Date: Fri, 26 May 1995 09:12:58 +0900
From: Stephen Turnbull <turnbull AT shako DOT sk DOT tsukuba DOT ac DOT jp>
To: dliu AT faraday-gw DOT njit DOT edu
Cc: junaid AT dino DOT eng DOT monash DOT edu DOT AU, sandmann AT praline DOT no DOT NeoSoft DOT com,
        djgpp AT sun DOT soe DOT clarkson DOT edu, mat AT ardi DOT com
Subject: Compiling gdb, dpmi DS:VRAM hack.

From: Dong Liu <dliu AT faraday-gw DOT njit DOT edu>

   >>>>> On Thu, 25 May 1995 12:27:27 +1000 (EST), "Junaid A. Walker" <junaid AT dino DOT eng DOT monash DOT edu DOT AU> said:


   Junaid> 	BTW the hack seems to work with OS/2, qdpmi101 (a wonder
   Junaid> anything works under qdpmi), and most probably everything else.
   Junaid> Would people please test the program under different DPMI
   Junaid> providers? Eg 386Max, Win NT, OS/2 2.x, OS/2 Warp, Linux DOS
   Junaid> emulator, etc.  	Presumably all dpmi providers add 1 to
   Junaid> the segment limit, to get the segment size, and with 32-bit ints
   Junaid> this invariably wraps around to 0 which is permissible
   Junaid> (=>disable segment access?). So the hack is going to work for a
   Junaid> long time to come, provided dpmi servers dont get smart and test
   Junaid> for a segment limit of -1.

   It won't work under Linux, DOSEMU of Linux don't allow a selector to be
   set if (base+limit < base) || (base + limit >= 0xc0000000). I guess this
   make DOSEMU the only smart DPMI host around :=).

And a good thing, too.  The idea that running anybody else's code in a
DOS box would be a Trojan that could splat anything in memory gives me
hives.  If this works under NT.... :-P  A Trojan could do *anything*.

I hope that all such programs will be required to carry a warning
label:

    Surgeon General's Warning: This program uses the 'Walker hack,' a
    steroid derivative which gives your program great strength, a
    thick neck, baldness, and is known to be closely linked with
    Alzheimer's disease.

But then, I use Linux for almost all daily work now, so I guess I
personally don't have to worry.

-- 
Stephen Turnbull  /  Yaseppochi-gumi  /  <turnbull AT shako DOT sk DOT tsukuba DOT ac DOT jp>
http://turnbull.sk.tsukuba.ac.jp/      anon FTP: turnbull.sk.tsukuba.ac.jp
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