Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!sri-spam!ames!amdahl!bnrmtv!perkins
From: perkins@bnrmtv.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Please explain this MASM/LINK behavior...
Message-ID: <2474@bnrmtv.UUCP>
Date: Tue, 1-Sep-87 15:30:40 EDT
Article-I.D.: bnrmtv.2474
Posted: Tue Sep  1 15:30:40 1987
Date-Received: Fri, 4-Sep-87 01:27:20 EDT
References: <88@wjh12.HARVARD.EDU>
Organization: BNR Inc., Mountain View, California
Lines: 49
Keywords: MASM LINK bug?
Summary: Problem is with MASM, not LINK

In article <88@wjh12.HARVARD.EDU>, lotto@wjh12.HARVARD.EDU (Jerry Lotto) writes:
> Code_Seg	Segment Para 'CODE'

> 	Assume	CS:Code_Seg
> 	Org	100H

> Begin:	mov	ax, Code_Seg:[2ch]

> Code_Seg	Ends
> 	End	Begin

> assembles fine, but generates a link error (invalid object module).

> If you rewrite the Begin line
> to read:

> Begin:	mov	ax, [2ch]

> everything works OK.  I repeat that MASM generates NO warnings
> or errors of any kind.

The problem is with MASM not complaining about the

	mov     ax, Code_Seg:[2ch]

line.  This SHOULD be written as

	mov     ax, cs:[2ch]

if you want to make use of the ASSUME directive and specify the
code segment.  There's no 8086 addressing mode that allows a
segment to be specified as immediate data for a MOV instruction.
Of course, since you're making a .COM file, you can make use of
the fact that CS and DS both already point to your one and only
segment, and omit the segment override, which then defaults to
using DS.  That's what you're doing in the example that works.
If you had any data declarations in this segment, you'd also
want to put in an

	Assume  DS:Code_Seg

In the several iterations of MASM, Microsoft has managed to make
it fairly reliable in assembling correct instructions, but they're
still woefully lacking in error handling capability.
-- 
{hplabs,amdahl,ames}!bnrmtv!perkins         --Henry Perkins

It is better never to have been born.  But who among us has such luck?
One in a million, perhaps.