Date: Fri, 8 Jun 2012 11:31:04 +0530
From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
To: Michael Ellerman <michael@ellerman.id.au>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>, oleg@redhat.com,
        lkml <linux-kernel@vger.kernel.org>, Paul Mackerras <paulus@samba.org>,
        Anton Blanchard <anton@samba.org>, Ingo Molnar <mingo@elte.hu>,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2/2] [POWERPC] uprobes: powerpc port
Message-ID: <20120608060104.GD13409@in.ibm.com>
Reply-To: ananth@in.ibm.com
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On Fri, Jun 08, 2012 at 03:51:54PM +1000, Michael Ellerman wrote:
> 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?

But MSR_PR=1 and hence emulate_step() will return -1 and hence we will
end up single-stepping using user_enable_single_step(). Same with rfid.

Ananth

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