Re: [uml-devel] Using SKAS, any examples?

[Blaisorblade <blaisorblade@yahoo.it>]

On Wednesday 04 May 2005 16:49, Ian Rogers wrote:
> Jeff Dike wrote:
> >On Wed, May 04, 2005 at 10:28:28AM +0100, Ian Rogers wrote:
> >>What I'm hoping to do is to use SKAS to create a second address
> >>space I can, map, unmap, peek and poke from the first. The reason for
> >>this is to allow an emulator to live in the first address space and the
> >>emulated data... to live in the second.
> >
> >UML obviously does this.  Look at arch/um/kernel/skas/mem_user.c for the
> >basic primitives.  The creation and destruction of address spaces is done
> >in arch/um/kernel/skas/mmu.c.
>
> I've had a play with a simple test, but I need to work further on it.
> mem_user.c seems clear enough but I am slightly baffled by what is
> happening with the file descriptors in mmu.c.
>
> >>I hope to be able to access the
> >>second by altering the i386 selector value.
> >
> >What's the i386 selector value?
>
> I hope, for example, to set LDT 0 to point to the second address space.
> I can then swap the value of 7 (index 0, LDT, ring 3) into fs or gs
> whenever I hope to address the second address space. I can do similar
> code with modify_ldt but I'm restricted to using mmap to allocate memory
> and therefore I don't get a fully addressable 4gb address space.
You'll never get that, sadly, because the upper 1G is used by the kernel 
itself... This can be achieved on x86_64, even with 32bit binaries (if they 
are run with the right emulation).
-- 
Paolo Giarrusso, aka Blaisorblade
Skype user "PaoloGiarrusso"
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade




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