OSDev.org

Posted: **Tue Jul 20, 2010 8:12 am**

bunkdeath wrote:Hi to all those are helping someone like me,

I am new to this forum, and sorry, if this question is already there in forum. I tried to search for this question, but there was many such words so I got nothing.

I have a boot strap loader, and a simple kernel.
From tutorial i got that, kernel can be loaded in 3 different ways.

i) Put kernel in bootstrap loader.( But my kernel is bigger than 512 b)
ii) Specify the kernel file and load.
iii) Run form specified location.

The first one is not suitable for me as well as while coding OS.
If any one could give me any idea(with code) in any of two method(ii, ii) to load kernel file?

And I think platform does not matter while coding for OS(I think), but also, I am using x86 architecture Windows 7 OS

Thanks

start.asm:

Code: Select all

extern k_main
global _loader
_loader:
     call k_main
     cli
     hlt

main.c

Code: Select all

k_main(){
     char *vidmem = (char *)0xb8000;//VIDMEM pointer
     int i = 0;
     while(1){
          vidmem[i*2] = "H";//Print H on screen
          vidmem[i+1] = 0x07;//Set H color to WHITE
          i++;
     }
};

This should start the k_main function and it will print a lot of H's
Use this makefile if you have troubles:

Code: Select all

all:
     @nasm -f aout ./src/start.asm -o ./src/start.o
     @gcc -c ./src/main.c -o ./src/main.o -fno-builtin -fno-stack-protector
     ld -T link.ld -o kernel.bin ./src/start.o ./src/main.o

This should compile correctly your boot sector, but if you want to use it whit grub:
start.asm:

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global _loader		; making entry point visible to linker
extern k_main		; KernelMain
; setting up the Multiboot header - see GRUB docs for details
MODULEALIGN equ  1<<0                   ; align loaded modules on page boundaries
MEMINFO     equ  1<<1                   ; provide memory map
FLAGS       equ  MODULEALIGN | MEMINFO  ; this is the Multiboot 'flag' field
MAGIC       equ    0x1BADB002           ; 'magic number' lets bootloader find the header
CHECKSUM    equ -(MAGIC + FLAGS)        ; checksum required
section .text
align 4
MultiBootHeader:
	dd MAGIC
	dd FLAGS
	dd CHECKSUM
	; reserve initial kernel stack space
	STACKSIZE equ 0x4000		; that's 16k.
	_loader:
	mov esp, stack+STACKSIZE; set up the stack
	cli
	mov eax, cr0
	or al, 1
	mov cr0, eax
	push eax		; pass Multiboot magic number
	push ebx		; pass Multiboot info structure
	; Immediately after that you have to jump to the code segment in the GDT:
	JMP 08h:k_main
	hlt			; halt machine should kernel return

Its ready to hold Protected Mode...
link.ld:

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ENTRY (_loader)
SECTIONS{
. = 0x00100000;
.text :{
*(.text)
}
.rodata ALIGN (0x1000) : {
*(.rodata)
}
.data ALIGN (0x1000) : {
*(.data)
}
.bss : {
_sbss = .;
*(COMMON)
*(.bss)
_ebss = .;
}
}

With this you can start your kernel. It's easy to use, you only need MagicISO to replace kernel.bin in the .img file with your own kernel.bin.
grub.img: http://www.megaupload.com/?d=5J3ZFSR0

Posted: **Tue Jul 20, 2010 8:47 am**

@Almamu:

Handing out code without any form of explanation is considered bad practice by many. Giving out utterly broken and braindead code is really, really bad. This is a random mix of some tutorials, does not compile, and reeks of you having absolutely no clue.

@OP:
You might want to run down a tutorial series to get some code and how it puts things together, otherwise you can just grab some known working starting code from the barebones tutorial (found on the wiki).

Posted: **Tue Jul 20, 2010 9:00 am**

Combuster wrote:@Almamu:

Handing out code without any form of explanation is considered bad practice by many. Giving out utterly broken and braindead code is really, really bad. This is a random mix of some tutorials, does not compile, and reeks of you having absolutely no clue.

@OP:
You might want to run down a tutorial series to get some code and how it puts things together, otherwise you can just grab some known working starting code from the barebones tutorial (found on the wiki).

Im using this code on my OS, and it compiles and works, it has some more lines...

Okokokokok.

Posted: **Tue Jul 20, 2010 9:27 am**

Code: Select all

k_main(){
     char *vidmem = (char *)0xb8000;//VIDMEM pointer
     int i = 0;
     while(1){
          vidmem[i*2] = "H";//Print H on screen
          vidmem[i+1] = 0x07;//Set H color to WHITE
          i++;
     }
}

That so-doesn't-work. 5 obvious bugs/compile errors in a 9 line function.

Posted: **Tue Jul 20, 2010 9:40 am**

first change

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vidmem[i+1] = 0x07;//Set H color to WHITE

to

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vidmem[i*2+1] = 0x07;//Set H color to WHITE

Posted: **Tue Jul 20, 2010 9:47 am**

3 more. (I mis-counted before)

Posted: **Tue Jul 20, 2010 9:49 am**

gedd wrote:first change
Code: Select all
vidmem[i+1] = 0x07;//Set H color to WHITE
to
Code: Select all
vidmem[i*2+1] = 0x07;//Set H color to WHITE

Ops, yeah, i have mistaked this... is the bad of write it by hand at the moment without any reference...

Posted: **Tue Jul 20, 2010 11:29 am**

This may still be a helpful thread if we can get the criticism to be constructive.

I prefer not handing out code samples to people asking for help with their question. Fixing problems is so much harder than taking somebody else's solution. Learning to fix your own problems should be the goal, not handing them code.

Posted: **Tue Jul 20, 2010 12:52 pm**

You might want to try using a simple boot loader that you already know works and just loads an exe or com file. Then you can work on getting all the fancy stuff to work in one section of code and decide late how much you want to push over to the loader and how much you want to leave in the main program. Getting a single section or function to work has always seemed to work as a better starting ground for me then tying to get several pieces to work and work together at the same time. http://alexfru.chat.ru/programming/bootprog.zip might be a loader you could try out.

Posted: **Tue Jul 20, 2010 4:37 pm**

Code: Select all

k_main(){
     char *vidmem = (char *)0xb8000;//VIDMEM pointer
     int i = 0;
     while(1){
          vidmem[i*2] = "H";//Print H on screen
          vidmem[i+1] = 0x07;//Set H color to WHITE
          i++;
     }
}

That should eventually triple fault. You should make sure the characters being printed stay within video RAM.

Posted: **Tue Jul 20, 2010 5:34 pm**

Code: Select all

vidmem[i*2] = "H";//Print H on screen

And that the characters are characters. (and not strings).

Posted: **Tue Jul 20, 2010 6:45 pm**

while(1){
vidmem[i*2] = "H";//Print H on screen
vidmem[i+1] = 0x07;//Set H color to WHITE
i++;
}

... and that your array offsets are valid.

Posted: **Tue Jul 20, 2010 7:49 pm**

Code: Select all

     int i = 0;
     while(1){
          vidmem[i*2] = "H";//Print H on screen
          vidmem[i+1] = 0x07;//Set H color to WHITE
          i++;
     }

And that your array index can't go negative.

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