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Combined .com executable/DOS driver (Announce)

posted by Arjay, 12.06.2010, 15:13

> snippety-snip... Just an detail which you may or may not remember
 LOL :) I'll keep this reply short....

> Actually, when loading a driver, MS-DOS (others ?) check only the
> segment part (high word) of this double word for the special value
> FFFFh.
Interesting. So have you produced or seen a combined SYS/COM previously?


> driver/ dot com executable, using the first two bytes as a short jump over
> the rest of the driver header.
Ok, I fully understand. e.g. using EB1Eh, FFFFh instead of FFFFh, FFFFh.

Unfortunately one small point I have noted already is if someone also wants to use UPX that UPX (at least v3.05w) flags up the following error (as you would expect) if the header on a SYS is not set to FFFFh FFFFh:
upx: xmgr3.sys: UnknownExecutableFormatException

So obviously if UPX packing is required (unless they do us an update?) an additional wrapper is also needed for UPX SYS drivers modified in this way.


> Of course, the init routine for the 'sys' specific part of the init
> code should replace FFFF at offset zero before giving back control
> to the DOS system initialisation routines...
 Yup. As the code will be short I might even give this a try this evening.

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