JMP to a Far Address Lists Segment First in Listing File

 Last reviewed: January 23, 1995
Article ID: Q69540
The information in this article applies to:
  • Microsoft Macro Assembler for MS-DOS, version 6.0, 6.0a, 6.0b, 6.1, 6.1a, and 6.11
  • Microsoft Macro Assembler for OS/2, version 6.0, 6.0a, and 6.0b

SUMMARY

In the Macro Assembler (MASM) version 6.0 and later, the opcode for a JMP to a far address is shown in the listing file with the segment first, then the offset. In the actual .OBJ file, the address is stored in the reversed order (offset then segment).

MORE INFORMATION

The following is the encoding for the JMP instruction from the listing (.LST) file generated from the sample program below: 

0000  EA ---- 0000 E            jmp faddr
The above address for faddr (---- 0000) is displayed with the segment listed first (----), then the offset(0000). Because the linker resolves this address at link time, the actual segment and offset is not known at assemble time, and is not listed in this file.

If you then look at the actual .OBJ or .EXE file produced by the above code (by using CodeView, for example), you will see the offset first in the file, then the segment.

This is expected behavior with MASM version 6.0 and later and is designed to make the segment:offset more readable. This is different from MASM version 5.1, which displayed the addresses for far JMP instructions in the reversed (offset then segment) form.

Sample Code

; Assemble options needed: /c /Fl

.MODEL large EXTRN faddr:far

.CODE 

   jmp faddr
END

Additional reference words: kbinf 6.00 6.00a 6.00b 6.10 6.10a jump object
KBCategory: kbtool
KBSubCategory: MLIss

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Last reviewed: January 23, 1995
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