The problem is specifically with vtable overrides in classes that are cloned into a thread (which is a cloned interpreter object). The sub object for the vtable override loses its 'seg' member, as demonstrated in the gdb output below. The particular vtable override in tests 13 and 14 of t/pmc/threads.t is 'get_string'.
Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000024 [Switching to process 26210 thread 0x2103] 0x0016f93e in Parrot_Sub_invoke (interp=0x1b17580, pmc=0x1cee0f8, next=0x0) at ./src/pmc/sub.pmc:231 231 pc = sub->seg->base.data + sub->start_offs; (gdb) bt #0 0x0016f93e in Parrot_Sub_invoke (interp=0x1b17580, pmc=0x1cee0f8, next=0x0) at ./src/pmc/sub.pmc:231 #1 0x000113c2 in runops_args (interp=0x1b17580, sub=0x1cee0f8, obj=0x1cecf88, meth_unused=0x1cf35e4, sig=0x24d200 "S", ap=0xb0182c54 "") at src/inter_run.c:185 #2 0x0001187a in Parrot_run_meth_fromc_args (interp=0x1b17580, sub=0x1cee0f8, obj=0x1cecf88, meth=0x1cf35e4, sig=0x24d200 "S") at src/inter_run.c:390 #3 0x001e29b0 in Parrot_Object_get_string (interp=0x1b17580, pmc=0x1cecf88) at ./src/pmc/object.c:2020 #4 0x0001646f in Parrot_oo_get_class (interp=0x1b17580, key=0x1cecf88) at src/oo.c:153 #5 0x00047f7e in Parrot_get_class_p_p (cur_opcode=0x2040ce4, interp=0x1b17580) at src/ops/object.ops:406 #6 0x000e4f1e in runops_slow_core (interp=0x1b17580, pc=0x2040ce4) at src/runops_cores.c:201 #7 0x000c4b53 in runops_int (interp=0x1b17580, offset=50) at src/interpreter.c:855 #8 0x00011266 in runops (interp=0x1b17580, offs=50) at src/inter_run.c:105 #9 0x00011508 in runops_args (interp=0x1b17580, sub=0x1ced3a8, obj=0x202dc48, meth_unused=0x0, sig=0x238314 "PF", ap=0xb0182e8c "H?\002\002") at src/inter_run.c:221 #10 0x00011648 in Parrot_runops_fromc_args (interp=0x1b17580, sub=0x1ced3a8, sig=0x238314 "PF") at src/inter_run.c:300 #11 0x0002d6cb in thread_func (arg=0x1ced468) at src/thread.c:426 #12 0x90024227 in _pthread_body () (gdb) print sub->seg $1 = (struct PackFile_ByteCode *) 0x0 (gdb)
