FIX: A2138 Error--Structure Member Span-Dependent Equate

MS-DOS                      | OS/2

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, versions 6.0, 6.0a, 6.0b, 6.1, and 6.1a
• Microsoft Macro Assembler for OS/2, versions 6.0, 6.0a, and 6.0b

SYMPTOMS

The process of assembling an application fails and the assembler generates an A2138 error message.

CAUSE

A structure member is initialized with an equate value that is computed as the difference between the addresses of two labels in the code (a span-dependent value).

RESOLUTION

To work around this problem, code an expression that evaluates to the difference between the addresses of the two labels. Initialize the structure using the expression.

STATUS

Microsoft has confirmed this to be a problem in MASM versions 6.0, 6.0a, 6.0b, 6.1, and 6.1a. This problem was corrected in MASM for MS-DOS version 6.11.

MORE INFORMATION

In the code below, the structure member Member2 is initialized with the TableSize equate. The value of TableSize is generated by subtracting the value of label Table1 from value of label Table2. Assembling the following code causes the A2138 error.

Sample Code

; Assemble options needed: /Fl

data SEGMENT para public 'DATA'

Table1 LABEL WORD

    DW 0, 1

    TableSize EQU Table2-Table1

    Member1 DW Table2-Table1    ; This works correctly
    Member2 DW TableSize        ; This triggers the error

Inside InStruc <>               ; The error is generated here

OutsideOK DW TableSize          ; Using the equate outside
                                ; the structure works

_text SEGMENT para public 'CODE' start:

    mov ax, 4C00h
    int 21h