Split bootloader into 2 stages. vga_print is broken
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82bb637147
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8ddc5288b9
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@ -17,10 +17,10 @@
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; do some basic setup and then call into the kernel
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[org 0x7c00] ; Address where the code expects to be loaded in. The BIOS always loads us here
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kernel_offset: equ 0x1000
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[bits 16] ; All x86 CPUs start in 16 bit (aka "real") mode, so we tell nasm to emit 16-bit code
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; We save the value of the current boot drive
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mov [boot_drive], dl
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kernel_offset: equ 0x1000
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reserved_sectors: equ 4
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; This isn't needed inside the qemu emulator, but
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; real hardware is unlikely to start up with the
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@ -31,6 +31,9 @@ mov ss, ax
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mov es, ax
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xor ax, ax
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; We save the value of the current boot drive
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mov [boot_drive], dl
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; Now we setup the stack by setting the
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; base pointer to a location that's far
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; enough from where the code for the BIOS
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@ -38,54 +41,78 @@ xor ax, ax
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mov sp, 0x9000
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mov bp, sp
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call bios_cls
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mov si, real_mode_msg
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mov si, loading_stage2_msg
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call bios_println
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call load_kernel
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call switch_to_protected_mode
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jmp $ ; Keeps jumping at the current address (loops forever)
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mov bx, stage2
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mov cl, 2
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mov dh, reserved_sectors
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mov dl, [boot_drive]
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call load_disk
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jmp stage2
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; Now we include our "function definitions" (after the
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; loop, so they're never executed unless explicitly called)
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; Variables needed in the boot
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; sector
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boot_drive: db 0
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loading_stage2_msg: db "TSBL - INFO: Stage 1 loaded, loading stage 2", 0
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; We include just the bare minimum needed to load the
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; second stage of our bootloader
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%include "src/boot/util/disk.s"
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%include "src/boot/util/io.s"
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%include "src/boot/gdt.s"
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%include "src/boot/switch32.s"
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; Padding and magic number
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times 510 - ($ - $$) db 0
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dw 0xaa55
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; Here we define our variables: They need to be defined after the
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; halting because otherwise they will be executed as code
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real_mode_msg: db "TSOS: Booting", 0
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protected_mode_msg: db "TSOS: Protected mode OK", 0
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loading_kernel_msg: db "TSOS: Loading kernel", 0
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boot_drive: db 0
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[bits 16] ; All x86 CPUs start in 16 bit (aka "real") mode, so we tell nasm to emit 16-bit code
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load_kernel: ; Loads the kernel into memory
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mov si, loading_kernel_msg
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[bits 16]
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stage2:
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; Here we're no longer limited by the size of the
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; boot sector, so we can perform the more complex
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; part of the boot process
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mov si, stage2_loaded_msg
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call bios_println
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call load_kernel
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call switch_to_protected_mode
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load_kernel:
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; Loads the kernel into memory
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mov bx, kernel_offset
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mov cl, 2
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mov cl, reserved_sectors + 1
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mov dh, 4
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mov dl, [boot_drive]
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call load_disk
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mov si, kernel_loaded_msg
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call bios_println
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ret
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[bits 32]
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BEGIN_32BIT: ; After the switch we will get here
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mov esi, protected_mode_msg
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; My modified print function takes an offset
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; to add to the start of the video memory that
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; is added before writing. We skip the first
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; 320 bytes so that we don't overwrite the log
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; messages we have already written
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mov ecx, 0x140
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call vga_print
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call enableA20
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mov esi, calling_kernel_msg
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call vga_print
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call kernel_offset
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cli
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hlt
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jmp $
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; Padding and magic number
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times 510 - ($-$$) db 0
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dw 0xaa55
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; Now we include the necessary files to switch to
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; 32-bit (aka protected) mode
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%include "src/boot/gdt.s"
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%include "src/boot/switch32.s"
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%include "src/boot/util/enablea20.s"
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; Here we define our variables used in the second stage
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protected_mode_msg: db "TSBL - INFO: Successfully switched to protected mode, enabling A20 line", 0
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kernel_loaded_msg: db "TSBL - INFO: Kernel loaded, switching to protected mode", 0
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calling_kernel_msg: db "TSBL - INFO: Calling kernel entrypoint", 0
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stage2_loaded_msg: db "TSBL - INFO: Stage 2 loaded, loading kernel", 0
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times (512 * reserved_sectors) - ($ - $$) db 0 ; Pads the section to exactly reserved_sectors
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@ -17,13 +17,7 @@
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[bits 16]
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switch_to_protected_mode:
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cli ; Now we disable interrupts
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; We enable the A20 line using
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; the ol' but (mostly) reliable
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; keyboard controller method
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mov al, 0xd1
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out 0x64, al
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mov al, 0xdf
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out 0x60, al
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lgdt [gdt_descriptor] ; Time to load the GDT descriptor
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; We set 32-bit mode in CR0. Almost done!
