Building for MMU-less vexpress targets

[Nicolas Pitre]

On Tue, 6 Nov 2012, Jamie Lokier wrote:

> Nicolas Pitre wrote:
> > I really think that it makes no sense at all to support !MMU kernels in 
> > a multi-platform kernel build, even if the set of included platforms 
> > were all !MMU.  The kernel has to be linked for the physical address of 
> > the target and not a common invariant virtual address.
> 
> Although there's likely to be approximately zero interest in
> multi-platform !MMU, relocating at boot time doesn't sound onerous,
> should it be needed.  x86 kernels already do that.  Maybe ARM kernels
> will eventually do that anyway for the same reason as x86.

We already have something similar but simpler: CONFIG_ARM_PATCH_PHYS_VIRT.
Except that the virtual address the kernel is using always remains the 
same, even if the physical address can move.  Although this is not the 
case at the moment, the ARM kdump implementation could take advantage of 
this ability and avoid the copying of memory around.


Nicolas