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Subject: Re: [PATCH] kexec based hibernation: a prototype of kexec
	multi-stage load
From: "Huang, Ying" <ying.huang@intel.com>
To: Vivek Goyal <vgoyal@redhat.com>
CC: "Eric W. Biederman" <ebiederm@xmission.com>, Pavel Machek <pavel@ucw.cz>,
       nigel@nigel.suspend2.net, "Rafael J. Wysocki" <rjw@sisk.pl>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Kexec Mailing List <kexec@lists.infradead.org>
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Date: Fri, 16 May 2008 10:19:34 +0800
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On Thu, 2008-05-15 at 22:00 -0400, Vivek Goyal wrote:
[...]
> IMHO, this kind of make more sense to me when keeping C function like
> semantics in mind.
> 
> Both the cases can be treated like calls to functions (calling BIOS function
> and jumping to kernel B). The basic difference between two cases is the
> re-entry point. In BIOS function case, we always re-enter the function at the
> start but in case of kernel B, except first entry, all other entries happen
> at a run time determined address, which needs to be communicated to kernel A.
> 
> I would think that second kernel B just should execute "ret" and new entry
> address of kernel B is passed to kernel A through %eax (return value of
> function).

The disadvantage of this solution is that kernel B must know it is
original kernel (A) or kexeced kernel (B). Different code should be used
by kernel A and kernel B. And after jump from A to B, jump from B to A,
when jump from A to B again, kernel A must use different code from the
first time.

Best Regards,
Huang Ying