RE: logical, linear, physical addresses

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From: Shakthi Kannan <shakthimaan@xxxxxxxxx>
Reply-To: Shakthi Kannan <shakthimaan@xxxxxxxxx>
To: kernelnewbies@xxxxxxxxxxxx
Subject: logical, linear, physical addresses
Date: Fri, 5 Nov 2004 22:11:22 +0530

Greetings!

I need some real-time example (with values) for x86 architecture
illustrating the relationship between logical, linear and physical
addresses.

I did go through Chapter 2 of Understanding the Linux kernel, and
Operating Systems by Harvey Deitel.

1/
I understand in the process of logical to linear address translation
that segment selector (in segment registers) points to a segment
descriptor in LDT/GDT. Within the segment descriptor we choose
base+limit to get the linear address. But, what does this base address
contain? How is it assigned? ------ (1)

Similarily, I understand that linear address is translated into
physical address through page tables, and the linear address consists
of page frame number and offset. ---- (2)

But, I don't see how the output of (1) corresponds to the input of
(2). What am I missing here? Most books explain only these concepts
rather than give a real-time example. Any pointers in this regard will
be helpful.

2/
If the base (0x00000000) in the segment descriptor is the same for the
different kernel segments, (code, data, et. al.)  it will overlap in
the linear address space. But, how can we access them separately if
they start from the same address location?

Any clarification will be really helpful.

Thanks,

Shaks

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