FIX: MASM Allows Alignments > Segment Alignment (81894)


The information in this article applies to:

  • Microsoft Macro Assembler (MASM) 5.1
  • Microsoft Macro Assembler (MASM) 5.1a
This article was previously published under Q81894

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
Modification Type:MajorLast Reviewed:10/22/2003
Keywords:kbfix KB81894
©2003 Microsoft Corporation. All rights reserved.