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Q59754: FIX: A2006: Phase Error May Be Caused By Incorrect NOP

Article: Q59754
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
========

Using the "SEG" directive in conjunction with forward reference to a procedure
or a segment name will produce the error

  A2006 : phase error between passes

CAUSE
=====

The assembler incorrectly places a "NOP" instruction in the code generated
during Pass 1. This NOP is not generated in Pass 2, so the assembler generates a
phase error. This phase error will most often happen on the next instruction
that is associated with a fixup.

STATUS
======

Microsoft has confirmed this to be a problem in MASM versions 5.1 and 5.10a.
This problem was fixed in MASM version 6.0.

RESOLUTION
==========

To work around this problem, introduce a NOP that is seen by the assembler only
during the second pass.

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

The following code produces the errors. The errors do not occur when the ax
register is used. They occur when the bx, cx, and dx registers are used. The
workaround is shown in commented out lines.

Sample Code:
------------

  ;Assemble options needed: none

  ;filler          MACRO                     ;macro that codes a nop
  ;                if2                       ;in the second pass of the
  ;                nop                       ;assembler
  ;                endif
  ;ENDM

  _text           SEGMENT PARA PUBLIC 'CODE'
                  ASSUME CS:_TEXT

                  MOV     cx, SEG proc1     ;error using cx, bx or dx
  ;                filler
                  MOV     ax, SEG proc1     ;no error using ax
                  MOV     cx, SEG stackseg  ;error using cx, bx, or dx
  ;                filler
                  MOV     ax, SEG stackseg  ;no error using ax

  STACKSEG        SEGMENT PARA PUBLIC 'STACK'
                  db 100 dup (?)
  STACKSEG        ENDS

  proc1           PROC    FAR
                  ret
  proc1           ENDP
  _text           ENDS
  END

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

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

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

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