Re: [Qemu-devel] [Question] dump memory when host pci device is used by guest

[Wen Congyang]

At 10/21/2011 03:11 PM, Jan Kiszka Write:
> On 2011-10-20 12:03, Wen Congyang wrote:
>> At 10/20/2011 05:41 PM, Jan Kiszka Write:
>>> On 2011-10-20 03:22, Wen Congyang wrote:
>>>>>> I didn't read full story but 'crash' is used for investigating kernel 
>>>>>> core generated
>>>>>> by kdump for several years. Considering support service guys, virsh dump 
>>>>>> should support
>>>>>> a format for crash because they can't work well at investigating vmcore 
>>>>>> by gdb.
>>>>>>
>>>>>> crash has several functionality useful for them as 'show kerne log', 
>>>>>> 'focus on a cpu'
>>>>>> 'for-each-task', 'for-each-vma', 'extract ftrace log' etc.
>>>>>>
>>>>>> Anyway, if a man, who is not developper of qemu/kvm, should learn 2 
>>>>>> tools for
>>>>>> investigating kernel dump, it sounds harmful.
>>>>>
>>>>> Right, that's why everything (live debugging & crash analysis) should be
>>>>> consolidated on the long run over gdb. crash is architecturally obsolete
>>>>> today - not saying it is useless!
>>>>
>>>> I do not know why crash is obsoleted today. Is there a new better tool to 
>>>> instead
>>>> crash?
>>>
>>> I'm not aware of equally powerful (python) scripts for gdb as
>>> replacement, but I think it's worth starting a porting effort at some point.
>>>
>>>>
>>>> At least, I always use crash to live debugging & crash analysis.
>>>
>>> Then you may answer some questions to me:
>>>  - Can you attach to a remote target (kgdb, qemu, etc.) and how?
>>
>> No. crash's live debugging only can work the kernel is live. I can use it get
>> some var's value, or some other information from kernel. If kernel panics,
>> we can use gdb to attach to a remote target as you said. But on end user 
>> machine,
>> we can not do it, we should dump the memory into a file and analyze it in 
>> another
>> machine while the end user's guest can be restart.
>>
>>>  - Can you use it with latest gdb versions or is the gdb functionality
>>>    hard-wired due to an embedded gdb core in crash (that's how I
>>>    understood Christoph's reply to this topic)
>>
>> If I use crash, I can not use latest gdb versions. Do we always need to use
>> the latest gdb versions? Currently, gdb-7.0 is embedded into crash, and it
>> is enough to me. If the gdb embedded into crash cannot anaylze the vmcore, I
>> think we can update it and rebuild crash.
> 
> crash is simply designed the wrong way around (from today's
> perspective): it should augment upstream gdb instead of forking it.

Cc Dave Anderson. He knows how crash uses gdb.

I think that crash does not fork a task to execute gdb, and gdb is a part of 
crash.

Thanks
Wen Congyang

> 
> Jan
>