Q74663: FIX: ALIGN Following DUP Operator or Structure May Fail

Article: Q74663
Product(s): Microsoft Macro Assembler
Version(s): MS-DOS: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
========

The Microsoft Macro Assembler (MASM) version 6.0 may generate an incorrect
alignment for the ALIGN or EVEN directives if a statement containing the DUP
operator or a structure definition is placed before the directive. For the
problem to occur, the DUP operator or structure definition can be placed
anywhere before the directive but within the segment.

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 programs below demonstrate the problem with the ALIGN directive. In
Sample Code 1, a statement with the DUP operator is used before the ALIGN
statement. The assembly listing shows:

     0000                _DATA segment dword
     0000 0005 [         buffer BYTE 5 dup (?)
               00
               ]
     0005 00             byte ?
                         ALIGN 4
     0007 00             nextvar BYTE ?
     0008                _DATA ends

It can be seen in the assembly listing that the offset for the variable "nextvar"
is incorrectly set to 7 rather than 8.

In Sample Code 2, a structure definition is placed before the ALIGN statement.
The assembly listing below shows the results:

     0005                structdecl struct
     0000 00             byte ?
     0001 00             byte ?
     0002 00             byte ?
     0003 00             byte ?
     0004 00             byte ?
                         structdecl ends

     0000                _DATA segment dword
     0000 00 00 00 00 00 mystruct structdecl <>
     0005 00             byte ?
                         ALIGN 4
     0009 00             nextvar BYTE ?
     000A                _DATA ends

Note that "nextvar" is incorrectly assigned offset 9 rather than 8.

Sample Code 1
-------------

  ; Assemble options needed: none

  _DATA segment dword
    buffer BYTE 5 dup (?)
    byte ?
    ALIGN 4
    nextvar BYTE ?
  _DATA ends

  end

Sample Code 2
-------------

  ; Assemble options needed: none

  structdecl struct
     byte ?
     byte ?
     byte ?
     byte ?
     byte ?
  structdecl ends

  _DATA segment dword
     mystruct structdecl <>
     byte ?
     ALIGN 4
     nextvar BYTE ?
  _DATA ends
  END

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

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

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