2018-12-20 18:03:39 +01:00
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;=----------------------------------------------------------------------------=;
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; GNU GPL OS/K ;
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; ;
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; Authors: spectral` ;
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; NeoX ;
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; ;
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2018-12-22 12:19:17 +01:00
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; Desc: Bootsector for OS/K ;
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2018-12-20 18:03:39 +01:00
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; (x86_64 architecture only) ;
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;=----------------------------------------------------------------------------=;
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2018-12-21 23:57:41 +01:00
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;; BOOT "SEGMENT"
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%define BOOT_SEG 0x07c0 ; (BOOT_SEG << 4) + BOOT_OFF = 0x007c00
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%define BOOT_OFF 0x0000
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;; STACK "SEGMENT"
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%define STACK_SEG 0x0600 ; (STACK_SEG << 4) + STACK_OFF = 0x007000
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%define STACK_OFF 0x1000
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;; DISK BUFFER "SEGMENT"
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%define BUFFER_SEG 0x2000 ; (BUFFER_SEG << 4) + BUFFER_OFF = 0x020000
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%define BUFFER_OFF 0x0000
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;; SECOND STAGE LOADER "SEGMENT"
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2018-12-22 12:19:17 +01:00
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%define LOAD_SEG 0x0000 ; (LOAD_SEG << 4) + LOAD_OFF = 0x001000
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2018-12-21 23:57:41 +01:00
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%define LOAD_OFF 0x1000
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[BITS 16] ; Ensure 16-bit code (because fuck UEFI)
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;---------------------------------------------------
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; Disk description table
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;---------------------------------------------------
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Intro:
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jmp short _start ; Jump over the BIOS PARAMETER BLOCK
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nop ; Required by BIOS to recognize the Disk
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BPB:
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%define OEMName bp+0x03 ; Disk label
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%define bytesPerSector bp+0x0b ; Bytes per sector
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%define sectorsPerCluster bp+0x0d ; Sectors per cluster
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%define reservedSectors bp+0x0e ; Reserved sectors
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%define fats bp+0x10 ; Number of fats
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%define rootDirEntries bp+0x11 ; Number of entries in root dir
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%define sectors bp+0x13 ; Logical sectors
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%define mediaType bp+0x15 ; Media descriptor byte
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%define fatSectors bp+0x16 ; Sectors per FAT
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%define sectorsPerTrack bp+0x18 ; Sectors per track
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%define heads bp+0x1a ; Number of sides/heads
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%define hiddenSectors bp+0x1c ; Hidden sectors
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%define hugeSectors bp+0x20 ; LBA sectors
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%define biosBootdrvNum bp+0x24 ; Bootdrv number
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%define reserved bp+0x25 ; This is not used
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%define bootSignature bp+0x26 ; Bootdrv signature
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%define volumeId bp+0x27 ; Volume ID
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%define volumeLabel bp+0x2b ; Volume Label
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%define fatTypeLabel bp+0x36 ; File system type
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times 0x3b db 0x00
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;; ENTRY POINT
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_start:
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jmp BOOT_SEG:$+5 ; Fix the cs:ip registers with a vaudou magical trip
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2018-12-20 18:19:51 +01:00
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2018-12-21 23:57:41 +01:00
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bootstrap:
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2018-12-22 12:19:17 +01:00
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jmp bootstrapper
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;; LOVELY DATA
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FileNotFound db "FStage ERR : NO LOADER", 0 ; File was not found
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DiskError db "FStage ERR : DISK", 0 ; Error while reading from the disk
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UserData dw 0 ; Start of the data sectors
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Bootdrv db 0 ; Boot Bootdrv number
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filename db "LOADER BIN" ; Filename
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;; GO !
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bootstrapper:
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2018-12-21 23:57:41 +01:00
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mov ax, BOOT_SEG ; Set segments to the location of the bootloader
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mov ds, ax
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mov es, ax
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;; INIT STACK
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cli
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mov ax, STACK_SEG ; Init the staaaaaack
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mov ss, ax ; Continue init the staaaaaaaack
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mov sp, STACK_OFF ; Ok man, the stack is in 4K :O
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sti
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mov bp, (0x7c0-STACK_SEG) << 4 ; Correct bp for the disk description table !
