FIX: Address Label Offset Incorrect in USE32 Data Segment

MS-DOS                 | OS/2

The information in this article applies to:

• Microsoft LINK for MS-DOS, versions 3.x, 4.x, 5.0x, 5.1x, and 5.2
• Microsoft LINK for OS/2, versions 5.0x, 5.1, 5.11, 5.13, and 5.15

SYMPTOMS

When a label corresponds to an absolute address and the label is defined in a USE32 data segment, LINK generates the incorrect offset for the label. As a result, the application accesses incorrect data through the label.

STATUS

Microsoft has confirmed this to be a problem in LINK versions 3.6, 3.61, 3.64, 3.65, 3.69, 5.01, 5.1, 5.11, 5.13, 5.15 and 5.2 for MS-DOS and versions 5.01, 5.11, 5.13, and 5.15 for OS/2. This problem was corrected in LINK version 5.3 for MS-DOS.

MORE INFORMATION

A label can represent an absolute address XXXX:YYYY by placing the label in a segment with the type "at XXXX" and after an org directive "org YYYY."

The following code example demonstrates this problem. The Microsoft Macro Assembler (MASM) generated the first listing. Note that the offset of Vector is 20h, as it should be. The CodeView debugger generated the second listing. Note that the offset of Vector is 28h, which is incorrect.

Sample Code

; Assemble options needed: none

                          .model small,c
                          .386

 0000                     Zero segment use32 at 0
                            org 32
 0020                       Vector label dword
 0020                     Zero ends

 0000                     .code
                          assume es:Zero
 0000                     start:
 0000  67& 66| 26: A3         mov [Vector], eax
       00000020 R
                          end start

1:      .model small,c
2:      .386
3:
4:      Zero segment use32 at 0
5:      org 32
6:
7:          Vector label dword
8:
9:      Zero ends
10:
11:     .code
12:
13:     assume es:Zero
14:
15:     start:
16:
17:         mov [Vector], eax
6A8F:0000 676626A32800000MOV       DWord Ptr ES:[00000028],EAX
18:
19:         end start