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    for each entry in the memory map:
        if(entry->type == USABLE_RAM) {
             start = (entry->start_address + 4095) & ~0xFFF;      // Align to next page boundary
             end = (entry->start_address + entry->size) & ~0xFFF; // Align to previous page boundary
             while(start < end) {
                 add_page_to_mapping(start);
             }
        }
    }

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void add_page_to_mapping(physical_address) {
    if(PDPT is needed at end_of_mapping) {
       use new physical page as PDPT;
    } else if(PD is needed at end_of_mapping) {
       use new physical page as PD;
    } else if(PT is needed at end_of_mapping) {
       use new physical page as PT;
    } else {
       create entry in existing page table to map physical page at end_of_mapping;
       end_of_mapping += 4096;
    }
}

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mov edi, 0x1000    ; Set the destination index to 0x1000.
mov cr3, edi       ; Set control register 3 to the destination index.
xor eax, eax       ; Nullify the A-register.
mov ecx, 4096      ; Set the C-register to 4096.
rep stosd          ; Clear the memory.
mov edi, cr3       ; Set the destination index to control register 3.

mov DWORD [edi], 0x2003      ; Set the double word at the destination index to 0x2003.
add edi, 0x1000              ; Add 0x1000 to the destination index.
mov DWORD [edi], 0x3003      ; Set the double word at the destination index to 0x3003.
add edi, 0x1000              ; Add 0x1000 to the destination index.
mov DWORD [edi], 0x4003      ; Set the double word at the destination index to 0x4003.
add edi, 0x1000              ; Add 0x1000 to the destination index.

mov ebx, 0000003          ; Set the B-register to 0x00000003.
mov ecx, 512              ; Set the C-register to 512.
.SetEntry:
mov DWORD [edi], ebx         ; Set the double word at the destination index to the B-register.
add ebx, 0x1000              ; Add 0x1000 to the B-register.
add edi, 8                   ; Add eight to the destination index.
loop .SetEntry               ; Set the next entry.

mov eax, cr4                 ; Set the A-register to control register 4.
or eax, 1 << 5               ; Set the PAE-bit, which is the 6th bit (bit 5).
mov cr4, eax                 ; Set control register 4 to the A-register.

Code: Select all

;The root table that contains 512 Page Table Directory Pointer Table's
PML4T: TIMES 4096 db 0
;The first Page Directory Pointer Table that contains 512 Page Directory Table's
PDPT_0: TIMES 4096 db 0
;The first Page Directory Table that contains 512 Page Table's
PDT_0: TIMES 4096 db 0
;The first Page Table that contains 512 Page's
PT_0: TIMES 4096 db 0 ;2Mb mapped
;The seond Page Table that contains 512 Page's
PT_1: TIMES 4096 db 0 ;2Mb mapped
;A total of 20kb of data.

;Each table has 512 64bit value entry's.

;Setups paging in 32bit mode.
Paging_Setup:
;First we want to set the first entry in the PLM4T to PDPT_0
mov rax, PDPT_0
push rax
push 64
push 1 ;On, Present
call Bit_Set
push 63
push 1 ;On, Read/Write
call Bit_Set
pop rax
mov dword[PML4T], eax
;Now set the first entry in PDPT_0 to PDT_0
mov rax, PDT_0
push rax
push 64
push 1 ;On, Present
call Bit_Set
push 63
push 1 ;On, Read/Write
call Bit_Set
pop rax
mov qword[PDPT_0], rax
;Now set the first entry in PDT_0 to PT_0
mov rax, PT_0
push rax
push 64
push 1 ;On, Present
call Bit_Set
push 63
push 1 ;On, Read/Write
call Bit_Set
pop rax
mov qword[PDT_0], rax
;Now the last thing to do is set the last entry in the PDT_0 to itself
mov rax, PDT_0
push rax
push 64
push 1 ;On, Present
call Bit_Set
push 63
push 1 ;On, Read/Write
call Bit_Set
pop rax
mov dword[PDT_0+4088], eax
;Now map all pages from 0 to 2mb
;So PT_0 contains 512 4k entrys which is 512*4096 = 2MB
;So lets start our mapping process.
mov rax, 0 ;Start address
mov rbx, PT_0 ;Start
mov rcx, PT_0 ;End
add rcx, 4096 ;End
;-------------------------------------------------------------------------------
.loop_0:
cmp rbx, rcx
jge .done_0
; Now we want to move the current address
; into the page table, but we first have to set the present and read/write flags.
push rax ;Save the address
push rbx ;Save ths start
push rcx ;Save the end
push rax
push 64
push 1 ;Present
call Bit_Set
push 63
push 1 ;Read/Write
call Bit_Set
pop rdx
pop rcx ;End
pop rbx ;Start
pop rax ;Address
; Now we will move the new address with the flags set into the page table
mov dword[rbx], edx
; Now add 0x1000:4096 to the address
add rax, 0x1000
add rbx, 8 ;Entry size
; Just loop back now
jmp .loop_0
.done_0:
; -------------------------------------------------------------------------------
mov rbx, PT_1 ;Start
mov rcx, PT_1 ;End
add rcx, 4096 ;End
.loop_1:
cmp rbx, rcx
jge .done_1
; Now we want to move the current address
; into the page table, but we first have to set the present and read/write flags.
push rax ;Save the address
push rbx ;Save ths start
push rcx ;Save the end
push rax
push 64
push 1 ;Present
call Bit_Set
push 63
push 1 ;Read/Write
call Bit_Set
pop rdx
pop rcx ;End
pop rbx ;Start
pop rax ;Address
; Now we will move the new address with the flags set into the page table
mov dword[rbx], edx
; Now add 0x1000:4096 to the address
add rax, 0x1000
add rbx, 8 ;Entry size
; Just loop back now
jmp .loop_1
.done_1:
;Now set the PML4T to the CR3 register to swap page tables
;this might kill the whole system...
mov rax, PML4T
mov cr3, rax
jmp os_hang