David is correct, another program having issues with Quickthreads is valgrind. With Quickthreads SystemC threads actually all live in a single pthread. When a SystemC thread yields to another one the stack is changed from one piece of storage to another in a discontinuous manner. The stack for that single pthread that SystemC is living ends up being discontinuous. With pthreads enabled each SystemC thread is in its own pthread and those stacks are continuous.