FIX: ALIGN Following DUP Operator or Structure May Fail

ID: Q74663

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS and 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

It can be seen in the assembly listing that the offset for the variable "nextvar" is incorrectly set to 7 rather than 8.

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

Note that "nextvar" is incorrectly assigned offset 9 rather than 8.

Sample Code 1


; Assemble options needed: none

_DATA segment dword
  buffer BYTE 5 dup (?)
  byte ?
  ALIGN 4
  nextvar BYTE ?
_DATA ends

end

Sample Code 2


; Assemble options needed: none

structdecl struct
   byte ?
   byte ?
   byte ?
   byte ?
   byte ?
structdecl ends

_DATA segment dword
   mystruct structdecl <>
   byte ?
   ALIGN 4
   nextvar BYTE ?
_DATA ends
END

Additional query words: 6.00 buglist6.00 fixlist6.00a

Keywords :
Version : MS-DOS:6.0
Platform : MS-DOS
Issue type :