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

[Jan Kiszka]

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.

Jan

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