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Initial commit: SUB-OS 64-Bit Production Monolithic Operating System with LazyBox userland suite
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@@ -0,0 +1,98 @@
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BITS 16
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ORG 0x7C00
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start:
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; Set up segments and stack
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cli
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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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sti
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; Save boot drive number from BIOS (DL)
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mov [BOOT_DRIVE], dl
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; Print greeting
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mov si, MSG_BOOT
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call print_string
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; Check for LBA extensions (INT 13h, AH=41h)
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mov ah, 0x41
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mov bx, 0x55AA
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mov dl, [BOOT_DRIVE]
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int 0x13
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jc load_chs
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cmp bx, 0xAA55
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jne load_chs
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load_lba:
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; Load stage 2 using LBA (INT 13h, AH=42h)
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; Read 15 sectors starting from LBA 1 to 0x0000:0x7E00
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mov ah, 0x42
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mov dl, [BOOT_DRIVE]
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mov si, dap
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int 0x13
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jc disk_error
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jmp jump_stage2
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load_chs:
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; Fallback: Load stage 2 using CHS (INT 13h, AH=02h)
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mov ah, 0x02
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mov al, 15 ; 15 sectors (sectors 2-16)
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mov ch, 0 ; Cylinder 0
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mov dh, 0 ; Head 0
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mov cl, 2 ; Sector 2
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xor bx, bx
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mov es, bx
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mov bx, 0x7E00 ; ES:BX = 0x0000:0x7E00
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mov dl, [BOOT_DRIVE]
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int 0x13
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jc disk_error
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jump_stage2:
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; Pass boot drive in DL to Stage 2
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mov dl, [BOOT_DRIVE]
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jmp 0x0000:0x7E00
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disk_error:
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mov si, MSG_DISK_ERR
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call print_string
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.halt:
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cli
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hlt
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jmp .halt
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; BIOS Teletype string print (SI = null-terminated string)
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print_string:
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pusha
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mov ah, 0x0E
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.loop:
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lodsb
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test al, al
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jz .done
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int 0x10
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jmp .loop
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.done:
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popa
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ret
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; Data
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BOOT_DRIVE db 0
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MSG_BOOT db "SUB-OS Bootloader...", 13, 10, 0
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MSG_DISK_ERR db "Boot Disk Error!", 13, 10, 0
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; Disk Address Packet for LBA
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align 4
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dap:
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db 0x10 ; DAP size (16 bytes)
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db 0 ; Reserved
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dw 15 ; Read 15 sectors
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dw 0x7E00 ; Offset
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dw 0x0000 ; Segment
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dq 1 ; Starting LBA (Sector 1)
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; Boot Sector Signature
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times 510 - ($ - $$) db 0
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dw 0xAA55
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@@ -0,0 +1,43 @@
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; Global Descriptor Table Definition
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align 16
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gdt_start:
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; Null descriptor (0x00)
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dq 0
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; 32-bit Code Segment (0x08)
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dw 0xFFFF ; Limit (low 16 bits)
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dw 0x0000 ; Base (low 16 bits)
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db 0x00 ; Base (next 8 bits)
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db 10011010b ; Access byte (Present, Ring 0, Code/Data, Executable, Read/Write)
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db 11001111b ; Flags (32-bit, 4KB granularity) and Limit (high 4 bits)
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db 0x00 ; Base (high 8 bits)
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; 32-bit Data Segment (0x10)
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dw 0xFFFF ; Limit
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dw 0x0000 ; Base
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db 0x00 ; Base
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db 10010010b ; Access byte (Present, Ring 0, Code/Data, Read/Write)
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db 11001111b ; Flags and Limit
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db 0x00 ; Base
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; 64-bit Code Segment (0x18)
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dw 0x0000 ; Limit (ignored)
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dw 0x0000 ; Base
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db 0x00 ; Base
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db 10011010b ; Access byte (Present, Ring 0, Code/Data, Executable, Read/Write)
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db 00100000b ; Flags (64-bit code segment, Long Mode) and Limit
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db 0x00 ; Base
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; 64-bit Data Segment (0x20)
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dw 0x0000 ; Limit (ignored)
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dw 0x0000 ; Base
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db 0x00 ; Base
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db 10010010b ; Access byte (Present, Ring 0, Code/Data, Read/Write)
