[Crash-utility] Re: crash with Xen dom0 image from kdump

[Kazuo Moriwaka]

Hello,

From: Dave Anderson <anderson at redhat.com>
Subject: Re: crash with Xen dom0 image from kdump
Date: Fri, 02 Jun 2006 09:28:07 -0400

> Kazuo Moriwaka wrote:
> 
> > Hello Dave,
> > # I append crash-utility list to Cc
> >
> > From: Dave Anderson <anderson at redhat.com>
> > Subject: Re: crash with Xen dom0 image from kdump
> > Date: Thu, 01 Jun 2006 08:39:01 -0400
> >
> > > Kazuo Moriwaka wrote:
> > >
> > > > Hello,
> > > >
> > > > From: Dave Anderson <anderson at redhat.com>
> > > > Subject: Re: crash with Xen dom0 image from kdump
> > > > Date: Wed, 31 May 2006 16:20:15 -0400
> > > >
> > > > >
> > > > > Hey guys,
> > > > >
> > > > > I've got the vmcore file from which Kazuo generated the
> > > > > "simulated" xendump dumpfile.  I have a question regarding
> > > > > the makeup of the the vmcore file -- are the physical addresses
> > > > > referred to by each PT_LOAD segment based upon:
> > > > >
> > > > > 1. machine addresses, or
> > > > > 2. pseudo-physical addresses as perceived by the dom0 vmlinux kernel?
> > > > >
> > > > > Dave
> > > >
> > > > It's 1.
> > > > vmcore is made by kexec-ed linux kernel (not on xen, but on machine) kdump.
> > > > The kernel doesn't know about xen or domains except register info.
> > > > Register info is for dom0.
> > > >
> > >
> > > Ok, good...
> > >
> > > Next question -- how did you find dom0's phys_to_machine_mapping[]
> > > array from the vmcore in order to create the xendump?
> >
> > I use xen executable binary with symbols to find 'dom0' global symbol
> > in xen.
> > In x86_32 arch, dom0->vcpu[0].arch->guest_table has pagetable address
> > for domain0 guest kernel.
> > After it, I found 'phys_to_machine_mapping'.
> > For other domains, 'domain_list' is point list of struct domain.
> >
> > I'll attach my latest dom0cut script.  'dom0cut_x86_32.py' contains
> > names of symbols and structs to get dom0 image.
> 
> The problem is that we're just going to want to work with the
> /proc/vmcore and vmlinux file as always.  Having to drag the xen
> executable binary into the picture should be unnecessary.
> 
> With a xendump, the phys_to_machine_mapping array can be
> found by following the page tables from any of the cr3 values
> found in the dump header.

Yes. It's enough to read dom0. 
I hoped that treating xen exec in this stage makes 
smooth path to support xen hypervisor, but embedding cr3 of dom0 
seems considerable shortcut for dom0 crash analysis.

> It would seem simple enough to have the xen/kdump code store
> a legitimate dom0 cr3 value somewhere in the ELF header.  Would
> that be possible to explore?  Note that I'm not really interested

Now the vmcore doesn't have cr3 values in header. It needs some 
changes for dump.

> in the other guest domains, at least at this point, but I could see
> it potentially helpful to recreate the crash environment for the
> guest domains as well, so perhap an array of per-domain cr3
> values in an ELF header note section would be possible?

I think writing cr3 values can be done.
But I'm not clear about restrictions around making dump images,
Horms can answer this question.

regards,
-- 
Kazuo Moriwaka <moriwaka at valinux.co.jp>