FIX: MASM 5.1/5.1a Cause LINK to Put Uninitialized Data in .EXE

The information in this article applies to:

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

SYMPTOMS

When using the .DATA? directive with the Microsoft Macro Assembler (MASM) versions 5.1 and 5.1a, uninitialized data elements may be incorrectly allocated space in the .EXE file.

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 .DATA? directive indicates the start of the uninitialized data segment, and data declared here is not allocated space in the resulting executable file. However, when declaring an array of structures under .DATA? in MASM 5.1a, space is incorrectly allocated in the .EXE, and the size of the executable program is correspondingly increased.

The example code below shows a structure and an array of 100 structure elements being declared. The resulting .EXE size is 1616 (the size of the code [516] plus 1100 [the data size]). However, This amount should only be the code size, 516, because these array elements are uninitialized.

Sample Code

; Assemble options needed: none

.MODEL small

.DATA? testing STRUC

    a DB 3 DUP(?)
    b DB 8 DUP(?)

array testing 100 DUP(<>)

.CODE

   mov ax,4C00h
   int 21h