boot0 menu editing possible?

[PCUser]

Is there any way to modify the boot0 menu that shows up at the beginning on a BIOS/Legacy system? I'd like to make changes to the displayed names, and there is one operating system that shows up as " ??" so would be ideal to have it named properly. (I also wonder if there is a way to emit a PC speaker beep at the screen?)

I found nothing in the boot0cfg command to make this happen. From what I know, the /boot/boot0 file is written in assembly code so it doesn't have a way to easily modify the values like for example GRUB provides.

 

[SirDice]

I found nothing in the boot0cfg command to make this happen.

Because the answer to your question is "No".

Here's the code: https://cgit.freebsd.org/src/tree/stand/i386/boot0/boot0.S

It simply looks at the partition info and does a bit of educated guessing. That's all it can do in a few bytes of code.

 

[atax1a]

iirc the boot0 code has to fit in a 512-byte PMBR. adding features would be a tight squeeze.

 

[SirDice]

iirc the boot0 code has to fit in a 512-byte PMBR

It's a little less than that, that 512 byte block also includes the partition table. There's 446 bytes left for actual code.

 

[atax1a]

in summary, x86 bios booting is a tire fire on top of a volcano

 

[T-Aoki]

It's a little less than that, that 512 byte block also includes the partition table. There's 446 bytes left for actual code.

See Structure of a classical generic MBR portion of Master boot record page in Wikipedia. If I understand correctly, this is the MBR structure that boot0 assumes.