linux-kernel - Re: [PATCH, re-send] Always trap on BUG()

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Date:	Tue, 23 Jul 2013 11:36:28 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Chen Gang <gang.chen@...anux.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH, re-send] Always trap on BUG()


* H. Peter Anvin <hpa@...or.com> wrote:

> On 07/15/2013 03:27 PM, Russell King - ARM Linux wrote:
> > On Mon, Jul 15, 2013 at 03:16:12PM -0700, Andrew Morton wrote:
> >> I've been thinking for a while that CONFIG_BUG=n is a pretty dumb thing
> >> to do, and that maintaining it (and trying to fix the warnings it
> >> produces) aren't worth the effort and that we should remove the whole
> >> thing.  Perhaps your patch changes that calculus, dunno.  Please discuss.
> > 
> > This isn't about introducing "CONFIG_BUG=n" - this is about making a
> > kernel with CONFIG_BUG=n build without producing tonnes and tonnes of
> > warnings, as it does today.  It makes building randconfig pretty
> > useless to find what could be more important warnings.
> > 
> 
> Well, there are three alternatives here, right:
> 
> 1. We can use unreachable(), which means that the compiler can assume it
> never happens.

AFAICS this is dangerous as it loses warnings and moves execution into 
la-la-land without any obvious sign at the C level.

> 2. We can trap without metadata.

This is what the patch does.

> 3. We can trap with metadata (current CONFIG_BUG=y).

That is still kept with the patch.

> I am *guessing* this does 2, but it isn't clear.

Yes, that's what it does - and I think it's the best of all worlds:

Acked-by: Ingo Molnar <mingo@...nel.org>

(the crazies can keep a separate patch to remove even more of BUG() to win 
a K or two.)

Thanks,

	Ingo
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