linux-kernel - Re: Please revert "debug: Make CONFIG_EXPERT select CONFIG_DEBUG

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Date:	Fri, 30 Sep 2011 17:25:23 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Adrian Bunk <bunk@...sta.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>
Subject: Re: Please revert "debug: Make CONFIG_EXPERT select
 CONFIG_DEBUG_KERNEL to unhide debug options"

On Fri, Sep 30, 2011 at 08:05:19AM -0700, Josh Triplett wrote:
> On Fri, Sep 30, 2011 at 04:42:45PM +0300, Adrian Bunk wrote:
> > I was just wondering why I was asked about all the debug options when I 
> > tried 3.1-rc8, and that was due to commit f505c553 (debug: Make 
> > CONFIG_EXPERT select CONFIG_DEBUG_KERNEL to unhide debug options),
> > the full commit is below.
> > 
> > It is wrong, and the author does not seem to understand how Kconfig works.
> > 
> > The commit message is:
> > 
> >     Several debugging options currently default to y, such as
> >     CONFIG_DEBUG_BUGVERBOSE and CONFIG_DEBUG_RODATA.  Embedded users
> >     might want to turn those options off to save space; however,
> >     turning them off requires turning on CONFIG_DEBUG_KERNEL to
> >     unhide them.  Since CONFIG_DEBUG_KERNEL exists specifically to
> >     unhide debugging options, and CONFIG_EXPERT exists specifically
> >     to unhide options potentially needed by experts and/or embedded
> >     users, make CONFIG_EXPERT automatically imply
> >     CONFIG_DEBUG_KERNEL.
> > 
> > 
> > Let me point at the obvious fact that both CONFIG_DEBUG_BUGVERBOSE and 
> > CONFIG_DEBUG_RODATA do depend on DEBUG_KERNEL, and are contrary to the 
> > claim of the author of this patch never enabled with 
> > CONFIG_DEBUG_KERNEL=n. [1]
> 
> Not true:
> 
> ~/src/linux-2.6$ rm .config
> ~/src/linux-2.6$ make allnoconfig
>   HOSTCC  scripts/basic/fixdep
>   HOSTCC  scripts/kconfig/conf.o
>   HOSTCC  scripts/kconfig/zconf.tab.o
>   HOSTLD  scripts/kconfig/conf
> scripts/kconfig/conf --allnoconfig Kconfig
> #
> # configuration written to .config
> #
> ~/src/linux-2.6$ grep BUGVERBOSE .config
> CONFIG_DEBUG_BUGVERBOSE=y
> ~/src/linux-2.6$ grep DEBUG_KERNEL .config
> # CONFIG_DEBUG_KERNEL is not set
> 
> DEBUG_BUGVERBOSE does not depend on DEBUG_KERNEL; it just only shows up
> with DEBUG_KERNEL (and EXPERT) set.  The *description* has a conditional
> on DEBUG_KERNEL and EXPERT:
> 
> config DEBUG_BUGVERBOSE
>         bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT
> 
> That doesn't mean the same thing as "depends on DEBUG_KERNEL".

Indeed.

But for DEBUG_RODATA it is the case. That said given the issue described
with DEBUG_BUGVERSBOSE, it makes only the changelog buggy, not the patch.

Also the patch was supposed to have a broader cleanup effect:
https://lkml.org/lkml/2011/6/6/641

But we applied an earlier version by accident.

All in one I think we chose a wrong way to fix the issue. It's annoying to
have all the configs that are only visible with CONFIG_EXPERT spread all
around in random config menu.

Anything that has "if CONFIG_EXPERT" should probably be moved under the CONFIG_EXPERT
menu so that it's visible and found right away.
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