2024-05-20 05:59:07 -04:00
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%define MAGIC 0x1BADB002
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%define FLAGS 0
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; Multiboot v1 Specification
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; https://www.gnu.org/software/grub/manual/multiboot/multiboot.html
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section .multiboot
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align 4
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dd MAGIC
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dd FLAGS
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dd -(MAGIC + FLAGS)
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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 the multiboot magic number the bootloader is supposed to give us
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cmp eax, 0x2BADB002
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jne halt
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lgdt [gdtp]
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mov ax, 0x10 ; Offset to kernel data descriptor
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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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jmp 0x8:.use_code_seg ; Offset to kernel code descriptor
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.use_code_seg:
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mov esp, stack_bottom
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2024-05-21 22:07:04 -04:00
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mov ebp, esp
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2024-05-20 05:59:07 -04:00
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push ebx
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extern kmain
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call kmain
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; If the kernel function somehow returns, disable interrupts and hang
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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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2024-05-21 22:07:04 -04:00
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global exception_handler
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exception_handler:
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add esp, 4
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mov byte [0xb8000], 'X'
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iret
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global ps2_isr
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ps2_isr:
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extern ps2_handler
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pushad
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cld
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call ps2_handler
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popad
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iret
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2024-05-20 05:59:07 -04:00
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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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gdt_start:
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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_start - 1
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dd gdt_start
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2024-05-21 22:07:04 -04:00
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2024-05-20 05:59:07 -04:00
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; Reserve 16KiB of kernel stack space
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section .bss
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2024-05-21 22:07:04 -04:00
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align 16
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2024-05-20 05:59:07 -04:00
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stack_top:
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resb 16384
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stack_bottom:
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