linux-kernel - Re: [RFC PATCH v3 3/6] uretprobes: generalize xol_get_insn

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Date:	Thu, 28 Feb 2013 21:01:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RFC PATCH v3 3/6] uretprobes: generalize xol_get_insn_slot()

Anton, I'll try to read this series asap. Just one note,

On 02/28, Anton Arapov wrote:
>
>   Generalize xol_take_insn_slot() to enable more consumers of the
> function, e.g. trampoline implementation for return probes.

Yes, this is can work too.

But I guess you misunderstood me, or I missed something...

Why do you need xol_area->rp_trampoline_vaddr at all? From the very
beginning I am trying to suggest to use the first slot for trampoline:

	Or. Perhaps even better, do not add this helper at all. xol_alloc_area()
	could reserve the first slot/bit for trampoline. And note that in this
	case we do not need xol_area->rp_trampoline_vaddr, it is always equal
	to xol_area->vaddr.

Doesn't this look simpler?

Oleg.

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