OSDev.org

Code: Select all

paging_init:
        ; alloc and clear pdir
        call    new_frame
        shl     eax, 12
        mov     [kernel_pd], eax ; move pointer to page directory into kernel_pd
        push    PAGE_SIZE
        push    eax
        call    zeromeml ; clear the page directory so we get error messages by access the wrong memory
        ; alloc tbl and setup pdir
        call    new_frame
        shl     eax, 12
        mov     [table], eax
        or      eax, PG_PRESENT or PG_WRITE
        mov     edx, [kernel_pd]
        mov     [edx+0*4], eax
        ; eax is verified to be 1204227 here
        ; setup ptbl
        mov     edx, [table]
        mov     eax, PG_PRESENT or PG_WRITE
        mov     ecx, 0
        .pageloop: 
        mov     [edx+ecx*4], eax
        add     eax, PAGE_SIZE 
        add     ecx, 1 
        cmp     ecx, 1024 
        jne     .pageloop
        ; circle map pdir
        ; here the magic mystic error maybe happens
        mov     eax, [kernel_pd] ; load pointer to page directory
        mov     edx, eax
        or      edx, PG_PRESENT or PG_WRITE
        mov     [eax+1023*4], edx

        ; print the first 4 bytes of the page directory by directly accessing the memory
        mov     eax, [kernel_pd]
        push    dword [eax]
        call    screen_puti

        ; enable paging 
        mov     eax, [kernel_pd]
        mov     cr3, eax 
        mov     eax, cr0 
        or      eax, PG_ENABLE_PAGING 
        mov     cr0, eax

        ; print the first 4 bytes of the page directory through virtual memory mapping
        mov     eax, [0xFFFFF000]
        push    eax
        call    screen_puti
ret