Bootloader is Not loading the kernel
Question
I am developing my Operating System.
I got error on booting my OS.
The error was:
KERNEL.BIN not found!
Here are the Codes:
Boot.asm
; The Aqua_Seven_OS Operating System bootloader
; ==================================================================
BITS 16
jmp short bootloader_start ; Jump past disk description section
nop ; Pad out before disk description
; ------------------------------------------------------------------
; Disk description table, to make it a valid floppy
; Note: some of these values are hard-coded in the source!
; Values are those used by IBM for 1.44 MB, 3.5" diskette
OEMLabel db "MIKEBOOT" ; Disk label
BytesPerSector dw 512 ; Bytes per sector
SectorsPerCluster db 1 ; Sectors per cluster
ReservedForBoot dw 1 ; Reserved sectors for boot record
NumberOfFats db 2 ; Number of copies of the FAT
RootDirEntries dw 224 ; Number of entries in root dir
; (224 * 32 = 7168 = 14 sectors to read)
LogicalSectors dw 2880 ; Number of logical sectors
MediumByte db 0F0h ; Medium descriptor byte
SectorsPerFat dw 9 ; Sectors per FAT
SectorsPerTrack dw 18 ; Sectors per track (36/cylinder)
Sides dw 2 ; Number of sides/heads
HiddenSectors dd 0 ; Number of hidden sectors
LargeSectors dd 0 ; Number of LBA sectors
DriveNo dw 0 ; Drive No: 0
Signature db 41 ; Drive signature: 41 for floppy
VolumeID dd 00000000h ; Volume ID: any number
VolumeLabel db "MIKEOS "; Volume Label: any 11 chars
FileSystem db "FAT12 " ; File system type: don't change!
; ------------------------------------------------------------------
; Main bootloader code
bootloader_start:
mov ax, 07C0h ; Set up 4K of stack space above buffer
add ax, 544 ; 8k buffer = 512 paragraphs + 32 paragraphs (loader)
cli ; Disable interrupts while changing stack
mov ss, ax
mov sp, 4096
sti ; Restore interrupts
mov ax, 07C0h ; Set data segment to where we're loaded
mov ds, ax
; NOTE: A few early BIOSes are reported to improperly set DL
cmp dl, 0
je no_change
mov [bootdev], dl ; Save boot device number
mov ah, 8 ; Get drive parameters
int 13h
jc fatal_disk_error
and cx, 3Fh ; Maximum sector number
mov [SectorsPerTrack], cx ; Sector numbers start at 1
movzx dx, dh ; Maximum head number
add dx, 1 ; Head numbers start at 0 - add 1 for total
mov [Sides], dx
no_change:
mov eax, 0 ; Needed for some older BIOSes
; First, we need to load the root directory from the disk. Technical details:
; Start of root = ReservedForBoot + NumberOfFats * SectorsPerFat = logical 19
; Number of root = RootDirEntries * 32 bytes/entry / 512 bytes/sector = 14
; Start of user data = (start of root) + (number of root) = logical 33
floppy_ok: ; Ready to read first block of data
mov ax, 19 ; Root dir starts at logical sector 19
call l2hts
mov si, buffer ; Set ES:BX to point to our buffer (see end of code)
mov bx, ds
mov es, bx
mov bx, si
mov ah, 2 ; Params for int 13h: read floppy sectors
mov al, 14 ; And read 14 of them
pusha ; Prepare to enter loop
read_root_dir:
popa ; In case registers are altered by int 13h
pusha
stc ; A few BIOSes do not set properly on error
int 13h ; Read sectors using BIOS
jnc search_dir ; If read went OK, skip ahead
call reset_floppy ; Otherwise, reset floppy controller and try again
jnc read_root_dir ; Floppy reset OK?
