From: Mathieu Desnoyers via lttng-dev <lttng-dev@lists.lttng.org>
To: Olivier Dion <olivier.dion@polymtl.ca>
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 09:24:52 -0400 (EDT) [thread overview]
Message-ID: <1851244021.9798.1594646692671.JavaMail.zimbra@efficios.com> (raw)
Message-ID: <20200713132452.CbmgXRtytnLXxXAhQP0Z4H1MdFYyG31HMOzXpcImgVo@z> (raw)
In-Reply-To: <87tuycybqx.fsf@clara>
----- 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.
>
>> 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.
Beware though that there are a few configurations which can be used for
probe providers (see lttng-ust(3)).
Thanks,
Mathieu
>
> --
> Olivier Dion
> PolyMtl
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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next prev parent reply other threads:[~2020-07-13 13:25 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 [this message]
2020-07-13 13:24 ` Mathieu Desnoyers via lttng-dev
2020-07-13 15:19 ` Olivier Dion via lttng-dev
2020-07-13 15:19 ` [lttng-dev] " 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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