Re: Kernels > 1M

H. Peter Anvin (hpa@transmeta.com)
Sat, 07 Aug 1999 16:28:26 -0700

Riley Williams wrote:

> >> The reason for this is that the current kernel loader uses the
> >> value of a 16-bit unsigned int in the boot sector as the number
> >> of 16-byte paragraphs of kernel source to load, thus only
> >> supporting kernels of not more than 0xFFFF0 (1,048,560) bytes in
> >> size. Worse still, the value stored in this word is the lower 16
> >> bits of the calculated value, so if the kernel was, say,
> >> 0x107630 (1,078,832) bytes ( in size, the stored value would be
> >> 0x00763 paragraphs, or about 30k !!!
>
> > The kernel would work fine, *unless* you use the pathetically old
> > bootsect.S loader.
>
> True. Am I right in thinking that LILO still uses it?

I would be highly surprised if it was.

> > However, fixing that bug is a plus.
>
> Do you think there's any chance my patch as posted in the previous
> email will get in the kernel, will I need to repost it when the rest
> of the patch is finished and that bug is eradicated, or should I just
> forget about it as being something that's not worth doing?

Well, I have volunteered to Linus to make sure that some kind of
*complete* patch gets in, so presumably it will happen :) I, of course,
am completely happy not to do the work, so feel free to send me patches.

However, this is probably how you want to do the semantics for now:

If the size < 0xffff0
old_field := (size+15) >> 4
new_field := size
else
old_field := 0xffff
new_field := size

... and look at the new_field only if the old_field is 0xffff; that was
we maximize compatibility.

Not that I think it matters much.

-hpa

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!


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