jmp reboot ; If not, fatal double error
search_dir:
popa
mov ax, ds ; Root dir is now in [buffer]
mov es, ax ; Set DI to this info
mov di, buffer
mov cx, word [RootDirEntries] ; Search all (224) entries
mov ax, 0 ; Searching at offset 0
next_root_entry:
xchg cx, dx ; We use CX in the inner loop...
mov si, kern_filename ; Start searching for kernel filename
mov cx, 11
rep cmpsb
je found_file_to_load ; Pointer DI will be at offset 11
add ax, 32 ; Bump searched entries by 1 (32 bytes per entry)
mov di, buffer ; Point to next entry
add di, ax
xchg dx, cx ; Get the original CX back
loop next_root_entry
mov si, file_not_found ; If kernel is not found, bail out
call print_string
jmp reboot
found_file_to_load: ; Fetch cluster and load FAT into RAM
mov ax, word [es:di+0Fh] ; Offset 11 + 15 = 26, contains 1st cluster
mov word [cluster], ax
mov ax, 1 ; Sector 1 = first sector of first FAT
call l2hts
mov di, buffer ; ES:BX points to our buffer
mov bx, di
mov ah, 2 ; int 13h params: read (FAT) sectors
mov al, 9 ; All 9 sectors of 1st FAT
pusha ; Prepare to enter loop
read_fat:
popa ; In case registers are altered by int 13h
pusha
stc
int 13h ; Read sectors using the BIOS
jnc read_fat_ok ; If read went OK, skip ahead
call reset_floppy ; Otherwise, reset floppy controller and try again
jnc read_fat ; Floppy reset OK?
; ******************************************************************
fatal_disk_error:
; ******************************************************************
mov si, disk_error ; If not, print error message and reboot
call print_string
jmp reboot ; Fatal double error
read_fat_ok:
popa
mov ax, 2000h ; Segment where we'll load the kernel
mov es, ax
mov bx, 0
mov ah, 2 ; int 13h floppy read params
mov al, 1
push ax ; Save in case we (or int calls) lose it
; Now we must load the FAT from the disk. Here's how we find out where it starts:
; FAT cluster 0 = media descriptor = 0F0h
; FAT cluster 1 = filler cluster = 0FFh
; Cluster start = ((cluster number) - 2) * SectorsPerCluster + (start of user)
; = (cluster number) + 31
load_file_sector:
mov ax, word [cluster] ; Convert sector to logical
add ax, 31
call l2hts ; Make appropriate params for int 13h
mov ax, 2000h ; Set buffer past what we've already read
mov es, ax
mov bx, word [pointer]
pop ax ; Save in case we (or int calls) lose it
push ax
stc
int 13h
jnc calculate_next_cluster ; If there's no error...
call reset_floppy ; Otherwise, reset floppy and retry
jmp load_file_sector
; In the FAT, cluster values are stored in 12 bits, so we have to
; do a bit of maths to work out whether we're dealing with a byte
; and 4 bits of the next byte -- or the last 4 bits of one byte
; and then the subsequent byte!
calculate_next_cluster:
mov ax, [cluster]
mov dx, 0
mov bx, 3
mul bx
mov bx, 2
div bx ; DX = [cluster] mod 2
mov si, buffer
add si, ax ; AX = word in FAT for the 12 bit entry
mov ax, word [ds:si]
or dx, dx ; If DX = 0 [cluster] is even; if DX = 1 then it's odd
jz even ; If [cluster] is even, drop last 4 bits of word
; with next cluster; if odd, drop first 4 bits
odd:
shr ax, 4 ; Shift out first 4 bits (they belong to another entry)
jmp short next_cluster_cont
even:
and ax, 0FFFh ; Mask out final 4 bits
next_cluster_cont:
mov word [cluster], ax ; Store cluster
cmp ax, 0FF8h ; FF8h = end of file marker in FAT12
jae end
add word [pointer], 512 ; Increase buffer pointer 1 sector length
jmp load_file_sector
end: ; We've got the file to load!
pop ax ; Clean up the stack (AX was pushed earlier)
mov dl, byte [bootdev] ; Provide kernel with boot device info
jmp 2000h:0000h ; Jump to entry point of loaded kernel!
