[Crash-utility] question about phys_base

[Wen Congyang]

At 02/28/2012 02:30 PM, HATAYAMA Daisuke Wrote:
> From: Wen Congyang <wency at cn.fujitsu.com>
> Subject: Re: [Crash-utility] question about phys_base
> Date: Tue, 28 Feb 2012 13:10:38 +0800
> 
>> At 02/27/2012 10:10 PM, Dave Anderson Wrote:
> 
>>>> The guest is in the second kernel(vcpu > 1)
>>>> ]# readelf /tmp/vm2.save2 -l| grep 0xffffffff8
>>>>   LOAD           0x0000000001017be0 0xffffffff81000000 0x0000000001000000
>>>>   LOAD           0x0000000001017be0 0xffffffff81000000 0x0000000001000000
>>>>   LOAD           0x0000000001017be0 0xffffffff81000000 0x0000000001000000
>>>>   LOAD           0x0000000004017be0 0xffffffff81000000 0x0000000004000000
>>>
>>> Again, it's not clear why there are multiple segments with the same
>>> same virtual address, but I'm guessing that the one segment that starts 
>>> at 0x0000000004000000 is associated with the second kernel, and the other
>>> ones are for vcpus that ran in the first kernel?
>>>  
>>>> The guest is in the second kernel(vcpu = 1)
>>>> [root at ghost ~]# readelf /tmp/vm2.save3 -l| grep 0xffffffff8
>>>>   LOAD           0x0000000004001e4c 0xffffffff81000000 0x0000000004000000
>>>>
>>>> I donot find differentiate qemu-genetated ELF headers from dump-generated ELF
>>>> headers.
>>>
>>> Kdump-generated vmcores cannot have multiple START_KERNEL_map segments.
>>> But with dumps where (vpcu = 1), there could be confusion since it's not obvious
>>> if START_KERNEL_map region belongs to the first or second kernel.  
>>>
>>> That being the case, I don't see how this can be supported cleanly by the crash'
>>> utility unless there is a NOTE, or some other obvious identifier, that absolutely
>>> confirms that the dumpfile was qemu-generated.
>>
>> The note information stored in qemu-generated core:
>> Program Headers:
>>   Type           Offset             VirtAddr           PhysAddr
>>                  FileSiz            MemSiz              Flags  Align
>>   NOTE           0x000000000000edd0 0x0000000000000000 0x0000000000000000
>>                  0x0000000000000590 0x0000000000000590         0
>>
>> I think its format is the same as kdump's vmcore. Does kdump-generated core's
>> virtaddr is always 0? If so, What about to set virt_addr to -1 in qemu-generated
>> core?
>>
> 
> In general, such characteristic should not be used. You should prepare
> a solid interface. Even if using them, it should be limited to as
> workaround to avoid some issue.
> 
> Why not use qemu's CPU state? Include it as note information with good
> name, and we can use it to distinguish which. Like:
> 
> $ readelf -n vmcore
> 
> Notes at offset 0x000001c8 with length 0x00000838:
>   Owner         Data size       Description
>   CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>   CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>   QEMU          0x00000557      Unknown note type: (0x00000000)
> 
> Or QEMUCPUState is better?

Good idea. I will try it, and hope gdb can also work.

Thanks
Wen Congyang


> 
> Thanks.
> HATAYAMA, Daisuke
> 
>