FIX: ALIGN Following DUP Operator or Structure May Fail

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, version 6.0
• Microsoft Macro Assembler for OS/2, version 6.0

SYMPTOMS

The Microsoft Macro Assembler (MASM) version 6.0 may generate an incorrect alignment for the ALIGN or EVEN directives if a statement containing the DUP operator or a structure definition is placed before the directive. For the problem to occur, the DUP operator or structure definition can be placed anywhere before the directive but within the segment.

STATUS

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

MORE INFORMATION

The sample programs below demonstrate the problem with the ALIGN directive. In Sample Code 1, a statement with the DUP operator is used before the ALIGN statement. The assembly listing shows:

   0000                _DATA segment dword
   0000 0005 [         buffer BYTE 5 dup (?)
             00
             ]
   0005 00             byte ?
                       ALIGN 4
   0007 00             nextvar BYTE ?
   0008                _DATA ends

In Sample Code 2, a structure definition is placed before the ALIGN statement. The assembly listing below shows the results:

   0005                structdecl struct
   0000 00             byte ?
   0001 00             byte ?
   0002 00             byte ?
   0003 00             byte ?
   0004 00             byte ?
                       structdecl ends

   0000                _DATA segment dword
   0000 00 00 00 00 00 mystruct structdecl <>
   0005 00             byte ?
                       ALIGN 4
   0009 00             nextvar BYTE ?
   000A                _DATA ends

Sample Code 1

; Assemble options needed: none

_DATA segment dword

  buffer BYTE 5 dup (?)
  byte ?
  ALIGN 4
  nextvar BYTE ?

end

Sample Code 2

; Assemble options needed: none

structdecl struct

   byte ?
   byte ?
   byte ?
   byte ?
   byte ?

_DATA segment dword

   mystruct structdecl <>
   byte ?
   ALIGN 4
   nextvar BYTE ?

END