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Q73684: FIX: MASM 6.0 May Initialize Every 256th Data Symbol

Article: Q73684
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 incorrectly initialize data
that is intended to be uninitialized. The problem will occur with every 256th
data symbol in a module that is defined using the "dup" operator.

RESOLUTION
==========

To work around the problem, either avoid using the dup operator when declaring a
variable or limit the number of occurrences to less than 256 per module.

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

Uninitialized data is created by specifying the ? (question mark) symbol as a
value at declaration time. It is primarily used to indicate that the initial
value of a data symbol is unimportant. It can also be used to indicate that a
symbol is actually defined in a separate compilation module and merely serves as
a place holder for this module.

If a segment contains only uninitialized data, the linker can reduce the size of
the resultant .EXE file by modifying the minalloc field in the header by the
corresponding amount. The loader will then allocate the space at run-time and
fix the addresses as required. Because the assembler incorrectly initializes
some data, the segment will not be completely uninitialized; therefore, LINK
copies the segment in its entirety into the .EXE file and the resulting disk
file is larger than necessary.

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

  ; Assemble options needed: none

  mymac    MACRO
           LOCAL   ldat
  ldat     DD      1      dup (?)
           ENDM

  data     SEGMENT

  REPEAT   512
           mymac
           ENDM

  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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