linux-kernel - Re: arch/arm/kernel/setup.c fails to compile for NOMMU

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Message-ID: <20170824161741.GX20805@n2100.armlinux.org.uk>
Date:   Thu, 24 Aug 2017 17:17:41 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: arch/arm/kernel/setup.c fails to compile for NOMMU

On Fri, Aug 18, 2017 at 01:24:02PM +0200, Michal Hocko wrote:
> Hi Russel,
> I have a battery of configs for compile testing and for some time I've
> been seeing the following compilation error with nommu config (attached)
> 
> arch/arm/kernel/setup.c: In function 'reserve_crashkernel':
> arch/arm/kernel/setup.c:1005:25: error: 'SECTION_SIZE' undeclared (first
> use in this function)
>              crash_size, SECTION_SIZE);
> 
> I didn't get to look what is going on here, maybe my config is just too
> artificial but the primary reason is that SECTION_SIZE is not defined in
> pgtable-nommu.h. To be honest I am not familiar with nommu very much and
> it smells like the whole reserve_crashkernel doesn't really make any
> sense on those configs. Could you have a look what is the best fix
> please?

Hi,

I suspect that mach-netx has never been tested in nommu configurations
(ditto for many of the older platforms, which pre-date merging nommu
support.)

Maybe the best solution is to make these old platforms depend on MMU.

However, I'm wondering whether kexec makes sense for !MMU - that's
probably something that hasn't been tested and doesn't actually work.
So maybe another approach would be to make kexec depend on MMU for
ARM - but I'm afraid I don't really know.

I only have very limited nommu experience.

-- 
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