Writing BootLoader

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Views: 693 | Replies: 2

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Join Date: Jun 2008

Location: India

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Newbie Poster

Writing BootLoader

Jun 24th, 2008

Hi,
Could someone please share your idea on how to write a simple Hello World Boot Loader. I have been using OpenSuse Linux and and x86. I was able to write a single letter using the corresponding Ascii key. What about a string?

Thanks,
Citizen.

Citizen

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Join Date: Aug 2005

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Re: Writing BootLoader

Jun 26th, 2008

Did you already write your bootloader? If yes, than most work is already done. You just place all the following stuff at the end of the loader, load that stuff into mem and execute it by setting CS to that point.

Displaying a string is the same as displaying a single char just in a loop. If you use C-strings with 0-termination the you loop through the string until a 0 occurs. Eg

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mystring DB 'Hello world!',0
XOR BX,BX
print:
MOV AL,[mystring+BX]
JZ end
;output AL (don't know the code itm)
LOOP print
end:

http://www.explosive-software.de/?lang=en

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Join Date: Jun 2008

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Re: Writing BootLoader

Jun 27th, 2008

thanks a lot for your reply and code snippet. I have a doubt here. the processor understands hexadecimal value and displays the corresponding ascii values. for eg. when use #0x41 as the value it will displays character 'A' (well, this is what I tried). How would the processor understands a string. When I tried a code similar to yours it only displayed some ascii characters. the code i tried is in http://linuxgazette.net/issue79/krishnakumar.html. Please let me know regarding this. I am getting really interested in OS and boot loader concepts, but only getting minimal guidance in this area.

Thanks a lot.

Citizen