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

[Eric W. Biederman]

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.

Eric
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