On Tue, Sep 24, 2013 at 01:13:53PM +0100, Jonathan Wakely wrote: > On 24 September 2013 02:22, Alan Modra wrote: > > > > Try compiling that testcase with -static rather than -Wl,--as-needed. > > You'll hit std::system_error just like you do here. I believe that is > > a libstdc++ bug, and can be solved by making libstdc++.a use strong > > references to pthread symbols from std::thread::join() (and perhaps > > other objects that provide c++ thread support, if there are such). > > It's the std::thread constructor template that needs pthread_create. > std::thread::join() needs pthread_join.
Ah, OK, I commented without looking at the source first, and it shows. :) > > Otherwise we'd need to solve the transitive reference somehow. > > ie. Teach the linker that a reference to std::thread::join() means > > that pthread_create is required. One obvious way to do that is have > > the compiler reference pthread_create in objects that use > > std::thread::join(). > > How would we have the compiler do that? The std::thread constructor needs to emit a strong reference to pthread_create in the user object file. Probably the best way to do that is as Jakub said, inline it and modify __gthread_create to only use weak references to pthread symbols when compiling for a shared library. (When I wrote the above comment I was thing more along the lines of a dummy reference via a pointer variable initialised to pthread_create, but inlining the lot is simpler.) -- Alan Modra Australia Development Lab, IBM
