[Crash-utility] question about phys_base

[Wen Congyang]

At 02/17/2012 12:30 AM, Dave Anderson Wrote:
> 
> 
> ----- Original Message -----
>>>
>>> OK, so then I don't understand what you mean by "may be the same"?
>>>
>>> You didn't answer my original question, but if I understand you  correctly,
>>> it would be impossible for the qemu host to create a PT_LOAD segment that
>>> describes an x86_64 guest's __START_KERNEL_map region, because the host
>>> doesn't know that what kind of kernel the guest is running.
>>
>> Yes. Even if the guest is linux, it is still impossible to do it.  Because
>> the guest maybe in the second kernel.
>>
>> qemu-dump walks all guest's page table and collect virtual address and
>> physical address mapping. If the page is not used by guest, the virtual is set
>> to 0.  I create PT_LOAD according to such mapping. So if the guest is linux,
>> there may be a PT_LOAD segment that describes __START_KERNEL_map region.
>> But the information stored in PT_LOAD maybe for the second kernel. If crash
>> uses it, crash will see the second kernel, not the first kernel.
> 
> Just to be clear -- what do you mean by the "second" kernel?  Do you
> mean that a guest kernel crashed guest, and did a kdump operation,
> and that second kdump kernel failed somehow, and now you're trying
> to do a "virsh dump" on the kdump kernel?

Yes, the second kernel means kdump kernel. If kdump failed, the user can
use it to dump the guest's memory.

Thanks
Wen Congyang

> 
> Dave
>