OSDev.org

Posted: **Mon Apr 12, 2010 3:25 am**

Hello,
I am using the following code for reading the kernel of 128 sectors.
when i allocate stack to the kernel and pass control to it,its code is not executed.Could you plz help me what is wrong in the following code??
Thanks,

########################################################
.equ BOOT_SEGMENT,0x07c0
.equ DISPLAY_SEGMENT,0xb800
equ SECTOR_SIZE, 0x0200

.text # Code segment
.globl _start # The entry point must be global
.code16 # Real mode

_start:
jmp over

os_size:
.long 0x00000000
drive_number:
.byte 0x00
max_sector:
.byte 0x00
max_head:
.byte 0x00

over:

movw $NEW_BOOT_SEGMENT, %ax #The address where the bios loaded the bootloader
movw %ax, %ds

movb %dl, drive_number #Address of the boot device

movb $0x08, %ah #getting parameters of boot device
int $0x13

andb $0x3f, %cl
movb %cl, max_sector

movb %dh, max_head

movw os_size, %bp #loop counter

movw $0x0002, %cx

movb $0x00, %dh

movw $0x0000, %ax
movw %ax, %es
movw $0x0100, %bx

read_sectors:

cmpw $0x0000, %bp #termination check
jng after_load
decw %bp

movw $0x0201, %ax #reading 1 sector at a time
int $0x13
jc error #if cf=1

cmpb max_sector, %cl
jnl next_head
incb %cl
jmp after_next

next_head:
movb $0x01, %cl
cmpb max_head, %dh
jnl next_cylinder
incb %dh
jmp after_next
next_cylinder:
movb $0x00, %dh
incb %ch
after_next:

addw $SECTOR_SIZE, %bx

jnc read_sectors

after_load:

movw $0x0003, %ax
int $0x10

mov $0x0e.%ah #after loading kernel at es:bx display a flag character
mov $'O',%al
int $0x10

mov $0x9000,%bx #allocate stack to the kernel
mov %bx,%ss
mov $0xfffe,%sp

ljmp 0x01000 #long jump to the kernel location

error:

mov $0x0e.%ah
mov $'E',%al
int $0x10

forever:
# Loop forever
hlt
jmp forever

Posted: **Mon Apr 12, 2010 8:22 am**

The problem with your code is that you forgot

Code: Select all

 tags

Also, this is AT&T syntax - how are you assembling/linking it and how did you put it on your bootable medium of choice? The defaults don't work.

Posted: **Mon Apr 12, 2010 8:26 pm**

Hello,
Thanks for your reply.I am using GNU assembler for compiling this code and I am writing bootloader and kernel code to an image file and then executing this image file using QEMU.could you plz tell where to put tags in the code.I have found these projects on the web site of princeton university and i am completing these projects for learning purpose.
Thanks,

Posted: **Mon Apr 12, 2010 10:46 pm**

He was refering to the habit to enclose posted snippets of code with appropriate tags, so it looks...

Code: Select all

// ...like this...

int main( void )
{
    return 0;
}

...because otherwise any indentation gets lost, and proportional fonts can do "funny" things to source, too.

See also: BBCode on Wikipedia.

OSDev.org

Bootloader code using at & t assembly syntax

Bootloader code using at & t assembly syntax

Re: Bootloader code using at & t assembly syntax

Re: Bootloader code using at & t assembly syntax

Re: Bootloader code using at & t assembly syntax