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

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Message-ID: <1339473706.14757.14.camel@concordia>
Date:	Tue, 12 Jun 2012 14:01:46 +1000
From:	Michael Ellerman <michael@...erman.id.au>
To:	ananth@...ibm.com
Cc:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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 Fri, 2012-06-08 at 14:51 +0530, Ananth N Mavinakayanahalli wrote:
> On Fri, Jun 08, 2012 at 04:38:17PM +1000, Michael Ellerman wrote:
> > On Fri, 2012-06-08 at 11:49 +0530, Ananth N Mavinakayanahalli wrote:
> > > On Fri, Jun 08, 2012 at 04:17:44PM +1000, Michael Ellerman wrote:
> > > > On Fri, 2012-06-08 at 11:31 +0530, Ananth N Mavinakayanahalli wrote:
> > > > > 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:
> > > > > 
> > > > > 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.
> > > > 
> > > > Right. But that was exactly Jim's point, you may be asked to emulate
> > > > those instructions even though you wouldn't expect to see them in
> > > > userspace code, so you need to handle it.
> > > > 
> > > > Luckily it looks like emulate_step() will do the right thing for you.
> > > > It'd be good to test it to make 100% sure.
> > > 
> > > Sure. Will add that check and send v2.
> > 
> > Sorry I didn't mean add a test in the code, I meant construct a test
> > case to confirm that it works as expected.
> 
> Michael,
> 
> I just hand-coded the instr to emulate_step() and here are the results:
> 
> MSR_PR is set
> insn = 7c600124, ret = 0 /* mtmsr */
> insn = 7c600164, ret = 0 /* mtmsrd */
> insn = 4c000024, ret = -1 /* rfid */
> insn = 4c000064, ret = 0 /* rfi */
> 
> Also verified that standalone programs with those instructions in inline
> asm will die with a SIGILL.
> 
> So, for mtmsr, mtmsrd and rfi, we have to single-step them which will
> result in a SIGILL in turn.

What happens in the rfid case? You don't handle -1 from emulate_step()
any differently AFAICS, so don't we try to single step that too?

cheers



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