Currently, my code just identity pages the first two MiB of memory, which should be plenty to hold the bootstrapper.
Here's my code:
Code: Select all
BITS 32
MODULEALIGN equ 1<<0
MEMINFO equ 1<<1
FLAGS equ MODULEALIGN | MEMINFO
MAGIC equ 0x1BADB002
CHECKSUM equ -(MAGIC + FLAGS)
PAGEDIRPTABLESIZE equ 4 * 8; 4 64-bit ints
PAGEDIRSIZE equ 512 * 8
PAGETABLESIZE equ 512 * 8
PAGESIZE equ 4096
BOOT32MAPSIZE equ 512 * PAGESIZE
section .text ; Next is the Grub Multiboot Header
align PAGESIZE
multiboot_header:
dd MAGIC
dd FLAGS
dd CHECKSUM
STACKSIZE equ 0x4000
boot:
mov esp, STACKSIZE+stack
push eax
push ebx
lgdt [gdtr]
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
call init_paging
;eax, ebx are already on the stack.
;call main
init_paging:
;Set up basic structure
;To do: consolidate movs?
mov eax, page_dir
mov [page_dir_ptable], eax
mov eax, page_table
or eax, 3
mov [page_dir], eax
;Identity map
mov ecx, BOOT32MAPSIZE - PAGESIZE
mov edi, page_table + PAGETABLESIZE - 8
map_identity:
mov eax, ecx
or eax, 3
mov [edi], eax
sub edi, 8
sub ecx, PAGESIZE
jnz map_identity
mov eax, ecx
or eax, 3
mov [edi], eax
;Enable PAE and paging
cli
mov eax, cr4
or eax, 1 << 5
mov cr4, eax
mov eax, page_dir_ptable
mov cr3, eax
mov eax, cr0
or eax, 1 << 31
mov cr0, eax
stop:
hlt
jmp stop
ret
;;----;;
;;Data;;
;;----;;
section .data
align PAGESIZE
gdtr:
dw gdt_end - gdt - 1 ; size of the GDT
dd gdt ; linear address of GDT
gdt:
dd 0, 0
db 0xFF, 0xFF, 0, 0, 0, 0x9A, 0xC0 | 0xF, 0
db 0xFF, 0xFF, 0, 0, 0, 0x92, 0xC0 | 0xF, 0
gdt_end:
section .bss
align PAGESIZE
stack:
resb STACKSIZE
page_dir:
resb PAGEDIRSIZE
page_table:
resb PAGETABLESIZE
page_dir_ptable:
resb PAGEDIRPTABLESIZE
