wrote a basic bootloader
This commit is contained in:
@@ -0,0 +1,55 @@
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[BITS 16]
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[ORG 0x7c00]
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start:
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mov ah,0x00 ; set mode
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mov al,0x03 ; set vga text buffer mode (80x25)
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int 0x10 ; call bios
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cli
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in al, 0x92
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or al, 2
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out 0x92, al
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xor ax, ax
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mov ds, ax
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lgdt [GDT_PTR]
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mov eax, 0x11
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mov cr0, eax
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jmp GDT_BOOT_CS-GDT:protmode
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[BITS 32]
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protmode:
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mov ax, GDT_BOOT_DS-GDT
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mov ds, ax
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mov ss, ax
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mov es, ax
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mov esp, 0x90000 ; temporary stack
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mov edi, 0xb8000
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mov eax, "P R "
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stosd
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hang:
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pause
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jmp hang
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GDT_PTR:
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dw GDT_END-GDT-1
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dd GDT
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align 16
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GDT:
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GDT_NULL: dq 0 ; segment zero cannot be used
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GDT_BOOT_DS: dq 0X00CF92000000FFFF
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GDT_BOOT_CS: dq 0X00CF9A000000FFFF
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GDT_END:
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times 510-$+start db 0;
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db 0x55;
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db 0xaa;
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@@ -0,0 +1,118 @@
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[BITS 16]
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[ORG 0x7C00]
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; Initialize segment registers
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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 ss, ax
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mov sp, 0x7C00
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; Reset disk system
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mov ah, 0
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int 0x13
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; Load FAT32 BPB
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mov si, bpb_oem_name
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mov di, 0x7E00
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mov cx, bpb_size
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rep movsb
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; Read FAT32 root directory
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mov ax, [bpb_reserved_sectors]
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mov [dapack.lba_start], ax
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mov ah, 0x42
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mov si, dapack
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int 0x13
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jc error
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; Find kernel file
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mov si, kernel_name
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mov di, 0x8000
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mov cx, 11 ; FAT32 8.3 filename length
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find_kernel:
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push cx
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push si
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push di
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rep cmpsb
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pop di
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pop si
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pop cx
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je found_kernel
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add di, 32 ; Move to next directory entry
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cmp di, 0x8200 ; Check if we've reached the end of the sector
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jl find_kernel
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; Kernel not found
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mov si, err_no_kernel
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call print
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jmp $
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found_kernel:
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; Get cluster number
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mov ax, [di + 20] ; High word
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shl eax, 16
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mov ax, [di + 26] ; Low word
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; Load kernel
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mov [cluster], eax
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call load_cluster
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; Jump to kernel
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jmp 0x8000
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error:
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mov si, err_disk
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call print
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jmp $
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print:
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lodsb
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or al, al
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jz .done
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mov ah, 0x0E
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int 0x10
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jmp print
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.done:
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ret
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load_cluster:
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; Convert cluster to LBA
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sub eax, 2
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mul dword [sectors_per_cluster]
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add eax, [first_data_sector]
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mov [dapack.lba_start], eax
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mov ah, 0x42
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mov si, dapack
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int 0x13
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ret
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align 4
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dapack:
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db 0x10 ; Size of packet
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db 0 ; Reserved
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dw 1 ; Number of sectors
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dw 0x8000 ; Offset
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dw 0 ; Segment
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dq 0 ; LBA
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cluster: dd 0
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sectors_per_cluster: dd 8
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first_data_sector: dd 0
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kernel_name: db "KERNEL BIN"
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err_disk: db "Disk error", 0
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err_no_kernel: db "No kernel", 0
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bpb_oem_name: times 8 db 0
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bpb_bytes_per_sector: dw 512
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bpb_sectors_per_cluster: db 8
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bpb_reserved_sectors: dw 32
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bpb_size: equ $ - bpb_oem_name
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times 510-($-$$) db 0
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dw 0xAA55
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@@ -0,0 +1,83 @@
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.section .efi.text, "ax"
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.global _start
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.code64 // UEFI is already in 64-bit protected mode
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_start:
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// Save UEFI parameters
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mov %rcx, uefi_image_handle
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mov %rdx, uefi_system_table
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// Get memory map
