linux-kernel - Re: [PATCH] Disable non-ABI-compliant optimisations for live patching

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Message-ID: <20160627065949.GA3399@lst.de>
Date:	Mon, 27 Jun 2016 08:59:49 +0200
From:	Torsten Duwe <duwe@....de>
To:	Pavel Machek <pavel@....cz>
Cc:	Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
	Josh Poimboeuf <jpoimboe@...hat.com>, matz@...e.de,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Disable non-ABI-compliant optimisations for live patching

On Mon, Jun 27, 2016 at 12:39:56AM +0200, Pavel Machek wrote:

> Would it be possible to document which kind of guarantees live
> patching needs from compiler?

Sure, here you go, all required guarantees:

Stick to the ABI.

> I always assumed that whoever is preparing the patch does manual
> investigation to see what needs to be changed and how, but apparantly
> that's not the case, so documentation would be good.

See above for the documentation. Imagine each architecture had a whole
hand-optimised assembler kernel. That would give some performance
improvement, right? Same issue here, only much smaller. It's ultimate
performance vs. maintainability.

HTH,
	Torsten