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Q111473: BUG: ORG in STRUCT Affects Current Segment Size with -Sf

Article: Q111473
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b,6.1,6.11,6.1a
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 6.0, 6.0a, 6.0b, 6.1, 6.1a, 6.11 
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SYMPTOMS
========

A STRUCT declaration containing an ORG directive will change the current segment
size when the -Sf switch is used and a listing file is produced with MASM 6.x.

CAUSE
=====

When adding a first-pass listing (the -Sf switch) to the listing file, MASM's
internal location counter is affected when the ORG directive is encountered
within a STRUCT declaration. This location counter is ultimately used to
determine segment size.

RESOLUTION
==========

When declaring a STRUCT that contains an ORG directive, place the declaration
outside of any open segments. Because this is a structure declaration rather
than an actual instance, the structure does not have to be within a segment and
can be placed outside all open segments where the location counter will not be
adversely affected.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft Macro Assembler
(MASM) versions 6.x. We are researching this problem and will post new
information here in the Microsoft Knowledge Base as it becomes available.

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

The following sample code illustrates this problem. When the structure is
declared within the open data segment, the size of the data segment is
increased. This can be viewed in the map file for the sample, as well as in the
listing file. Move the structure declaration before the .DATA and .STACK
directives to obtain the expected behavior.

An ORG directive is permitted in a structure declaration beginning with MASM
version 6.0. This enables the generation of a template that can ease references
to the internals of data structures that are predefined, for instance by the
operating system, the operating platform, or a high-level language compiler.

For additional information about this MASM construct as well as sample code
demonstrating its use, please see the following article(s) in the Microsoft
Knowledge Base:

  Q111474 PRB: Usage of an ORG Directive in a STRUCT Declaration

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

  ; Assemble options needed: -Fl -Sf -Fm
  .MODEL SMALL,C
  .386
   
  NUMLINES     EQU 25
  NUMCOLS      EQU 80
   
  .STACK
   
  .DATA
  status STRUCT                          ; Move STRUCT declaration
      org (NUMLINES - 2) * NUMCOLS * 2   ;  before .DATA and .STACK
      line1   db ?                       ;  to work around problem.
      attrib1 db ?
      org (NUMLINES - 1) * NUMCOLS * 2
      line2   db ?
      attrib2 db ?
  status ENDS                            ; end STRUCT declaration
   
      msg db "Sample code", 13, 10, "$"
   
  .CODE
  .STARTUP
  <BLOCKQUOTE>
      mov dx, OFFSET msg
      mov ah, 9
      int 21h                               ; output string
  .EXIT

Additional query words: 6.00 6.00a 6.00b 6.10 6.10a 6.11 6.1x buglist6.10 buglist6.10a buglist6.11 buglist6.00 buglist6.00a buglist6.00b

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM610 kbMASM611 kbMASM610a kbMASM600a kbMASM600b
Version           : :6.0,6.0a,6.0b,6.1,6.11,6.1a

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

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