Re: [Fastboot] Re: Query: Kdump: Core Image ELF Format

From: Eric W. Biederman
Date: Thu Mar 10 2005 - 02:00:39 EST

Vivek Goyal <vgoyal@xxxxxxxxxx> writes:

> I want to fill the virtual addresses of linearly mapped region. That is
> physical addresses from 0 to MAXMEM (896 MB) are mapped by kernel at
> virtual addresses PAGE_OFFSET to (PAGE_OFFSET + MAXMEM). Values of
> PAGE_OFFSET and MAXMEM are already known and hard-coded.

PAGE_OFFSET has a common value of 0xc0000000, on x86. However
that value is by no means fixed. The 4G/4G split changes it
as do some other patches floating around at the time.
On x86-64 I don't know how stable those kinds of offsets are.

> I think I used the terminology kernel virtual address and that is adding
> to the confusion. Kernel virtual addresses are not necessarily linearly
> mapped. What I meant was kernel logical addresses whose associated
> physical addresses differ only by a constant offset.

I know what you meant. I simply meant that things don't look that
constant to me. Especially in Linux where there are enough people
to try most of the reasonable possibilities.

I don't even think it is a bad idea. But I do think we have a different
idea of what is constant.

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