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digression : MSDOS 7 and SHARE.EXE revisited (Miscellaneous)

posted by Ninho(R) E-mail, 18.12.2009, 17:19

Now there's an algorithm, that's better than hand waving :-D

I'd like to applaud, I sincerely hoped you'd have something in your sleeve that I'd not perceived from your earlier hints; unfortunately your method is flawed, totally depending on the contents of interrupt vectors 30& 31h not being modified by a previous runner. DOS works perfectly without the CPM compatibility call in vector 30 of course - indeed I wonder why MS so carefully kept the mechanics of that completely unusable and obsolete interface! No program exists which relies on it, or if you could find one, it would be so old that it would probably face major problems on anything newer than MSDOS version 2 :-)

You tell me "somebody touching int 30 is not a serious threat" ? Probably not, but it's easier to imagine than some driver modifying the share hooks.


>> You could probably decide where to search for the patch location
>> using the CALL 5 handler instead of the Int27 handler as well.

No salvation here : DOS "exec" function just fills the 'call 5' location in the PSP from the contents of int vectors 30/31, whatever they may be. If you stuff FF FF FF FF FF at 0:C0, you'll find "FF FF FF FF" at the destination of the call 5 of all programs you'll launch thereafter. Try it if you don't believe me!

This, I think, closes the digression

Thanks, and regards...

---
Ninho

 

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