struct zbi_kernel_t

The kernel image. In a bootable ZBI this item must always be first,

immediately after the ZBI_TYPE_CONTAINER header. The contiguous memory

image of the kernel is formed from the ZBI_TYPE_CONTAINER header, the

ZBI_TYPE_KERNEL_{ARCH} header, and the payload.

The boot loader loads the whole image starting with the container header

through to the end of the kernel item's payload into contiguous physical

memory. It then constructs a partial ZBI elsewhere in memory, which has

a ZBI_TYPE_CONTAINER header of its own followed by all the other items

that were in the booted ZBI plus other items synthesized by the boot

loader to describe the machine. This partial ZBI must be placed at an

address (where the container header is found) that is aligned to the

machine's page size. The precise protocol for transferring control to

the kernel's entry point varies by machine.

On all machines, the kernel requires some amount of scratch memory to be

available immediately after the kernel image at boot. It needs this

space for early setup work before it has a chance to read any memory-map

information from the boot loader. The `reserve_memory_size` field tells

the boot loader how much space after the kernel's load image it must

leave available for the kernel's use. The boot loader must place its

constructed ZBI or other reserved areas at least this many bytes after

the kernel image.

x86-64

The kernel assumes it was loaded at a fixed physical address of

0x100000 (1MB). zbi_kernel_t.entry is the absolute physical address

of the PC location where the kernel will start.

TODO(https://fxbug.dev/42098994): Perhaps this will change??

The processor is in 64-bit mode with direct virtual to physical

mapping covering the physical memory where the kernel and

bootloader-constructed ZBI were loaded.

The %rsi register holds the physical address of the

bootloader-constructed ZBI.

All other registers are unspecified.

ARM64

zbi_kernel_t.entry is an offset from the beginning of the image

(i.e., the ZBI_TYPE_CONTAINER header before the ZBI_TYPE_KERNEL_ARM64

header) to the PC location in the image where the kernel will

start. The processor is in physical address mode at EL1 or

above (i.e., SCTLR_ELx.M = 0), which in turn necessitates that its

instruction and data caches are also disabled (i.e.,

SCTLR_ELx.{I, D} = 0). The kernel image and the bootloader-constructed

ZBI each can be loaded anywhere in physical memory. The x0 register

holds the physical address of the bootloader-constructed ZBI.

All other registers are unspecified.

The address range corresponding to the loaded kernel image must be

cleaned - but not necessarily invalidated - to the point of coherency

in the data cache (reserve memory included) and invalidated in the

instruction cache (reserve memory not necessarily included).

RISCV64

zbi_kernel_t.entry is an offset from the beginning of the image (i.e.,

the ZBI_TYPE_CONTAINER header before the ZBI_TYPE_KERNEL_RISCV64 header)

to the PC location in the image where the kernel will start. The

processor is in S mode, satp is zero, sstatus.SIE is zero. The kernel

image and the bootloader-constructed ZBI each can be loaded anywhere in

physical memory, aligned to 4KiB. The a0 register holds the HART ID,

and the a1 register holds the 4KiB-aligned physical address of the

bootloader-constructed ZBI. All other registers are unspecified.