[Xen-devel] Question: Dynamic code in x86_64 Xen

["Santos, Jose Renato G" <joserenato.santos@xxxxxx>]

(Sorry, hit the send button too soon, in the last message)

Keir,

Could you please help me understand some Xen code profile 
that I cannot explain?
When running netperf on x86_64 Xen, oprofile reports that 2% 
of the PC samples are not recognized (i.e. they correspond 
to code outside the ".text" section reported on xen image 
file). I added some instrumentation in oprofile and observed 
that these PC samples are located in:
1) for dom0: in Xen BSS section (more specifically on cpu0_stack)
2) for domU: outside any section specified in Xen image file 
 (i.e. dynamically allocated memory)
 
I suspect case 2 is also a stack for a different CPU which 
is dynamically allocated (and used in the CPU that the guest 
is executing) but I am not sure...
 
Anyway, why whould Xen execute any code from the stack? Is 
this expected Xen behavior or this is a bug somewhere 
(probably in xenoprofile)?
I did not see this behavior in the past when I was using x86_32 Xen.
Could you please shed some light on this ...

Thanks

Renato
  
>> 

>> -----Original Message-----
>> From: Santos, Jose Renato G 
>> Sent: Tuesday, July 10, 2007 11:44 AM
>> To: 'Keir Fraser'
>> Subject: Question: Dynamic code in x86_64 Xen
>> 
>>  
>> Keir,
>> 
>> Could you please help me understand some Xen code profile 
>> that I cannot explain?
>> When running netperf on x86_64 Xen, oprofile reports that 2% 
>> of the PC samples are not recognized (i.e. they correspond 
>> to code outside the ".text" section reported on xen image 
>> file). I added some instrumentation in oprofile and observed 
>> that these PC samples are located in:
>> 1) for dom0: in Xen BSS section (more specifically on cpu0_stack)
>> 2) for domU: outside any section specified in Xen image file 
>> (i.e. dynamically allocated memory)
>> 
>> I suspect case 2 is also a stack for a different CPU which 
>> is dynamically allocated (and used in the CPU that the guest 
>> is executing) but I am not sure...
>> 
>> Anyway, why whould Xen execute any code from the stack? Is 
>> this expected Xen behavior or this is a bug somewhere 
>> (probably in xenoprofile)?
>> I did not see this behavior in the past when I was using x86_32 Xen.
>> Could you please
>>  
>> 

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