; Routine which can be directly called from the basic level which in turn
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; calls an absolute address.
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;
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;Entry:
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; The actual number of parameters is variable, and depends on the routine
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; that ABSOLUTE will in turn call. The LAST parameter pushed MUST be the DS
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; offset of an integer variable containing the offset of the routine to be
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; called. The current DEF SEG is used as the segment for the call.
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;
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;Exit:
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; Whatever the called routine elects. We do NOT return here.
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;
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;Uses:
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; This routine follows convention, but does no saving or checking of the code
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; actually called.
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;
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;Notes:
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; The called routine receives control with all parameters passed to ABSOLUTE,
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; except the offset integer, on the stack in Pascal convention. The return
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; address present is back to the BASIC level code which CALLed ABSOLUTE.
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;
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; Stack on call to ABSOLUTE:
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;
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;
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; \ Variable number of parameters \
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; | to routine to be CALLed |
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; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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; | Near pointer to I2 var containing |
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; | the offset of the routine to CALL |
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; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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; |CS |
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; + Far return address to caller of ABSOLUTE +
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; [SP] -> |IP |
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; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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;
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; Stack on transfer to called routine:
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;
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; \ Variable number of parameters \
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; | to routine to be CALLed |
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; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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; |CS |
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; + Far return address to caller of ABSOLUTE +
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; [SP] -> |IP |
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; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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;
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;******************************************************************************
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.CODE
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ABSOLUTE PROC FAR
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POP AX ;return offset
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POP DX ;return segment
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POP BX ;get pointer to routine address
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PUSH DX ;restore return address
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PUSH AX
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PUSH [b$seg] ;stack DEF SEG segment
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PUSH [BX] ;stack routine offset
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RET ;jump to ABSOLUTE routine
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ABSOLUTE ENDP
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END
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