In the context of Linux, the boot loader is responsible for some predefined tasks. As this question is arm tagged, I think that ARM booting might be a useful resource. Specifically, the boot loader was/is responsible for setting up an ATAG list that describing the amount of RAM, a kernel command line, and other parameters. … Read more
I recently wrote some General Bootloader Tips in a Stackoverflow answer that may be of some use to you. Likely Tip #1 applies to your problem: When the BIOS jumps to your code you can’t rely on CS,DS,ES,SS,SP registers having valid or expected values. They should be set up appropriately when your bootloader starts. You … Read more
I can deduce you are using NASM (or NASM compatible) assembler. I don’t know what OS you are using to build the bootloader, but I’ll assume Linux or Windows. Other environments would be somewhat similar. You should split your bootloader into two parts to make this easier. One is the bootloader, and the second being … Read more
Your code assumes that DS is set to 0. You can’t assume that. First part of your code should explicitly set DS to 0 if you are using org 0x7c00. You should seriously considering defining your stack by setting SS:SP. You don’t know where the existing one is or whether it is large enough to … Read more
You included stuff at the top of your bootloader, where it will executes first. Instead include extra functions where they aren’t in the main path of execution and are only reached by call. This should work, placing the %include directives where it’s safe to put extra function or data, just like if you were writing … Read more
If you are on Linux you can do it with DD utility. There is a version of DD for Microsoft Windows as well. General DD usage If you wish to make a zero filled virtual disk image the size of a 720K floppy you can use dd like this: dd if=/dev/zero of=disk.img bs=1024 count=720 This … Read more
On x86 you would do the following (simplified): Have the bootloader load the n-th sector of the disk/floppy (wherever you’re booting from) into memory and execute it (i.e. load segment/offset and do retf). A better alternative is to search the filesystem for a certain filename (e.g. KERNEL.BIN) — but you’d need to know the file … Read more
With AT&T syntax you can put a label at the start of your bootloader and then use something like this: .global _start .text .code16 _start: jmp . .space 510-(.-_start) .word 0xaa55 Period . is the current location counter relative to the beginning of the current section. The difference between period . and _start is an … Read more