Re: [RFC] UML/x86_64 module loader

Rusty Russell
2011-08-23T03:54:13Z

On Mon, 22 Aug 2011 23:38:43 +0200, Richard Weinberger <richard@nod.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.