From: Denis Vlasenko <vda@ilport.com.ua>
To: Andi Kleen <ak@suse.de>
Subject: Re: Segfault on the i386 enter instruction
Date: Fri, 12 May 2006 17:03:23 +0300
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Cc: Tomasz Malesinski <tmal@mimuw.edu.pl>, linux-kernel@vger.kernel.org
References: <20060512131654.GB2994@duch.mimuw.edu.pl> <p734pzv73oj.fsf@bragg.suse.de>
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On Friday 12 May 2006 16:50, Andi Kleen wrote:
> Tomasz Malesinski <tmal@mimuw.edu.pl> writes:
> 
> > The code attached below segfaults on the enter instruction. It works
> > when a stack frame is created by the three commented out
> > instructions and also when the first operand of the enter instruction
> > is small (less than about 6500 on my system).
> 
> The difference is the value of the stack pointer when the page fault
> of extending the stack downwards occurs. For the long sequence 
> ESP is already changed when it happens. For ENTER the CPU undoes
> the change before raising the fault. The page fault handler
> checks the page fault against ESP to catch invalid references below
> the stack.
> 
> I don't think the 64bit kernel does anything different here than the 
> 32bit kernel. I tested it on a 32bit box and it faulted there too.

For me, it doesn't fault. I looked with strace. It doesn't fault even with
enter $64008, $0

Is it something in newest kernels? Mine is 2.6.16-rc5.
--
vda
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