linux-kernel - Re: [PATCH] kconfig: Make allnoconfig disable options behind EMBEDDED and EXPERT

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Date:	Tue, 25 Feb 2014 17:45:03 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dwight Engen <dwight.engen@...cle.com>,
	Eric Paris <eparis@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Kyungsik Lee <kyungsik.lee@....com>,
	Michal Hocko <mhocko@...e.cz>, Michal Marek <mmarek@...e.cz>,
	Mike Frysinger <vapier@...too.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rob Landley <rob@...dley.net>,
	"Yann E. MORIN" <yann.morin.1998@...e.fr>,
	linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kconfig: Make allnoconfig disable options behind
 EMBEDDED and EXPERT

On Tue, Feb 25, 2014 at 01:09:25PM -0800, Andrew Morton wrote:
> On Sun, 23 Feb 2014 18:20:26 -0800 Josh Triplett <josh@...htriplett.org> wrote:
> > "make allnoconfig" exists to ease testing of minimal configurations.
> > Documentation/SubmitChecklist includes a note to test with allnoconfig.
> > This helps catch missing dependencies on common-but-not-required
> > functionality, which might otherwise go unnoticed.
> > 
> > However, allnoconfig still leaves many symbols enabled, because they're
> > hidden behind CONFIG_EMBEDDED or CONFIG_EXPERT.  For instance,
> > allnoconfig still has CONFIG_PRINTK and CONFIG_BLOCK enabled, so drivers
> > don't typically get build-tested with those disabled.
> > 
> > To address this, introduce a new Kconfig option "allnoconfig_y", used on
> > symbols which only exist to hide other symbols.  Set it on
> > CONFIG_EMBEDDED (which then selects CONFIG_EXPERT).  allnoconfig will
> > then disable all the symbols hidden behind those.
> 
> Now look what you've done!
> 
> kernel/sched/core.c: In function 'pick_next_task':
> kernel/sched/core.c:2613: warning: control reaches end of non-void function

Hey, look, now allnoconfig turns off more of the more-rarely-disabled
options, and turns up bugs and warnings that most people don't see!
Yay! ;)

So, yes, we should go ahead and get BUG() fixed properly, at a minimum
by using __builtin_unreachable().  I'll send a patch for that, as a
followup to the thread where Arnd mentioned how to do so.

- Josh Triplett
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