Date: Thu, 24 Mar 2016 09:04:49 +0100
From: Torsten Duwe <torsten@lst.de>
To: Balbir Singh <bsingharora@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>, Petr Mladek <pmladek@suse.com>,
        jeyu@redhat.com, jkosina@suse.cz, jikos@kernel.org,
        linux-kernel@vger.kernel.org, rostedt@goodmis.org,
        kamalesh@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org,
        live-patching@vger.kernel.org, mbenes@suse.cz
Subject: Re: [PATCH/RFC] ppc64 livepatch: frameless klp_return_helper using
	odd TOC
Message-ID: <20160324080449.GA13139@lst.de>
References: <20160323155858.GB27110@lst.de> <56F34F85.7020408@gmail.com>
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On Thu, Mar 24, 2016 at 01:23:01PM +1100, Balbir Singh wrote:
> On 24/03/16 02:58, Torsten Duwe wrote:
> >
> > 1. Heuristics are bad. The better they are, the more subtly the
> >    way they might fail.
[...]
> I missed this yesterday, not on cc, but caught it on the list today

I replied to Michael's last post and removed the back reference to start
a new thread. The list is rather long... sorry I didn't notice.

> Thanks for working on this. I did a quick look, so the CR+4 code

Yes. It's only a proof of concept. That idea is yours, no doubt, and
should be mentioned in the final submission. I already wrote it in my
previous version, where I also have changed the arithmetic to produce
small positive deltas.

> plus heuristics for global/local call detection?

Nope, definitely not! I flag global entries unambiguously.
I had a version with R12/LR heuristics on Monday which I dumped.

>  I'll review this soon - hopefully tonight, but we have a long weekend coming up, so there might be delays. In the meanwhile feel free to add my signed-off-by for the CR+4 code. I am also looking at a different approach -- per thread lr0 stack.

This CR+4 code leaves only 1 slot, so sibling calls are extremely dangerous,
as I mentioned. But with a little attention, this patch works very well.

I mostly wanted to hear opinions about a transient odd TOC value
before I start polishing.

	Torsten