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2018-12-20 18:03:39 +01:00
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2018-12-21 23:57:41 +01:00
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;; INITIALIZE BOOT DISK
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or dl, dl ; Verifying dl points actually to the boot drive
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jz loadRoot
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mov byte [Bootdrv], dl ; Another soul (the disk) saved !
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mov ah, 0x08
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int 0x13 ; int 0x13 : read drive parameters/geom
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jc loadRoot
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and cx, 0x003f ; Maximum sector number is the high bits 6-7 of cl
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mov word [sectorsPerTrack], cx ; And whose low 8 bits are in ch
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mov dl, dh ; Convert the maximum head number to a word with another vaudou magical trip
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xor dh, dh
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inc dx ; because head numbers start at zero
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mov word [heads], dx ; Another soul (the heads number) saved !
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;; LOAD THE ROOT DIRECTORY FROM DISK
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loadRoot:
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xor cx, cx
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mov ax, 32 ; Size of root dir = (rootDirEntries * 32) / bytesPerSector
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mul word [rootDirEntries] ; multiply by the total size of the root directory
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div word [bytesPerSector] ; divide by the number of bytes used per sector
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xchg cx, ax
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mov al, byte [fats] ; Location of root dir = (fats * fatSectors) + reservedSectors
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mul word [fatSectors] ; multiply by the sectors used
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add ax, word [reservedSectors] ; increase ax by the reserved sectors
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2018-12-22 12:19:17 +01:00
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mov word [UserData], ax ; Start of user data = startOfRoot + numberOfRoot
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add word [UserData], cx ; Add the size and location of the root directory
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2018-12-20 18:03:39 +01:00
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2018-12-21 23:57:41 +01:00
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mov di, BUFFER_SEG ; Set the extra segment to the disk buffer
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mov es, di
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mov di, BUFFER_OFF ; Set es:di and load the root directory into the disk buffer
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call readSectors ; Read the sectoooooooors !
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;; FIND THE SECOND STAGE LOADER
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mov di, BUFFER_OFF ; Set es:di to the disk buffer
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mov cx, word [rootDirEntries] ; Search through all of the root dir entries
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xor ax, ax ; Clear ax for the file entry offset
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searchRoot:
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xchg cx, dx ; Save cx because it's a loop counter
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mov si, filename ; Load the filename
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mov cx, 11 ; Compare first 11 bytes
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rep cmpsb ; Compare si and di cx times
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je loadFat ; We found the LOADEEEEEEEER!!!
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add ax, 32 ; File entry offset
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mov di, BUFFER_OFF ; Point back to the start of the entry
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add di, ax ; Add the offset to point to the next entry
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xchg dx, cx
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loop searchRoot ; Continue to search for the file
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2018-12-20 18:19:51 +01:00
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2018-12-21 23:57:41 +01:00
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;; ERROR...
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2018-12-22 12:19:17 +01:00
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mov si, FileNotFound ; Could not find the file
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2018-12-21 23:57:41 +01:00
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call print
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;; REBOOT
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reboot:
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xor ax, ax
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int 0x16 ; Get a single keypress
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mov ah, 0x0e ; Teletype output
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mov al, 0x0d ; Carriage return
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int 0x10 ; Video interupt
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mov al, 0x0a ; Line feed
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int 0x10 ; Video interupt
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mov al, 0x0a ; Line feed
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int 0x10 ; Video interupt
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xor ax, ax
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int 0x19 ; Reboot the system
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2018-12-20 18:19:51 +01:00
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2018-12-21 23:57:41 +01:00
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;; LOAD THE FAT FROM THE FILE
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loadFat:
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mov ax, word [es:di + 15] ; Get the file cluster at offset 26
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push ax ; Store the FAT cluster
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xor ax, ax ; Size of fat = (fats * fatSectors)
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mov al, byte [fats] ; Move number of fats into al
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mul word [fatSectors] ; Move fat sectors into bx
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mov cx, ax ; Store in cx
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mov ax, word [reservedSectors] ; Convert the first fat on the disk
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mov di, BUFFER_OFF ; Set es:di and load the fat sectors into the disk buffer
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call readSectors ; Read the sectooooooooooors !!!
