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From: lotto@wjh12.HARVARD.EDU (Jerry Lotto)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Please explain this MASM/LINK behavior...
Message-ID: <90@wjh12.HARVARD.EDU>
Date: Wed, 2-Sep-87 13:19:28 EDT
Article-I.D.: wjh12.90
Posted: Wed Sep  2 13:19:28 1987
Date-Received: Sat, 5-Sep-87 06:20:05 EDT
References: <88@wjh12.HARVARD.EDU> <2474@bnrmtv.UUCP>
Reply-To: lotto@wjh12.UUCP (Jerry Lotto)
Organization: Harvard Univ. Chem. Dept.
Lines: 36
Keywords: MASM LINK bug?

In article <2474@bnrmtv.UUCP> perkins@bnrmtv.UUCP (Henry Perkins) writes:
>
>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.

Whoa! Segment overrides to operand fetches are NOT a function of the
instruction.  These two cases above should generate the same code!
The CS assume should work two ways. MASM "knows" that Code_Seg is in
CS: and should not have to be told twice.

You are absolutely correct that using CS: explicity works. The point
was that using CS: implicitly fails (but should not).

You also correctly pointed out that my posted workaround ends up using
DS: (the default). I should have specified your line above as the
workaround example in my original posting to illustrate the problem more
clearly.

BTW, Microsoft tech support acknowledged this as a known bug after my
posting and are supposed to be getting back to me with a real work
around that permits me to use a segname. Explicit use of CS: because
there is other code that has to look at stuff in Code_Seg from the
outside. They claim that MASM 5.0 does not share this problem.
-- 
Gerald Lotto - Harvard Chemistry Dept.
UUCP:  {seismo,harpo,ihnp4,linus,allegra,ut-sally}!harvard!lotto
ARPA:  lotto@harvard.harvard.edu