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global start
global heap_start
extern kernel_main
bits 32
; base, limit, access, flags
%macro gdt_entry 4
db %2 & 0xff
db (%2 >> 8) & 0xff
db %1 & 0xff
db (%1 >> 8) & 0xff
db (%1 >> 16) & 0xff
db %3
db ((%2 >> 16) & 0x0f) | (%4 << 4)
db (%1 >> 24) & 0xff
%endmacro
MAGIC equ 0xe85250d6
LENGTH equ mb_end - mb_start
CHECKSUM equ -(MAGIC + LENGTH)
section .multiboot
align 8
mb_start:
dd MAGIC
dd 0
dd LENGTH
dd CHECKSUM
dw 0
dw 0
dd 8
mb_end:
section .bss
align 16
stack_end:
resb 16384
stack_top:
section .rodata
align 16
gdt_start:
gdt_entry 0, 0, 0, 0
gdt_entry 0, 0xFFFFF, 0x9A, 0xC
gdt_entry 0, 0xFFFFF, 0x92, 0xC
gdt_end:
gdt_descriptor:
dw gdt_end - gdt_start - 1
dd gdt_start
section .text
align 8
start:
cli
lgdt [gdt_descriptor]
mov eax, cr0
or al, 1
mov cr0, eax
jmp 0x08:after_lgdt
after_lgdt:
mov ax, 0x10
mov ds, ax
mov ss, ax
mov es, ax
mov fs, ax
mov gs, ax
mov esp, stack_end
mov ebp, stack_end
sti
push ebx
call kernel_main
cli
halt:
hlt
jmp halt
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