The main problem is the unwinding lock. Memory allocation is a bit unfortunate, too, but much less so.

Note that I am trying to fix the unwinding problem, I have submitted a patch to libunwind to eliminate the contention during unwinding:

https://reviews.llvm.org/D120243

It require application support, unfortunately, as there is currently no way that libunwind can figure out if a shared library has been added or removed. But if you are willing to indicate that from within the application the performance problem is mostly fixed. The memory allocation issue remains, but I can live with that. I cannot live with single threaded unwinding.