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Date: Thu, 11 Aug 2011 13:56:19 +0200
From: Michal Marek <mmarek@suse.cz>
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Subject: Re: [PATCH 2/2] Enable 'make CONFIG_FOO=y oldconfig'
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To: David Woodhouse <dwmw2@infradead.org>
Cc: Andreas Schwab <schwab@redhat.com>, Arnaud Lacombe <lacombar@gmail.com>, "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org

On 11.8.2011 13:40, David Woodhouse wrote:
> On Thu, 2011-08-11 at 13:15 +0200, Andreas Schwab wrote:
>>> That would be cute, but I'm not sure how to undefine something set on
>>> the command line:
>>>
>>> $ cat > Makefile <<EOF
>>> undefine BAR
>>
>> override undefine BAR
> 
> Thanks. So we don't really need to change the auto.conf syntax; we could
> just do:
> 
> $(foreach var, $(filter CONFIG_%,$(.VARIABLES)), $(eval override undefine $(var)))
> 
> But still I suspect we might *not* want that for options set on the
> command line. We *don't* want 'make CONFIG_FOO=y oldconfig bzImage' to
> say 'you can't enable CONFIG_FOO' and then build the bzImage anyway.

If you do
$ echo 'CONFIG_FOO=y' >all.config
$ make allnoconfig bzImage
then it will also build bzImage even if kconfig wasn't able to set
CONFIG_FOO=y. IMO printing a warning that CONFIG_FOO could not be set is
sufficient, as long as CONFIG_FOO is consistently unset.

Michal