diff --git a/README.md b/README.md
index 3486fc0..f845592 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,16 @@ modify the disk image with your favorit tool (e.g. gparted) and re-generate disk
sfdisk -d > disk.sfdisk
+# Multiboot
+
+In arch/x86/boot, you can choose the assembly used to start the C part by removing the .opt extension
+
+* boot.asm: intel syntax with multiboot support
+* boot.S: GNU As syntax with multiboot support
+* boot_multiboot2.S: GNU As syntax with multiboot2 support
+
+/!\ multiboot2 is not supported by qemu for -kernel option (https://gitlab.com/qemu-project/qemu/-/issues/389).
+So you may have to use the fd.iso image and modify the grub configuration from `multiboot /boot/kernel` to `multiboot2 /boot/kernel`
# Features
diff --git a/arch/x86/boot/boot.asm b/arch/x86/boot/boot.asm.opt
similarity index 100%
rename from arch/x86/boot/boot.asm
rename to arch/x86/boot/boot.asm.opt
diff --git a/arch/x86/boot/boot_multiboot2.S.opt b/arch/x86/boot/boot_multiboot2.S.opt
new file mode 100644
index 0000000..42a8fc6
--- /dev/null
+++ b/arch/x86/boot/boot_multiboot2.S.opt
@@ -0,0 +1,125 @@
+/* Inspired by from https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html#boot_002eS */
+
+/* boot.S - bootstrap the kernel */
+/* Copyright (C) 1999, 2001, 2010 Free Software Foundation, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see .
+ */
+
+#define ASM_FILE 1
+#include
+
+.section .multiboot
+.align 4
+ /* Multiboot header. */
+multiboot_header:
+ /* magic */
+ .long MULTIBOOT2_HEADER_MAGIC
+ /* ISA: i386 */
+ .long MULTIBOOT_ARCHITECTURE_I386
+ /* Header length. */
+ .long multiboot_header_end - multiboot_header
+ /* checksum */
+ .long -(MULTIBOOT2_HEADER_MAGIC + MULTIBOOT_ARCHITECTURE_I386 + (multiboot_header_end - multiboot_header))
+multiboot_header_end:
+
+.section .bss
+.align 4096
+stack_bottom:
+.skip 16384 # 16 KiB
+stack_top:
+
+
+.section .text
+.global _start
+.type _start, @function
+_start:
+ /*
+ The bootloader has loaded us into 32-bit protected mode on a x86
+ machine. Interrupts are disabled. Paging is disabled. The processor
+ state is as defined in the multiboot standard. The kernel has full
+ control of the CPU. The kernel can only make use of hardware features
+ and any code it provides as part of itself. There's no printf
+ function, unless the kernel provides its own header and a
+ printf implementation. There are no security restrictions, no
+ safeguards, no debugging mechanisms, only what the kernel provides
+ itself. It has absolute and complete power over the
+ machine.
+ */
+
+ /*
+ To set up a stack, we set the esp register to point to the top of our
+ stack (as it grows downwards on x86 systems). This is necessarily done
+ in assembly as languages such as C cannot function without a stack.
+ */
+ mov $stack_top, %esp
+ mov $stack_bottom, %ebp
+
+ /*
+ This is a good place to initialize crucial processor state before the
+ high-level kernel is entered. It's best to minimize the early
+ environment where crucial features are offline. Note that the
+ processor is not fully initialized yet: Features such as floating
+ point instructions and instruction set extensions are not initialized
+ yet. The GDT should be loaded here. Paging should be enabled here.
+ C++ features such as global constructors and exceptions will require
+ runtime support to work as well.
+ */
+
+ /* Reset EFLAGS. */
+ pushl $0
+ popf
+
+
+ /*
+ Enter the high-level kernel. The ABI requires the stack is 16-byte
+ aligned at the time of the call instruction (which afterwards pushes
+ the return pointer of size 4 bytes). The stack was originally 16-byte
+ aligned above and we've since pushed a multiple of 16 bytes to the
+ stack since (pushed 0 bytes so far) and the alignment is thus
+ preserved and the call is well defined.