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;; LOAD THE CLUSTERS OF THE LOADER AND JUMP
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loadFile:
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mov di, LOAD_SEG
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mov es, di ; Set es:bx to where the file will load
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mov di, LOAD_OFF
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pop ax ; File cluster restored
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call readClusters ; Read clusters from the file
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mov dl, byte [Bootdrv] ; Pass the boot Bootdrv into dl
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jmp LOAD_SEG:LOAD_OFF ; Jump to the file loaded!
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hlt ; This should never be hit...
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; ...
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; ...
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; I hope....
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; ...
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;---------------------------------------------------;
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; FUNCTIONS ;
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;---------------------------------------------------;
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readClusters:
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;---------------------------------------------------;
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; Read file clusters, starting at the given cluster,;
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; expects FAT to be loaded into the disk buffer. ;
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; Please note that this may allocate up to 128KB ;
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; of ram. ;
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; ;
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; Expects: AX = Starting cluster ;
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; ES:DI = Location to load clusters ;
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; ;
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; Returns: None ;
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; ;
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;---------------------------------------------------;
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2018-12-20 18:19:51 +01:00
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push ax
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push bx
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push cx
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2018-12-21 23:57:41 +01:00
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push dx
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push di
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push es
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.clusterLoop:
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xor bh, bh
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xor dx, dx
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2018-12-22 12:19:17 +01:00
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push ax ; Get the cluster start = (cluster - 2) * sectorsPerCluster + UserData
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2018-12-21 23:57:41 +01:00
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sub ax, 2 ; Subtract 2
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mov bl, byte [sectorsPerCluster] ; Sectors per cluster is a byte value
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mul bx ; multiply (cluster - 2) * sectorsPerCluster
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2018-12-22 12:19:17 +01:00
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add ax, word [UserData] ; add the UserData
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2018-12-21 23:57:41 +01:00
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xor ch, ch
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mov cl, byte [sectorsPerCluster] ; Sectors to read
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call readSectors ; Read the sectors
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pop ax ; Current cluster number
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xor dx, dx
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.calculateNextSector16: ; Get the next sector for FAT16 (cluster * 2)
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mov bx, 2 ; Multiply the cluster by two (cluster is in ax)
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mul bx
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.loadNextSector:
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push ds
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push si
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mov si, BUFFER_SEG
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mov ds, si ; Temporarly set ds:si to the FAT buffer
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mov si, BUFFER_OFF
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add si, ax ; Point to the next cluster in the FAT entry
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mov ax, word [ds:si] ; Load ax to the next cluster in FAT
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pop si
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pop ds
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.nextSectorCalculated:
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cmp ax, 0xfff8 ; Check if we are at the end of the file?
