FIX: MASM Aligns on 4-Byte Boundary After Offset 8000h

MS-DOS     | OS/2

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, versions 5.1 and 5.1a
• Microsoft Macro Assembler for OS/2, versions 5.1 and 5.1a

SYMPTOMS

The module below demonstrates a problem with the Microsoft Macro Assembler (MASM) versions 5.1 and 5.1a. If an EVEN directive is used after an offset of 8000h within a segment, the assembler will try to align the next instruction or data element on a 4-byte boundary. In other words, more bytes for padding will be added than are necessary to achieve even alignment.

STATUS

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 following is the assembly listing that is generated for the example below.

Assembly Listing

Code Generated   Source
--------------   ------

F8               clc
90               EVEN
F8               clc
                 ORG 8000h
F8               clc
87 DB 90         EVEN
F8               clc

Sample Code

; Assemble options needed: none

_TEXT SEGMENT PARA PUBLIC 'CODE' ASSUME CS:_TEXT start:

    clc
    EVEN
    clc
    ORG 8000h
    clc
    EVEN
    clc

END start