[lttng-dev] [PATCH lttng-ust] Add lttng_ust_notrace to static inline functions

[Woegerer, Paul]

Thanks for your feedback.

You made me think again how to address this issue from a different
angle. I found a nice practical solution.

Suppose you have a tracepoint provider:

ackermann_tracepoint.c + ackermann_tracepoint.h

To make the tracepoint provider robust against -finstrument-functions
you just need to change ackermann_tracepoint.c from:

#define TRACEPOINT_CREATE_PROBES
#include "ackermann_tracepoint.h"

to:

#pragma GCC optimize ("no-instrument-functions")
#define TRACEPOINT_CREATE_PROBES
#include "ackermann_tracepoint.h"

If you don't mind using _Pragma (C99)
(see: https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html)
we should be able to make this happen automatically (#ifdef
TRACEPOINT_CREATE_PROBES _Pragma ... )


--
Paul


On 07/07/2014 05:46 PM, Mathieu Desnoyers wrote:
> ----- Original Message -----
>> From: "Paul Woegerer" <Paul_Woegerer at mentor.com>
>> To: "Mathieu Desnoyers" <mathieu.desnoyers at efficios.com>
>> Cc: lttng-dev at lists.lttng.org
>> Sent: Monday, July 7, 2014 11:34:19 AM
>> Subject: Re: [PATCH lttng-ust] Add lttng_ust_notrace to static inline functions
>>
>> On 07/07/2014 04:57 PM, Mathieu Desnoyers wrote:
>>> Merged into master and stable-2.4, thanks!
>>
>> Thanks !
>>
>> Hmmm ... but what to do about static inline function cds_list_empty
>> (included via lttng/ust-tracepoint-event.h -> urcu/rculist.h ->
>> urcu/list.h). Would you accept a patch that introduces rcu_cds_notrace
>> in urcu/compiler.h + respective changes in urcu/*.h ?
> 
> It starts to look like a cat and mouse game honestly. Especially if
> we consider "contexts", those can call external functions, which might
> not have notrace attribute.
> 
> I think the proper solution here would be to use a per-thread nesting
> value, and check it in the finstrument-function callback, and return
> immediately if we are nested.
> 
> Thoughts ?
> 
> Thanks,
> 
> Mathieu
> 
>>
>> --
>> Paul
>>
>>>
>>> Mathieu
>>>
>>> ----- Original Message -----
>>>> From: "Paul Woegerer" <paul_woegerer at mentor.com>
>>>> To: lttng-dev at lists.lttng.org, "mathieu desnoyers"
>>>> <mathieu.desnoyers at efficios.com>
>>>> Cc: "Paul Woegerer" <paul_woegerer at mentor.com>
>>>> Sent: Monday, July 7, 2014 10:04:21 AM
>>>> Subject: [PATCH lttng-ust] Add lttng_ust_notrace to static inline
>>>> functions
>>>>
>>>> The static inline functions
>>>> __tracepoint_provider_mismatch_<TRACEPOINT_PROVIDER> and
>>>> __tracepoint_provider_check_<TRACEPOINT_PROVIDER> are missing the
>>>> lttng_ust_notrace attribute to prevent them from getting instrumented
>>>> with -finstrument-functions (if e.g. defined in CFLAGS). This patch is
>>>> adding the attribute to those functions.
>>>>
>>>> Signed-off-by: Paul Woegerer <paul_woegerer at mentor.com>
>>>> ---
>>>>  include/lttng/ust-tracepoint-event.h | 4 ++++
>>>>  1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/include/lttng/ust-tracepoint-event.h
>>>> b/include/lttng/ust-tracepoint-event.h
>>>> index d12e8bb..8895310 100644
>>>> --- a/include/lttng/ust-tracepoint-event.h
>>>> +++ b/include/lttng/ust-tracepoint-event.h
>>>> @@ -75,6 +75,8 @@
>>>>  /* Reset all macros within TRACEPOINT_EVENT */
>>>>  #include <lttng/ust-tracepoint-event-reset.h>
>>>>  
>>>> +static inline lttng_ust_notrace
>>>> +void _TP_COMBINE_TOKENS(__tracepoint_provider_mismatch_,
>>>> TRACEPOINT_PROVIDER)(void);
>>>>  static inline
>>>>  void _TP_COMBINE_TOKENS(__tracepoint_provider_mismatch_,
>>>>  TRACEPOINT_PROVIDER)(void)
>>>>  {
>>>> @@ -88,6 +90,8 @@ void _TP_COMBINE_TOKENS(__tracepoint_provider_mismatch_,
>>>> TRACEPOINT_PROVIDER)(vo
>>>>  #define TRACEPOINT_EVENT_INSTANCE(_provider, _template, _name, _args)	\
>>>>  	__tracepoint_provider_mismatch_##_provider();
>>>>  
>>>> +static inline lttng_ust_notrace
>>>> +void _TP_COMBINE_TOKENS(__tracepoint_provider_check_,
>>>> TRACEPOINT_PROVIDER)(void);
>>>>  static inline
>>>>  void _TP_COMBINE_TOKENS(__tracepoint_provider_check_,
>>>>  TRACEPOINT_PROVIDER)(void)
>>>>  {
>>>> --
>>>> 2.0.1
>>>>
>>>>
>>>
>>
>>
>> --
>> Paul Woegerer, SW Development Engineer
>> Sourcery Analyzer <http://go.mentor.com/sourceryanalyzer>
>> Mentor Graphics, Embedded Software Division
>>
> 


-- 
Paul Woegerer, SW Development Engineer
Sourcery Analyzer <http://go.mentor.com/sourceryanalyzer>
Mentor Graphics, Embedded Software Division