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jae .done
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add di, 512 ; Add to the pointer offset
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jnc .clusterLoop
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.fixBuffer: ; An error will occur if the buffer in memory
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mov dx, es ; overlaps a 64k page boundry, when di overflows
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add dh, 0x10 ; it will trigger the carry flag, so correct
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mov es, dx ; extra segment by 0x1000
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jmp .clusterLoop ; Load the next file cluster
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.done:
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pop es
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pop di
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pop dx
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2018-12-20 18:19:51 +01:00
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pop cx
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pop bx
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pop ax
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2018-12-21 23:57:41 +01:00
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ret
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readSectors:
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;---------------------------------------------------;
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; Read sectors starting at a given sector by ;
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; the given times and load into a buffer. Please ;
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; note that this may allocate up to 128KB of ram. ;
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; ;
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; Expects: AX = Starting sector ;
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; CX = Number of sectors to read ;
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; ES:DI = Location to load sectors ;
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; ;
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; Returns: None ;
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; ;
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;---------------------------------------------------;
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push ax
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push bx
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push cx
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push dx
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push di
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push es
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mov bx, di ; Convert es:di to es:bx for int 13h
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.sectorLoop:
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push ax
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push cx
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xor dx, dx
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div word [sectorsPerTrack] ; Divide the lba (value in ax) by sectorsPerTrack
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mov cx, dx ; Save the absolute sector value
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inc cx
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xor dx, dx ; Divide by the number of heads
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div word [heads] ; to get absolute head and track values
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mov dh, dl ; Move the absolute head into dh
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mov ch, al ; Low 8 bits of absolute track
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shl ah, 1 ; High 2 bits of absolute track
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shl ah, 1
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shl ah, 1
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shl ah, 1
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shl ah, 1
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shl ah, 1
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or cl, ah ; Now cx is set with respective track and sector numbers
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mov dl, byte [Bootdrv] ; Set correct Bootdrv for int 13h
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mov di, 5 ; Try five times to read the sector because i love 5
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.attemptRead:
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mov ax, 0x0201 ; Read Sectors func of int 13h, read one sector
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int 0x13 ; Call int 13h (BIOS disk I/O)
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jnc .readOk ; If no carry set, the sector has been read
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xor ah, ah ; Reset Bootdrv func of int 13h
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int 0x13 ; Call int 13h (BIOS disk I/O)
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dec di ; Decrease read attempt counter
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jnz .attemptRead ; Try to read the sector again
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2018-12-22 12:19:17 +01:00
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mov si, DiskError ; Error reading the disk :/
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2018-12-21 23:57:41 +01:00
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call print
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jmp reboot
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.readOk:
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|
|
pop cx
|
|
|
|
|
pop ax
|
|
|
|
|
inc ax ; Increase the next sector to read
|
|
|
|
|
add bx, word [bytesPerSector] ; Add to the buffer address for the next sector
|
|
|
|
|
jnc .nextSector
|
|
|
|
|
.fixBuffer: ; An error will occur if the buffer in memory
|
|
|
|
|
mov dx, es ; overlaps a 64k page boundry, when bx overflows
|
|
|
|
|
add dh, 0x10 ; it will trigger the carry flag, so correct
|
|
|
|
|
mov es, dx ; es segment by 0x1000
|
|
|
|
|
.nextSector:
|
|
|
|
|
loop .sectorLoop
|
|
|
|
|
pop es
|
|
|
|
|
pop di
|
|
|
|
|
pop dx
|
2018-12-20 18:19:51 +01:00
|
|
|
pop cx
|
|
|
|
|
pop bx
|
|
|
|
|
pop ax
|
|
|
|
|
ret
|
|
|
|
|
|
2018-12-21 23:57:41 +01:00
|
|
|
print:
|
|
|
|
|
;---------------------------------------------------;
|
|
|
|
|
; Print out a simple string. ;
|
|
|
|
|
; ;
|
|
|
|
|
; Expects: DS:SI = String to print ;
|
|
|
|
|
; ;
|
|
|
|
|
; Returns: None ;
|
|
|
|
|
; ;
|
|
|
|
|
;---------------------------------------------------;
|
|
|
|
|
lodsb ; Load byte from ds:si to al
|
|
|
|
|
or al, al ; If al is empty stop looping
|
|
|
|
|
jz .done ; Done looping and return
|
|
|
|
|
mov ah, 0x0e ; Teletype output
|
|
|
|
|
int 0x10 ; Video interupt
|
|
|
|
|
jmp print ; Loop untill string is null
|
|
|
|
|
.done:
|
2018-12-20 18:19:51 +01:00
|
|
|
ret
|
2018-12-21 23:57:41 +01:00
|
|
|
|
|
|
|
|
;; END
|
|
|
|
|
times 510 - ($ - $$) db 0 ; Pad remainder of boot sector with zeros
|
|
|
|
|
dw 0xaa55 ; Boot signature
|
|
|
|
|
|
