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Q78862: FIX: Incorrect Code Generated If Operand Is [eax][eax]

Article: Q78862
Product(s): Microsoft Macro Assembler
Version(s): 6.0
Operating System(s): 
Keyword(s): 
Last Modified: 04-MAY-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Macro Assembler (MASM), version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

In the Microsoft Macro Assembler (MASM) version 6.0, incorrect code is generated
for instructions, such as the following, using the operand [eax][eax]:

  lea edi, [eax][eax]
  mov edi, [eax][eax]

RESOLUTION
==========

A workaround for this problem is to embed the opcode for the instruction
directly in the code. The sample code below demonstrates this method.

STATUS
======

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

MORE INFORMATION
================

A listing file from the following program will show that the instruction lea
edi, [eax][eax] is encoded as 8D 3C 3A. However, the code actually placed into
the executable is 8D 3C. The correct code in the case of lea edi, [eax][eax] is
8D 3C 00. Note that the operand [eax][eax] is available only when using the .386
or .486 directives.

Sample Code
-----------

  ; Assembler options needed: none

  .386
  .MODEL small

  CODE32 SEGMENT DWORD PUBLIC USE32 'CODE'
  ASSUME CS:CODE32
  main PROC
      lea edi, [eax][eax] ; Replace this by BYTE 8Dh, 3Ch, 00h
                          ; since the code generated by it is
                          ; 8D 3C 3A, which is incorrect.
      mov edi, [eax][eax] ; Replace this by BYTE 8Bh, 3Ch, 00h
                          ; since the code generated by it is
                          ; 8B 3C 3A, which is incorrect.
      ret
  main ENDP
  CODE32 ENDS

  END main

Additional query words: 6.00 buglist6.00 fixlist6.00a

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600
Version           : :6.0
Solution Type     : kbfix

=============================================================================

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