Thank you for your answer: Here some more information: I compiled with -g -o0, but it doesn't look like there is more infromation. I used debugger "lldb" and it tells the stuff at the end of this mail. hmm.. doesn't like my source. The "randomSwap" function is sadly pretty large. I can't make it smaller without loosing speed, by speed is very important for timetabling, since it might run many hours to find solutions. Is there an other way how I can debug it? Here the lldb results: vd@Mini-von-Volker fet-6.9.6_BENCHMARK % lldb /Users/vd/Downloads/fet-6.9.6_BENCHMARK/fet.app/Contents/MacOS/fet (lldb) target create "/Users/vd/Downloads/fet-6.9.6_BENCHMARK/fet.app/Contents/MacOS/fet" Current executable set to '/Users/vd/Downloads/fet-6.9.6_BENCHMARK/fet.app/Contents/MacOS/fet' (arm64). (lldb) r Process 7992 launched: '/Users/vd/Downloads/fet-6.9.6_BENCHMARK/fet.app/Contents/MacOS/fet' (arm64) 2023-10-21 21:19:11.202644+0200 fet[7992:30690] [default] CGSWindowShmemCreateWithPort failed on port 0 2023-10-21 21:19:11.219299+0200 fet[7992:30690] [default] CGSWindowShmemCreateWithPort failed on port 0 Process 7992 stopped thread #10, stop reason = EXC_BAD_ACCESS (code=2, address=0x17014bff8) frame #0: 0x0000000189791e7c libsystem_pthread.dylib`___chkstk_darwin + 60 libsystem_pthread.dylib`: -> 0x189791e7c <+60>: ldur x11, [x11, #-0x8] 0x189791e80 <+64>: mov x10, sp 0x189791e84 <+68>: cmp x9, #0x1, lsl #12 ; =0x1000 0x189791e88 <+72>: b.lo 0x189791ea0 ; <+96> Target 0: (fet) stopped. (lldb)