FIX: ASSUME Using SEG on Communal Far Data Item

MS-DOS          | OS/2

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, versions 5.1, 5.1a and 6.0
• Microsoft Macro Assembler for OS/2, versions 5.1, 5.1a, and 6.0

SYMPTOMS

When the ASSUME directive uses the SEG operator on a communal far data item in the Microsoft Macro Assembler (MASM) versions 5.1, 5.1a, and 6.0, it may generate an error incorrectly. The statement "cmp dog, 0" in the sample code below incorrectly generates the following message when assembled with MASM 5.1 or 5.1a:

   A2068: Cannot address with segment register

   A2074: cannot access label through segment registers

RESOLUTION

The following workarounds may be used to eliminate the error messages:

   1. Use the segment name instead of the SEG operator on a label, such
      as "ASSUME ds:FAR_DATA" instead of "ASSUME ds:SEG dog".

   2. Specify the segment register along with the label, such as
      "cmp ds:dog, 0" instead of "cmp dog, 0".

   3. With MASM 6.0, specify that the communal data is far, such as
      "COMM FAR dog:BYTE instead of "COMM dog:BYTE".

STATUS

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

MORE INFORMATION

The following sample code can be used to demonstrate the problem.

Sample Code

; Assemble options needed: none

.MODEL large, C

.FARDATA COMM dog:BYTE

.CODE cat PROC

    ASSUME ds:SEG dog
    mov ax, SEG dog
    mov ds, ax
    cmp dog, 0
    ret