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

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Date:	Fri, 30 Sep 2011 08:05:19 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Adrian Bunk <bunk@...sta.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	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 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".

Also see Ingo Molnar's mail with Message-Id
<20110605093445.GA19927@...e.hu>, which explicitly recommended this
approach.

- Josh Triplett
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