Re: [Xen-devel] Unable to create guest PV domain on OMAP5432

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 17 November 2017 at 12:15, Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx> wrote:
> Hi Jayadev,
>
> On 17 November 2017 at 13:53, Andrii Anisov <andrii_anisov@xxxxxxxx> wrote:
>>>
>>> Is there a way to debug which one of the above two possibilities has lead
>>> to the issue ?
>>
>> Four years ago I did it in a following way:
>>     - wire up to UART2 pins on an expansion connector (this sheet might be
>> useful for you: http://www.ti.com/lit/ug/swcu130/swcu130.pdf)
>>     - assign UART2 IOMEM ranges to DomU
>>     - enable in domu kernel earlyprintk and patch it to output to omap UART2
>>
>> Nowadays assigning UART2 IOMEM ranges might be a bit more complex due to XEN
>> evolution.
>>
>> Another way is to use JTAG which understands virtualization, and allows you
>> to debug DomU.
> I want to add some debugging techniques:
>  - By tapping CTRL+A three times to switch to XEN console. Then `d`
> will show you CPU register states. You will be able to see where your
> DomU executes right now. This can help along with addr2line, objdump
> and other tools.
>
>  - You can modify traps.c in XEN to crash domain when SMC instruction
> is trapped. Then you can put SMC invocation into various parts of
> kernel code, to see if it reaches that place. This can help on early
> stages, when console is not available.

No need for modifying the Xen. Xen already provides debug facilities when
CONFIG_DEBUG=y.

You can have a look at do_debug_trap. The ones you likely want are:

  - hvc 0xffff will show the state of the vCPU
  - hvc 0xfffe will print the PC

Cheers,

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