linux-kernel - Re: [PATCH] Kbuild: Move -Wmaybe-uninitialized to W=1

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Message-ID: <20160728170413.GA15229@gmail.com>
Date:	Thu, 28 Jul 2016 19:04:13 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	lkml <linux-kernel@...r.kernel.org>, Michael Matz <matz@...e.de>,
	linux-kbuild@...r.kernel.org, x86-ml <x86@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] Kbuild: Move -Wmaybe-uninitialized to W=1


* Ingo Molnar <mingo@...nel.org> wrote:

> But that's my point, I believe the false positive rate is pretty low in fact, due 
> to three factors:
> 
>  - 90% of the warnings get fixed by developers, we never see them upstream
> 
>  - I'd say a majority (say 70%) of the remaining warnings are flagging 'complexity 
>    bugs'
>  
>  - only a residual 3% are obnoxious ones.
> 
> But these remaining 3% are the ones we are seeing again and again in various 
> compiler output, so we tend to get a subjective impression that this warning 
> produces countless false positives.

And note that I am well aware of the real risk this poses: people will ignore real 
warnings if there are so many residual false positives.

I think this approach worked pretty well for perf:

> So I *think* the better option would be to do what we are doing in the perf 
> tooling: force a build error for these warnings (by default, with an option 
> available to make it build). That flushes them out and also makes it sure that 
> those questionable sequences of code never get upstream to begin with.

... but might not be appropriate for the kernel which is a 2 orders of magnitude 
larger code base.

Thanks,

	Ingo