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the DOS code segment hunt, results/questions (Miscellaneous)

posted by cm(R) Homepage E-mail, Düsseldorf, Germany, 15.12.2009, 21:19

> > Look for SHARE.EXE hooks; they're listed in the Int21.52 (DOS data)
> > description.
>
> That listing always puzzled me. I don't believe anyone ever had any
> evidence of any Microsoft code accessing the SHARE hooks relative to the
> address returned by int 21h function 52h. As you noted, SHARE uses
> hard-coded offsets for these pointers (005Ch or 0090h). It's one of those
> programs that know the layout of DOS data depends on the indicator at
> offset 04h.

The Int21.52 description apparently has all the structures from the DOS data segment that didn't fit better at other locations. There are other structures there which aren't closely related to the main SYSVARS.

> I'm pretty sure it doesn't and never has. Once the code's at its final
> position, the segment only has to persist in far pointers that connect
> data to code. For instance, if DOS actually has ended up in the HMA, then
> there's a pointer so that int 21h can get from the stub in low memory to
> the code in high memory, but that pointer otherwise won't be meaningful.
> Of course, in the "otherwise" case, you can find the code segment by other
> ways.

You're correct; in case the code isn't moved to the HMA the interrupt vectors just point into DOS directly.

---
l

 

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