linux-kernel - Re: [PATCH 01/12] extarray: define helpers for arrays defined in linker scripts

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Message-ID: <20161017090930.GT3142@twins.programming.kicks-ass.net>
Date:   Mon, 17 Oct 2016 11:09:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     Vegard Nossum <vegard.nossum@...cle.com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>, stable@...r.kernel.org,
        Ming Lei <ming.lei@...onical.com>,
        Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 01/12] extarray: define helpers for arrays defined in
 linker scripts

On Mon, Oct 17, 2016 at 11:01:13AM +0200, Jiri Slaby wrote:
> On 10/17/2016, 10:33 AM, Peter Zijlstra wrote:
> > On Sun, Oct 16, 2016 at 05:16:05PM +0200, Vegard Nossum wrote:
> >> The test in this loop:
> >>
> >> 	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
> >>
> >> was getting completely compiled out by my gcc, 7.0.0 20160520. The result
> >> was that the loop was going beyond the end of the builtin_fw array and
> >> giving me a page fault when trying to dereference b_fw->name.
> >>
> >> This is because __start_builtin_fw and __end_builtin_fw are both declared
> >> as (separate) arrays, and so gcc conludes that b_fw can never point to
> >> __end_builtin_fw.
> >>
> > 
> > Urgh, isn't that the kind of 'optimizations' we should shoot in the head
> > for the kernel? Just like the -fno-strict-aliassing crap?
> 
> Unfortunately, there is no such switch for this optimization.

Should we get one?

> On the top of that, it's incorrect C according to the standard. 

According to the standard non of the kernel has any chance in hell of
working, so don't pretend you care about that :-)