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Q79821: FIX: MASM 6.0 May Incorrectly Generate A4000 for CMP

Article: Q79821
Product(s): Microsoft Macro Assembler
Version(s): 6.0
Operating System(s): 
Keyword(s): 
Last Modified: 04-MAY-2001

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The information in this article applies to:

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

Microsoft Macro Assembler (MASM) version 6.0 will incorrectly generate the
following error when the sample code below is assembled:

  A4000: cannot modify READONLY segment

CAUSE
=====

This problem occurs because the segment is tagged as READONLY, and MASM treats
the CMP instruction as if it modifies memory. This is incorrect behavior because
the CMP instruction does not modify any memory.

RESOLUTION
==========

To work around this problem, either remove the READONLY tag from the segment or
ignore the warning when it is generated for CMP instructions.

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

The sample code below reproduces the problem.

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

  ; Assemble options needed: none

  code    SEGMENT word public readonly 'code'
          ASSUME cs:code
          cmp word ptr cs:[di], 0
  code    ENDS

  END

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

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

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