+ */
+ /* Push the pointer to the Multiboot information structure. */
+ pushl %ebx
+ /* Push the magic value. */
+ pushl %eax
+ call kmain
+
+ /*
+ If the system has nothing more to do, put the computer into an
+ infinite loop. To do that:
+ 1) Disable interrupts with cli (clear interrupt enable in eflags).
+ They are already disabled by the bootloader, so this is not needed.
+ Mind that you might later enable interrupts and return from
+ kernel_main (which is sort of nonsensical to do).
+ 2) Wait for the next interrupt to arrive with hlt (halt instruction).
+ Since they are disabled, this will lock up the computer.
+ 3) Jump to the hlt instruction if it ever wakes up due to a
+ non-maskable interrupt occurring or due to system management mode.
+ */
+ cli
+1: hlt
+ jmp 1b
+
+/*
+Set the size of the _start symbol to the current location '.' minus its start.
+This is useful when debugging or when you implement call tracing.
+*/
+.size _start, . - _start
+.global _stack_bottom
+_stack_bottom:
+ .long stack_bottom
+.global _stack_top
+_stack_top:
+ .long stack_top
diff --git a/core/multiboot2.h b/core/multiboot2.h
new file mode 100644
index 0000000..081e286
--- /dev/null
+++ b/core/multiboot2.h
@@ -0,0 +1,418 @@
+/* Taken from https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html#multiboot2_002eh */
+/* multiboot2.h - Multiboot 2 header file. */
+/* Copyright (C) 1999,2003,2007,2008,2009,2010 Free Software Foundation, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL ANY
+ * DEVELOPER OR DISTRIBUTOR BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+ * IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef MULTIBOOT_HEADER
+#define MULTIBOOT_HEADER 1
+
+/* How many bytes from the start of the file we search for the header. */
+#define MULTIBOOT_SEARCH 32768
+#define MULTIBOOT_HEADER_ALIGN 8
+
+/* The magic field should contain this. */
+#define MULTIBOOT2_HEADER_MAGIC 0xe85250d6
+
+/* This should be in %eax. */
+#define MULTIBOOT2_BOOTLOADER_MAGIC 0x36d76289
+
+/* Alignment of multiboot modules. */
+#define MULTIBOOT_MOD_ALIGN 0x00001000
+
+/* Alignment of the multiboot info structure. */
+#define MULTIBOOT_INFO_ALIGN 0x00000008
+
+/* Flags set in the ’flags’ member of the multiboot header. */
+
+#define MULTIBOOT_TAG_ALIGN 8
+#define MULTIBOOT_TAG_TYPE_END 0
+#define MULTIBOOT_TAG_TYPE_CMDLINE 1
+#define MULTIBOOT_TAG_TYPE_BOOT_LOADER_NAME 2
+#define MULTIBOOT_TAG_TYPE_MODULE 3
+#define MULTIBOOT_TAG_TYPE_BASIC_MEMINFO 4
+#define MULTIBOOT_TAG_TYPE_BOOTDEV 5
+#define MULTIBOOT_TAG_TYPE_MMAP 6
+#define MULTIBOOT_TAG_TYPE_VBE 7
+#define MULTIBOOT_TAG_TYPE_FRAMEBUFFER 8
+#define MULTIBOOT_TAG_TYPE_ELF_SECTIONS 9
+#define MULTIBOOT_TAG_TYPE_APM 10
+#define MULTIBOOT_TAG_TYPE_EFI32 11
+#define MULTIBOOT_TAG_TYPE_EFI64 12
+#define MULTIBOOT_TAG_TYPE_SMBIOS 13
+#define MULTIBOOT_TAG_TYPE_ACPI_OLD 14
+#define MULTIBOOT_TAG_TYPE_ACPI_NEW 15
+#define MULTIBOOT_TAG_TYPE_NETWORK 16
+#define MULTIBOOT_TAG_TYPE_EFI_MMAP 17
+#define MULTIBOOT_TAG_TYPE_EFI_BS 18
+#define MULTIBOOT_TAG_TYPE_EFI32_IH 19
+#define MULTIBOOT_TAG_TYPE_EFI64_IH 20
+#define MULTIBOOT_TAG_TYPE_LOAD_BASE_ADDR 21
+
+#define MULTIBOOT_HEADER_TAG_END 0
+#define MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST 1
+#define MULTIBOOT_HEADER_TAG_ADDRESS 2
+#define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS 3
+#define MULTIBOOT_HEADER_TAG_CONSOLE_FLAGS 4
+#define MULTIBOOT_HEADER_TAG_FRAMEBUFFER 5
+#define MULTIBOOT_HEADER_TAG_MODULE_ALIGN 6
