On Mon, May 27, 2013 at 06:20:21PM -0400, Ryan Johnson wrote: > I'm not sure whether this is an oversight, a known problem that's > hard to fix, or a feature (e.g. somehow required for reliable > unwinding). I suspect the former, because _Unwind_Find_FDE tries a > call to _Unwind_Find_registered_FDE before falling back to > dl_iterate_phdr, but the former never succeeds in my trace > (iterate_phdr is always called).
Your suspicion is unfounded. The locking is required to support dlopen (or at least, you need some sort of thread synchronisation here). _Unwind_Find_registered_FDE is to support an older method of finding FDEs. Newer executables and shared libraries on linux will use PT_GNU_EH_FRAME, so don't expect _Unwind_Find_registered_FDE to do anything except waste time! google eh_frame_hdr for more info. C++ and threading is a minefield. -- Alan Modra Australia Development Lab, IBM
