linux-kernel - Re: [PATCH 2/1] init/Kconfig: Split expert menu into a separate file, init/Kconfig.expert

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Date:	Thu, 28 May 2015 10:13:11 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Andy Lutomirski <luto@...capital.net>,
	Bertrand Jacquin <beber@...eeweb.net>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Iulia Manda <iulia.manda21@...il.com>,
	Pranith Kumar <bobby.prani@...il.com>,
	Clark Williams <clark.williams@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	Randy Dunlap <rdunlap@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/1] init/Kconfig: Split expert menu into a separate
 file, init/Kconfig.expert

[Yes, this patch is superseded by your series starting at
https://lkml.org/lkml/2015/5/14/447 . But I wanted to jot this down
somewhere.]

On Tue, 2015-05-12 at 00:15 +0200, Paul Bolle wrote:
> On Mon, 2015-05-11 at 15:04 -0700, Josh Triplett wrote:
> > On Mon, May 11, 2015 at 11:50:21PM +0200, Paul Bolle wrote:
> > > On Mon, 2015-05-11 at 13:23 -0700, Josh Triplett wrote:
> > > > +config KALLSYMS_ALL
> > > > +	bool "Include all symbols in kallsyms"
> > > 
> > > (For some reason this entry doesn't have if EXPERT but it seems to
> > > behave as expected. Odd.)
> > 
> > Because it depends on KALLSYMS.  Magic!
> 
> Welcome to the land of Kconfig!

It's even more subtle (at least currently, ie before this patch is
applied).

KALLSYMS_ALL's prompt doesn't depend on EXPERT. KALLSYMS's prompt does.
For some reason, perhaps because KALLSYMS_ALL depends on KALLSYMS, this
makes both entries visible under EXPERT's menu even if EXPERT is _not_
set.

But, in contrast to BPF_SYSCALL, this doesn't influence the following
symbols that do have a prompt that depends on EXPERT.

Adding "if EXPERT" to the prompt of KALLSYMS_ALL does hide that symbol
_and_ KALLSYMS (when EXPERT is not set, of course).

(This may be documented, or clearly commented in the code. I didn't
check.)

> > > > +	depends on DEBUG_KERNEL && KALLSYMS
> > > > +	help
> > > > +	   Normally kallsyms only contains the symbols of functions for nicer
> > > > +	   OOPS messages and backtraces (i.e., symbols from the text and inittext
> > > > +	   sections). This is sufficient for most cases. And only in very rare
> > > > +	   cases (e.g., when a debugger is used) all symbols are required (e.g.,
> > > > +	   names of variables from the data sections, etc).
> > > > +
> > > > +	   This option makes sure that all symbols are loaded into the kernel
> > > > +	   image (i.e., symbols from all sections) in cost of increased kernel
> > > > +	   size (depending on the kernel configuration, it may be 300KiB or
> > > > +	   something like this).
> > > > +
> > > > +	   Say N unless you really need all symbols.

Thanks,


Paul Bolle

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