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SubjectRe: Bug in kernel - how to make big kernel bootable with GRUB (was Re: Linux 2.4.0-Test{1,2} with Grub (I think I found the answer))
In <Pine.LNX.4.10.10007131739430.810-100000@penguin.transmeta.com> Linus Torvalds (torvalds@transmeta.com) wrote:


> On Fri, 14 Jul 2000, Khimenko Victor wrote:
>>
>> Huh. Patch is trivial. Really trivial. Just one problem: I do not think it'll
>> be applied. Since it's TWO patches: one for kernel and one for GRUB.

> Actually, the only problem with the patch is that it is not
> byte-order-safe, which means that you cannot cross-compile from a
> big-endian host.

Ah. I forgot about this :-( Sorry.

> I don't see any real problem in extending syssize to be 4 bytes, as the
> two ne wbytes that it writes over are the "swap_dev" bytes that I don't
> think anybody ever used. We might as well get rid of them. And thanks to
> being little-endian, it would not change for loaders that don't know about
> the new 4-byte format (the two low bytes are still the same).

> So I won't apply the patch as-is, but fix it to be endian-safe and get
> some input from other bootloaders (assuming they all agree that swap_dev
> is a non-issue - which I think they will) and I _will_ apply it.

Big thnx.

>> Who's the bright idea was to extend maximum kernel beyond 1MB and STILL write
>> only two bytes of sys_size in boot sector anyway ? And why it was done via
>> buf in first place ?

> I'd be careful about calling other people stupid if you don't understand
> the code.

Ok, part about buf was my stupidity, I agree here. But about extending
sys_size it WAS NOT. Some other "bright" soul changed code so sys_size
bigger then $FFFF will be accepted and not done anything about two byte
field where sys_size is stored in the end. THAT can be called stupid, no?

> Using "buf" the way the code used it meant that people whose native
> byte-order was big-endian would still be able to build images. Performance
> was never a big issue here, so it works fine. It may not be pretty, but I
> doubt beauty was a big issue either ;)

Agree 100%.

> The field never got extended because nobody really needed it extended.
> That's as simple as it can get, no?

No. When you have field 2 bytes in size and you want to store there number
bigger than $FFFF you MUST increase field. Otherwise what's the point ?
I'm little surprised nobody noticed it for so long :-(




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