Help debugging domain builder, qemu upstream and hvmloader

Help debugging domain builder, qemu upstream and hvmloader

[Daniel Castro]

Hello All,

I run into this problem when I modify seabios.
(XEN) hvm.c:1131:d13 Triple fault on VCPU 0 - invoking HVM system reset.

Since there is no fault handlers in the early stages of guest boot I
am in the need to debug the domain builder, upstream qemu and/or
hvmloader to see where exactly the fault is being generated.

I have no experience on debugging and this seems like a good time to start.

Any pointers, or guides anyone can provide me will be of great help.
After this I will document the process for later uses.

PD: Xen is compiled with debugging on, so is qemu and seabios.

Thanks,

Daniel

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| |   | Daniel Castro,                |
| |   | Consultant/Programmer.|
| |   | U Andes                         |
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Re: Help debugging domain builder, qemu upstream and hvmloader

[Keir Fraser]

On 27/07/2011 04:53, "Daniel Castro" <evil.dani@gmail.com> wrote:

> Hello All,
> 
> I run into this problem when I modify seabios.
> (XEN) hvm.c:1131:d13 Triple fault on VCPU 0 - invoking HVM system reset.
> 
> Since there is no fault handlers in the early stages of guest boot I
> am in the need to debug the domain builder, upstream qemu and/or
> hvmloader to see where exactly the fault is being generated.

You can put 'on_reboot = preserve' in your domain config file so that the
crashed domain is not automatically destroyed and restarted. Then you can
use the tool xenctx to grab the register state including crashing EIP value.

 -- Keir

> I have no experience on debugging and this seems like a good time to start.
> 
> Any pointers, or guides anyone can provide me will be of great help.
> After this I will document the process for later uses.
> 
> PD: Xen is compiled with debugging on, so is qemu and seabios.
> 
> Thanks,
> 
> Daniel

Re: Help debugging domain builder, qemu upstream and hvmloader

[Wei Liu]

On Wed, 2011-07-27 at 12:53 +0900, Daniel Castro wrote:
> Hello All,
> 
> I run into this problem when I modify seabios.
> (XEN) hvm.c:1131:d13 Triple fault on VCPU 0 - invoking HVM system reset.
> 
> Since there is no fault handlers in the early stages of guest boot I
> am in the need to debug the domain builder, upstream qemu and/or
> hvmloader to see where exactly the fault is being generated.
> 
> I have no experience on debugging and this seems like a good time to start.

Ian Campbell once mentioned his trick to debug QEMU (following
paragraphs quoted from his email):

=====================================================================
When I have an issue with qemu I often specify the device model in my
guest configuration as a script containing:
       echo $@ > /tmp/qemu-dm
       sleep 1h

Then immediately after running "xl create" I can examine /tmp/qemu-dm
and run the qemu by hand in the foreground, or under gdb etc. (there is
a timeout in xl waiting for qemu to announce itself so you need to be
reasonably prompt...)
=====================================================================

Wei.

Re: Help debugging domain builder, qemu upstream and hvmloader

[Wei Liu]

Adding @xen-devel back in CC list.

On Wed, 2011-07-27 at 18:53 +0900, Daniel Castro wrote:
> > Ian Campbell once mentioned his trick to debug QEMU (following
> > paragraphs quoted from his email):
> >
> > =====================================================================
> > When I have an issue with qemu I often specify the device model in my
> > guest configuration as a script containing:
> >       echo $@ > /tmp/qemu-dm
> >       sleep 1h
> >
> > Then immediately after running "xl create" I can examine /tmp/qemu-dm
> > and run the qemu by hand in the foreground, or under gdb etc. (there is
> > a timeout in xl waiting for qemu to announce itself so you need to be
> > reasonably prompt...)
> > =====================================================================
> 
> Works perfectly, now I need to learn how to use gdb. Any good document
> comes to mind?
> 

Google helps a lot.

GDB manual is the best document I know.

Wei.