On Thu Aug 19, 2010 at 13:40:54 +0200, Alexander Graf wrote:
>
> On 19.08.2010, at 13:36, Adam Lackorzynski wrote:
>
> >
> > On Thu Aug 19, 2010 at 13:27:32 +0200, Alexander Graf wrote:
> >>
> >> On 19.08.2010, at 13:24, Adam Lackorzynski wrote:
> >>
> >>> A via -kernel supplied x86_64 ELF image is being started in 32bit mode.
> >>> Detect and exit if a 64bit image has been supplied.
> >>
> >> According to the multiboot spec, this is the expected behavior, no? At
> >> least Xen does it that way...
> >
> > Yes, but then the supplied ELF-image should say it's a 32bit one and
> > switch to 64bit mode itself. That's at least how we do load a 64bit
> > kernel.
>
> Hrm - maybe you're right:
>
> busu:~ # readelf -a /boot/xen
> ELF Header:
> Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
> Class: ELF32
>
> What does the spec say here? What does grub do?
Grub starts the (multiboot-)OS in 32bit mode. Starting directly in 64bit
mode would require to setup page-tables etc. which is not done.
The Spec doesn't mention 64bit OS at all, and says that 32bit OSs are
fine ("An OS image may be an ordinary 32-bit executable file in the
standard format for that particular operating system, except that it may
be linked at a non-default load address to avoid loading on top of the
...");
Adam
--
Adam a...@os.inf.tu-dresden.de
Lackorzynski http://os.inf.tu-dresden.de/~adam/
