_    _                 _
                  | |  | |               | |
                  | |__| | __ _ _ __   __| | _____   _____ _ __
                  |  __  |/ _` | '_ \ / _` |/ _ \ \ / / _ \ '__|
                  | |  | | (_| | | | | (_| | (_) \ V /  __/ |
                  |_|  |_|\__,_|_| |_|\__,_|\___/ \_/ \___|_|

                     A simple and extensible boot protocol

Design Goals

• One contiguous area of memory makes it easy to hand it around.
• Easy to parse using on contiguous array of records.
• Centered around the memory map
• No callbacks, no state.

Overview

Handover Request

struct HandoverRequest
{
    uint32_t tag;
    uint32_t flags;
    uint64_t more;
};

Handover Payload

struct HandoverPayload
{
    uint32_t magic, agent, size, count;
    HandoverRecord records[];
};


struct HandoverRecord
{
    uint32_t tag;
    uint32_t flags;
    uint64_t start;
    uint64_t size;
    uint64_t more;
};

Machine State

Except what stated bellow the machine state is undefined.

x86_64

• rdi: will contain the 0xc001b001 magic number
• rsi: will contain the address of the handover payload in the kernel space

Paging is enabled and the following ranges are mapped

• Some LOADER regions are mapped to the same physical memory address for the initial spinup
• The first 4gio at 0xffffffff80000000 refered as I/O space
• KERNEL, STACK and SELF regions are mapped at 0xffff800000000000 and are refered as kernel space.

Features

FREE - 0x00000000

Free for general use

SELF - 0xa24f988d

The handover structure

STACK - 0xf65b391b

CPU stack

KERNEL - 0xbfc71b20

Kernel region where the kernel code reside

LOADER - 0xf1f80c26

Memory allocated by the loaded and reclaimable by the kernel.

This might include page-tables so make sure the create your own before freeing this

FILE - 0xcbc36d3b

Loaded file

RSDP - 0x8d3bbb

ACPI RSDP

FDT - 0xb628bbc1

Flatten device tree blob

FB - 0xe2d55685

Framebuffer

CMDLINE - 0x435140c4

Kernel command line

END - 0xffffffff

End marker

Definitions

• C - handover.h