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From: scroll@reef.cis.ufl.edu (Steve Croll)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: 68K Assembly language question (stack frames)
Message-ID: <27097@uflorida.cis.ufl.EDU>
Date: 23 Feb 91 05:50:55 GMT
References: <DLBRES14.91Feb21073854@pc.usl.edu>
Sender: news@uflorida.cis.ufl.EDU
Distribution: comp
Organization: UF CIS Dept.
Lines: 31

In article <DLBRES14.91Feb21073854@pc.usl.edu> dlbres14@pc.usl.edu (Brumley David M) writes:
>Ok, my question has to do with the lines:
>
>	MOVE.W	8(A6),D0	* Get parameter 1 to D0     
>	CMP.W 	10(A6),D0	* Test against parameter 2 
>
>I simply don't understand how 8(A6) references parameter 1 and 10(A6)
>references parameter 2 when param1 was pushed onto the stack before
>param2!

The references are backwards.  Assuming a7 contained $4000 before the
parameters where pushed, the following stack frame exists immediately
after the link instruction.

$4000
$3FFE <contents of d0.w> ; parameter 1, reference with 10(a6)
$3FFC <contents of d1.w> ; parameter 2, reference with  8(a6)
$3FF8 <return address>
$3FF4 <frame pointer>    ; 'old' a6
$3FF0 <unitialized local storage>

a7 contains $3FF0, a6 contains $3FF4

Note: if your are interfacing C with assembly, parameters are
generally pushed in REVERSE order.  For example, when the call to 
function foo(x,y,z) is made, z is pushed on the stack first, y is pushed
on next, and finally z is pushed on the stack.

-- 
--
Steve Croll (internet: scroll@reef.cis.ufl.edu  home: 904-373-8389)