86 lines
1.3 KiB
NASM
86 lines
1.3 KiB
NASM
%define MAGIC 0x1BADB002
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%define ALIGN 1<<0
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%define MMAP 1<<1
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%define VID 1<<2
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%define FLAGS (ALIGN | MMAP | VID)
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section .multiboot
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dd MAGIC
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dd FLAGS
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dd -(MAGIC + FLAGS)
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dd 0 ; header_addr
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dd 0 ; load_addr
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dd 0 ; load_end_addr
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dd 0 ; bss_end_addr
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dd 0 ; entry_addr
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dd 1 ; mode_type
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dd 80 ; width
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dd 25 ; height
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dd 0 ; depth
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section .text
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global _start
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_start:
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cli
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; Check if EAX contains this magic value that our bootloader should've set
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cmp eax, 0x2BADB002
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jne halt
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; Load GDT
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lgdt [gdtp]
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; Offset to kernel data descriptor
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mov ax, 0x10
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mov es, ax
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mov ds, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax
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; Offset to kernel code descriptor
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jmp 0x8:.use_code_seg
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.use_code_seg:
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mov esp, stack_bottom
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mov ebp, esp
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push ebx
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and esp, 0xfffffff0
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extern kernel
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call kernel
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cli
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halt:
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hlt
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jmp halt
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section .data
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; GDT for a flat memory layout
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; We get access to all memory and can utilize paging
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global gdt
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gdt:
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gdt_null:
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dq 0
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gdt_kern_code:
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dw 0xffff
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dw 0x0000
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db 0x00
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db 0b10011010
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db 0b11001111
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db 0x00
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gdt_kern_data:
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dw 0xffff
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dw 0x0000
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db 0x00
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db 0b10010010
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db 0b11001111
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db 0x00
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gdt_end:
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gdtp:
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dw gdt_end - gdt - 1
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dd gdt
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section .bss
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align 16
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stack_top:
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resb 16384
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stack_bottom:
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