linux-kernel - Re: [PATCH] x86: Don't randomize stack unless current->personality permits it

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Date:	Mon, 17 Jul 2006 16:50:02 +0100
From:	Paulo Marques <pmarques@...popie.com>
To:	Al Boldi <a1426z@...ab.com>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Frank van Maarseveen <frankvm@...nkvm.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [PATCH] x86: Don't randomize stack unless current->personality
 permits it

Al Boldi wrote:
>[...] > void fn() {
> 
> 	long i = 9999999;
> 	double x,y;
> 
> 	elapsed(1);
> 	while (i--) fn2(&x,&y);
> 	printf("%4lu ",elapsed(0));
> }

You are not initializing x and y and with -Os at least my gcc really 
uses floating point load/store operations to handle that code.

Maybe the coprocessor has a hard time normalizing certain garbage on the 
stack, but without/with randomization the data comes from other 
addresses and you're just lucky with the contents.

Does this also happens if you add a "x=0, y=0;" line to that function?

-- 
Paulo Marques - www.grupopie.com

Pointy-Haired Boss: I don't see anything that could stand in our way.
            Dilbert: Sanity? Reality? The laws of physics?
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