lgdt from real mode

[lg]

Hi,
one question about GDT's, hope it's not too stupid
but couldn't really find the answer in intel's documentation.
If i execute lgdt [addr] from real mode, addr specifies the 16 bit offset of the descriptor-like
thingy that points to the GDT, right?
But it's an offset relative to WHICH segment register?
Is it safe to assume DS?

lg

[Guest]

>On 2001-06-18 16:22:08, lg wrote:
>Hi,
>one question about GDT's, hope it's not too stupid
>but couldn't really find the answer in intel's documentation.
>If i execute lgdt [addr] from real mode, addr specifies the 16 bit offset of the descriptor-like
>thingy that points to the GDT, right?
>But it's an offset relative to WHICH segment register?
>Is it safe to assume DS?

LGDT operates the same in real mode and pmode:
lgdt m16&32

From my blue book:
LGDT: loads a linear base address and limit
value from a six-byte data oeprand in memory
into GDTR.

Hope that helps
j.weeks

[Chris Giese]

>On 2001-06-18 16:22:08, lg wrote:
>If i execute lgdt [addr] from real mode, addr specifies the 16 bit offset of the descriptor-like
>thingy that points to the GDT, right?

Correct.

>But it's an offset relative to WHICH segment register?
>Is it safe to assume DS?

Yes, it's DS.

--
geezer@ | pmode tutorial, homebrew OS:
execpc.com | http://www.execpc.com/~geezer/os

[Guest]

Thank you everybody :^)

[Crystalline]

>On 2001-06-18 16:22:08, lg wrote:
>Hi,
>one question about GDT's, hope it's not too stupid
>but couldn't really find the answer in intel's documentation.
>If i execute lgdt [addr] from real mode, addr specifies the 16 bit offset of the descriptor-like
>thingy that points to the GDT, right?
>But it's an offset relative to WHICH segment register?
>Is it safe to assume DS?
>
>lg

In my experience its not safe to assume anything, you should always use overrides, but
if you dont override it will usually assume DS