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call get_memory_map
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// Exit boot services
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mov uefi_image_handle, %rcx
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mov memory_map_key, %rdx
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call exit_boot_services
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// Disable interrupts
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cli
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// Load GDT for long mode
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lgdt gdt64_pointer(%rip)
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// Setup page tables (identity map first 2MB + map kernel to higher half)
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call setup_page_tables
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// Enable PAE
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mov %cr4, %rax
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or $(1 << 5), %rax
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mov %rax, %cr4
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// Set long mode bit
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mov $0xC0000080, %ecx
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rdmsr
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or $(1 << 8), %eax
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wrmsr
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// Enable paging
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mov %cr0, %rax
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or $0x80000000, %rax
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mov %rax, %cr0
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// Long jump to higher half kernel
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lea higher_half(%rip), %rax
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jmp *%rax
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.align 8
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higher_half:
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// Now in long mode at higher half
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// Setup stack and jump to Rust code
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mov $kernel_stack_top, %rsp
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call kmain
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// GDT for long mode
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.align 16
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gdt64:
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.quad 0 // Null descriptor
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.quad 0x00AF9A000000FFFF // Code segment
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.quad 0x00CF92000000FFFF // Data segment
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gdt64_pointer:
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.word gdt64_pointer - gdt64 - 1
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.quad gdt64
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.section .efi.data, "aw"
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uefi_image_handle: .quad 0
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uefi_system_table: .quad 0
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memory_map_key: .quad 0
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.section .bss
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.align 4096
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kernel_stack_bottom:
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.skip 16384 // 16 KB stack
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kernel_stack_top:
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// Page tables
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.align 4096
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pml4_table:
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.skip 4096
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pdpt_table:
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.skip 4096
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pd_table:
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.skip 4096
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@@ -0,0 +1,94 @@
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.section .efi.text
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// Function to get UEFI memory map
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get_memory_map:
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push %rbp
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mov %rsp, %rbp
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// Local variables for memory map
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sub $48, %rsp
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mov $0, -8(%rbp) // memory_map_size
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mov $0, -16(%rbp) // memory_map_buffer
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mov $0, -24(%rbp) // map_key
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mov $0, -32(%rbp) // descriptor_size
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mov $0, -40(%rbp) // descriptor_version
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// First call to get size
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lea -8(%rbp), %rcx // memory_map_size
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mov $0, %rdx // memory_map
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lea -24(%rbp), %r8 // map_key
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lea -32(%rbp), %r9 // descriptor_size
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push $0 // descriptor_version
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call boot_services_get_memory_map
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// Allocate buffer
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mov -8(%rbp), %rcx // size
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add $1000, %rcx // Add some extra space
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mov $8, %rdx // alignment
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lea -16(%rbp), %r8 // buffer pointer
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call boot_services_allocate_pool
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// Get actual map
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mov -8(%rbp), %rcx
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mov -16(%rbp), %rdx
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lea -24(%rbp), %r8
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lea -32(%rbp), %r9
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push -40(%rbp)
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call boot_services_get_memory_map
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// Save map key
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mov -24(%rbp), %rax
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mov %rax, memory_map_key
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leave
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ret
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// Function to exit boot services
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exit_boot_services:
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push %rbp
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mov %rsp, %rbp
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// Parameters already in rcx (image_handle) and rdx (map_key)
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call boot_services_exit
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leave
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ret
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// Function to set up page tables
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setup_page_tables:
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push %rbp
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mov %rsp, %rbp
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// Clear tables
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mov $pml4_table, %rdi
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mov $12288, %ecx // 3 pages (PML4, PDPT, PD)
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xor %eax, %eax
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rep stosb
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// Set up identity mapping for first 2MB
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// PML4[0] -> PDPT
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mov $pdpt_table, %eax
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or $3, %eax // Present + Write
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mov %eax, pml4_table
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// PDPT[0] -> PD
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mov $pd_table, %eax
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or $3, %eax
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mov %eax, pdpt_table
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// PD[0] -> 2MB page
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mov $0x83, %eax // Present + Write + Huge
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mov %eax, pd_table
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// Map kernel to higher half
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// PML4[511] -> PDPT
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mov $pdpt_table, %eax
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or $3, %eax
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mov %eax, pml4_table + 4088
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// Load CR3
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mov $pml4_table, %rax
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mov %rax, %cr3
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leave
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ret
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