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

ID Number: Q74670

5.10 5.10a

MS-DOS

buglist5.10 buglist5.10a fixlist6.00

Summary:

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(?)

testing ENDS

array testing 100 DUP(<>)

.CODE

mov ax,4C00h

int 21h

END

Additional reference words: 5.10 5.10a 6.00