Limine Bare Bones: Difference between revisions
m
Wording fix.
[unchecked revision] | [unchecked revision] |
(Use base revision 1) |
m (Wording fix.) |
||
(22 intermediate revisions by 4 users not shown) | |||
Line 3:
{{Template:Kernel designs}}
The Limine Boot Protocol is the native boot protocol provided by the [[Limine]] bootloader.
It provides cutting edge features such as 5-level paging support, 64-bit [[Long Mode]] support, and direct higher half kernel loading.
Line 9:
The Limine boot protocol is firmware and architecture agnostic. The Limine bootloader supports x86-64, IA-32, aarch64, and riscv64.
This article will demonstrate how to write a small Limine-compliant x86-64
For this example, we will create these 2 files to create the basic directory tree of our project:
* src/
* linker.ld
Line 25:
Obviously, this is just a bare bones example, and one should always refer to the [https://github.com/limine-bootloader/limine/blob/trunk/PROTOCOL.md Limine protocol specification] for more details and information.
===src/
This is the kernel "main".
<
#include <stdint.h>
#include <stddef.h>
Line 35:
#include <limine.h>
// Set the base revision to
// base revision described by the Limine boot protocol specification.
// See specification for further info.
__attribute__((used, section(".requests")))
static volatile LIMINE_BASE_REVISION(
// The Limine requests can be placed anywhere, but it is important that
// the compiler does not optimise them away, so,
// be made volatile or equivalent, _and_ they should be accessed at least
// once or marked as used with the "used" attribute as done here.
__attribute__((used, section(".requests")))
static volatile struct limine_framebuffer_request framebuffer_request = {
.id = LIMINE_FRAMEBUFFER_REQUEST,
.revision = 0
};
// Finally, define the start and end markers for the Limine requests.
// These can also be moved anywhere, to any .c file, as seen fit.
__attribute__((used, section(".requests_start_marker")))
static volatile LIMINE_REQUESTS_START_MARKER;
__attribute__((used, section(".requests_end_marker")))
static volatile LIMINE_REQUESTS_END_MARKER;
// GCC and Clang reserve the right to generate calls to the following
Line 135 ⟶ 147:
// Note: we assume the framebuffer model is RGB with 32-bit pixels.
for (size_t i = 0; i < 100; i++) {
volatile uint32_t *fb_ptr = framebuffer->address;
fb_ptr[i * (framebuffer->pitch / 4) + i] = 0xffffff;
}
Line 143 ⟶ 155:
}
</syntaxhighlight>
===linker.ld===
Line 149 ⟶ 161:
This is going to be our linker script describing where our sections will end up in memory.
<
/* Tell the linker that we want an x86_64 ELF64 output file */
OUTPUT_FORMAT(elf64-x86-64)
Line 161 ⟶ 173:
PHDRS
{
text PT_LOAD FLAGS(
rodata PT_LOAD FLAGS(
data PT_LOAD FLAGS(
dynamic PT_DYNAMIC FLAGS(
}
Line 180 ⟶ 192:
/* Move to the next memory page for .rodata */
.
.rodata : {
Line 187 ⟶ 199:
/* Move to the next memory page for .data */
.
.data : {
*(.data .data.*)
/* Place the sections that contain the Limine requests as part of the .data */
/* output section. */
KEEP(*(.requests_start_marker))
KEEP(*(.requests))
KEEP(*(.requests_end_marker))
} :data
Line 207 ⟶ 225:
} :data
/* Discard .note.* and .eh_frame* since they may cause issues on some hosts. */
/* Also discard the program interpreter section since we do not need one. This is */
/* more or less equivalent to the --no-dynamic-linker linker flag, except that it */
/* works with ld.gold. */
/DISCARD/ : {
*(.eh_frame*)
*(.note .note.*)
*(.interp)
}
}
</syntaxhighlight>
==Building the kernel and creating an image==
Line 224 ⟶ 246:
GNU make will process it.
<
# Nuke built-in rules and variables.
override MAKEFLAGS += -rR
Line 245 ⟶ 267:
# We are using the standard "cc" here, it may work by using
# the host system's toolchain, but this is not guaranteed.
override
$(eval $(call DEFAULT_VAR,
# Same thing for "ld" (the linker).
override
$(eval $(call DEFAULT_VAR,
# User controllable C flags.
override
$(eval $(call DEFAULT_VAR,
# User controllable C preprocessor flags. We set none by default.
override
$(eval $(call DEFAULT_VAR,
# User controllable nasm flags.
override
$(eval $(call DEFAULT_VAR,
# User controllable linker flags. We set none by default.
override
$(eval $(call DEFAULT_VAR,
# Internal C flags that should not be changed by the user.
override
-Wall \
-Wextra \
Line 287 ⟶ 309:
# Internal C preprocessor flags that should not be changed by the user.
override
-I src \
$(
-MMD \
-MP
# Internal linker flags that should not be changed by the user.
override
-m elf_x86_64 \
-nostdlib \
-pie \
-z text \
-z max-page-size=0x1000 \
Line 305 ⟶ 325:
# Internal nasm flags that should not be changed by the user.
override
-Wall \
-f elf64
Line 322 ⟶ 342:
