help with porting perf lkm to later kernel

help with porting perf lkm to later kernel

[Chris Freehill]

Hello,

I am trying to get my linux kernel module that extends perf support to
work in a later kernel version. The lkm had been working in 3.0.51.

In the new target kernel to which I am trying to port, 3.8.13, I get
warnings at the modpost stage complaining about symbols that can no
longer be found. If I attempt to load that module, I get errors saying
the same thing (those symbols can't be found).

The symbols that can't be found are

".perf_pmu_enable"
".perf_event_update_userpage"
".perf_pmu_disable"
".perf_event_overflow"
".perf_pmu_unregister"
".perf_pmu_register"

Does anyone have any tips or advice as to how code that calls these
previously working functions should now be handled when built against
later kernels?

Chris

help with porting perf lkm to later kernel

[Chris Freehill]

Another way to ask this, is why are these symbols no longer exported
(previously exported in core.c with EXPORT_SYMBOL_GPL), and how are
people who built lkm's using the previously existing interface
supposed to port them? Is it perhaps documented somewhere? I have not
been able to find this via google or in git comments.

Is this the wrong forum for this question (which I grant may be a
"newbie" question), or is there just no good answer?

thanks,
chris


> I am trying to get my linux kernel module that extends perf support to work
> in a later kernel version. The lkm had been working in 3.0.51.
>
> In the new target kernel to which I am trying to port, 3.8.13, I get
> warnings at the modpost stage complaining about symbols that can no longer
> be found. If I attempt to load that module, I get errors saying the same
> thing (those symbols can't be found).
>
> The symbols that can't be found are
>
> ".perf_pmu_enable"
>
> ".perf_event_update_userpage"
>
> ".perf_pmu_disable"
>
> ".perf_event_overflow"
>
> ".perf_pmu_unregister"
>
> ".perf_pmu_register"
>
> Does anyone have any tips or advice as to how code that calls these
> previously working functions should now be handled when built against later
> kernels?

Re: help with porting perf lkm to later kernel

[David Ahern]

[Added Ingo, Peter and Arnaldo for opinions on the symbol exports - or 
lack of]

On 8/28/13 4:53 PM, Chris Freehill wrote:
> Another way to ask this, is why are these symbols no longer exported
> (previously exported in core.c with EXPORT_SYMBOL_GPL), and how are
> people who built lkm's using the previously existing interface
> supposed to port them? Is it perhaps documented somewhere? I have not
> been able to find this via google or in git comments.
>
> Is this the wrong forum for this question (which I grant may be a
> "newbie" question), or is there just no good answer?
>
> thanks,
> chris
>
>
>> I am trying to get my linux kernel module that extends perf support to work
>> in a later kernel version. The lkm had been working in 3.0.51.
>>
>> In the new target kernel to which I am trying to port, 3.8.13, I get
>> warnings at the modpost stage complaining about symbols that can no longer
>> be found. If I attempt to load that module, I get errors saying the same
>> thing (those symbols can't be found).
>>
>> The symbols that can't be found are
>>
>> ".perf_pmu_enable"
>>
>> ".perf_event_update_userpage"
>>
>> ".perf_pmu_disable"
>>
>> ".perf_event_overflow"
>>
>> ".perf_pmu_unregister"
>>
>> ".perf_pmu_register"
>>
>> Does anyone have any tips or advice as to how code that calls these
>> previously working functions should now be handled when built against later
>> kernels?
> --
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Re: help with porting perf lkm to later kernel

[Peter Zijlstra]

On Wed, Aug 28, 2013 at 05:04:27PM -0600, David Ahern wrote:
> On 8/28/13 4:53 PM, Chris Freehill wrote:
> >>I am trying to get my linux kernel module that extends perf support to work
> >>in a later kernel version. The lkm had been working in 3.0.51.
> >>
> >>In the new target kernel to which I am trying to port, 3.8.13, I get
> >>warnings at the modpost stage complaining about symbols that can no longer
> >>be found. If I attempt to load that module, I get errors saying the same
> >>thing (those symbols can't be found).
> >>
> >>The symbols that can't be found are
> >>
> >>".perf_pmu_enable"
> >>
> >>".perf_event_update_userpage"
> >>
> >>".perf_pmu_disable"
> >>
> >>".perf_event_overflow"
> >>
> >>".perf_pmu_unregister"
> >>
> >>".perf_pmu_register"
> >>
> >>Does anyone have any tips or advice as to how code that calls these
> >>previously working functions should now be handled when built against later
> >>kernels?

# git show v3.0:kernel/events/core.c | grep EXPORT_SYMBOL
EXPORT_SYMBOL_GPL(perf_event_release_kernel);
EXPORT_SYMBOL_GPL(perf_event_read_value);
EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);
EXPORT_SYMBOL_GPL(perf_tp_event);
EXPORT_SYMBOL_GPL(perf_event_create_kernel_counter);

IOW. how can your module have ever used those functions in 3.0 ?

Typically the answer to 'why did the export get removed' is simply
'because there are no users'.

help with porting perf lkm to later kernel

[Chris Freehill]

>> >>previously working functions should now be handled when built against later
>> >>kernels?
>
> # git show v3.0:kernel/events/core.c | grep EXPORT_SYMBOL
> EXPORT_SYMBOL_GPL(perf_event_release_kernel);
> EXPORT_SYMBOL_GPL(perf_event_read_value);
> EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
> EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
> EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);
> EXPORT_SYMBOL_GPL(perf_tp_event);
> EXPORT_SYMBOL_GPL(perf_event_create_kernel_counter);
>
> IOW. how can your module have ever used those functions in 3.0 ?
>
> Typically the answer to 'why did the export get removed' is simply
> 'because there are no users'.
>

Thanks Peter and David. You set me on the right path.

Your answer made me check...surely enough, the kernel I had been using
was (unexpectedly to me) patched to export those symbols. I realize in
hindsight I should have checked that first.

Thanks again,
Chris