On aarch64 physBase is the constant that points to the bottom of
physical memory (RAM).
Prior to this change the kernel window was mapped directly to physBase,
which is usually not a 0 paddr. As a consequence the kernel could not
access any memory below physBase.
This change fixes this issue by mapping the start of the kernel window
to 0 in the physical address space.
- add new constant PADDR_LOAD, the location of the kernel image in the
physical address space.
- add new constant PADDR_BASE, the start of the physical address space
(0).
- add new constant KERNEL_ELF_BASE, the location of the kernel image in
kernel virtual memory.
A consequence of this change is that on aarch64, the kernelBase constant
now points to the start of the kernel window in virtual memory, but
*not* to the start of the kernel image as these are now different.
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