linux-kernel - Re: [PATCH 11/12] jump_label: declare jump table as external array

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Message-ID: <79893565-c7bb-6abc-0a18-de78c1a0c9cc@oracle.com>
Date:   Sun, 16 Oct 2016 18:50:55 +0200
From:   Vegard Nossum <vegard.nossum@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Jason Baron <jbaron@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 11/12] jump_label: declare jump table as external array

On 10/16/2016 06:25 PM, Peter Zijlstra wrote:
> On Sun, Oct 16, 2016 at 05:16:15PM +0200, Vegard Nossum wrote:
>> Cc: Jason Baron <jbaron@...hat.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
>
> NAK, -ENOCHANGELOG.
>

Hi Peter,

It's true I didn't put an RFC tag on this (mostly because git-send-email
doesn't seem to have an option for it?), but the whole point of doing
these other patches (03-12) was to demonstrate what the patches would
look like for some other kernel code and ask for feedback on the overall
interface/approach. I don't know if you read the introduction and first
patch in the series, but I'd expect that to be more than enough to
understand the problem.

If we really have to repeat the rationale for every patch, can we reuse
this?

"Comparisons between pointers to different arrays is technically
undefined behaviour and recent GCCs may incorrectly optimise away loop
termination conditions. Use the external array accessor macros to
prevent this from happening."

Vegard