linux-kernel - Re: [PATCH 2/2] [POWERPC] uprobes: powerpc port

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Message-ID: <20120608043605.GB13409@in.ibm.com>
Date:	Fri, 8 Jun 2012 10:06:05 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>, oleg@...hat.com,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/2] [POWERPC] uprobes: powerpc port

On Wed, Jun 06, 2012 at 11:08:04AM -0700, Jim Keniston wrote:
> On Wed, 2012-06-06 at 15:05 +0530, Ananth N Mavinakayanahalli wrote:
> > On Wed, Jun 06, 2012 at 11:27:02AM +0200, Peter Zijlstra wrote:
> > > On Wed, 2012-06-06 at 14:51 +0530, Ananth N Mavinakayanahalli wrote:

...

> > For the kernel, the only ones that are off limits are rfi (return from
> > interrupt), mtmsr (move to msr). All other instructions can be probed.
> > 
> > Both those instructions are supervisor level, so we won't see them in
> > userspace at all; so we should be able to probe all user level
> > instructions.
> 
> Presumably rfi or mtmsr could show up in the instruction stream via an
> erroneous or mischievous asm statement.  It'd be good to verify that you
> handle that gracefully.

That'd be flagged elsewhere, by the architecture itself -- you'd get a
privileged instruciton exception if you try execute any instruction not
part of the UISA. I therefore don't think its a necessary check in the
uprobes code.

Ananth

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