This patch introduces a hack to make non-relocatable kernels
bootable too. Non-relocatable kernels absolutely want to run
at 0x100000 and are not at all happy about being at 0x200000.
Fortunately, thanks to crazy programs like LOADLIN, Linux has
a couple of hooks in its boot process which can be used to
play games. The 'code32_switch' hook is executed immediately
following the switch to protected mode. To quote the kernel
docs
[quote Documentation/i386/boot.txt]
code32_start:
A 32-bit flat-mode routine *jumped* to immediately after the
transition to protected mode, but before the kernel is
uncompressed. No segments, except CS, are set up; you should
set them up to KERNEL_DS (0x18) yourself.
After completing your hook, you should jump to the address
that was in this field before your boot loader overwrote it.
IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
%edi across invocation.
[/quote]
So, this patch installs a hook at 0x200000+kernel_size. The hook
is hand crafted assembly which sets up all the segments as needed,
then essentially does memmove(0x100000,0x200000,kernel_size) and
finally does an unconditional jmp to 0x100000.
Amazingly this actually really does work. It has been successfully
tested with RHEL-2.1 and Fedora Core 6 install kernels on i386, and
Fedora Core 6 and 7 kernels on x86_64.
pc.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 93 insertions(+), 2 deletions(-)
Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx>
Regards,
Dan.
--
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xen-hvm-kernel-boot-nonrelocatable.patch
Description: Text document
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