+#define MULTIBOOT_HEADER_TAG_EFI_BS 7
+#define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI32 8
+#define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64 9
+#define MULTIBOOT_HEADER_TAG_RELOCATABLE 10
+
+#define MULTIBOOT_ARCHITECTURE_I386 0
+#define MULTIBOOT_ARCHITECTURE_MIPS32 4
+#define MULTIBOOT_HEADER_TAG_OPTIONAL 1
+
+#define MULTIBOOT_LOAD_PREFERENCE_NONE 0
+#define MULTIBOOT_LOAD_PREFERENCE_LOW 1
+#define MULTIBOOT_LOAD_PREFERENCE_HIGH 2
+
+#define MULTIBOOT_CONSOLE_FLAGS_CONSOLE_REQUIRED 1
+#define MULTIBOOT_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED 2
+
+#ifndef ASM_FILE
+
+typedef unsigned char multiboot_uint8_t;
+typedef unsigned short multiboot_uint16_t;
+typedef unsigned int multiboot_uint32_t;
+typedef unsigned long long multiboot_uint64_t;
+
+struct multiboot_header
+{
+ /* Must be MULTIBOOT_MAGIC - see above. */
+ multiboot_uint32_t magic;
+
+ /* ISA */
+ multiboot_uint32_t architecture;
+
+ /* Total header length. */
+ multiboot_uint32_t header_length;
+
+ /* The above fields plus this one must equal 0 mod 2^32. */
+ multiboot_uint32_t checksum;
+};
+
+struct multiboot_header_tag
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+};
+
+struct multiboot_header_tag_information_request
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t requests[0];
+};
+
+struct multiboot_header_tag_address
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t header_addr;
+ multiboot_uint32_t load_addr;
+ multiboot_uint32_t load_end_addr;
+ multiboot_uint32_t bss_end_addr;
+};
+
+struct multiboot_header_tag_entry_address
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t entry_addr;
+};
+
+struct multiboot_header_tag_console_flags
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t console_flags;
+};
+
+struct multiboot_header_tag_framebuffer
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t width;
+ multiboot_uint32_t height;
+ multiboot_uint32_t depth;
+};
+
+struct multiboot_header_tag_module_align
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+};
+
+struct multiboot_header_tag_relocatable
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t min_addr;
+ multiboot_uint32_t max_addr;
+ multiboot_uint32_t align;
+ multiboot_uint32_t preference;
+};
+
+struct multiboot_color
+{
+ multiboot_uint8_t red;
+ multiboot_uint8_t green;
+ multiboot_uint8_t blue;
+};
+
+struct multiboot_mmap_entry
+{
+ multiboot_uint64_t addr;
+ multiboot_uint64_t len;
+#define MULTIBOOT_MEMORY_AVAILABLE 1
+#define MULTIBOOT_MEMORY_RESERVED 2
+#define MULTIBOOT_MEMORY_ACPI_RECLAIMABLE 3
+#define MULTIBOOT_MEMORY_NVS 4
+#define MULTIBOOT_MEMORY_BADRAM 5
+ multiboot_uint32_t type;
+ multiboot_uint32_t zero;
+};
+typedef struct multiboot_mmap_entry multiboot_memory_map_t;
+
+struct multiboot_tag
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+};
+
+struct multiboot_tag_string
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ char string[0];
+};
+
+struct multiboot_tag_module
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t mod_start;
+ multiboot_uint32_t mod_end;
+ char cmdline[0];
+};
+
+struct multiboot_tag_basic_meminfo
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t mem_lower;
+ multiboot_uint32_t mem_upper;
+};
+
+struct multiboot_tag_bootdev
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t biosdev;
+ multiboot_uint32_t slice;
+ multiboot_uint32_t part;
+};
+
+struct multiboot_tag_mmap
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t entry_size;