; ------------------------------------------------------------------
; BOOTLOADER SUBROUTINES
reboot:
mov ax, 0
int 16h ; Wait for keystroke
mov ax, 0
int 19h ; Reboot the system
print_string: ; Output string in SI to screen
pusha
mov ah, 0Eh ; int 10h teletype function
.repeat:
lodsb ; Get char from string
cmp al, 0
je .done ; If char is zero, end of string
int 10h ; Otherwise, print it
jmp short .repeat
.done:
popa
ret
reset_floppy: ; IN: [bootdev] = boot device; OUT: carry set on error
push ax
push dx
mov ax, 0
mov dl, byte [bootdev]
stc
int 13h
pop dx
pop ax
ret
l2hts: ; Calculate head, track and sector settings for int 13h
; IN: logical sector in AX, OUT: correct registers for int 13h
push bx
push ax
mov bx, ax ; Save logical sector
mov dx, 0 ; First the sector
div word [SectorsPerTrack]
add dl, 01h ; Physical sectors start at 1
mov cl, dl ; Sectors belong in CL for int 13h
mov ax, bx
mov dx, 0 ; Now calculate the head
div word [SectorsPerTrack]
mov dx, 0
div word [Sides]
mov dh, dl ; Head/side
mov ch, al ; Track
pop ax
pop bx
mov dl, byte [bootdev] ; Set correct device
ret
; ------------------------------------------------------------------
; STRINGS AND VARIABLES
kern_filename db "KERNEL BIN" ; kernel filename
disk_error db "Floppy error! Press any key...", 0
file_not_found db "KERNEL.BIN not found!", 0
bootdev db 0 ; Boot device number
cluster dw 0 ; Cluster of the file we want to load
pointer dw 0 ; Pointer into Buffer, for loading kernel
; ------------------------------------------------------------------
; END OF BOOT SECTOR AND BUFFER START
times 510-($-$$) db 0 ; Pad remainder of boot sector with zeros
dw 0AA55h ; Boot signature (DO NOT CHANGE!)
buffer: ; Disk buffer begins (8k after this, stack starts)
; ==================================================================
I found the boot code on internet.
Kernel.asm
[bits 16]
mov ax, 0 ; set up segments
mov ds, ax
mov es, ax
mov ss, ax ; setup stack
mov sp, 0x7C00 ; stack grows downwards from 0x7C00
mov ah, 9
mov bl, 9
mov cx, 11
int 10h
mov DX, boota
int 21H
mov si, boota ;Print boot message
call print_string
mainloop:
mov si, prompt
call print_string ; prompt db ">"
mov di, buffer
call get_string
mov si, buffer
cmp byte [si], 0 ; blank line?
je mainloop ; yes, ignore it
mov si, buffer
mov di, cmd_reb ; "reboot" command
call strcmp
jc .reboot
mov si, buffer
mov di, cmd_shut ; "shutdown" command
call strcmp
jc .shut
mov si,badcommand
call print_string ; What if there is no such command?
jmp mainloop ; jmp mainloop :-)
.reboot: ; reboot function
db 0x0ea
dw 0x0000
dw 0xffff
.shut: ;shutdown function
mov al, 02h
mov ah, 00h
int 10h
mov si, shutm
call print_string
mov ax, 0x1000
mov ax, ss
mov sp, 0xf000
mov ax, 0x5307
mov bx, 0x0001
mov cx, 0x0003
int 0x15
; ------Variables-------------
shutm db 'The MCOS shutdowned sucessfully. Now you may power off the computer.', 0x0d, 0x0a, 0
boota db 'Booting MotoSoft COS 1...', 0x0d, 0x0a, 0
buffer times 64 db 0
prompt db '>', 0
badcommand db 'Bad command entered.', 0x0D, 0x0A, 0
cmd_reb db 'reboot', 0
; ================
; calls start here
; ================
print_string:
lodsb ; grab a byte from SI
or al, al ; logical or AL by itself
jz .done ; if the result is zero, get out
mov ah, 0x0E
int 0x10 ; otherwise, print out the character!
