From: Andi Kleen <ak@suse.de>
To: piet@bluelane.com
Subject: Re: linux-2.6 x86_64 kgdb issue
Date: Wed, 31 May 2006 11:41:43 +0200
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Cc: "Amit S. Kale" <amitkale@linsyssoft.com>,
       "Vladimir A. Barinov" <vbarinov@ru.mvista.com>,
       Andrew Morton <akpm@osdl.org>, kgdb-bugreport@lists.sourceforge.net,
       trini@kernel.crashing.org, linux-kernel@vger.kernel.org
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> My bet is that in this case I was storing a LOT of 
> data in the thread structure, so the space left for 
> the stack was massively reduced. 

Ok so it was your bug. Don't do that.

> Sure but the debugger environment must tolerate larger stacks.

No, Linux doesn't tolerate larger stacks.

> But this can miss a minor abuse. The interrupt check
> is a quick and simple hack but I wonder if it's really
> optimal for commercial implementations.

In practice if you overwrite thread_info you crash eventually
and it's noticed.  If you write below thread_info but keep
ti intact then the redzone would likely not catch it either.

I don't think an additional red zone would improve overflow detection 
in a significant way.

> I think all modules should be ABLE to be built in.

If you have a working module it can be easily built in too.
Just hacks that don't work with modules are bad.

-Andi
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