Re: Patch to reorder functions in the vmlinux to a defined order

[ebiederm@xmission.com (Eric W. Biederman)]

Rene Herman <rene.herman@keyaccess.nl> writes:

> Linus Torvalds wrote:
>
>> On Thu, 23 Feb 2006, Rene Herman wrote:
>
>>> Okay. I suppose the only other option is to make "physical_start" a variable
>>> passed in by the bootloader so that it could make a runtime decision? Ie,
>>> place us at min(top_of_mem, 4G) if it cared to. I just grepped for
>>> PHYSICAL_START and this didn't look _too_ bad.
>> No can do. You'd have to make the kernel relocatable, and do load-time
>> fixups. Very invasive.
>
> Yes, that wasn't too smart. I believe in principe most of it _could_ be done via
> some pagetable trickery though, with the kernel still at a fixed virtual
> address?

The page table trickery is actually the more invasive approach.  I believe
for 32 bit kernels the real problem is giving up the identity mapping of
low memory.  Short of the moving the kernel to end of the address space
where vmalloc and the fixmaps are now I don't think there is a reasonable chunk
of the address space we can use.

Eric