jmp print_string
.done:
ret
get_string:
xor cl, cl
.loop:
mov ah, 0
int 0x16 ; wait for keypress
cmp al, 0x08 ; backspace pressed?
je .backspace ; yes, handle it
cmp al, 0x0D ; enter pressed?
je .done ; yes, we're done
cmp cl, 0x3F ; 63 chars inputted?
je .loop ; yes, only let in backspace and enter
mov ah, 0x0E
int 0x10 ; print out character
stosb ; put character in buffer
inc cl
jmp .loop
.backspace:
cmp cl, 0 ; beginning of string?
je .loop ; yes, ignore the key
dec di
mov byte [di], 0 ; delete character
dec cl ; decrement counter as well
mov ah, 0x0E
mov al, 0x08
int 10h ; backspace on the screen
mov al, ' '
int 10h ; blank character out
mov al, 0x08
int 10h ; backspace again
jmp .loop ; go to the main loop
.done:
mov al, 0 ; null terminator
stosb
mov ah, 0x0E
mov al, 0x0D
int 0x10
mov al, 0x0A
int 0x10 ; newline
ret
strcmp:
.loop:
mov al, [si] ; grab a byte from SI
mov bl, [di] ; grab a byte from DI
cmp al, bl ; are they equal?
jne .notequal ; nope, we're done.
cmp al, 0 ; are both bytes (they were equal before) null?
je .done ; yes, we're done.
inc di ; increment DI
inc si ; increment SI
jmp .loop ; loop!
.notequal:
clc ; not equal, clear the carry flag
ret
.done:
stc ; equal, set the carry flag
ret
cmd_shut db 'shutdwon', 0```
I got all these codes from internet and i am making my HOBBY OS.
And the compiling Codes:-
nasm -f bin -o boot.bin boot.asm
nasm -f bin -o kernel.bin kernel.asm
dd if=/dev/zero of=disk.img bs=512 count=2880
dd if=boot.bin of=disk.img bs=512 conv=notrunc
dd if=kernel.bin of=disk.img bs=512 seek=1 conv=notrunc
When I boot my OS, it shows
KERNEL.BIN not found!
Image of error:
1 answers
solution1
6 ACCPTED 2019-12-20 20:40:19
If you intend on using the MIKEOS bootloader then you need to create a FAT12 formatted 1.44MiB floppy disk image to be compatible with the volume boot record (VBR) in boot.asm . You then need to copy your KERNEL.BIN into that image.
This process is quite simple with the mtools package. mtools has online documentation . This answer isn't a complete guide to using mtools but enough to do what you need to boot. If you are using Debian or a Debian based distro like Ubuntu you can install the mtools package as root user with:
apt-get install mtools
The mtools package comes with a mformat program that can create 1.44MiB disk image; format it as FAT12; and have it automatically place your boot.bin program in the first sector. The command would be:
mformat -f1440 -B boot.bin -C -i disk.img
This should create a 1.44MiB disk image file called disk.img . To copy a file like KERNEL.BIN into disk.img you'd use the command:
mcopy -D o -i disk.img KERNEL.BIN ::/
The -D o option forces mcopy to overwrite a file if it exists. -i disk.img specifies the name of the disk image file KERNEL.BIN is the file we want to copy into the image (source file(s)). :: is a special device name to refer to the disk image itself. The / is the root directory. Together ::/ at the end of the command is the target location to put the file - in the root directory of the disk image.
