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

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Message-ID: <20120817051307.GA4782@in.ibm.com>
Date:	Fri, 17 Aug 2012 10:43:07 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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 05:21:12PM +0200, Oleg Nesterov wrote:

...

> > So, the arch agnostic code itself
> > takes care of this case...
> 
> Yes. I forgot about install_breakpoint()->is_swbp_insn() check which
> returns -ENOTSUPP, somehow I thought arch_uprobe_analyze_insn() does
> this.
> 
> > or am I missing something?
> 
> No, it is me.
> 
> > 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.
> 
> Hmm, I am not sure. is_swbp_insn(insn), as it is used in the arch agnostic
> code, should only return true if insn == UPROBE_SWBP_INSN (just in case,
> this logic needs more fixes but this is offtopic).

I think it does...

> If powerpc has another insn(s) which can trigger powerpc's do_int3()
> counterpart, they should be rejected by arch_uprobe_analyze_insn().
> I think.

The insn that gets passed to arch_uprobe_analyze_insn() is copy_insn()'s
version, which is the file copy of the instruction. We should also take
care of the in-memory copy, in case gdb had inserted a breakpoint at the
same location, right? Updating is_swbp_insn() per-arch where needed will
take care of both the cases, 'cos it gets called before
arch_analyze_uprobe_insn() too.

> > I will need to update the patches based on changes being made by Oleg
> > and Sebastien for the single-step issues.
> 
> Perhaps you can do this in a separate change?
> 
> We need some (simple) changes in the arch agnostic code first, they
> should not break poweppc. These changes are still under discussion.
> Once we have "__weak  arch_uprobe_step*" you can reimplement these
> hooks and fix the problems with single-stepping.

OK. Agreed.

Ananth

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