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Hi,
I am trying to develop my own kernel. I am a newbee in kernel programming, so i am taking help of one of the article on Bona Fide OS Development, http://www.osdever.net/bkerndev/index.php. For your information, I am using Fedora Core 1 for development. The rest is same i.e gcc, nasm etc...

I am following the article step by step and building and booting the kernel as soon as I finish up one step to see if everything is going fine. So, when I first created the start.asm and link.ld and build the kernel, it all worked fine. When I created the main.c, called it from start.asm and booted this kernel it gave me a problem. The error was something like this:
[Multiboot-kludge, load_addr = 0x100000....
Error 13: Invalid or unsupported file format

I am not getting why this problem is coming as I have done everything exactly as mentioned in that article. I tried searching on google but could not find anything relevant. If anyone wants to check my code, then you can check it out at:
kernel.asm: http://www.slexy.org/paste/4324
link.ld: http://www.slexy.org/paste/4325
main.c: http://www.slexy.org/paste/4326
system.h: http://www.slexy.org/paste/4327

I will really be thankful if you can help me out that where exactly I am doing wrong.

it looks like you're not linking correctly. can we see the commands you used to compile and link it?

Well, I checked my commands again as per your suggestion, tried to twist them a little bit, and I am now able to boot the kernel. I even added the code to print "Hello World !!" and its working fine.

Earlier, I was using following commands:
1. nasm -faout kernel.asm -o kernel.o
2. gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o main.o main.c
3. ld -T link.ld kernel.o main.o -o kernel.bin

This time, I am using the same commands but with 2 modification:
1. I removed the very first line from link.ld, which was OUTPUT_FORMAT("binary")
2. ld -T link.ld kernel.o main.o -o kernel

Well, so this issue to closed now. But I have a second query now. Whats the difference between these two commands:
nasm -faout kernel.asm -o kernel.o and
nasm -felf kernel.asm -o kernel.o

The reason I am asking this question is that currently I have got following kernel code which basically prints "Hello World !!" on the screen:
1. kernel.asm: http://www.slexy.org/paste/4540
2. link.ld: http://www.slexy.org/paste/4541
3. main.c: http://www.slexy.org/paste/4542
4. scrn.c: http://www.slexy.org/paste/4543
5. system.h: http://www.slexy.org/paste/4544

When i am trying to build this code as follows:
1. nasm -faout kernel.asm -o kernel.o
2. gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o main.o main.c
3. gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o scrn.o scrn.c
4. ld -T link.ld kernel.o main.o scrn.o -o kernel
It successfully prints "Hello World !!" on screen on booting the kernel.

But, when I build it like this:
1. nasm -felf kernel.asm -o kernel.o
2. gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o main.o main.c
3. gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o scrn.o scrn.c
4. ld -T link.ld kernel.o main.o scrn.o -o kernel
It gives me an error as follows:
[piyushkansal@localhost 3]$ ld -T link.ld -o kernel kernel.o main.o scrn.o
ld: kernel: Not enough room for program headers, try linking with -N
ld: final link failed: Bad value
[piyushkansal@localhost 3]$

I then used the following command:
ld -N -T link.ld -o kernel kernel.o main.o scrn.o
It got build successfully but when i booted the kernel, it gave me following error:
Error 28: Selected item cannot fit into memory

-felf creates an ELF executable while -faout creates an aout executable. and to get GRUB to work with an aout file you have to strip the headers if i'm not mistaken.