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db 00000000b ; Flags and Limit
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db 0x00 ; Base
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gdt_end:
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gdt_descriptor:
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dw gdt_end - gdt_start - 1 ; Size of GDT minus 1
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dd gdt_start ; Base address of GDT
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+272
@@ -0,0 +1,272 @@
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BITS 16
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ORG 0x7E00
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start2:
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cli
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; Ensure segment registers are zero
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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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sti
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; Save boot drive number passed from stage 1 in DL
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mov [boot_drive], dl
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; Print Stage 2 startup message
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mov si, msg_stage2_start
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call print_string_16
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; -------------------------------------------------------------
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; Step 1: Enable A20 Line
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; -------------------------------------------------------------
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mov si, msg_a20
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call print_string_16
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in al, 0x92
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test al, 2
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jnz .a20_done
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or al, 2
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and al, 0xFE
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out 0x92, al
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.a20_done:
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; -------------------------------------------------------------
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; Step 2: Detect Memory via INT 15h, EAX=0xE820
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; Destination: 0x9000 (count at 0x9000, entries at 0x9008)
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; -------------------------------------------------------------
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mov si, msg_mmap
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call print_string_16
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; Zero out count at 0x9000
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mov dword [0x9000], 0
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mov dword [0x9004], 0
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mov di, 0x9008 ; Memory map entries destination
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xor ebx, ebx ; Continuation value
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xor bp, bp ; Entry counter
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mov edx, 0x534D4150 ; 'SMAP' signature
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mov eax, 0xE820
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mov ecx, 24 ; Buffer size
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int 0x15
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jc .mmap_error
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.mmap_loop:
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inc bp
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add di, 24
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test ebx, ebx
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jz .mmap_finished
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mov edx, 0x534D4150
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mov eax, 0xE820
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mov ecx, 24
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int 0x15
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jc .mmap_finished
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jmp .mmap_loop
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.mmap_error:
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; If E820 failed, create 1 fallback entry (128MB usable)
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mov dword [0x9000], 1
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mov dword [0x9004], 0
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mov dword [0x9008], 0x100000 ; base = 1MB
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mov dword [0x900C], 0
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mov dword [0x9010], 0x07F00000 ; length = 127MB
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mov dword [0x9014], 0
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mov dword [0x9018], 1 ; type = 1 (USABLE)
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mov dword [0x901C], 1
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jmp .mmap_store_done
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.mmap_finished:
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mov word [0x9000], bp
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mov word [0x9002], 0
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mov dword [0x9004], 0
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.mmap_store_done:
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; -------------------------------------------------------------
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; Step 3: Load Kernel from Disk to 0x10000 (Conventional RAM)
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; 4 chunks x 64 sectors = 256 sectors (128 KB)
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; -------------------------------------------------------------
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mov si, msg_kernel_load
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call print_string_16
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mov word [kernel_dap_off], 0x0000
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mov word [kernel_dap_seg], 0x1000
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mov dword [kernel_dap_lba], 16
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mov dword [kernel_dap_lba + 4], 0
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mov cx, 4 ; 4 chunks * 64 sectors = 256 sectors (128 KB)
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.kernel_chunk_loop:
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push cx
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mov ah, 0x42
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mov dl, [boot_drive]
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mov si, kernel_dap
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int 0x13
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jc .kernel_disk_error
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; Advance LBA by 64 sectors
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add dword [kernel_dap_lba], 64
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; Advance Segment by 0x800 (64 sectors * 512 bytes = 32768 bytes = 0x800 paragraphs)
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add word [kernel_dap_seg], 0x0800
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pop cx
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loop .kernel_chunk_loop
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.kernel_loaded_ok:
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; -------------------------------------------------------------
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; Step 4: Set up Identity Paging for Long Mode (All 4 GB)
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; -------------------------------------------------------------
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; Clear 24 KB for 6 page tables (0x1000 - 0x6FFF)
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mov ax, 0x0000
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mov es, ax
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mov di, 0x1000
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mov cx, 6144
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xor eax, eax
