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Re: Bootloader - the first 512 bytes

From: SteveSi
Subject: Re: Bootloader - the first 512 bytes
Date: Mon, 8 May 2023 21:20:20 +0100

00 is not NOP
90hex is NOP

Normally, the start of code contains a 2 byte or 3 byte jump instruction

Why not just show us your code?

On Mon, 8 May 2023, 21:10 Gijs Slijpen, <> wrote:

> Hello,
> For a while now I have been trying to get a boot loader written in
> Assembly to work on a Dell Gateway 5000 and a Dell Latitude 5590 both have
> intel i5 processors. My boot loader is a simpel one: it outputs the words
> "Hello World" to the screen. The code works in a virtual machine that I
> have set up in Virtual Box. However, when trying it out on a both of the
> machines mentioned before only “Hell” is being printed (maybe my computer
> is trying to tell me something).
> I figured out that if I use some padding in my boot loader right after the
> first command (for example defining 24 bytes of 0) and then continue my
> code the boot loader actually works on both my Dell machines but I do not
> know why. Then, just today, I thought I’d have a look at the Grub boot
> loader boot.S file to see whether I could get that to work on my Dell
> machines. Funny thing: I found there are 25 nop’s in there right after the
> first instruction.
> Would anyone maybe care to explain why this is? I have been looking around
> and not been able to find any documentation on this yet, there is a chance
> that I will find it in Intel’s software development manual but I thought
> I’d also ask it here.
> I am looking forward to a reply.
> Thanks in advance!
> Best regards,
> Gijs Slijpen

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