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Aha! Share was a *red herring* ! Hunt over !!! (Miscellaneous)

posted by Ninho(R) E-mail, 15.12.2009, 22:32

> I don't like this. Say, a user loads FIXWRAP using DEVLOAD. This is of
> course not what users should do but they are able to. It's just no general
> solution to find the code segment, even restricting the OS to MS 7+.


> Say, a user loads FIXWRAP using DEVLOAD. This is of
> course not what users should do but they are able to.

Your user is a vicious type, I assume s/he also loaded SHARE.EXE before trying to DEVLOAD FIXWRAP.SYS ? :-) Let'm get what they deserve !


> It's just no general
> solution to find the code segment, even restricting the OS to MS 7+.

I find it good enough, until offered a better one, so let's read on :

> I'd suggest you use the far jump at 0:C0 instead (the CP/M "CALL 5"
> compatibility entry).

Oh! CP/M to the rescue! No, I don't think so :-D


> This either points directly to the DOS code segment
> or to one of the stubs in the DOS data segment. You can identify the stub
> and if it's one, you have to retrieve the address that it jumps to in its
> last instruction; this address points to the DOS code segment.

Those stubs are NOT used and the segment therein is bogus whenever DOS=LOW and no XMS is loaded. Excuse me, I understand you are proud of your gimmick but so am I with mine own. Your method arrives at the same point as mine through more detours. And what if the motherf^cker of a user you have in mind (the one who devloads FIXWRAP) also messes with int 30 ? This is not serious !

To appease your fears, FIXWRAP could check whether it is being initiated by DOS or whether by a DEVLoader, it is not very difficult.

> the patch location using the CALL 5 handler instead of the Int27 handler
> as well.

I chose int 27 because it leads us almost right to the point of interest !

Cheers

---
Ninho

 

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