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

From: Wen Congyang <wency@cn.fujitsu.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
	qemu-devel <qemu-devel@nongnu.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	"Richard W.M. Jones" <rjones@redhat.com>
Subject: Re: [Qemu-devel] [Question] dump memory when host pci device is used by guest
Date: Thu, 20 Oct 2011 18:03:35 +0800	[thread overview]
Message-ID: <4E9FF1F7.7070104@cn.fujitsu.com> (raw)
In-Reply-To: <4E9FECE5.2000802@siemens.com>

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.

Thanks
Wen Congyang.

> 
> Thanks,
> Jan
> 