----- 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. > >> 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 _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
