linux-kernel - Re: [RFC] UML/x86

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Message-ID: <878vqk4wel.fsf@rustcorp.com.au>
Date:	Tue, 23 Aug 2011 13:22:18 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Richard Weinberger <richard@....at>, linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, rostedt@...dmis.org, jbaron@...hat.com,
	akpm@...ux-foundation.org, vapier@...too.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [RFC] UML/x86_64 module loader

On Mon, 22 Aug 2011 23:38:43 +0200, Richard Weinberger <richard@....at> wrote:
> Hi!
> 
> UserModeLinux is using the arch specific module functions from 
> arch/x86/kernel/module.c.
> On i386 this works perfectly fine but on x86_64 it causes problems.
> 
> apply_relocate_add() assumes modules compiled with -mcmodel=kernel 
> because the kernel lives in the negative 2GiB of the address space.
> This assumption is not true for UML.
> On an UML instance with more than 512MiB of memory no modules can be 
> loaded because vmalloc() locates the module near the 2GiB limit and the
> ELF relocations causes an overflow. (Detected by "if ((s64)val != *(s32 
> *)loc)" in apply_relocate_add()).
> 
> Now I'm not sure how to fix this.
> Mostly because I'm not a module loader nor an ELF expert. 8-)

I think you need to write your own routines.  It shouldn't be that hard,
just keep implementing relocations until you're done :)

Cheers,
Rusty.
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