# Link rules for the final kernel executable.
# The magic printf/dd command is used to force the final ELF file type to ET_DYN.
# GNU binutils, for silly reasons, forces the ELF type to ET_EXEC even for
# relocatable PIEs, if the base load address is non-0.
# See https://sourceware.org/bugzilla/show_bug.cgi?id=31795 for more information.
bin/$(KERNEL): GNUmakefile linker.ld $(OBJ)
mkdir -p "$$(dirname $@)"
$(
printf '\003' | dd of=$@ bs=1 count=1 seek=16 conv=notrunc
# Include header dependencies.
Line 332 ⟶ 357:
obj/%.c.o: src/%.c GNUmakefile
mkdir -p "$$(dirname $@)"
$(
# Compilation rules for *.S files.
obj/%.S.o: src/%.S GNUmakefile
mkdir -p "$$(dirname $@)"
$(
# Compilation rules for *.asm (nasm) files.
obj/%.asm.o: src/%.asm GNUmakefile
mkdir -p "$$(dirname $@)"
nasm $(
# Remove object files and the final executable.
Line 348 ⟶ 373:
clean:
rm -rf bin obj
</syntaxhighlight>
===limine.cfg===
Line 354 ⟶ 379:
This file is parsed by Limine and it describes boot entries and other bootloader configuration variables. Further information [https://github.com/limine-bootloader/limine/blob/trunk/CONFIG.md here].
<
# Timeout in seconds that Limine will use before automatically booting.
TIMEOUT=5
# The entry name that will be displayed in the boot menu.
:myOS
# We use the Limine boot protocol.
PROTOCOL=limine
# Disable KASLR (it is enabled by default for relocatable kernels)▼
KASLR=no▼
# Path to the kernel to boot. boot:/// represents the partition on which limine.cfg is located.
KERNEL_PATH=boot:///boot/myos
# Same thing, but
:myOS (
PROTOCOL=limine
KERNEL_PATH=boot:///boot/myos▼
▲ # Disable KASLR (it is enabled by default for relocatable kernels)
</syntaxhighlight>
▲ KASLR=no
▲ KERNEL_PATH=boot:///myos
===Compiling the kernel===
Line 384 ⟶ 409:
''If you are not using macOS, you can skip this section.''
The macOS Xcode toolchain uses Mach-O binaries, and not the ELF binaries
===Creating the image===
Line 398 ⟶ 423:
These are shell commands. They can also be compiled into a script or Makefile.
<
# Download the latest Limine binary release for the 7.x branch.
git clone https://github.com/limine-bootloader/limine.git --branch=
# Build "limine" utility.
make -C limine
Line 409 ⟶ 434:
# Copy the relevant files over.
mkdir -p iso_root/boot
cp -v bin/myos limine.cfg limine/limine-bios.sys \▼
cp -v
mkdir -p iso_root/boot/limine
limine/limine-uefi-cd.bin iso_root/boot/limine/
# Create the EFI boot tree and copy Limine's EFI executables over.
Line 418 ⟶ 446:
# Create the bootable ISO.
xorriso -as mkisofs -b boot/limine/limine-bios-cd.bin \
-no-emul-boot -boot-load-size 4 -boot-info-table \
--efi-boot boot/limine/limine-uefi-cd.bin \
-efi-boot-part --efi-boot-image --protective-msdos-label \
iso_root -o image.iso
Line 426 ⟶ 454:
# Install Limine stage 1 and 2 for legacy BIOS boot.
./limine/limine bios-install image.iso
</syntaxhighlight>
====Creating a hard disk/USB drive image====
Line 436 ⟶ 464:
These are shell commands. They can also be compiled into a script or Makefile.
<
# Create an empty zeroed-out 64MiB image file.
dd if=/dev/zero bs=1M count=0 seek=64 of=image.hdd
Line 443 ⟶ 471:
sgdisk image.hdd -n 1:2048 -t 1:ef00
# Download the latest Limine binary release for the 7.x branch.
git clone https://github.com/limine-bootloader/limine.git --branch=
# Build "limine" utility.
make -C limine
Line 455 ⟶ 483:
mformat -i image.hdd@@1M
# Make relevant subdirectories.
mmd -i image.hdd@@1M ::/EFI ::/EFI/BOOT ::/boot ::/boot/limine
# Copy over the relevant files.
mcopy -i image.hdd@@1M bin/myos
mcopy -i image.hdd@@1M limine.cfg limine/limine-bios.sys ::/boot/limine
mcopy -i image.hdd@@1M limine/BOOTX64.EFI ::/EFI/BOOT
mcopy -i image.hdd@@1M limine/BOOTIA32.EFI ::/EFI/BOOT
</syntaxhighlight>
==Conclusions==
|