linux-kernel - Re: [PATCH] Fix ARCH=um segfault on x86-64.

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Date:	Fri, 6 Mar 2009 16:20:04 -0600
From:	Rob Landley <rob@...dley.net>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix ARCH=um segfault on x86-64.

On Friday 06 March 2009 03:50:38 Geert Uytterhoeven wrote:
> On Fri, Mar 6, 2009 at 09:48, Américo Wang <xiyou.wangcong@...il.com> wrote:
> > On Fri, Mar 06, 2009 at 12:42:14AM -0600, Rob Landley wrote:
> >>Apparently, nobody other than me has ever attempted to use User Mode
> >> Linux built from 2.6.28 on x86-64, because it doesn't work.  It still
> >> doesn't work in current git.  I complained about it not working back in
> >> January:
> >>
> >>http://sourceforge.net/mailarchive/forum.php?thread_name=200901130159.043
> >>89.rob%40landley.net&forum_name=user- mode-linux-devel
> >>http://lkml.indiana.edu/hypermail/linux/kernel/0901.2/00669.html
> >>
> >>And today, I bothered to track down why.
> >>
> >>This is the commit that broke it, when Peter Anvin merged x86 and x86-64
> >> for ARCH=um: http://kernel.org/hg/linux-2.6/rev/117978
> >>
> >>Here's a patch that fixes it for me:
> >
> > Thanks, Bob!
>
> I've just did a build of plain v2.6.28 on amd64 aka x86-64. The
> resulting image ran fine.
>
> I attached my .config.

Which contains:
CONFIG_3_LEVEL_PGTABLES=y

So the question is, why is your config saving that value, and mine isn't?

Ah, I found it.  You enabled CONFIG_EXPERIMENTAL, and I didn't.  That's the 
difference.

Ok, CONFIG_EXPERIMENTAL is required in order for UML to initialize its memory 
management.  That makes a bit more sense why other people haven't seen this...

Rob
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