From: Olivier Dion via lttng-dev <lttng-dev@lists.lttng.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: lttng-dev <lttng-dev@lists.lttng.org>
Subject: Re: [lttng-dev] [PATCH lttng-ust] Add ctor/dtor priorities for tracepoints/events
Date: Mon, 13 Jul 2020 11:19:18 -0400 [thread overview]
Message-ID: <87r1tfxx1l.fsf@clara> (raw)
Message-ID: <20200713151918.RW68IL5cy6OMyLSW4lUW8oKXyqTqER5ajaZQPNpD6vQ@z> (raw)
In-Reply-To: <1851244021.9798.1594646692671.JavaMail.zimbra@efficios.com>
On Mon, 13 Jul 2020, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> ----- On Jul 12, 2020, at 11:49 AM, Olivier Dion olivier.dion@polymtl.ca wrote:
>
>> On Sun, 12 Jul 2020, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
>>> ----- On Jul 11, 2020, at 11:29 AM, lttng-dev lttng-dev@lists.lttng.org wrote:
>>>
>>>> Some library might want to generate events in their ctor/dtor. If
>>>> LTTng initialize/finalize its tracepoints/events at the wrong time,
>>>> events are lost.
>>>>
>>>> Order of execution of the ctor/dtor is determined by priority. When
>>>> some priorities are equal, the order of execution seems to be
>>>> determined by:
>>>>
>>>> a) Order of appearance if in the same compilation unit
>>>>
>>>> b) Order of link if in different compilation units
>>>>
>>>> c) Order of load by ld-linux.so or dlopen(3) for
>>>> share objects
>>>
>>> I recall different rules about constructor priorities. Can you provide
>>> links to documentation stating the priority order you describe above ?
>>
>> I haven't found any documentation on that. This is purely empirical.
>> Although I'm sure that we can dig something if chatting on GCC's IRC.
>
> If it is not documented, then I am reluctant on depending on a behavior
> which may be what happens today, but may not be the same for past/future
> toolchains.
Agree.
>>> Also, we should compare two approaches to fulfill your goal:
>>> one alternative would be to have application/library constructors
>>> explicitly call tracepoint constructors if they wish to use them.
>>
>> I would prefer this way. The former solution might not work in some
>> cases (e.g. with LD_PRELOAD and priority =101) and I prefer explicit
>> initialization in that case.
>>
>> I don't see any cons for the second approach, except making the symbols
>> table a few bytes larger. I'll post a patch soon so we can compare and
>> try to find more documentation on ctor priority.
>
> And users will have to explicitly call the constructor on which they
> depend, but I don't see it as a huge burden.
The burden is small indeed. But users should pay close attention to
release the references in a destructor too.
> Beware though that there are a few configurations which can be used for
> probe providers (see lttng-ust(3)).
I'm not following you here. I don't see any configuration for provider
except TRACEPOINT_LOGLEVEL. What should I be aware of?
--
Olivier Dion
PolyMtl
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next prev parent reply other threads:[~2020-07-13 15:18 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-11 15:29 [PATCH lttng-ust] Add ctor/dtor priorities for tracepoints/events Olivier Dion via lttng-dev
2020-07-11 15:29 ` [lttng-dev] " Olivier Dion via lttng-dev
2020-07-12 13:49 ` Mathieu Desnoyers via lttng-dev
2020-07-12 13:49 ` [lttng-dev] " Mathieu Desnoyers via lttng-dev
2020-07-12 15:49 ` Olivier Dion via lttng-dev
2020-07-12 15:49 ` [lttng-dev] " Olivier Dion via lttng-dev
2020-07-13 13:24 ` Mathieu Desnoyers via lttng-dev
2020-07-13 13:24 ` [lttng-dev] " Mathieu Desnoyers via lttng-dev
2020-07-13 15:19 ` Olivier Dion via lttng-dev [this message]
2020-07-13 15:19 ` Olivier Dion via lttng-dev
2020-07-13 15:28 ` Mathieu Desnoyers via lttng-dev
2020-07-13 15:28 ` [lttng-dev] " Mathieu Desnoyers via lttng-dev
2020-07-13 18:46 ` Olivier Dion via lttng-dev
2020-07-13 18:46 ` [lttng-dev] " Olivier Dion via lttng-dev
2020-07-13 18:58 ` Mathieu Desnoyers via lttng-dev
2020-07-13 18:58 ` [lttng-dev] " Mathieu Desnoyers via lttng-dev
2020-07-13 19:44 ` Olivier Dion via lttng-dev
2020-07-13 19:44 ` [lttng-dev] " Olivier Dion via lttng-dev
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