linux-kernel - Re: [PATCH v2] kconfig: autogenerated config_is

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Message-ID: <32557.1305572616@localhost>
Date:	Mon, 16 May 2011 15:03:36 -0400
From:	Valdis.Kletnieks@...edu
To:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
Cc:	Michal Marek <mmarek@...e.cz>, Arnaud Lacombe <lacombar@...il.com>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	x86@...nel.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2] kconfig: autogenerated config_is_xxx macro

On Fri, 13 May 2011 10:09:09 +0200, Jean-Christophe PLAGNIOL-VILLARD said:
> On 10:52 Mon 09 May     , Michal Marek wrote:
> > Do you have proof of concept patches that make use of the
> > config_is_xxx macros? Acked by the respective subsystem maintainers?
> > It would be a good idea to send them along to show that this feature
> > is going to be actually used.
> I've seen thousands of place in the kernel we can use
> so I'll just take one example on x86
>
> the patch attached is just an example

Out of curiosity, will this Do The Right Thing for cases where things simply won't
build for some configs?  For example, consider this code snippet from kernel/timer.c,
in __mod_timer() (near line 682):

        debug_activate(timer, expires);

        cpu = smp_processor_id();

#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
        if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
                cpu = get_nohz_timer_target();
#endif
        new_base = per_cpu(tvec_bases, cpu);

If you convert this to an if statement, will it still compile?  Which will
happen first, dead code elimination, or the warning that get_nohz_timer_target()
is an implicit declaration because the definition in the .h file is also
guarded by #ifdef CONFIG_NO_HZ?


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