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

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

[Nicholas Amon]

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?

Thanks,

Nicholas

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

[Jan Kiszka]

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?

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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

[Jan Kiszka]

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

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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

[Jan Kiszka]

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
>>
>>   

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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

[Nicholas Amon]

Thanks Jan.  That fixed it.

Nicholas

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
>>>
>>>   
>>>       
>
>   

-- 
Nicholas Amon
Senior Software Engineer
Xceedium Inc.
Office: 201-536-1000 x127
Cell: 732-236-7698
namon@Xceedium.com

See How to Control & Track High-Risk Users: Join our Webinar on Tuesday, 
June 2
Network World Names Xceedium GateKeeper "RSA 2009 Best of Show"

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

[Nicholas Amon]

So now I can step instruction but my breakpoints do not work.  I have 
verified that disabling kvm restores the breakpoint functionality.  Any 
suggestions?

Thanks,

Nicholas

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
>>>
>>>   
>>>       
>
>   

-- 
Nicholas Amon
Senior Software Engineer
Xceedium Inc.
Office: 201-536-1000 x127
Cell: 732-236-7698
namon@Xceedium.com

See How to Control & Track High-Risk Users: Join our Webinar on Tuesday, 
June 2
Network World Names Xceedium GateKeeper "RSA 2009 Best of Show"

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

[Jan Kiszka]

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
>>>>
>>>>   
>>>>       

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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

[Nicholas Amon]

Jan Kiszka wrote:
> 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
>>>>>
>>>>>   
>>>>>       
>>>>>           
>
>   
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
See How to Control & Track High-Risk Users: Join our Webinar on Tuesday, 
June 2
Network World Names Xceedium GateKeeper "RSA 2009 Best of Show"