should kernel image destination address be picked up by kernel itself?

[Ming Lei]

Hi Eric,

Do you know what's this purgatory directory for? I saw it is linked with
kexec in a weird way.

Another note for current code base is that there is merged directory
arch/powerpc since linux kernel 2.6.23, but kexec-tools still has ppc
and ppc64 separated. Is there anyone working on this merged arch?

Thanks
Ming


-----Original Message-----
From: Eric W. Biederman [mailto:ebiederm at xmission.com] 
Sent: Tuesday, February 03, 2009 1:43 PM
To: Ming Lei
Cc: kexec at lists.infradead.org
Subject: Re: should kernel image destination address be picked up by
kernel itself?

"Ming Lei" <mlei at Brocade.COM> writes:

> Hi Eric,
>
> I tried run latest kexec-tools v2.0 on ppc freescale 85xx platforms.
>
>>- All of the policy decisions are made in user space (such as where to
>>  execute from)
> Is where to execute from the physical address or the virtual address?
> How do we know it is available to kexec, it may be taken.

It should be physical and there should be an API in linux like
/proc/iomem which will report which addresses are memory.  ppc
is a little different than x86 so I'm not up to speed on how it
reports things.  I think it is with the device tree.

>>- standalone executables are loaded into an address space where
>>  physical address and virtual address are the same.
> There may be case that physical address and virtual address not the
same
> on linux, such as vmalloc.

In the environment that kexec exports there should not be any.

>>What problem do you see in that model?
>>Why is it a problem for you?
>
> Can we put something like -1 to indicate to kernel that user space
wants
> kernel to choose the virtual address to load the standalone
executable,
> then linux kernel can kmalloc this area and then load the standalone
> executable.

You can do something like create a proper static ET_DYN executable and
then 
/sbin/kexec will look for an address and load it there.

Eric