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mov eax, cr0
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@ -45,5 +39,4 @@ switch32: ; We're not in 32 bit mode, yay!
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mov ebp, 0x1f8400 ; We also make the stack larger (2MiB)
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mov esp, ebp
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call BEGIN_32BIT ; We call back into mbr.s which loads the kernel
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@ -42,6 +42,8 @@ disk_error:
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call bios_print
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mov dh, ah ; Error code is in ah
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call bios_printh
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mov si, parenthesis
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call bios_print
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call bios_newline
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jmp disk_loop
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@ -55,5 +57,6 @@ disk_loop:
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jmp $
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disk_read_error_msg: db "TSOS: Read error: ", 0
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disk_sectors_error_msg: db "TSOS: Incomplete read", 0
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parenthesis: db ')', 0
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disk_read_error_msg: db "TSOS - ERROR: Disk read failed (error code ", 0
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disk_sectors_error_msg: db "TSOS - ERROR: Disk read failed (sector number mismatch)", 0
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@ -124,7 +124,10 @@ HEX_OUT: db '0x0000', 0 ; reserve memory for our new string
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[bits 32]
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; I/O routines that directly manipulate video memory
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; I/O routines that work with the VGA controller and video memory
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; to print to the screen
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VMEM_START: equ 0xb8000 ; Video memory always starts at this address
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; A character on the screen in VGA text mode is composed of 2 bytes:
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; the first byte is the ASCII codepoint to be printed, while the next
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@ -135,27 +138,23 @@ TEXT_COLOR: equ 0x07
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vga_print:
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; Prints a null-terminated string located
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; on the esi register. Offsets the write
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; by ecx bytes
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; on the esi register.
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pusha
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mov edx, VMEM_START
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add edx, ecx
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mov ebx, VMEM_START
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vga_print_loop:
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mov al, [esi]
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mov ah, TEXT_COLOR
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cmp al, 0
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je vga_print_done ; If we're at the null byte, we exit
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mov [edx], ax ; Write the 2-byte character to video memory
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je vga_print_done
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mov ah, TEXT_COLOR
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mov [ebx], ax ; Write the 2-byte character to video memory
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inc esi ; Go to the next character in the string
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add edx, 2 ; Go to the next character in video memory
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add ebx, 2
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jmp vga_print_loop
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vga_print_done:
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popa
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ret
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vga_printh:
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; Prints the value of edx in hexadecimal format
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pusha
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@ -24,9 +24,10 @@ i32 kmain(void) {
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The kernel entry point of TSOS
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*/
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// We skip the log messages from
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// the bootloader
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kprintln("\n\n\n\nTSOS: Kernel load OK");
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// TODO: Set VGA cursor position from assembly. Skipping
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// log messages like this is just awful
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kprintln("\n\n\nTSKL - INFO: Kernel booted successfully");
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// TODO...
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return 0x022172; // :D
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}
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