72 lines
1.2 KiB
NASM
72 lines
1.2 KiB
NASM
|
%define MAGIC 0x1BADB002
|
||
|
|
%define FLAGS 0
|
||
|
|
|
||
|
|
; Multiboot v1 Specification
|
||
|
|
; https://www.gnu.org/software/grub/manual/multiboot/multiboot.html
|
||
|
|
section .multiboot
|
||
|
|
align 4
|
||
|
|
dd MAGIC
|
||
|
|
dd FLAGS
|
||
|
|
dd -(MAGIC + FLAGS)
|
||
|
|
|
||
|
|
section .text
|
||
|
|
global _start
|
||
|
|
_start:
|
||
|
|
cli
|
||
|
|
|
||
|
|
; Check if EAX contains the multiboot magic number the bootloader is supposed to give us
|
||
|
|
cmp eax, 0x2BADB002
|
||
|
|
jne halt
|
||
|
|
|
||
|
|
lgdt [gdtp]
|
||
|
|
mov ax, 0x10 ; Offset to kernel data descriptor
|
||
|
|
mov es, ax
|
||
|
|
mov ds, ax
|
||
|
|
mov fs, ax
|
||
|
|
mov gs, ax
|
||
|
|
mov ss, ax
|
||
|
|
jmp 0x8:.use_code_seg ; Offset to kernel code descriptor
|
||
|
|
.use_code_seg:
|
||
|
|
mov esp, stack_bottom
|
||
|
|
push ebx
|
||
|
|
extern kmain
|
||
|
|
call kmain
|
||
|
|
|
||
|
|
; If the kernel function somehow returns, disable interrupts and hang
|
||
|
|
cli
|
||
|
|
halt:
|
||
|
|
hlt
|
||
|
|
jmp halt
|
||
|
|
|
||
|
|
; GDT for a flat memory layout
|
||
|
|
; We get access to all memory and can utilize paging
|
||
|
|
gdt_start:
|
||
|
|
gdt_null:
|
||
|
|
dq 0
|
||
|
|
gdt_kern_code:
|
||
|
|
dw 0xffff
|
||
|
|
dw 0x0000
|
||
|
|
db 0x00
|
||
|
|
db 0b10011010
|
||
|
|
db 0b11001111
|
||
|
|
db 0x00
|
||
|
|
gdt_kern_data:
|
||
|
|
dw 0xffff
|
||
|
|
dw 0x0000
|
||
|
|
db 0x00
|
||
|
|
db 0b10010010
|
||
|
|
db 0b11001111
|
||
|
|
db 0x00
|
||
|
|
gdt_end:
|
||
|
|
|
||
|
|
gdtp:
|
||
|
|
dw gdt_end - gdt_start - 1
|
||
|
|
dd gdt_start
|
||
|
|
|
||
|
|
; Reserve 16KiB of kernel stack space
|
||
|
|
section .bss
|
||
|
|
align 4
|
||
|
|
stack_top:
|
||
|
|
resb 16384
|
||
|
|
stack_bottom:
|