Q40225: The Assemble Command with ADD Instructions

Article: Q40225
Product(s): See article
Version(s): 2.20 2.30  | 2.20 2.30
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | buglist2.20 buglist2.30 | mspl13_basic
Last Modified: 9-AUG-1989

Problem:

In CodeView, I'm using the assemble command to change my ADD
instruction, and it changes all the code from that point on.

Response:

If you had the instruction ADD AL,44, for example, and you wanted to
change the 44 to 45 (or any other number), you could use the Assemble
command to do it. The Microsoft Macro Assembler generates a 04 44 for
that instruction; however, when changing the 44 to 45, CodeView
generates an 80 C0 45, which is still the correct instruction of ADD
AL,45. However, it's a 3-byte instruction. Inserting one extra byte
into your code will cause each op code from that point on to be off by
one.

Microsoft has confirmed this to be a problem in Versions 2.20
and 2.30 of CodeView. We are researching this problem and will
post new information as it becomes available.

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