Re: bootxx needs to fit within 0th track of MBR partition?

Hi,

Thank you guys for comments, and sorry for the late reply.

The original problem itself has already been fixed by christos@;
optimization flags for libi386 was unintentionally missing.

However, sparse room for bootxx_ffsv2 is still less than a sector,
and fix will be necessary in the near future.

I found bootxx works as follows:

(1) mbr(8) or BIOS load 1st sector of bootxx into the memory
(2) bootxx loads itself by "int 13h" calls (CHS ah:0x02 or LBA ah:0x42)

For (2), we use hardcoded 15-sectors (one track for 5" 2HD disk).
"int 13h" for old machines may have 1-track restriction, but
I still have not found any documentation.

Even if single reads had 1-track restriction, it should be OK to
use multiple BIOS calls, IMO.

Therefore, I *guess* that we can use entire sectors for target
filesystems even for old machines, in principle.

But this needs careful assembler coding and tests...

BTW:

On Fri, Aug 25, 2023 at 9:08 PM Tobias Nygren <[email protected]> wrote:
> Side note I think there are other issues with boot code built with
> clang. For example I've encountered that bootx64.efi hangs for
> me when built with clang.

I could not reproduce this problem on QEMU with OVMF. Can you
please share more details? In my limited experience, I can say
printf debugging is useful for efiboot; at least you can find out
where it stalls.

Thanks,
rin