85 lines
1.7 KiB
NASM
85 lines
1.7 KiB
NASM
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global _start
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extern kmain
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; Multiboot-related constants
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MODULEALIGN equ 1 << 0
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MEMINFO equ 1 << 1
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FLAGS equ MODULEALIGN | MEMINFO
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MAGIC equ 0x1BADB002
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CHECKSUM equ -(MAGIC + FLAGS)
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; Other constants
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STACKSIZE equ 0x1000
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; #############################################################################
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; ############################## text segment #################################
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; #############################################################################
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section .setup
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align 4
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global g_before_gdt
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; Multiboot header
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MultiBootHeader:
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dd MAGIC
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dd FLAGS
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dd CHECKSUM
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; Actual entry point
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_start:
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lgdt [falsegdt]
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mov cx, 0x10
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mov ds, cx
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mov es, cx
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mov fs, cx
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mov gs, cx
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mov ss, cx
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g_before_gdt:
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jmp 0x08:higherhalf
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section .text
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align 4
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higherhalf:
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mov esp, g_stack_start + STACKSIZE
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push eax
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push ebx
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call kmain
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cli
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; If we are here, just loop - we're dead anyway
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ohshit:
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hlt
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jmp ohshit
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; #############################################################################
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; ############################## setup segment ################################
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; #############################################################################
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section .setup
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falsegdt:
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dw gdt_end - gdt - 1
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dd gdt
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gdt:
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dd 0, 0
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db 0xFF, 0xFF, 0, 0, 0, 10011010b, 11001111b, 0x40
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db 0xFF, 0xFF, 0, 0, 0, 10010010b, 11001111b, 0x40
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gdt_end:
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; #############################################################################
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; ############################### bss segment #################################
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; #############################################################################
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section .bss
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align 4
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; here be 4k stack
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g_stack_start:
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resb STACKSIZE
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