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

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Date:	Wed, 22 Aug 2012 14:02:25 +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 Tue, Aug 21, 2012 at 03:09:30PM +0200, Oleg Nesterov wrote:

...

> > This is true for Intel like architectures that have *one* swbp
> > instruction. On Powerpc, gdb for instance, can insert a trap variant at
> > the address. Therefore, is_swbp_insn() by definition should return true
> > for all trap variants.
> 
> Not in this case, I think.
> 
> OK, I was going to do this later, but this discussion makes me think
> I should try to send the patch sooner.
> 
> set_swbp()->is_swbp_at_addr() is simply unneeded and in fact should
> be considered as unnecessary pessimization.
> 
> set_orig_insn()->is_swbp_at_addr() makes more sense, but it can't fix
> all races with userpace. Still it should die.
> 
> > OK. I will separate out the is_swbp_insn() change into a separate patch.
> 
> Great thanks. And if we remove is_swbp_insn() from set_swbp() and
> set_orig_insn() then the semantics of is_swbp_insn() will much more
> clear, and in this case I powerpc probably really needs to change it.

Oleg,

I have posted a new version for review [1] without the is_swbp_insn()
change. I will await your changes around is_swbp_at_addr() and make
changes to the powerpc code if necessary.

Regards,
Ananth

[1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2012-August/100524.html

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