[lttng-dev] SystemTap integration and C++ tracepoints

[Thibault, Daniel]

   Inspired by Jérémie's https://gist.github.com/jgalar/5706595, I tinkered with lttng-ust/doc/examples/easy-ust to make the sample application use a small C++ object (and turning itself into sample.cpp).  It links and works fine except if LTTNG_UST_HAVE_SDT_INTEGRATION is #defined, in which case I get a "template with C linkage" error on line 71 of sdt.h, followed by a slew of "template specialization with C linkage" errors.
 
   What is odd is that even if I #undef LTTNG_UST_HAVE_SDT_INTEGRATION in sample.cpp just before the #include "sample_component_provider.h", it somehow gets turned back on by the time lttng/tracepoint.h checks it.  If I modify tracepoint.h to comment out the #ifdef in order to leave only its else branch, sample.cpp compiles just fine.

   Two questions, then:
1) how come #undef LTTNG_UST_HAVE_SDT_INTEGRATION doesn't work?
2) can LTTng be used to trace a C++ application when SystemTap is installed?

   I can supply a small tarball of the source code and makefile (just drop those in lttng-ust/doc/examples/easy-ust and "make cppdynamic" to see the problem occur).

Daniel U. Thibault
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