Re: Unable to single-step in kvm, always results in a resume

Nicholas Amon
2010-01-29T03:51:33Z

>> So now I can step instruction but my breakpoints do not work. I have
>> verified that disabling kvm restores the breakpoint functionality. Any
>> suggestions?
>>
>
> What kind of breakpoints, hardware-assisted or normal BPs? Are you
> trying to break into real-mode code (as stated below - BTW, top-postings
> should be avoided!) that happens to run on a non-brand-new Intel host? I
> never fully tested how well guest debugging works if KVM has to emulate
> instructions, and I wouldn't be surprised if there are "limitations".
>
> Jan
>
>
>> Jan Kiszka wrote:
>>
>>> Hi Nicholas,
>>>
>>> please don't drop CCs on reply.
>>>
>>> Nicholas Amon wrote:
>>>
>>>
>>>> Hi Jan,
>>>>
>>>> Thanks for responding. Yes, I am able to step instruction when I
>>>> disable kvm w/ the no-kvm option. My host kernel is 64bit 2.6.27 and
>>>> the program that I am debugging is 32 bit but starts in real mode. But
>>>> the KVM module I am running is from kvm-88. Is there anyway I can check
>>>> the version definitively?
>>>>
>>>>
>>> kvm modules issue a message when being loaded, check your kernel log.
>>> qemu-kvm gives you the version via -version.
>>>
>>> OK, the problems you see is likely related to the very old versions you
>>> use. Update to recent kvm-kmod (2.6.32 series) and qemu-kvm (0.12
>>> series) and retry.
>>>
>>> Jan
>>>
>>>
>>>
>>>> Thanks,
>>>>
>>>> Nicholas
>>>>
>>>> Jan Kiszka wrote:
>>>>
>>>>
>>>>> Jan Kiszka wrote:
>>>>>
>>>>>
>>>>>
>>>>>> Nicholas Amon wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Hi All,
>>>>>>>
>>>>>>> I am trying to single-step through my kernel using qemu and kvm. I have
>>>>>>> run qemu via: qemu-system-x86_64 -s -S -hda
>>>>>>> /home/nickamon/lab1/obj/kernel.img and also connected to the process
>>>>>>> using gdb.
>>>>>>>
>>>>>>> Problem is that whenever I try and step instruction, it seems to resume
>>>>>>> my kernel rather than allowing me to progress instruction by
>>>>>>> instruction. I have built the kvm snapshot from git and still no luck.
>>>>>>> Tried following the code for a few hours and have no luck. Any
>>>>>>> suggestions?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> What's you host kernel or kvm-kmod version?
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> ...and does -no-kvm make any difference (except that it's much slower)?
>>>>>
>>>>> Jan
>>>>>
>>>>>
>>>>>
>>>>>
>
>
My apologies for the late response. Normal breakpoints and yes I am
breaking in real mode. This isn't a big issue for me since I am able to
break when I disable kvm. So basically I disable kvm when I want to
debug and enable it during normal execution. Thanks for all your help.

Nick

Nicholas Amon
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