linux-kernel - Re: [ANNOUNCE] kmemcheck v7

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Date:	Sun, 11 May 2008 00:05:07 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	John Reiser <jreiser@...Wagon.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Bart Van Assche <bart.vanassche@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <clameter@....com>,
	Daniel Walker <dwalker@...sta.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Josh Aune <luken@...er.org>, Pekka Paalanen <pq@....fi>
Subject: Re: [ANNOUNCE] kmemcheck v7

John Reiser wrote:
> The valgrind+uml patches added a callback, "I am switching stacks >NOW<."
>   
Hm, I never particularly liked that approach because unless you do the 
whole thing in assembly it was never certain that there wasn't a 
basic-block break between them (ie, atomic with respect to valgrind).  
For the kernel that may be possible, but I was thinking of the general 
case where you might want to use setjmp or something.

> If possible then it is better to tell an interpreter what is happening,
> rather than requiring that the interpreter [try to] figure it out.
>   

Matter of taste really, but I tend to disagree.  If you say something 
like "addresses A-B, C-D, E-F are stacks", then the stack pointer 
changing from the range A-B to C-D is a pretty clear indication of stack 
switch, regardless of the mechanism you use to do it.  Of course, an 
explicit hint prevents an accidental push/pop of 32k onto an 8K stack 
from being considered a stack switch, but unless you actually know where 
the stacks are, you can't warn about it or prevent it from 
validating/invalidating a pile of innocent memory.

    J
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