You can use the mdir command to get a file listing of the root directory.
mdir -i disk.img ::/
This works similar to dir / in DOS. The output would look something like:
Volume in drive : has no label Volume Serial Number is 6F67-C526 Directory for ::/ KERNEL BIN 74 2019-12-20 13:25 1 file 74 bytes 1 457 152 bytes free
I have created a kernel.asm that replaces yours as yours has problems that are beyond the scope of your question. I provide this one as a sample that should work:
ORG 0x0000
start:
mov ax, 0x2000 ; Mike OS'es bootloader loads us at 0x2000:0x0000
mov ds, ax ; Set DS = ES = 0x2000
mov es, ax
; Stack just below 0x2000:0x0000 starting at 0x1000:0x0000.
; First push will set SS:SP to 0x1000:0xfffe because SP will wrap.
mov ax, 0x1000
mov ss, ax
xor sp, sp
cld ; Clear Direction Flag (DF=0 is forward string movement)
mov si, testCodeStr
call print_string
cli
.end_loop:
hlt
jmp .end_loop
testCodeStr: db 0x0d, 0x0a, "KERNEL.BIN loaded and running...", 0
; Function: print_string
; Display a string to the console on display page 0
;
; Inputs: SI = Offset of address to print
; Clobbers: AX, BX, SI
print_string:
mov ah, 0x0e ; BIOS tty Print
xor bx, bx ; Set display page to 0 (BL)
jmp .getch
.repeat:
int 0x10 ; print character
.getch:
lodsb ; Get character from string
test al,al ; Have we reached end of string?
jnz .repeat ; if not process next character
.end:
ret
This code is intended to work with MIKEOS's bootloader that loads and runs the kernel from 0x2000:0x0000 in memory. I use an ORG 0x0000 at the top and set DS and ES to 0x2000 to correspond to where we are loaded in memory. I also set SS:SP to an initial value of 0x1000:00000. The first time you push a 16-bit value on the stack SS:SP will be 0x1000:0xFFFE (physical address 0x1FFFE) just below the load address of the kernel at 0x2000:0x0000 (physical address 0x20000).
When assembled and the disk image built and run in QEMU with the commands:
nasm -f bin boot.asm -o boot.bin
nasm -f bin kernel.asm -o KERNEL.BIN
mformat -f1440 -B boot.bin -C -i disk.img
mcopy -D o -i disk.img KERNEL.BIN ::/
qemu-system-i386 -fda disk.img
The output should look similar to:
Kernel problems
The main problems in your kernel.asm are:
Incorrectly setting the DS segment register. MIKEOS loaded your kernel at 0x2000:0x0000 (segment:offset) in memory. You need an
ORGthat matches the offset portion. You will want to load the DS (and if need be the ES ) with the segment portion (0x2000).Before using string instructions like LODS/STOS/SCAS you want to ensure the Direction Flag (DF) is set the way you expect. Using CLD will set DF=0 for forward movement which is what your code expects.
It also appears that you call
int 21hto print. It seems that code was left over from a DOS program and you meant to remove it.You misspelled
shutdownin thecmd_shutstring. You incorrectly spelled it asshutdwon.It is unclear what you wanted to do with this code:
mov ah, 9 ; Unclear what you were trying to do here? mov bl, 9 mov cx, 11 int 10h ; ????
You may wish to consider deleting it.
The beginning of your code could be modified to look like:
[bits 16]
ORG 0x0000
mov ax, 0x2000 ; set up segments to match CS=0x2000
mov ds, ax
mov es, ax
xor ax, ax
mov ss, ax ; set stack segment to 0x0000
mov sp, 0x7C00 ; stack grows downwards from 0x0000:0x7C00
cld ; Clear Direction Flag (DF=0 is forward string movement)
mov ah, 9 ; Unclear what you were trying to do here?
mov bl, 9
mov cx, 11
int 10h ; ????
mov si, boota ; Print boot message
call print_string
[snip]
You spelled shutdown incorrectly so it won't be properly recognized as a command. It should be:
cmd_shut db 'shutdown', 0
With these changes the code looks like this when run:
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