linux-kernel - Re: [GIT] kbuild: kconfig changes

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Date:	Tue, 10 Aug 2010 16:25:20 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Arve Hj?nnev?g <arve@...roid.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	JBeulich@...ell.com, aris@...hat.com, catalin.marinas@....com,
	jacmet@...site.dk, justinmattock@...il.com, lizf@...fujitsu.com,
	ulfalizer.lkml@...il.com, zippel@...ux-m68k.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT] kbuild: kconfig changes

> > 
> > The reason why your patch cured it was that we then no
> > longer triggered the bug (at least I guess so I did not look to close).
> > 
> > I will look into this as time permits. I assume the fix is simple
> > when I find the reason.
> 
> I'm looking into it now, but understanding the kconfig internals is not
> easy...
Nope...

What I have understood so far...

If we have a choice then the choice is represented by a symbol.
symbol->def[S_DEF_USER] is set to the selected symbol.
If we read all the choice values then we set:
symbol->flags |= SYMBOL_DEF_USER

If we have a choice where we do not have all choice_values
which is the case with the minimal defconfig then the
missing choice_value results in that SYMBOL_DEF_USER
is not set.
[See confdata:conf_read after the sym_ok label]

Later in symbol.c:sym_calc_value the visibility
is set to mod if we do not have all values.

And therefore the coice value is set to m not y.

I will look a bit more at it tonight.

	Sam
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