pthread_attr_setstack
int pthread_attr_setstack(pthread_attr_t *, void *, size_t);
RZ(pthread_attr_setstack(&attr, stack, SIGSTKSZ + i));
RZ(pthread_attr_setstack(&attr, stack + i, SIGSTKSZ));
RZ(pthread_attr_setstack(&attr, C->addr, C->size));
RZ(pthread_attr_setstack(&attr2, C->addr, C->size));