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rep stosd
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; PML4[0] -> PDPT at 0x2000
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mov dword [0x1000], 0x2003
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mov dword [0x1004], 0
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; PDPT -> 4 PDs
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mov dword [0x2000], 0x3003
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mov dword [0x2004], 0
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mov dword [0x2008], 0x4003
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mov dword [0x200C], 0
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mov dword [0x2010], 0x5003
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mov dword [0x2014], 0
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mov dword [0x2018], 0x6003
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mov dword [0x201C], 0
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; Map 4GB (2048 x 2MB pages)
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mov di, 0x3000
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mov eax, 0x00000083
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mov cx, 2048
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.map_4gb_loop:
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mov [di], eax
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mov dword [di + 4], 0
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add eax, 0x200000
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add di, 8
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loop .map_4gb_loop
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; -------------------------------------------------------------
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; Step 5: Switch to 32-bit Protected Mode
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; -------------------------------------------------------------
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mov si, msg_entering_pm
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call print_string_16
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cli
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lgdt [gdt_descriptor]
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mov eax, cr0
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or eax, 1
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mov cr0, eax
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jmp 0x08:pm_entry
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.kernel_disk_error:
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mov si, msg_kernel_err
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call print_string_16
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.halt16:
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cli
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hlt
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jmp .halt16
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print_string_16:
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pusha
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mov ah, 0x0E
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.p_loop:
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lodsb
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test al, al
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jz .p_done
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int 0x10
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jmp .p_loop
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.p_done:
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popa
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ret
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; -----------------------------------------------------------------
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; 32-Bit Protected Mode Entry Point
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; -----------------------------------------------------------------
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BITS 32
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pm_entry:
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mov ax, 0x10
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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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mov esp, 0x7C00
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; Copy kernel from 0x10000 to 0x100000 (1MB mark) - 256 KB (512 sectors)
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mov esi, 0x10000
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mov edi, 0x100000
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mov ecx, (512 * 512) / 4
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rep movsd
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; Enable PAE in CR4
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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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; Load CR3
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mov eax, 0x1000
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mov cr3, eax
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; Enable Long Mode in EFER MSR
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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 and Protected Mode
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mov eax, cr0
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or eax, (1 << 31) | (1 << 0)
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mov cr0, eax
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jmp 0x18:lm_entry
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; -----------------------------------------------------------------
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; 64-Bit Long Mode Entry Point
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; -----------------------------------------------------------------
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BITS 64
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lm_entry:
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mov ax, 0x20
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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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; Arguments: RDI = 0x9008 (entries), RSI = count at 0x9000
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mov rdi, 0x9008
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mov rsi, [0x9000]
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mov rax, 0x100000
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jmp rax
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; -----------------------------------------------------------------
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; Data Section
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; -----------------------------------------------------------------
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BITS 16
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align 4
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boot_drive: db 0
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msg_stage2_start: db "Stage 2: Loaded", 13, 10, 0
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msg_a20: db "Stage 2: A20 enabled", 13, 10, 0
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msg_mmap: db "Stage 2: Memory map detected", 13, 10, 0
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msg_kernel_load: db "Stage 2: Loading kernel...", 13, 10, 0
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msg_entering_pm: db "Stage 2: Jumping to 64-bit mode...", 13, 10, 0
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msg_kernel_err: db "Stage 2: Kernel Disk Read Error!", 13, 10, 0
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align 4
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kernel_dap:
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db 0x10
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db 0
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dw 64 ; 64 sectors per chunk (32 KB)
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kernel_dap_off:
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dw 0x0000
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kernel_dap_seg:
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dw 0x1000
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kernel_dap_lba:
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dq 16
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%include "gdt.asm"
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