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Subject: Re: [PATCH 2/2] [POWERPC] uprobes: powerpc port
From: Michael Ellerman <michael@ellerman.id.au>
To: ananth@in.ibm.com
Date: Fri, 08 Jun 2012 15:51:54 +1000
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Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>,
 Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
 Peter Zijlstra <peterz@infradead.org>, lkml <linux-kernel@vger.kernel.org>,
 oleg@redhat.com, Paul Mackerras <paulus@samba.org>,
 Anton Blanchard <anton@samba.org>, Ingo Molnar <mingo@elte.hu>,
 linuxppc-dev@lists.ozlabs.org
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On Fri, 2012-06-08 at 10:06 +0530, Ananth N Mavinakayanahalli wrote:
> 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.

But you're not executing the instruction, you're passing it to
emulate_step(). Or am I missing something?

cheers