On Mon, 13 Jul 2020, Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote: > ----- On Jul 12, 2020, at 11:49 AM, Olivier Dion olivier.d...@polymtl.ca > wrote: > >> On Sun, 12 Jul 2020, Mathieu Desnoyers <mathieu.desnoy...@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 _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
