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	$(LD) $(LDFLAGS) $(OBJFILES)
	sudo losetup /dev/loop0 boot/floppy.img
	sudo mount /dev/loop0 /mnt
	#sudo mkdir /mnt/boot
	#sudo mkdir /mnt/system
	sudo cp kernel.bin /mnt/system/kernel.bin
	sudo cp boot/menu.cfg /mnt/boot/menu.cfg
	sudo umount /dev/loop0
	sudo losetup -d /dev/loop0
	#These lines open Bochs!
	sudo losetup /dev/loop0 boot/floppy.img
	sudo bochs -f confbochs.txt
	sudo losetup -d /dev/loop0

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...
global _loader, bootinfo
extern _main

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...
mov (bootinfo-ADDRADJUST), ebx
...

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nasm -felf -o boot/loader.o boot/loader.asm
boot/loader.asm:58: error: symbol `bootinfo' undefined

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global _loader, bootinfo	; Make entry point visible to linker.
extern _main			; _main is defined elsewhere

; setting up the Multiboot header - see GRUB docs for details
MODULEALIGN	equ	1<<0			; align loaded modules on page boundaries
MEMINFO		equ	1<<1			; provide memory map
FLAGS		equ	MODULEALIGN | MEMINFO	; this is the Multiboot 'flag' field
MAGIC		equ	0x1BADB002		; 'magic number' lets bootloader find the header
CHECKSUM	equ	-(MAGIC + FLAGS)	; checksum required


; Page directory.

K_PDE	equ	0x1000

; Kernel page table #0 (4MB).

K_PTE	equ	0x2000

; First 4MB Identity-map page table.

I_PTE	equ	0x3000
ADDRADJUST	equ	0xBFF00000
KERNEL_VIRTUAL_BASE	equ	0xC0000000                  ; 3GB
KERNEL_PAGE_NUMBER	equ	(KERNEL_VIRTUAL_BASE >> 22)  ; Page directory index of kernel's 4MB PTE.


section .data
align 0x1000
BootPageDirectory:
	; This page directory entry identity-maps the first 4MB of the 32-bit physical address space.
	; All bits are clear except the following:
	; bit 7: PS The kernel page is 4MB.
	; bit 1: RW The kernel page is read/write.
	; bit 0: P  The kernel page is present.
	; This entry must be here -- otherwise the kernel will crash immediately after paging is
	; enabled because it can't fetch the next instruction! It's ok to unmap this page later.
	dd 0x00000083
	times (KERNEL_PAGE_NUMBER - 1) dd 0                 ; Pages before kernel space.
	; This page directory entry defines a 4MB page containing the kernel.
	dd 0x00000083
	times (1024 - KERNEL_PAGE_NUMBER - 1) dd 0  ; Pages after the kernel image.

section .text
align 4
MultiBootHeader:
	dd MAGIC
	dd FLAGS
	dd CHECKSUM

align 4
bootinfo:
	dd 0

; reserve initial kernel stack space -- that's 16k.
STACKSIZE equ 0x4000

_loader:
	; Turn off floppy motor
	mov dx, 0x3f2

	mov al, 0x0c

	out dx, al

	; Salva il puntatore alla struttura multiboot
	mov [bootinfo - KERNEL_VIRTUAL_BASE], ebx

	


	; NOTE: Until paging is set up, the code must be position-independent and use physical
	; addresses, not virtual ones!
	mov ecx, (BootPageDirectory - KERNEL_VIRTUAL_BASE)
	mov cr3, ecx                                        ; Load Page Directory Base Register.

	mov ecx, cr4
	or ecx, 0x00000010                          ; Set PSE bit in CR4 to enable 4MB pages.
	mov cr4, ecx

	mov ecx, cr0
	or ecx, 0x80000000                          ; Set PG bit in CR0 to enable paging.
	mov cr0, ecx

	; Start fetching instructions in kernel space.
	lea ecx, [StartInHigherHalf]
 	jmp ecx                                                     ; NOTE: Must be absolute jump!

StartInHigherHalf:
	; Unmap the identity-mapped first 4MB of physical address space. It should not be needed
	; anymore.
	mov dword [BootPageDirectory], 0
 	invlpg [0]

	; NOTE: From now on, paging should be enabled. The first 4MB of physical address space is
	; mapped starting at KERNEL_VIRTUAL_BASE. Everything is linked to this address, so no more
	; position-independent code or funny business with virtual-to-physical address translation
	; should be necessary. We now have a higher-half kernel.
	mov esp, stack+STACKSIZE           ; set up the stack
	push eax                           ; pass Multiboot magic number

	; pass Multiboot info structure -- WARNING: This is a physical address and may not be
	; in the first 4MB!
	push ebx

	call  _main                  ; call kernel proper
	hlt                          ; halt machine should kernel return


section .bss
align 32
stack:
	resb STACKSIZE      ; reserve 16k stack on a quadword boundary

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//The symbol table for a.out format.

struct aout_symbol_table_t {

	unsigned long tab_size;

	unsigned long str_size;

	unsigned long address;

	unsigned long reserved;

};



//The section header table for ELF format.

struct elf_section_header_table_t {

	unsigned long num;

	unsigned long size;

	unsigned long address;

	unsigned long shndx;

};



//The multiboot informations.

struct multiboot_info_t

{

	unsigned long flags;

	unsigned long mem_lower;

	unsigned long mem_upper;

	unsigned long boot_device;

	unsigned long cmdline;

	unsigned long mods_addr;

	union

	{

		struct aout_symbol_table_t aout_sym_t;

		struct elf_section_header_table_t elf_sec_t;

	} u;

	unsigned long mmap_length;

	unsigned long mmap_addr;

};
extern struct multiboot_info_t *bootinfo;




if( bootinfo->flags & 0x02 )


	physical_memory = (bootinfo->mem_upper) * 1024;


else


	halt();