Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load

From: ebiederm@xmission.com (Eric W. Biederman)
To: "Huang, Ying" <ying.huang@intel.com>
Cc: nigel@nigel.suspend2.net,
	Kexec Mailing List <kexec@lists.infradead.org>,
	linux-kernel@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
	Pavel Machek <pavel@ucw.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load
Date: Thu, 15 May 2008 19:25:00 -0700	[thread overview]
Message-ID: <m14p8zgf43.fsf@frodo.ebiederm.org> (raw)
In-Reply-To: <1210902114.23707.156.camel@caritas-dev.intel.com> (Ying Huang's message of "Fri, 16 May 2008 09:41:54 +0800")

"Huang, Ying" <ying.huang@intel.com> writes:

> On Thu, 2008-05-15 at 11:39 -0700, Eric W. Biederman wrote:
> [...]
>> 2) After we figure out our address read the stack pointer from
>>    a fixed location and simply set it.  (This is my preference)
>
> Just for confirmation (My English is poor).
>
> Do you mean that kernel A just read the stack top as re-entry point,
> regardless of whether it is return address or argument 1?

What I was thinking was:

In kernel A()

relocate_new_kernel:

        ...

        call	*%eax

kexec_jump_back_entry:
        /* This code should be PIC so figure out where we are */
        call	1f
1:
        popl	%edi
        subl	$(1b - relocate_kernel), %edi

        /* Setup a safe stack */
        leal    PAGE_SIZE(%edi), %esp
        ...

Then in purgatory we can read the address of kexec_jump_back_entry
by examining 0(%esp) and export it in whatever fashion is sane.

However we reach kexec_jump_back_entry we should be fine.

Eric

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