Re: [PATCH 2/2] [POWERPC] uprobes: powerpc port

[Ananth N Mavinakayanahalli <ananth@in.ibm.com>]

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.

Ananth