linux-kernel - Re: [PATCH] sched/fair: Replace zero-length array with flexible-array member

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Message-ID: <c7df22d3f248c784e8960841c79fe2836d7ea8ab.camel@perches.com>
Date:   Thu, 13 Feb 2020 14:02:10 -0800
From:   Joe Perches <joe@...ches.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Replace zero-length array with
 flexible-array member

On Thu, 2020-02-13 at 18:06 +0100, Peter Zijlstra wrote:
> On Thu, Feb 13, 2020 at 10:58:31AM -0600, Gustavo A. R. Silva wrote:
> > > Hurmph, and where are all the other similar changes for kernel/sched/ ?
> > > Because this really isn't the only such usage and I really don't see the
> > > point in having a separate patch for every single one of them.
> > > 
> > 
> > Yeah. I can do that. I'll send a patch for the whole kernel/sched.
> 
> Thanks!
> 
> > > Also; couldn't you've taught the compiler to also warn about [0] ?
> > > There's really no other purpose to having a zero length array.
> > > 
> > 
> > Yeah, this is something we'd like to see in the short future.
> > Unfortunately, for now, the only way for the compiler to warn
> > about zero-length arrays in through the use of "-pedantic".
> > And we definitely don't want to follow this path.
> > 
> > What we can do, in the meantime, is to add a test for it to
> > checkpatch.
> 
> Oh, I means, warn if it isn't the last member of a struct. Not warn on
> any use. Or we mean the same and I'm just confused.

That might be a somewhat difficult thing to add to checkpatch
as it is effectively a per-line scanner:

Try something like:

$ git grep -P -A1 '^\s*(?!return)(\w+\s+){1,3}\w+\[0\];' -- '*.[ch]'

and look at the results.

In checkpatch that could be something like:

	if ($line =~ /^.\s*$Type\s+$Ident\s*\[\s*0\s*\]\s*;/) {
		warn...
	}