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Q81894: FIX: MASM Allows Alignments > Segment Alignment

Article: Q81894
Product(s): Microsoft Macro Assembler
Version(s): 5.1,5.1a
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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

- Microsoft Macro Assembler (MASM), versions 5.1, 5.1a 
-------------------------------------------------------------------------------

SYMPTOMS
========

The Microsoft Macro Assembler (MASM) versions 5.1 and 5.1a incorrectly allow
ALIGN directives that are greater than the alignment of the segment they appear
within. MASM 5.1 does not generate errors for these statements; however, it
cannot guarantee that the item following these ALIGN directives will be aligned
on the given boundary.

RESOLUTION
==========

Microsoft has confirmed this to be a problem in MASM versions 5.1 and 5.1a. This
problem was corrected in MASM version 6.0.

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

The maximum ALIGN value for data or code is the alignment used when defining the
segment. When a segment is declared, it is guaranteed to start only at its
specified alignment. Since the assembler can align items relative only to the
start of a segment, any ALIGN statement greater than the segment's alignment
should generate an error. If the following sample code is assembled with MASM
5.1 or MASM 5.1a, no error is generated. Padding is inserted after the ALIGN 4
directive, but it will not align the next statement on the indicated boundary.
MASM 6.0 correctly generates the following error:

  A2189: invalid combination with segment alignment : 4

Valid segment alignments include: BYTE, WORD, DWORD, PARA, or PAGE. PARA is the
default.

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

  ; Assemble options needed: none

  STACK  SEGMENT PARA STACK 'STACK'
         DB      100h DUP('x')
  STACK  ENDS

  _DATA  SEGMENT WORD PUBLIC 'DATA'
  msg    DB      "Hello World!", 13, 10, '$'
  _DATA  ENDS

  _TEXT1 SEGMENT WORD PUBLIC 'CODE'
         ASSUME CS:_TEXT1
  retrn: ret
  _TEXT1 ENDS

  _TEXT2 SEGMENT WORD PUBLIC 'CODE'
         ASSUME CS:_TEXT2, DS:_DATA
  start: mov     ax, SEG msg
         mov     ds, ax

         ALIGN   4

         mov     dx, OFFSET msg
         mov     ah, 09h
         int     21h

         mov     ax, 4C00h
         int     21h
  _TEXT2 ENDS

  END    start

Additional query words: 5.10 5.10a 6.00 buglist5.10 buglist5.10a fixlist6.00

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM510a
Version           : :5.1,5.1a
Solution Type     : kbfix

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

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