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

Jan Kiszka
2010-01-22T15:06:28Z

Nicholas Amon wrote:
> 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