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Path: utzoo!linus!decvax!ittvax!sii!mem
From: mem@sii.UUCP (Mark Mallett)
Newsgroups: net.micro.68k
Subject: Re: nargs
Message-ID: <363@sii.UUCP>
Date: Mon, 26-Dec-83 23:40:44 EST
Article-I.D.: sii.363
Posted: Mon Dec 26 23:40:44 1983
Date-Received: Tue, 27-Dec-83 04:16:39 EST
Lines: 31

b
To the nargs() routine submitted by fortune!shah, I'd suggest recognizing
an LEA stack adjustment instruction, i.e.,

	LEA	n*4(SP),SP

While I know of no 68000 C compilers that generate this sort of fixup,
it is the sort of thing that assembler language programmers would think
of first (me, anyway); and it seems worth anticipating of future compilers.

I'd also like to opine that looking at the instruction after the call
instruction to determine the number of arguments is not a 100% accurate
way to get the number of arguments passed, for these reasons:

    - It doesn't take into account different argument types (e.g.
      doubles).

    - I can imagine compilers generating stack-fixup instructions in
      dealing with variables bound to local scopes.  Can't you?

    - The Whitesmith's compiler seems to keep a free location on the
      top of the stack to deal with calls to routines where only one
      value is passed.  At least this is what it appears to do; I'm
      easily fooled.  This is something that can't be detected by the
      subroutine, and is an optimization I'd easily expect of compiler
      writers.

But I can't think of any other way to do it.

Mark E. Mallett
decvax!sii!mem