156 lines
3.3 KiB
NASM
156 lines
3.3 KiB
NASM
global _start
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global pml4
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extern entry
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%define FLAGS 0b10
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%define MAGIC 0x1BADB002
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%define CHECKSUM -(MAGIC + FLAGS)
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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 CHECKSUM
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section .bss
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align 16
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resb 32768
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stack_top:
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section .bss
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align 4096
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pml4:
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resb 4096
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pdpt:
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resb 4096
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pd:
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resb 4096
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section .data
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align 8
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gdt64:
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dq 0x0000000000000000
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.code:
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dq 0x00AF9A000000FFFF
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.descriptor:
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dw .end - gdt64 - 1
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dq gdt64
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.end:
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section .data
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align 8
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multiboot_info:
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dd 0
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multiboot_magic:
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dd 0
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section .text
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bits 32
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_start:
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mov esp, stack_top
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; Save multiboot info pointer for later
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mov [multiboot_magic], eax
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mov [multiboot_info], ebx
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; Check if cpuid is available by flipping bit 21
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; in the eflags register and checking if the cpu flipped it back
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pushfd
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pop eax
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mov ecx, eax
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xor eax, 1 << 21
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push eax
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popfd
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pushfd
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pop eax
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; If cpuid is available, eax should be different than ecx
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xor eax, ecx
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jz error
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; Finally restore eflags register to the original value
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push ecx
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popfd
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; Check if extended cpuid is available by calling cpuid with 0x80000000,
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; If cpuid is available, eax will be greater than 0x80000000 after the call
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mov eax, 0x80000000
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cpuid
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cmp eax, 0x80000001
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jb error
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; Check if long mode is available by calling cpuid with 0x80000001
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; this will place the extended features of the cpu in edx
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; Bit 29 tells us if long mode is supported or not
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mov eax, 0x80000001
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cpuid
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test edx, 1 << 29
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jz error
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; Enable PAE by setting bit 5 in cr4 to 1
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mov eax, cr4
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or eax, 1 << 5
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mov cr4, eax
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; pml4[0] -> pdpt
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mov eax, pdpt
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or eax, 0x03
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mov [pml4], eax
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; pdpt[0] -> pd
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mov eax, pd
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or eax, 0x03
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mov [pdpt], eax
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; Map first 32 2mb pages for the kernel for a total of 64mb
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mov edi, pd
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mov eax, 0x83
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mov ecx, 32
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.setup_pd:
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mov [edi], eax
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add eax, 0x200000
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add edi, 8
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loop .setup_pd
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; Load cr3 with the address of pml4
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mov eax, pml4
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mov cr3, eax
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lgdt [gdt64.descriptor]
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; Enable long mode by setting bit 8 to 1 in EFER (Extended Feature Enable Register)
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mov ecx, 0xc0000080
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rdmsr
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or eax, 1 << 8
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wrmsr
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; Enable paging by setting bit 31 in cr0 to 1
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mov eax, cr0
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or eax, 1 << 31
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mov cr0, eax
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jmp 0x8:long_mode
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error:
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cli
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mov byte [0xb8000], 'E'
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mov byte [0xb8002], 'R'
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mov byte [0xb8004], 'R'
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.hang:
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hlt
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jmp .hang
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section .text
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bits 64
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long_mode:
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; Clear segment registers in long mode
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xor ax, ax
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mov ds, ax
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mov es, 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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; Finally, we call in to c
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mov edi, [multiboot_magic]
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mov esi, [multiboot_info]
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call entry
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.hang:
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hlt
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jmp .hang |