+ multiboot_uint32_t entry_version;
+ struct multiboot_mmap_entry entries[0];
+};
+
+struct multiboot_vbe_info_block
+{
+ multiboot_uint8_t external_specification[512];
+};
+
+struct multiboot_vbe_mode_info_block
+{
+ multiboot_uint8_t external_specification[256];
+};
+
+struct multiboot_tag_vbe
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+
+ multiboot_uint16_t vbe_mode;
+ multiboot_uint16_t vbe_interface_seg;
+ multiboot_uint16_t vbe_interface_off;
+ multiboot_uint16_t vbe_interface_len;
+
+ struct multiboot_vbe_info_block vbe_control_info;
+ struct multiboot_vbe_mode_info_block vbe_mode_info;
+};
+
+struct multiboot_tag_framebuffer_common
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+
+ multiboot_uint64_t framebuffer_addr;
+ multiboot_uint32_t framebuffer_pitch;
+ multiboot_uint32_t framebuffer_width;
+ multiboot_uint32_t framebuffer_height;
+ multiboot_uint8_t framebuffer_bpp;
+#define MULTIBOOT_FRAMEBUFFER_TYPE_INDEXED 0
+#define MULTIBOOT_FRAMEBUFFER_TYPE_RGB 1
+#define MULTIBOOT_FRAMEBUFFER_TYPE_EGA_TEXT 2
+ multiboot_uint8_t framebuffer_type;
+ multiboot_uint16_t reserved;
+};
+
+struct multiboot_tag_framebuffer
+{
+ struct multiboot_tag_framebuffer_common common;
+
+ union
+ {
+ struct
+ {
+ multiboot_uint16_t framebuffer_palette_num_colors;
+ struct multiboot_color framebuffer_palette[0];
+ };
+ struct
+ {
+ multiboot_uint8_t framebuffer_red_field_position;
+ multiboot_uint8_t framebuffer_red_mask_size;
+ multiboot_uint8_t framebuffer_green_field_position;
+ multiboot_uint8_t framebuffer_green_mask_size;
+ multiboot_uint8_t framebuffer_blue_field_position;
+ multiboot_uint8_t framebuffer_blue_mask_size;
+ };
+ };
+};
+
+struct multiboot_tag_elf_sections
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t num;
+ multiboot_uint32_t entsize;
+ multiboot_uint32_t shndx;
+ char sections[0];
+};
+
+struct multiboot_tag_apm
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint16_t version;
+ multiboot_uint16_t cseg;
+ multiboot_uint32_t offset;
+ multiboot_uint16_t cseg_16;
+ multiboot_uint16_t dseg;
+ multiboot_uint16_t flags;
+ multiboot_uint16_t cseg_len;
+ multiboot_uint16_t cseg_16_len;
+ multiboot_uint16_t dseg_len;
+};
+
+struct multiboot_tag_efi32
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t pointer;
+};
+
+struct multiboot_tag_efi64
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint64_t pointer;
+};
+
+struct multiboot_tag_smbios
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint8_t major;
+ multiboot_uint8_t minor;
+ multiboot_uint8_t reserved[6];
+ multiboot_uint8_t tables[0];
+};
+
+struct multiboot_tag_old_acpi
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint8_t rsdp[0];
+};
+
+struct multiboot_tag_new_acpi
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint8_t rsdp[0];
+};
+
+struct multiboot_tag_network
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint8_t dhcpack[0];
+};
+
+struct multiboot_tag_efi_mmap
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t descr_size;
+ multiboot_uint32_t descr_vers;
+ multiboot_uint8_t efi_mmap[0];
+};
+
+struct multiboot_tag_efi32_ih
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t pointer;
+};
+
+struct multiboot_tag_efi64_ih
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint64_t pointer;
+};
+
+struct multiboot_tag_load_base_addr
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t load_base_addr;
+};
+
+#endif /* ! ASM_FILE */
+
+#endif /* ! MULTIBOOT_HEADER */