section .boot
BITS 32
multibootHeader:
dd 0xe85250d6
dd 0
dd .end - multibootHeader
dd 0x100000000 - (0xe85250d6 + 0 + (.end - multibootHeader))
dw 0
dw 0
dd 8
.end:
extern kernelMain
%define pageDirectory 0x500000
%define kernelPageTable 0x501000
%define kernelInfoPageTable 0x502000
%define kernelInfoStart 0x500000
%define stackEnd 0x8FFFFF ; end of the kernel info page table
%define mappedStackEnd 0xFFBFFFFF
%define originalPageTable 0x503000
ebxStart: db 0x00000000
global _start
_start:
mov [ebxStart], ebx
mov esp, stackEnd
lgdt [gdt32.end]
mov ax, 16
mov ds, ax
mov ss, ax
mov es, ax
mov fs, ax
mov gs, ax
jmp 0x08:.setupPaging
.setupPaging:
mov eax, pageDirectory
mov ebx, originalPageTable
mov ecx, 0
call setupFullPageTable
mov eax, pageDirectory + 0xFFC
mov ebx, kernelInfoPageTable
mov ecx, 0x100000
call setupFullPageTable
mov eax, pageDirectory + 0xFF8
mov ebx, kernelPageTable
mov ecx, kernelInfoStart
call setupFullPageTable
.enablePaging:
mov eax, pageDirectory
mov cr3, eax
mov eax, cr0
or eax, 0x80000001
mov cr0, eax
mov esp, mappedStackEnd
jmp higherKernelEntry
; eax: directory entry address
; ebx: pageTable address
; ecx: target address
setupFullPageTable:
push eax
push ebx
push ecx
push edx
.enterDirectoryEntry:
mov edx, ebx
add edx, 3
mov [eax], edx
.fillPageTable:
mov edx, 0x400
add ecx, 3
.loop:
mov [ebx], ecx
add ecx, 0x1000
add ebx, 4
dec edx
jnz .loop
pop edx
pop ecx
pop ebx
pop eax
ret
ALIGN 4
gdt32:
dq 0
.code:
dw 0xffff
dw 0
db 0
db 10011010b
db 11001111b
db 0
.data:
dw 0xffff
dw 0
db 0
db 10010010b
db 11001111b
db 0
.userCode:
dw 0xffff
dw 0
db 0
db 10011010b
db 11001111b
db 0
.userData:
dw 0xffff
dw 0
db 0
db 10010010b
db 11001111b
db 0
.end:
dw .end - gdt32 - 1
dd gdt32
section .text
higherKernelEntry:
mov ebx, [ebxStart]
push ebx
.cleanOriginalEntryCode:
mov eax, 0xFF800000
mov dword [eax], 0
call kernelMain
jmp $
