linux-kernel - Re: [PATCH] arm: remove tautologic #ifdefs in proc-v7-3level.S

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Date:	Tue, 29 Mar 2016 10:48:59 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux@....linux.org.uk
Subject: Re: [PATCH] arm: remove tautologic #ifdefs in proc-v7-3level.S

On Tuesday 29 March 2016 10:29:11 Jonas Rabenstein wrote:
> On Tue, Mar 29, 2016 at 10:05:58AM +0200, Arnd Bergmann wrote:
> > On Tuesday 29 March 2016 09:37:51 Jonas Rabenstein wrote:
> > > The file arch/arm/mm/proc-v7-3level.S is only used by the #include
> > > directive in arch/arm/mm/proc-v7.S:23. This #include is conditional and
> > > depends on  CONFIG_ARM_LPAE (otherwise proc-v7-2level.S is used).
> > > CONFIG_ARM_LPAE has a dependency on CONFIG_MMU defined in Kconfig.
> > > Consequently, checks for CONFIG_MMU in proc-v7-3level.S are superfluous.
> > > 
> > > Signed-off-by: Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
> > > ---
> > >  I detected the issue with chimaera, a tool I currently develop for my bachelor
> > >  thesis extending the undertaker tool suite (https://undertaker.cs.fau.de).
> > 
> > Nice catch!
> > 
> > Reviewed-by: Arnd Bergmann <arnd@...db.de>
> > 
> > I guess you should submit the same thing for the other file as well,
> > either in the same patch or as a series.
> I do not get, what you mean with 'the other file'? For the
> proc-v7-2level.S this precondition does not hold, as proc-v7-2level.S is
> included if !CONFIG_ARM_LPAE. Consequently, no evidence about the MMU
> state is available in their.

My mistake. I misread this as the both files being used only for
MMU-enabled kernels, which would make sense because they deal with
page tables that are not being used without MMU, but they are in fact
being compiled anyway.

> > You can also add
> > 
> > Fixes: 8d2cd3a38fd6 ("ARM: LPAE: Factor out classic-MMU specific code into proc-v7-2level.S")
> Shouldn't it be:
> Fixes: 1b6ba46b7efa ("ARM: LPAE: MMU setup for the 3-level page table
> format")?

Nevermind then. My line was incorrect, and the other one is a bit
redundant as it is the one that adds the file in the first place.

	Arnd