On 18/04/14 05:34, Nicolas Pitre wrote:
>> I'm not suggesting to break anything or changing existing platforms,
>> > but how do we improve the Image format in a compatible way. If
>> > bootloaders want to support booting Image files or vmlinux directly,
>> > then we should support that including any compatible changes to make
>> > things work better.
> And why would bootloaders want that? Just to create confusion with
> the established boot protocol?
I'd say that they don't. My original concern was how the different
architectures negotiate if more than one arch wants a special text
offset, not how to write a correct bootloader.
The existing uImage files already provide sufficient information to load
the kernel regardless of the TEXT_OFFSET chosen by negotiation among the
enabled architectures.
The entry point is PAGE_OFFSET + TEXT_OFFSET and, although only
implicitly defined, the entry point cannot be set to any other value
without making a backward incompatible to arm/Booting:
"The boot loader is expected to call the kernel image by jumping
directly to the first instruction of the kernel image."
Therefore providing PAGE_OFFSET remains 1G aligned and the hardware
meets the not-unreasonably-stupid test (i.e. TEXT_OFFSET < 1G) then
deriving the right value for TEXT_OFFSET is a trivial mask operation on
the entry point.
Daniel.
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