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From: peter@megamax.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: Megamax WON'T compile .... structures passed to functions
Message-ID: <754@megamax.UUCP>
Date: Wed, 27-May-87 13:31:56 EDT
Article-I.D.: megamax.754
Posted: Wed May 27 13:31:56 1987
Date-Received: Fri, 29-May-87 04:46:31 EDT
References: <280@nikhefh.UUCP>
Reply-To: peter@megamax.UUCP (Peter Taliancich)
Organization: Megamax, Inc; Dallas, TX
Lines: 123
Keywords: megamax

> 
> In response to the denial of a few persons that Megamax won't accept 
> passing of structures to functions: The Megamax compiler will accept the C
> code. It will not issue any warning, but the code it generates it 
> totally wrong!
> 
> 
> Megamax disassembler V1.0, Copyright (C) 1986 by Megamax Inc.
> 
> CODE SEG "main"
> main:/* global */
>	LINK	A6,L$0
>	PEA	-4(A6)				!!! here main pushes the  ADDRESS of the structure
>								test, when it should push the contents of it.
>	JSR	ftest(PC)
>	ADDQ.L	#4,A7
> L1:
>	UNLK	A6
>	RTS
> L$0:	.EQU	#-4
> _initargcv:/* global */
>	RTS
> ftest:/* global */
>	LINK	A6,L$2
>	MOVE	#1,8(A6)		!!! this would be t.t1 = 1, the ftest function
>								apparantly expects the structure to be on
>								stack, unfortunately only the address of the
>								structure is on the stack. (Bomb!!)
>	MOVE	#2,10(A6)
> L3:
>	UNLK	A6
>	RTS
> L$2:	.EQU	#0
> 
> 
> 
> This example was compiled with version 1.1 of the Megamax compiler.
> I hope this makes clear that Megamax does not 'allow' structure passing.
> 
> Gert Poletiek.

	Structure passing and assignment have been a part of the Megamax C 
language since the very first day on the Atari.  The code that was generated by
the compiler using the example program that was sent is as follows:

This is the test program:


typedef struct {
	int	t1;
	int	t2;
} test;

extern test ftest();

main()
{
	test test;

	ftest(test);
}

ftest(t)
	test t;
{
	t.t1 = 1;
	t.t2 = 2;

	return t;
}


This is the disassembled object module:


CODE SEG "main"
main:	/* global */
	LINK	A6,L$0
	LEA	-4(A6),A1

	SUBA	#4,A7
	MOVE.L	A7,A0
	MOVEQ	#1,D0
	JSR	_blockmv(PC)   <--  place structure onto the stack

	JSR	ftest(PC)      <--  do structure thing
	ADDQ.L	#4,A7

	LEA	-4(A6),A0
	MOVEQ	#1,D0
	JSR	_blockmv(PC)   <-- assign struct with returned struct from function
L1:
	UNLK	A6
	RTS
L$0:	.EQU	#-4

BSS SEG "bss"
1struct:
	.WORD	#4         <-- hold place for returned structure

CODE SEG "main"
ftest:	/* global */
	LINK	A6,L$2
	MOVE	#1,8(A6)    <-- access members of structure on the stack
	MOVE	#2,10(A6)

	LEA	8(A6),A1
	LEA	1struct(A4),A0
	MOVEQ	#1,D0
	JSR	_blockmv(PC)    <-- hold place for returning structure 
	LEA	1struct(A4),A1

	UNLK	A6
	RTS
L$2:	.EQU	#0


This source file was compiled with Megamax C v1.1.  Even though it is generally 
not good practice to depend on structure passing with other C systems the 
Megamax system definitely supports it.  If your Megamax C compiler doesn't seem 
to generate the proper code, send in your disks.  The upgrade to version 1.1 of 
the Megamax Development System is free (please send Self Addressed and Stamped 
Disk Mailer.)