linux-kernel - Re: [PATCH 2/2] mm: fix undefined reference to `.kernel_map

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Date:	Fri, 23 Jan 2015 15:24:51 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Kim Phillips <kim.phillips@...escale.com>
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	josh@...htriplett.org, LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...com>, Minchan Kim <minchan@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Johannes Weiner <hannes@...xchg.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] mm: fix undefined reference to `.kernel_map_pages'
 on PPC builds

On Thu, 2015-01-22 at 21:20 -0600, Kim Phillips wrote:
> On Fri, 23 Jan 2015 08:49:36 +0900
> Akinobu Mita <akinobu.mita@...il.com> wrote:
> 
> > 2015-01-23 5:41 GMT+09:00 Kim Phillips <kim.phillips@...escale.com>:
> > > Thanks. Now I get this:
> > >
> > >   LD      init/built-in.o
> > > mm/built-in.o: In function `kernel_map_pages':
> > > include/linux/mm.h:2076: undefined reference to `.__kernel_map_pages'
> > > include/linux/mm.h:2076: undefined reference to `.__kernel_map_pages'
> > > include/linux/mm.h:2076: undefined reference to `.__kernel_map_pages'
> > > Makefile:925: recipe for target 'vmlinux' failed
> > > make: *** [vmlinux] Error 1
> > >
> > > but, AFAICT, that's not because this patch is invalid: it's because
> > > __kernel_map_pages() isn't implemented in
> > > arch/powerpc/mm/pgtable_64.c, i.e., for non-PPC_STD_MMU_64 PPC64
> > > machines.
> > 
> > Then, in order to use generic __kernel_map_pages() in mm/debug-pagealloc.c,
> > CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC shouldn't be selected in
> > arch/powerpc/Kconfig, when CONFIG_PPC_STD_MMU_64 isn't defined.
> 
> Thanks.  I'm still build-testing this now:
> 
> From 082911ee947246ff962ef21863c45ec467455c40 Mon Sep 17 00:00:00 2001
> From: Kim Phillips <kim.phillips@...escale.com>
> Date: Thu, 22 Jan 2015 20:42:40 -0600
> Subject: [PATCH v2] mm: fix undefined reference to  `.__kernel_map_pages' on FSL
>  PPC64
> 
> arch/powerpc has __kernel_map_pages implementations in mm/pgtable_32.c, and
> mm/hash_utils_64.c, of which the former is built for PPC32, and the latter
> PPC64's without PPC_STD_MMU.

That last part is wrong.

hash_utils_64.c is built for CONFIG_PPC_STD_MMU_64, which is:

config PPC_STD_MMU_64
	def_bool y
	depends on PPC_STD_MMU && PPC64

The problem is when you have PPC64 && !PPC_STD_MMU.

cheers




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