After talking with some folks at ELC and getting a feel for some things, here is a series to start addressing some issues with the ARM64 port.
The following RFC series corrects our passing of args to the Linux kernel and cleans up the vexpress_aemv8a config a bit (and corrects some values too).
This also adds support for Image booting. This isn't 100% ready to merge in that it exposes an issue which will be addressed in the kernel soon. The Image format doesn't say how big it is, so for now I hack in a value of 16MB. I've been told this will change in the future (and one of the reserved fields will be unreserved), so I'll adapt when we can adapt. The other thing not yet handled is automatic detection of a compressed image. We should be able to tell if the address passed is a gzip archive and if so, uncompress a block so we can tell where to decompress to. This however will open up the possibility of decompression overwriting ourselves unless we get loaded into a high enough location to start with. Coming up with a good default there will in turn require knowing how far another future change (randomization of text_offset, ala CONFIG_RANDOMIZE_BASE for x86 I imagine) can push where things may be. It's possible we'll just have to say for safety to do it as two steps, but we'll see.
Note that we also need do a fix in arch/arm/cpu/armv8/transition.S wrt cnthctl_el2 in that we shouldn't rely on a valid value to be in there at reset to orr against but instead set the values directly.