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Date: Wed, 08 Aug 2012 17:02:33 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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To: Oleg Nesterov <oleg@redhat.com>
CC: linux-kernel@vger.kernel.org, x86@kernel.org,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Roland McGrath <roland@redhat.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Ananth N Mavinakaynahalli <ananth@in.ibm.com>, stan_shebs@mentor.com
Subject: Re: [PATCH 2/5] x86/uprobes: implement x86 specific arch_uprobe_*_step
References: <1344355952-2382-1-git-send-email-bigeasy@linutronix.de> <1344355952-2382-3-git-send-email-bigeasy@linutronix.de> <20120808125709.GA4504@redhat.com> <50226700.9000606@linutronix.de> <20120808145345.GA8171@redhat.com>
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On 08/08/2012 04:53 PM, Oleg Nesterov wrote:
>> Why? I tried 'lock popf' and I got invalid instruction. The same for
>> 'rep popf'.
>
> 	int main(void)
> 	{
> 		asm volatile ("pushf; rep; popf");
>
> 		return 0;
> 	}
>

Just tested and it works. Hmm.

> OK, probably nobody should do this (although the kernel should not
> assume this imho), but
>
> 	asm volatile ("pushfw; popfw");
>
> doesn't look bad and the code is
>
> 	000000000040047c<main>:
> 	  40047c:       55                      push   %rbp
> 	  40047d:       48 89 e5                mov    %rsp,%rbp
> 	  400480:       66 9c                   pushfw
> 	  400482:       66 9d                   popfw
> 	  400484:       b8 00 00 00 00          mov    $0x0,%eax
> 	  400489:       c9                      leaveq
> 	  40048a:       c3                      retq

Yes, that one works as well.

> And in any case it would be better to re-use auprobe->fixups.

Okay.

> Oleg.
>

Sebastian
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