Re: [PATCH] Fix GDT limit in setup.S for 2.0 and 2.2

[Richard B. Johnson]

Sorry about my last response. I noticed from the code, that
the LGDT instruction isn't pointing to where I though it
was.

The first  WORD (16-bit int) that the LGDT points to
is supposed to be the byte-length -1 of the real GDT.
The next WORD is supposed to be the low address of the
physical location of the real GDT and the next WORD is
supposed to be the high address of the physical location
of the read GDT.

In the subject code, the real GDT is only 32 bytes in length,
the variable you are changing truly should only be 0x1f, the
length of the GDT - 1.


Earlier on, I just grabbed your patch and found my kernel
wouldn't boot (with 0x800) as the length. This was
probably because the current 0x8000, when loaded, creates
some kind of alias that lets it work, but changing it to
0x800 removes that alias. Anyway, I am about to boot
this system with a mere 0x1f in that entry and see if
it even boots.......


On Mon, 23 Feb 2004, Richard B. Johnson wrote:

> On Mon, 23 Feb 2004, Coywolf Qi Hunt wrote:
>
> > Hello,
> >
> > I posted this problem days ago. Just now I check FreeBSD code and find
> > theirs code goes no this problem. Please take my patches for 2.0 and 2.2
> > 2.4 patch have been already sent to Anvin.
> >
> > (patches for 2.0 and 2.2 enclosed)
> >
> >
> > 	Coywolf
> >
>
> Please review pages 5-10 thru 5-11 or the Intel 484 Programmer's
> Reference manual and then tell me what you think you are doing.
>
> Screwing around with that GDT will cause large kernels, i.e.,
> kernels that have RAM disks, to fail to load. I already explained
> what the elements in the GDT mean. You seem to think you know
> more than those at Intel who wrote the book.
>
> As the text in page 5-11 shows, if the granularity bit is '1'
> The limit value is from 4 kilobytes to 4 gigabytes in increments
> of 4K bytes. You just set that value to 2048 * 4096 = 8,388,608 bytes.
> This means I can't load a 10 megabyte RAM disk. Stop screwing
> with the startup code, you absolutely-positively don't have a clue
> what you are doing.
>
>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips).
>             Note 96.31% of all statistics are fiction.
>
>
>

Cheers,
Dick Johnson
Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips).
            Note 96.31% of all statistics are fiction.


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