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[extern main]
[extern _kernel_stack_loc]
enter_longmode:
cli
; TODO check if a20 is already set
mov al, 0x92
or al, 2
out 0x92, al
lgdt [protected_gdt.descriptor]
mov eax, cr0
or eax, 0x1
mov cr0, eax
mov eax, 0x8
mov ds, eax
jmp 0x8:init_longmode
bits 32
init_longmode:
mov ebp, 0xffff
mov esp, ebp
mov ax, PROTECTED_DATA_SEGMENT
mov ds, ax
mov ss, ax
mov es, ax
mov fs, ax
mov gs, ax
mov edi, 0x3000 ; this is where our page tables will be
mov cr3, edi
mov eax, 0 ; what we'll be putting there
mov ecx, 4096 ; how many times we'll put it there
rep stosd ; kinda like memset(&edi, ecx, edi)
mov edi, cr3
mov DWORD [edi], 0x4003 ; pml4e[0] = pdpe
add edi, 0x1000
mov DWORD [edi], 0x5003 ; pdpe[0] = pde
add edi, 0x1000
mov DWORD [edi], 0x6003 ; pde[0] = pte
add edi, 0x1000
mov ebx, 0x00000003 ; the flags
mov ecx, 512; the loop counter, will map 2 mib
.idmap_pte_loop:
mov DWORD [edi], ebx
add ebx, 0x1000 ; physical address. Should leave us at 0x7000
add edi, 8 ; position in page table
loop .idmap_pte_loop
mov eax, cr4
or eax, 1 << 5
mov cr4, eax
mov ecx, 0xc0000080
rdmsr
or eax, 1 << 8
wrmsr
mov eax, cr0
or eax, 1 << 31 | 1 << 0 ; this is where we set paging and protected mode (respectively)!
mov cr0, eax
mov ecx, 0xc0000080
rdmsr
or eax, 1 << 8
wrmsr
mov eax, cr0
or eax, 1 << 31
mov cr0, eax
lgdt [long_gdt.descriptor]
jmp LONG_CODE_SEGMENT:enter_kernel
enter_kernel:
bits 64
mov rbp, _kernel_stack_loc
mov rsp, _kernel_stack_loc
call main ; where we actually call the kernel
jmp $
ret
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