linux-kernel - Re: [PATCH] kbuild: Add option to turn incompatible pointer check into error

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Date:	Tue, 8 Mar 2016 10:19:41 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Daniel Wagner <wagi@...om.org>, Michal Marek <mmarek@...e.com>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Daniel Wagner <daniel.wagner@...-carit.de>
Subject: Re: [PATCH] kbuild: Add option to turn incompatible pointer check
 into error


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Tue, 8 Mar 2016, Daniel Wagner wrote:
> 
> > From: Daniel Wagner <daniel.wagner@...-carit.de>
> > 
> > With the introduction of the simple wait API we have two very
> > similar APIs in the kernel. For example wake_up() and swake_up()
> > is only one character away. Although the compiler will warn
> > happily the wrong usage it keeps on going an even links the kernel.
> > Thomas and Peter would rather like to see early missuses reported
> > as error early on.
> > 
> > In a first attempt we tried to wrap all swait and wait calls
> > into a macro which has an compile time type assertion. The result
> > was pretty ugly and wasn't able to catch all wrong usages.
> > woken_wake_function(), autoremove_wake_function() and wake_bit_function()
> > are assigned as function pointers. Wrapping them with a macro around is
> > not possible. Prefixing them with '_' was also not a real option
> > because there some users in the kernel which do use them as well.
> > All in all this attempt looked to intrusive and too ugly.
> > 
> > An alternative is to turn the pointer type check into an error which
> > catches wrong type uses. Obviously not only the swait/wait ones. That
> > isn't a bad thing either.
> > 
> > Signed-off-by: Daniel Wagner <daniel.wagner@...-carit.de>
> > Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> 
> Acked-by: Thomas Gleixner <tglx@...utronix.de>

Note that there will be a few build failures triggered by this, for example this 
fix from linux-next is needed:

> commit db9b60400f9253c25ae639797df2d0ff7a35d9d8
> Author: Sudip Mukherjee <sudipm.mukherjee@...il.com>
> Date:   Tue Feb 2 11:35:55 2016 +0530
>
>     drm/gma500: remove helper function

Other than that:

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo