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mintsuki e261a96fa4 docs/protocol: Fix typo and mandate ra and gp registers to be 0 for rv64

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The Limine Boot Protocol

The Limine boot protocol is a modern, minimal, fast, and extensible boot protocol, with a focus on backwards and forwards compatibility, created from the experience gained by working on the stivale boot protocols.

This file serves as the official centralised collection of features that the Limine boot protocol is composed of. Other bootloaders may support extra unofficial features, but it is strongly recommended to avoid fragmentation and submit new features by opening a pull request to this repository.

The limine.h file provides an implementation of all the structures and constants described in this document, for the C and C++ languages.

General Notes

All pointers are 64-bit wide. All pointers point to the object with the higher half direct map offset already added to them, unless otherwise noted.

The calling convention matches the C ABI for the specific architecture (SysV for x86, AAPCS for aarch64).

Features

The protocol is centered around the concept of request/response - collectively named "features" - where the kernel requests some action or information from the bootloader, and the bootloader responds accordingly, if it is capable of doing so.

In C terms, a feature is composed of 2 structure: the request, and the response.

A request has 3 mandatory members at the beginning of the structure:

struct limine_example_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_example_response *response;
    ... optional members follow ...
};

id - The ID of the request. This is an 8-byte aligned magic number that the bootloader will scan for inside the executable file to find requests. Requests may be located anywhere inside the executable as long as they are 8-byte aligned. There may only be 1 of the same request. The bootloader will refuse to boot an executable with multiple of the same request IDs. Alternatively, it is possible to provide a list of requests explicitly via an executable file section. See "Limine Requests Section".
revision - The revision of the request that the kernel provides. This starts at 0 and is bumped whenever new members or functionality are added to the request structure. Bootloaders process requests in a backwards compatible manner, always. This means that if the bootloader does not support the revision of the request, it will process the request as if were the highest revision that the bootloader supports.
response - This field is filled in by the bootloader at load time, with a pointer to the response structure, if the request was successfully processed. If the request is unsupported or was not successfully processed, this field is left untouched, meaning that if it was set to NULL, it will stay that way.

A response has only 1 mandatory member at the beginning of the structure:

struct limine_example_response {
    uint64_t revision;
    ... optional members follow ...
};

revision - Like for requests, bootloaders will instead mark responses with a revision number. This revision is not coupled between requests and responses, as they are bumped individually when new members are added or functionality is changed. Bootloaders will set the revision to the one they provide, and this is always backwards compatible, meaning higher revisions support all that lower revisions do.

This is all there is to features. For a list of official Limine features, read the "Feature List" section below.

Limine Requests Section

If the executable kernel file contains a .limine_reqs section, the bootloader will, instead of scanning the executable for requests, fetch the requests from a NULL-terminated array of pointers to the provided requests, contained inside said section.

Entry memory layout

The protocol mandates kernels to load themselves at or above 0xffffffff80000000. Lower half kernels are not supported.

At handoff, the kernel will be properly loaded and mapped with appropriate MMU permissions at the requested virtual memory address (provided it is at or above 0xffffffff80000000).

No specific physical memory placement is guaranteed, except that the kernel is guaranteed to be physically contiguous. In order to determine where the kernel is loaded in physical memory, see the Kernel Address feature below.

Alongside the loaded kernel, the bootloader will set up memory mappings as such:

 Base Physical Address -                    Size                    ->  Virtual address
  0x0000000000001000   - 4 GiB plus any additional memory map entry -> 0x0000000000001000
  0x0000000000000000   - 4 GiB plus any additional memory map entry -> HHDM start

Where HHDM start is returned by the Higher Half Direct Map feature (see below). These mappings are supervisor, read, write, execute (-rwx).

The bootloader page tables are in bootloader-reclaimable memory (see Memory Map feature below), and their specific layout is undefined as long as they provide the above memory mappings.

If the kernel is a position independent executable, the bootloader is free to relocate it as it sees fit, potentially performing KASLR (as specified by the config).

Entry machine state

x86_64

rip will be the entry point as defined as part of the executable file format, unless the an Entry Point feature is requested (see below), in which case, the value of rip is going to be taken from there.

At entry all segment registers are loaded as 64 bit code/data segments, limits and bases are ignored since this is 64-bit mode.

The GDT register is loaded to point to a GDT, in bootloader-reclaimable memory, with at least the following entries, starting at offset 0:

Null descriptor
16-bit code descriptor. Base = 0, limit = 0xffff. Readable.
16-bit data descriptor. Base = 0, limit = 0xffff. Writable.
32-bit code descriptor. Base = 0, limit = 0xffffffff. Readable.
32-bit data descriptor. Base = 0, limit = 0xffffffff. Writable.
64-bit code descriptor. Base and limit irrelevant. Readable.
64-bit data descriptor. Base and limit irrelevant. Writable.

The IDT is in an undefined state. Kernel must load its own.

IF flag, VM flag, and direction flag are cleared on entry. Other flags undefined.

PG is enabled (cr0), PE is enabled (cr0), PAE is enabled (cr4), WP is enabled (cr0), LME is enabled (EFER), NX is enabled (EFER) if available. If 5-level paging is requested and available, then 5-level paging is enabled (LA57 bit in cr4).

The A20 gate is opened.

Legacy PIC and IO APIC IRQs are all masked.

If booted by EFI/UEFI, boot services are exited.

rsp is set to point to a stack, in bootloader-reclaimable memory, which is at least 64KiB (65536 bytes) in size, or the size specified in the Stack Size Request (see below). An invalid return address of 0 is pushed to the stack before jumping to the kernel.

All other general purpose registers are set to 0.

aarch64

PC will be the entry point as defined as part of the executable file format, unless the an Entry Point feature is requested (see below), in which case, the value of PC is going to be taken from there.

The contents of the VBAR_EL1 register are undefined, and the kernel must load it's own.

The MAIR_EL1 register will contain at least these entries, in an unspecified order:

Normal, Write-back RW-Allocate non-transient (0b11111111),
Unspecified, correct for use with the framebuffer.

The kernel and the lower-half identity mapping will be mapped with Normal write-back memory, while the framebuffer is mapped with the correct caching mode. The kernel must ensure that MMIO it wants to access is mapped with the correct caching mode.

All interrupts are masked (PSTATE.{D, A, I, F} are set to 1).

The kernel is entered in little-endian AArch64 EL1t (EL1 with PSTATE.SP set to 0, PSTATE.E set to 0, and PSTATE.nRW set to 0).

Other fields of PSTATE are undefined.

At entry: the MMU (SCTLR_EL1.M) is enabled, the I-Cache and D-Cache (SCTLR_EL1.{I, C}) are enabled, data alignment checking (SCTLR_EL1.A) is disabled. SP alignment checking (SCTLR_EL1.{SA, SA0}) is enabled. Other fields of SCTLR_EL1 are reset to 0 or to their reserved value.

Higher ELs do not interfere with accesses to vector or floating point instructions or registers.

Higher ELs do not interfere with accesses to the generic timer and counter.

The used translation granule size is undefined.

If booted by EFI/UEFI, boot services are exited.

SP is set to point to a stack, in bootloader-reclaimable memory, which is at least 64KiB (65536 bytes) in size, or the size specified in the Stack Size Request (see below).

All other general purpose registers (including X29 and X30) are set to 0. Vector registers are in an undefined state.

riscv64

At entry the machine is executing in Supervisor mode.

pc will be the entry point as defined as part of the executable file format, unless the an Entry Point feature is requested (see below), in which case, the value of pc is going to be taken from there.

x1(ra) is set to 0, the kernel must not return from the entry point.

x2(sp) is set to point to a stack, in bootloader-reclaimable memory, which is at least 64KiB (65536 bytes) in size, or the size specified in the Stack Size Request (see below).

x3(gp) is set to 0, kernel must load its own global pointer if needed.

All other general purpose registers, with the exception of x5(t0), are set to 0.

If booted by EFI/UEFI, boot services are exited.

stvec is in an undefined state. sstatus.SIE and sie are set to 0.

sstatus.FS and sstatus.XS are both set to Off.

Paging is enabled with the paging mode specified by the Paging Mode feature (see below).

The (A)PLIC, if present, is in an undefined state.

Feature List

Request IDs are composed of 4 64-bit unsigned integers, but the first 2 are common to every request:

#define LIMINE_COMMON_MAGIC 0xc7b1dd30df4c8b88, 0x0a82e883a194f07b

Bootloader Info Feature

ID:

#define LIMINE_BOOTLOADER_INFO_REQUEST { LIMINE_COMMON_MAGIC, 0xf55038d8e2a1202f, 0x279426fcf5f59740 }

Request:

struct limine_bootloader_info_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_bootloader_info_response *response;
};

Response:

struct limine_bootloader_info_response {
    uint64_t revision;
    char *name;
    char *version;
};

name and version are 0-terminated ASCII strings containing the name and version of the loading bootloader.

Stack Size Feature

ID:

#define LIMINE_STACK_SIZE_REQUEST { LIMINE_COMMON_MAGIC, 0x224ef0460a8e8926, 0xe1cb0fc25f46ea3d }

Request:

struct limine_stack_size_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_stack_size_response *response;
    uint64_t stack_size;
};

stack_size - The requested stack size in bytes (also used for SMP processors).

Response:

struct limine_stack_size_response {
    uint64_t revision;
};

HHDM (Higher Half Direct Map) Feature

ID:

#define LIMINE_HHDM_REQUEST { LIMINE_COMMON_MAGIC, 0x48dcf1cb8ad2b852, 0x63984e959a98244b }

Request:

struct limine_hhdm_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_hhdm_response *response;
};

Response:

struct limine_hhdm_response {
    uint64_t revision;
    uint64_t offset;
};

offset - the virtual address offset of the beginning of the higher half direct map.

Terminal Feature

Note: This feature is deprecated, do not use if possible.

ID:

#define LIMINE_TERMINAL_REQUEST { LIMINE_COMMON_MAGIC, 0xc8ac59310c2b0844, 0xa68d0c7265d38878 }

Request:

typedef void (*limine_terminal_callback)(struct limine_terminal *, uint64_t, uint64_t, uint64_t, uint64_t);

struct limine_terminal_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_terminal_response *response;
    limine_terminal_callback callback;
};

callback - Pointer to the callback function.

Response:

typedef void (*limine_terminal_write)(struct limine_terminal *terminal, const char *string, uint64_t length);

struct limine_terminal_response {
    uint64_t revision;
    uint64_t terminal_count;
    struct limine_terminal **terminals;
    limine_terminal_write write;
};

terminal_count - How many terminals are present.
terminals - Pointer to an array of terminal_count pointers to struct limine_terminal structures.
write - Physical pointer to the terminal write() function. The function is not thread-safe, nor reentrant, per-terminal. This means multiple terminals may be called simultaneously, and multiple callbacks may be handled simultaneously. The terminal parameter points to the struct limine_terminal structure to use to output the string; the string parameter points to a string to print; the length parameter contains the length, in bytes, of the string to print.

struct limine_terminal {
    uint64_t columns;
    uint64_t rows;
    struct limine_framebuffer *framebuffer;
};

columns and rows - Columns and rows provided by the terminal.
framebuffer - The framebuffer associated with this terminal.

Note: Omitting this request will cause the bootloader to not initialise the terminal service.

Terminal callback

The callback is a function that is part of the kernel, which is called by the terminal during a write() call whenever an event or escape sequence cannot be handled by the bootloader's terminal alone, and the kernel may want to be notified in order to handle it itself.

Returning from the callback will resume the write() call which will return to its caller normally.

Not returning from a callback may leave the terminal in an undefined state and cause issues.

The callback function has the following prototype:

void callback(struct limine_terminal *terminal, uint64_t type, uint64_t, uint64_t, uint64_t);

The terminal argument is a pointer to the Limine terminal structure which represents the terminal that caused the callback.

The purpose of the last 3 arguments changes depending on the type argument.

The callback types are as follows:

LIMINE_TERMINAL_CB_DEC - (type value: 10)

This callback is triggered whenever a DEC Private Mode (DECSET/DECRST) sequence is encountered that the terminal cannot handle alone. The arguments to this callback are: terminal, type, values_count, values, final.

values_count is a count of how many values are in the array pointed to by values. values is a pointer to an array of uint32_t values, which are the values passed to the DEC private escape. final is the final character in the DEC private escape sequence (typically l or h).

LIMINE_TERMINAL_CB_BELL - (type value: 20)

This callback is triggered whenever a bell event is determined to be necessary (such as when a bell character \a is encountered). The arguments to this callback are: terminal, type, unused1, unused2, unused3.

LIMINE_TERMINAL_CB_PRIVATE_ID - (type value: 30)

This callback is triggered whenever the kernel has to respond to a DEC private identification request. The arguments to this callback are: terminal, type, unused1, unused2, unused3.

LIMINE_TERMINAL_CB_STATUS_REPORT - (type value 40)

This callback is triggered whenever the kernel has to respond to a ECMA-48 status report request. The arguments to this callback are: terminal, type, unused1, unused2, unused3.

LIMINE_TERMINAL_CB_POS_REPORT - (type value 50)

This callback is triggered whenever the kernel has to respond to a ECMA-48 cursor position report request. The arguments to this callback are: terminal, type, x, y, unused3. Where x and y represent the cursor position at the time the callback is triggered.

LIMINE_TERMINAL_CB_KBD_LEDS - (type value 60)

This callback is triggered whenever the kernel has to respond to a keyboard LED state change request. The arguments to this callback are: terminal, type, led_state, unused2, unused3. led_state can have one of the following values: 0, 1, 2, or 3. These values mean: clear all LEDs, set scroll lock, set num lock, and set caps lock LED, respectively.

LIMINE_TERMINAL_CB_MODE - (type value: 70)

This callback is triggered whenever an ECMA-48 Mode Switch sequence is encountered that the terminal cannot handle alone. The arguments to this callback are: terminal, type, values_count, values, final.

values_count is a count of how many values are in the array pointed to by values. values is a pointer to an array of uint32_t values, which are the values passed to the mode switch escape. final is the final character in the mode switch escape sequence (typically l or h).

LIMINE_TERMINAL_CB_LINUX - (type value 80)

This callback is triggered whenever a private Linux escape sequence is encountered that the terminal cannot handle alone. The arguments to this callback are: terminal, type, values_count, values, unused3.

values_count is a count of how many values are in the array pointed to by values. values is a pointer to an array of uint32_t values, which are the values passed to the Linux private escape.

Terminal context control

The write() function can additionally be used to set and restore terminal context, and refresh the terminal fully.

In order to achieve this, special values for the length argument are passed. These values are:

/* Response revision 0 */
#define LIMINE_TERMINAL_CTX_SIZE ((uint64_t)(-1))
#define LIMINE_TERMINAL_CTX_SAVE ((uint64_t)(-2))
#define LIMINE_TERMINAL_CTX_RESTORE ((uint64_t)(-3))
#define LIMINE_TERMINAL_FULL_REFRESH ((uint64_t)(-4))
/* Response revision 1 */
#define LIMINE_TERMINAL_OOB_OUTPUT_GET ((uint64_t)(-10))
#define LIMINE_TERMINAL_OOB_OUTPUT_SET ((uint64_t)(-11))

For CTX_SIZE, the ptr variable has to point to a location to which the terminal will write a single uint64_t which contains the size of the terminal context.

For CTX_SAVE and CTX_RESTORE, the ptr variable has to point to a location to which the terminal will save or restore its context from, respectively. This location must have a size congruent to the value received from CTX_SIZE.

For FULL_REFRESH, the ptr variable is unused. This routine is to be used after control of the framebuffer is taken over and the bootloader's terminal has to fully repaint the framebuffer to avoid inconsistencies.

If the response revision is equal or greater than 1 OOB_OUTPUT_GET and OOB_OUTPUT_SET allow getting and setting the out-of-band terminal output settings. ptr points to a location to where the terminal will write or read a single uint64_t value containing the bits representing the settings. The possible settings are as follows:

#define LIMINE_TERMINAL_OOB_OUTPUT_OCRNL (1 << 0)
#define LIMINE_TERMINAL_OOB_OUTPUT_OFDEL (1 << 1)
#define LIMINE_TERMINAL_OOB_OUTPUT_OFILL (1 << 2)
#define LIMINE_TERMINAL_OOB_OUTPUT_OLCUC (1 << 3)
#define LIMINE_TERMINAL_OOB_OUTPUT_ONLCR (1 << 4)
#define LIMINE_TERMINAL_OOB_OUTPUT_ONLRET (1 << 5)
#define LIMINE_TERMINAL_OOB_OUTPUT_ONOCR (1 << 6)
#define LIMINE_TERMINAL_OOB_OUTPUT_OPOST (1 << 7)

The effect of each of these options matches the effect of the stty(1) options by the same name.

x86_64

Additionally, the kernel must ensure, when calling write(), that:

Either the GDT provided by the bootloader is still properly loaded, or a custom GDT is loaded with at least the following descriptors in this specific order:
- Null descriptor
- 16-bit code descriptor. Base = 0, limit = 0xffff. Readable.
- 16-bit data descriptor. Base = 0, limit = 0xffff. Writable.
- 32-bit code descriptor. Base = 0, limit = 0xffffffff. Readable.
- 32-bit data descriptor. Base = 0, limit = 0xffffffff. Writable.
- 64-bit code descriptor. Base and limit irrelevant. Readable.
- 64-bit data descriptor. Base and limit irrelevant. Writable.
The currently loaded virtual address space is still the one provided at entry by the bootloader, or a custom virtual address space is loaded which identity maps the framebuffer memory region associated with the terminal, and all the bootloader reclaimable memory regions, with read, write, and execute permissions.
The routine is called by its physical address (the value of the function pointer is already physical), which should be identity mapped.
Bootloader-reclaimable memory entries are left untouched until after the kernel is done utilising bootloader-provided facilities (this terminal being one of them).

Notes regarding segment registers and FPU:

The values of the FS and GS segments are guaranteed preserved across the call. All other segment registers may have their "hidden" portion overwritten, but Limine guarantees that the "visible" portion is going to be restored to the one used at the time of call before returning.

No registers other than the segment registers and general purpose registers are going to be used. Especially, this means that there is no need to save and restore FPU, SSE, or AVX state when calling the terminal write function.

aarch64

Additionally, the kernel must ensure, when calling write(), that:

The currently loaded virtual address space is still the one provided at entry by the bootloader, or a custom virtual address space is loaded which identity maps the framebuffer memory region associated with the terminal, and all the bootloader reclaimable memory regions, with read, write, and execute permissions.
The routine is called by its physical address (the value of the function pointer is already physical), which should be identity mapped.
Bootloader-reclaimable memory entries are left untouched until after the kernel is done utilising bootloader-provided facilities (this terminal being one of them).

Notes regarding the usage of registers:

No registers other than the general purpose registers are going to be used. Especially, this means that there is no need to save and restore SIMD state when calling the terminal write function.

Terminal characteristics

The terminal should strive for Linux console compatibility.

Framebuffer Feature

ID:

#define LIMINE_FRAMEBUFFER_REQUEST { LIMINE_COMMON_MAGIC, 0x9d5827dcd881dd75, 0xa3148604f6fab11b }

Request:

struct limine_framebuffer_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_framebuffer_response *response;
};

Response:

struct limine_framebuffer_response {
    uint64_t revision;
    uint64_t framebuffer_count;
    struct limine_framebuffer **framebuffers;
};

framebuffer_count - How many framebuffers are present.
framebuffers - Pointer to an array of framebuffer_count pointers to struct limine_framebuffer structures.

// Constants for `memory_model`
#define LIMINE_FRAMEBUFFER_RGB 1

struct limine_framebuffer {
    void *address;
    uint64_t width;
    uint64_t height;
    uint64_t pitch;
    uint16_t bpp; // Bits per pixel
    uint8_t memory_model;
    uint8_t red_mask_size;
    uint8_t red_mask_shift;
    uint8_t green_mask_size;
    uint8_t green_mask_shift;
    uint8_t blue_mask_size;
    uint8_t blue_mask_shift;
    uint8_t unused[7];
    uint64_t edid_size;
    void *edid;

    /* Response revision 1 */
    uint64_t mode_count;
    struct limine_video_mode **modes;
};

modes is an array of mode_count pointers to struct limine_video_mode describing the available video modes for the given framebuffer.

struct limine_video_mode {
    uint64_t pitch;
    uint64_t width;
    uint64_t height;
    uint16_t bpp;
    uint8_t memory_model;
    uint8_t red_mask_size;
    uint8_t red_mask_shift;
    uint8_t green_mask_size;
    uint8_t green_mask_shift;
    uint8_t blue_mask_size;
    uint8_t blue_mask_shift;
};

Paging Mode Feature

The Paging Mode feature allows the kernel to control which paging mode is enabled before control is passed to it.

ID:

#define LIMINE_PAGING_MODE_REQUEST { LIMINE_COMMON_MAGIC, 0x95c1a0edab0944cb, 0xa4e5cb3842f7488a }

Request:

struct limine_paging_mode_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_paging_mode_response *response;
    uint64_t mode;
    uint64_t flags;
};

Both the mode and flags fields are architecture-specific.

The LIMINE_PAGING_MODE_DEFAULT macro is provided by all architectures to select the default paging mode (see below).

Response:

struct limine_paging_mode_response {
    uint64_t revision;
    uint64_t mode;
    uint64_t flags;
};

The response indicates which paging mode was actually enabled by the bootloader. Kernels must be prepared to handle the case where the requested paging mode is not supported by the hardware.

x86_64

Values for mode:

#define LIMINE_PAGING_MODE_X86_64_4LVL 0
#define LIMINE_PAGING_MODE_X86_64_5LVL 1

#define LIMINE_PAGING_MODE_DEFAULT LIMINE_PAGING_MODE_X86_64_4LVL

No flags are currently defined.

The default mode (when this request is not provided) is LIMINE_PAGING_MODE_X86_64_4LVL.

aarch64

Values for mode:

#define LIMINE_PAGING_MODE_AARCH64_4LVL 0
#define LIMINE_PAGING_MODE_AARCH64_5LVL 1

#define LIMINE_PAGING_MODE_DEFAULT LIMINE_PAGING_MODE_AARCH64_4LVL

No flags are currently defined.

The default mode (when this request is not provided) is LIMINE_PAGING_MODE_AARCH64_4LVL.

riscv64

Values for mode:

#define LIMINE_PAGING_MODE_RISCV_SV39 0
#define LIMINE_PAGING_MODE_RISCV_SV48 1
#define LIMINE_PAGING_MODE_RISCV_SV57 2

#define LIMINE_PAGING_MODE_DEFAULT LIMINE_PAGING_MODE_RISCV_SV48

No flags are currently defined.

The default mode (when this request is not provided) is LIMINE_PAGING_MODE_RISCV_SV48.

5-Level Paging Feature

Note: This feature has been deprecated in favor of the Paging Mode feature and will be removed entirely in a future release.

ID:

#define LIMINE_5_LEVEL_PAGING_REQUEST { LIMINE_COMMON_MAGIC, 0x94469551da9b3192, 0xebe5e86db7382888 }

Request:

struct limine_5_level_paging_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_5_level_paging_response *response;
};

Response:

struct limine_5_level_paging_response {
    uint64_t revision;
};

Notes: The presence of this request will prompt the bootloader to turn on x86_64 5-level paging. It will not be turned on if this request is not present. If the response pointer is changed to a valid pointer, 5-level paging is engaged.

SMP (multiprocessor) Feature

ID:

#define LIMINE_SMP_REQUEST { LIMINE_COMMON_MAGIC, 0x95a67b819a1b857e, 0xa0b61b723b6a73e0 }

Request:

struct limine_smp_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_smp_response *response;
    uint64_t flags;
};

flags - Bit 0: Enable X2APIC, if possible. (x86_64-only)

x86_64:

Response:

struct limine_smp_response {
    uint64_t revision;
    uint32_t flags;
    uint32_t bsp_lapic_id;
    uint64_t cpu_count;
    struct limine_smp_info **cpus;
};

flags - Bit 0: X2APIC has been enabled.
bsp_lapic_id - The Local APIC ID of the bootstrap processor.
cpu_count - How many CPUs are present. It includes the bootstrap processor.
cpus - Pointer to an array of cpu_count pointers to struct limine_smp_info structures.

Notes: The presence of this request will prompt the bootloader to bootstrap the secondary processors. This will not be done if this request is not present.

struct limine_smp_info;

typedef void (*limine_goto_address)(struct limine_smp_info *);

struct limine_smp_info {
    uint32_t processor_id;
    uint32_t lapic_id;
    uint64_t reserved;
    limine_goto_address goto_address;
    uint64_t extra_argument;
};

processor_id - ACPI Processor UID as specified by the MADT
lapic_id - Local APIC ID of the processor as specified by the MADT
goto_address - An atomic write to this field causes the parked CPU to jump to the written address, on a 64KiB (or Stack Size Request size) stack. A pointer to the struct limine_smp_info structure of the CPU is passed in RDI. Other than that, the CPU state will be the same as described for the bootstrap processor. This field is unused for the structure describing the bootstrap processor. For all CPUs, this field is guaranteed to be NULL when control is first passed to the bootstrap processor.
extra_argument - A free for use field.

aarch64:

Response:

struct limine_smp_response {
    uint64_t revision;
    uint32_t flags;
    uint64_t bsp_mpidr;
    uint64_t cpu_count;
    struct limine_smp_info **cpus;
};

flags - Always zero
bsp_mpidr - MPIDR of the bootstrap processor (as read from MPIDR_EL1, with Res1 masked off).
cpu_count - How many CPUs are present. It includes the bootstrap processor.
cpus - Pointer to an array of cpu_count pointers to struct limine_smp_info structures.

Notes: The presence of this request will prompt the bootloader to bootstrap the secondary processors. This will not be done if this request is not present.

struct limine_smp_info;

typedef void (*limine_goto_address)(struct limine_smp_info *);

struct limine_smp_info {
    uint32_t processor_id;
    uint32_t gic_iface_no;
    uint64_t mpidr;
    uint64_t reserved;
    limine_goto_address goto_address;
    uint64_t extra_argument;
};

processor_id - ACPI Processor UID as specified by the MADT
gic_iface_no - GIC CPU Interface number of the processor as specified by the MADT (possibly always 0)
mpidr - MPIDR of the processor as specified by the MADT or device tree
goto_address - An atomic write to this field causes the parked CPU to jump to the written address, on a 64KiB (or Stack Size Request size) stack. A pointer to the struct limine_smp_info structure of the CPU is passed in X0. Other than that, the CPU state will be the same as described for the bootstrap processor. This field is unused for the structure describing the bootstrap processor.
extra_argument - A free for use field.

riscv64

Response:

struct limine_smp_response {
    uint64_t revision;
    uint32_t flags;
    uint64_t bsp_hartid;
    uint64_t cpu_count;
    struct limine_smp_info **cpus;
};

flags - Always zero
bsp_hartid - Hart ID of the bootstrap processor as reported by the UEFI RISC-V Boot Protocol or the SBI.
cpu_count - How many CPUs are present. It includes the bootstrap processor.
cpus - Pointer to an array of cpu_count pointers to struct limine_smp_info structures.

Notes: The presence of this request will prompt the bootloader to bootstrap the secondary processors. This will not be done if this request is not present.

struct limine_smp_info;

typedef void (*limine_goto_address)(struct limine_smp_info *);

struct limine_smp_info {
    uint32_t processor_id;
    uint64_t hartid;
    uint64_t reserved;
    limine_goto_address goto_address;
    uint64_t extra_argument;
};

processor_id - ACPI Processor UID as specified by the MADT (always 0 on non-ACPI systems).
hartid - Hart ID of the processor as specified by the MADT or Device Tree.
goto_address - An atomic write to this field causes the parked CPU to jump to the written address, on a 64KiB (or Stack Size Request size) stack. A pointer to the struct limine_smp_info structure of the CPU is passed in x10(a0). Other than that, the CPU state will be the same as described for the bootstrap processor. This field is unused for the structure describing the bootstrap processor.
extra_argument - A free for use field.

Memory Map Feature

ID:

#define LIMINE_MEMMAP_REQUEST { LIMINE_COMMON_MAGIC, 0x67cf3d9d378a806f, 0xe304acdfc50c3c62 }

Request:

struct limine_memmap_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_memmap_response *response;
};

Response:

struct limine_memmap_response {
    uint64_t revision;
    uint64_t entry_count;
    struct limine_memmap_entry **entries;
};

entry_count - How many memory map entries are present.
entries - Pointer to an array of entry_count pointers to struct limine_memmap_entry structures.

// Constants for `type`
#define LIMINE_MEMMAP_USABLE                 0
#define LIMINE_MEMMAP_RESERVED               1
#define LIMINE_MEMMAP_ACPI_RECLAIMABLE       2
#define LIMINE_MEMMAP_ACPI_NVS               3
#define LIMINE_MEMMAP_BAD_MEMORY             4
#define LIMINE_MEMMAP_BOOTLOADER_RECLAIMABLE 5
#define LIMINE_MEMMAP_KERNEL_AND_MODULES     6
#define LIMINE_MEMMAP_FRAMEBUFFER            7

struct limine_memmap_entry {
    uint64_t base;
    uint64_t length;
    uint64_t type;
};

Note: Memory between 0 and 0x1000 is never marked as usable memory. The kernel and modules loaded are not marked as usable memory. They are marked as Kernel/Modules. The entries are guaranteed to be sorted by base address, lowest to highest. Usable and bootloader reclaimable entries are guaranteed to be 4096 byte aligned for both base and length. Usable and bootloader reclaimable entries are guaranteed not to overlap with any other entry. To the contrary, all non-usable entries (including kernel/modules) are not guaranteed any alignment, nor is it guaranteed that they do not overlap other entries.

Entry Point Feature

ID:

#define LIMINE_ENTRY_POINT_REQUEST { LIMINE_COMMON_MAGIC, 0x13d86c035a1cd3e1, 0x2b0caa89d8f3026a }

Request:

typedef void (*limine_entry_point)(void);

struct limine_entry_point_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_entry_point_response *response;
    limine_entry_point entry;
};

entry - The requested entry point.

Response:

struct limine_entry_point_response {
    uint64_t revision;
};

Kernel File Feature

ID:

#define LIMINE_KERNEL_FILE_REQUEST { LIMINE_COMMON_MAGIC, 0xad97e90e83f1ed67, 0x31eb5d1c5ff23b69 }

Request:

struct limine_kernel_file_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_kernel_file_response *response;
};

Response:

struct limine_kernel_file_response {
    uint64_t revision;
    struct limine_file *kernel_file;
};

kernel_file - Pointer to the struct limine_file structure (see below) for the kernel file.

Module Feature

ID:

#define LIMINE_MODULE_REQUEST { LIMINE_COMMON_MAGIC, 0x3e7e279702be32af, 0xca1c4f3bd1280cee }

Request:

#define LIMINE_INTERNAL_MODULE_REQUIRED (1 << 0)

struct limine_internal_module {
    const char *path;
    const char *cmdline;
    uint64_t flags;
};

struct limine_module_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_module_response *response;

    /* Request revision 1 */
    uint64_t internal_module_count;
    struct limine_internal_module **internal_modules;
};

internal_module_count - How many internal modules are passed by the kernel.
internal_modules - Pointer to an array of internal_module_count pointers to struct limine_internal_module structures.

Note: Internal modules are honoured if the module response has revision >= 1.

As part of struct limine_internal_module:

path - Path to the module to load. This path is relative to the location of the kernel.
cmdline - Command line for the given module.
flags - Flags changing module loading behaviour:
- LIMINE_INTERNAL_MODULE_REQUIRED: Fail if the requested module is not found.

Internal Limine modules are guaranteed to be loaded before user-specified (configuration) modules, and thus they are guaranteed to appear before user-specified modules in the modules array in the response.

Response:

struct limine_module_response {
    uint64_t revision;
    uint64_t module_count;
    struct limine_file **modules;
};

module_count - How many modules are present.
modules - Pointer to an array of module_count pointers to struct limine_file structures (see below).

File Structure

struct limine_uuid {
    uint32_t a;
    uint16_t b;
    uint16_t c;
    uint8_t d[8];
};

#define LIMINE_MEDIA_TYPE_GENERIC 0
#define LIMINE_MEDIA_TYPE_OPTICAL 1
#define LIMINE_MEDIA_TYPE_TFTP 2

struct limine_file {
    uint64_t revision;
    void *address;
    uint64_t size;
    char *path;
    char *cmdline;
    uint32_t media_type;
    uint32_t unused;
    uint32_t tftp_ip;
    uint32_t tftp_port;
    uint32_t partition_index;
    uint32_t mbr_disk_id;
    struct limine_uuid gpt_disk_uuid;
    struct limine_uuid gpt_part_uuid;
    struct limine_uuid part_uuid;
};

revision - Revision of the struct limine_file structure.
address - The address of the file. This is always at least 4KiB aligned.
size - The size of the file.
path - The path of the file within the volume, with a leading slash.
cmdline - A command line associated with the file.
media_type - Type of media file resides on.
tftp_ip - If non-0, this is the IP of the TFTP server the file was loaded from.
tftp_port - Likewise, but port.
partition_index - 1-based partition index of the volume from which the file was loaded. If 0, it means invalid or unpartitioned.
mbr_disk_id - If non-0, this is the ID of the disk the file was loaded from as reported in its MBR.
gpt_disk_uuid - If non-0, this is the UUID of the disk the file was loaded from as reported in its GPT.
gpt_part_uuid - If non-0, this is the UUID of the partition the file was loaded from as reported in the GPT.
part_uuid - If non-0, this is the UUID of the filesystem of the partition the file was loaded from.

RSDP Feature

ID:

#define LIMINE_RSDP_REQUEST { LIMINE_COMMON_MAGIC, 0xc5e77b6b397e7b43, 0x27637845accdcf3c }

Request:

struct limine_rsdp_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_rsdp_response *response;
};

Response:

struct limine_rsdp_response {
    uint64_t revision;
    void *address;
};

address - Address of the RSDP table.

SMBIOS Feature

ID:

#define LIMINE_SMBIOS_REQUEST { LIMINE_COMMON_MAGIC, 0x9e9046f11e095391, 0xaa4a520fefbde5ee }

Request:

struct limine_smbios_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_smbios_response *response;
};

Response:

struct limine_smbios_response {
    uint64_t revision;
    void *entry_32;
    void *entry_64;
};

entry_32 - Address of the 32-bit SMBIOS entry point. NULL if not present.
entry_64 - Address of the 64-bit SMBIOS entry point. NULL if not present.

EFI System Table Feature

ID:

#define LIMINE_EFI_SYSTEM_TABLE_REQUEST { LIMINE_COMMON_MAGIC, 0x5ceba5163eaaf6d6, 0x0a6981610cf65fcc }

Request:

struct limine_efi_system_table_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_efi_system_table_response *response;
};

Response:

struct limine_efi_system_table_response {
    uint64_t revision;
    void *address;
};

address - Address of EFI system table.

Boot Time Feature

ID:

#define LIMINE_BOOT_TIME_REQUEST { LIMINE_COMMON_MAGIC, 0x502746e184c088aa, 0xfbc5ec83e6327893 }

Request:

struct limine_boot_time_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_boot_time_response *response;
};

Response:

struct limine_boot_time_response {
    uint64_t revision;
    int64_t boot_time;
};

boot_time - The UNIX time on boot, in seconds, taken from the system RTC.

Kernel Address Feature

ID:

#define LIMINE_KERNEL_ADDRESS_REQUEST { LIMINE_COMMON_MAGIC, 0x71ba76863cc55f63, 0xb2644a48c516a487 }

Request:

struct limine_kernel_address_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_kernel_address_response *response;
};

Response:

struct limine_kernel_address_response {
    uint64_t revision;
    uint64_t physical_base;
    uint64_t virtual_base;
};

physical_base - The physical base address of the kernel.
virtual_base - The virtual base address of the kernel.

Device Tree Blob Feature

ID:

#define LIMINE_DTB_REQUEST { LIMINE_COMMON_MAGIC, 0xb40ddb48fb54bac7, 0x545081493f81ffb7 }

Request:

struct limine_dtb_request {
    uint64_t id[4];
    uint64_t revision;
    struct limine_dtb_response *response;
};

Response:

struct limine_dtb_response {
    uint64_t revision;
    void *dtb_ptr;
};

dtb_ptr - Virtual pointer to the device tree blob.

Note: If the DTB cannot be found, the response will not be generated.

Note: Information contained in the /chosen node may not reflect the information given by bootloader tags, and as such the /chosen node properties should be ignored.

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The Limine Boot Protocol

General Notes

Features

Limine Requests Section

Entry memory layout

Entry machine state

x86_64

aarch64

riscv64

Feature List

Bootloader Info Feature

Stack Size Feature

HHDM (Higher Half Direct Map) Feature

Terminal Feature

Terminal callback

Terminal context control

x86_64

aarch64

Terminal characteristics

Framebuffer Feature

Paging Mode Feature

x86_64

aarch64

riscv64

5-Level Paging Feature

SMP (multiprocessor) Feature

x86_64:

aarch64:

riscv64

Memory Map Feature

Entry Point Feature

Kernel File Feature

Module Feature

File Structure

RSDP Feature

SMBIOS Feature

EFI System Table Feature

Boot Time Feature

Kernel Address Feature

Device Tree Blob Feature

40 KiB

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