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From: frank@sagan.UUCP (Frank Whaley)
Newsgroups: net.micro.pc,net.micro
Subject: Re: Microsoft Assembler (Bug?)
Message-ID: <194@sagan.UUCP>
Date: Tue, 28-Jan-86 20:17:07 EST
Article-I.D.: sagan.194
Posted: Tue Jan 28 20:17:07 1986
Date-Received: Sat, 1-Feb-86 02:36:04 EST
References: <231@argon.kcl-cs.UUCP>
Reply-To: frank@sagan.UUCP (Frank Whaley)
Organization: MicroPro Int'l Corp., San Rafael, CA
Lines: 43
Xref: watmath net.micro.pc:6743 net.micro:13647

In article <231@argon.kcl-cs.UUCP> phil@kcl-cs.UUCP writes:
>I think that the following should assemble without problems:
>PUBLIC	foo
>foo	PROC NEAR
>	mov	[si],OFFSET bar
>foo	ENDP
>
>bar	PROC NEAR
>bar	ENDP
>All of this being in the code segment of course. The error message from MASM
>is:
>	error 35: Operand must have size
>This happens with both V3.0 and V4.0 of MASM. Is this a bug and how do I get
>around it?

The assembler first converts the "OFFSET bar" into a (relative) 
constant, thus forgetting its type (size).  This confuses the opcode 
generator, which doesn't know if SI is pointing to a byte- or 
word-sized data.  Thus MASM complains.  

The only work-around I found was:
	mov	[si],Word Ptr (OFFSET bar)
which looks funny, but assembles correctly.  The parentheses are 
necessary, as: 
	mov	[si],Word Ptr OFFSET bar
again confuses the assembler.  The fact that the compiler outputs this
code is probably a case of premature optimization (the coder missed one
of the cases).  I usually see compilers output something like:
	mov	ax,OFFSET bar
	mov	[si],ax
which is one more byte but one less clock (on an 8088).
-- 
...Frank Whaley, MicroPro Product Development
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