Microsoft KB Archive/29735

= FIX: LES Instruction Assembles Incorrectly =

Article ID: 29735

Article Last Modified on 10/20/2003

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APPLIES TO


 * Microsoft Macro Assembler 5.1 Standard Edition
 * Microsoft Macro Assembler 5.1a

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This article was previously published under Q29735



SYMPTOMS
The program example below demonstrates a problem with the LES instructions in Microsoft Macro Assembler (MASM) versions 5.1 and 5.1a. The first LES instruction (Parm1) assembles correctly, but the second instruction (Parm2) generates the error message:

error A2056: Immediate mode illegal

The only difference between the two instructions is the order of the arguments. In earlier versions of MASM, they produced identical code.



CAUSE
The problem is with the type operator and the way it handles registers inside brackets ([]). The type operator makes things a constant on the left of the expression.

Parm1 works because it handles registers inside brackets differently. &quot;TYPE x&quot; turns bp into a constant; +10 then turns it back into an addressing mode.

However, in Parm2, bp+10 has been turned into an addressing mode, which is then turned into a constant by &quot;TYPE x&quot;. This difference is demonstrated in the sample code below.



STATUS
Microsoft has confirmed this to be a problem in MASM versions 5.1 and 5.1a. This problem was corrected in MASM version 6.0.



Sample Code
; Assemble options needed: none

.MODEL  small

x STRUC y DD ? x ENDS

Parm1 EQU DWORD PTR [bp+TYPE x+10] Parm2 EQU DWORD PTR [bp+10+TYPE x]

.CODE begin: les di,Parm1 les di,Parm2

END begin

Additional query words: 5.10 5.10a buglist5.10 buglist5.10a fixlist6.00

Keywords: kbfix KB29735

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