Date: Fri, 21 Sep 2001 19:58:40 +0300
From: "Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Sender: halo1 AT zahav DOT net DOT il
To: sandmann AT clio DOT rice DOT edu
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In-reply-to: <10109211311.AA18258@clio.rice.edu> (sandmann@clio.rice.edu)
Subject: Re: UPX'ed image and debugger note [was Re: gcc-3.01 ...]
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> From: sandmann AT clio DOT rice DOT edu (Charles Sandmann)
> Date: Fri, 21 Sep 2001 08:11:32 -0500 (CDT)
> > 
> > Is UPX built with DJGPP?  If not, what use is it to try to debug it
> > with DJGPP debuggers?
> 
> I mean images compressed with UPX.

So did I.  Sorry for an unclear wording.

> > Right, and for a good reason.  We could of course avoid doing that if
> > UPX is involved, but we need a way to detect this situation.  Can you
> > suggest how to detect that?
> 
> How about a flag that says if the current CS:IP is < 4096 then allow
> reads?

Sounds good to me.

> > A user of a debugger might also want to turn off null page protection
> > if they want to put a watchpoint on it.  This might come handy for
> > debugging on Windows, where we don't get a SIGSEGV in the debuggee
> > when it dereferences a NULL pointer.
> 
> True.  But the debuggers internally treat 0 as the flag to disable
> a watchpoint, so this would need to be changed.

At least in GDB, it's not easy to change that.  But you could always
work around that by setting a watchpoint at address 1 instead of
zero.