linux-kernel - Re: [PATCH v3 2/2] powerpc: Uprobes port to powerpc

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Message-ID: <20120816050030.GA12060@in.ibm.com>
Date:	Thu, 16 Aug 2012 10:30:30 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
	lkml <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>, michael@...erman.id.au,
	Ingo Molnar <mingo@...e.hu>, peterz@...radead.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 2/2] powerpc: Uprobes port to powerpc

On Thu, Aug 16, 2012 at 07:41:53AM +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2012-08-15 at 18:59 +0200, Oleg Nesterov wrote:
> > On 07/26, Ananth N Mavinakayanahalli wrote:
> > >
> > > From: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> > >
> > > This is the port of uprobes to powerpc. Usage is similar to x86.
> > 
> > I am just curious why this series was ignored by powerpc maintainers...
> 
> Because it arrived too late for the previous merge window considering my
> limited bandwidth for reviewing things and that nobody else seems to
> have reviewed it :-)
> 
> It's still on track for the next one, and I'm hoping to dedicate most of
> next week going through patches & doing a powerpc -next.

Thanks Ben!

> > Of course I can not review this code, I know nothing about powerpc,
> > but the patches look simple/straightforward.
> > 
> > Paul, Benjamin?
> > 
> > Just one question... Shouldn't arch_uprobe_pre_xol() forbid to probe
> > UPROBE_SWBP_INSN (at least) ?
> > 
> > (I assume that emulate_step() can't handle this case but of course I
> >  do not understand arch/powerpc/lib/sstep.c)
> > 
> > Note that uprobe_pre_sstep_notifier() sets utask->state = UTASK_BP_HIT
> > without any checks. This doesn't look right if it was UTASK_SSTEP...
> > 
> > But again, I do not know what powepc will actually do if we try to
> > single-step over UPROBE_SWBP_INSN.
> 
> Ananth ?

set_swbp() will return -EEXIST to install_breakpoint if we are trying to
put a breakpoint on UPROBE_SWBP_INSN. So, the arch agnostic code itself
takes care of this case... or am I missing something?

However, I see that we need a powerpc specific is_swbp_insn()
implementation since we will have to take care of all the trap variants.

I will need to update the patches based on changes being made by Oleg
and Sebastien for the single-step issues. Will incorporate the powerpc
specific is_swbp_insn() change along with the changes required for the
single-step part and send out the next version.

Ananth

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