Bootloader not working

[Ch H]

So I've made this bootloader, and for some reason it isn't working, I'll post a link to my repo here. Would love some feedback, thx.

https://github.com/Computermann8086/floppy_boot/blob/main/bootsector.asm

[Daniel Barry]

You need to describe what "working" and "not working" are in the context of this bootloader.

On Sun, Nov 30, 2025 at 2:13 PM Ch H <chwam...@gmail.com> wrote:

So I've made this bootloader, and for some reason it isn't working, I'll post a link to my repo here. Would love some feedback, thx.

https://github.com/Computermann8086/floppy_boot/blob/main/bootsector.asm

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[Ch H]

By 'not working' I meant that it just isn't loading the kernel, it simply crashes, I do know that is not in the file searching loop, and that

it probably is a bug in the read loop (the loop that reads the kernel into memory that is)

[Daniel Barry]

For debugging runtime behaviour, it can be useful to print a character to tell you what code is being run and why. Your theory is that it is the read loop, but you should test and prove this.

As the bootloader is quite limited in space, you may want to just print a single character. You could have a function such as:

; print_char()
;

; Print a single character. AX is unmodified.
;

; @param AL The character to be printed.

print_char :

  push ax

  mov ah, 0eh

  int 10h

  pop ax

  ret

Then to use it, you could just run:

mov al, '!' ; Explanation mark to let us know this was run

call print_char

If you need to, you can use `push` and `pop` and `mov` to keep registers unmodified as needed.

Other notes:

1. I highly recommend commits with good messages. There is no way you know what "Update bootsector.asm" (repeated) does from 2024: https://github.com/Computermann8086/floppy_boot/commits/main/

2. An old-old kernel I wrote based on MikeOS where the bootloader is the kernel: https://bitbucket.org/danielbarry/saxoperatingsystem/src/master/KERNEL/KERN.ASM

To view this discussion, visit https://groups.google.com/d/msgid/mikeos/e7f915dd-cbeb-438d-9105-cf8d8f2da13bn%40googlegroups.com.