Aurix Boot Protocol (revision 0.2)

The Aurix Boot Protocol presents a simple and minimal protocol for booting the AurixOS kernel.

Note

This document is still a work in progress and may contain incomplete information.

Machine state

All general purpose registers are zeroed out
Interrupts are disabled
Framebuffer is set to the best available video mode (graphics mode if available)

Architecture-specific

x86_64

Write Protection bit in CR0 is disabled
GDT is set up as follows:

Name	Base	Limit	Flags
NULL Descriptor	`0x00`	`0x0000`	`0x00`
32-bit Code Descriptor	`0x00`	`0xFFFFFFFF`	Read only
32-bit Data Descriptor	`0x00`	`0xFFFFFFFF`	Read/Write
64-bit Code Descriptor	`0x00`	`0x0000`	Read only
64-bit Data Descriptor	`0x00`	`0x0000`	Read/Write

Paging

~~If available, 5-level paging is set up (see Kernel Parameters)~~ 5-level paging is not yet supported in AxBoot
The memory map is identity mapped
Kernel is mapped to the higher half if desired

Kernel parameters

The bootloader passes abp_boot_info structure as a parameter to the kernel.

A non-zero value in lvl5_paging indicates that 5-level paging has been set up and is available.

struct abp_boot_info {
    // General
    char *bootloader_name;
    char *bootloader_version;
    char *protocol_version;

    // ACPI and SMBIOS
    struct acpi_info acpi;
    struct smbios_info smbios;

    // Memory
    struct memory_map *memmap;
    int lvl5_paging;

    // Framebuffer
    struct framebuffer_info framebuffer;
};

ACPI and SMBIOS

These structures contain pointers to the Root System Description Pointer (ACPI) and System Management BIOS Entry Point (SMBIOS). If is_valid is set to a non-zero value, the pointer is guaranteed to be valid. Otherwise, the pointer is set to NULL and should not be used.

struct acpi_info {
    uint8_t is_valid;
    void *rsdp;
};

struct smbios_info {
    uint8_t is_valid;
    void *entry_point;
};

Memory map

The memory map is a singly linked list containing the physical address of the entry, its length and type, as well as a pointer to the next entry.

Entries are guaranteed to not overlap with each other, and sorted by base address from low to high.

#define ABP_MEMORY_RESERVED 0xf0
#define ABP_MEMORY_USABLE 0xf1
#define ABP_MEMORY_BOOTLOADER_RECLAIMABLE 0xf2
#define ABP_MEMORY_MMIO 0xf3
#define ABP_MEMORY_ACPI_NVS 0xf4
#define ABP_MEMORY_ACPI_RECLAIMABLE 0xf5
#define ABP_MEMORY_KERNEL 0xf7
#define ABP_MEMORY_NOT_USABLE 0xff

struct memory_map {
    uint64_t base;
    uint64_t length;
    uint64_t type;

    struct memory_map *next;
};

Framebuffer

struct framebuffer_info {
    void *addr;
    uint32_t width;
    uint32_t height;
    uint16_t bpp;
};

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