qemu-m68k: python runtime failures, "The futex facility returned an unexpected error code." Description of problem: The python interpreter (both Python 3.9 and Python 3.10) crashes during a rebuild of Python itself (fairly reproducible but not always at the same point of the build; using MAKEOPTS=-j1 or running under high system load decreases the probability, as does using the qemu -systrace switch). The output is ``` The futex facility returned an unexpected error code. ``` Digging into glibc sources, this error together with an abort occurs when the return value of a futex call is not in a short list of allowed values, see ``nptl/futex-internal.c`` and ``sysdeps/nptl/futex-internal.h``. Running qemu with QEMU_STRACE=1 decreases the probability of the error greatly, but after some attempts I was able to get a log. Several threads seem to write at the same time, leading to rather garbled output, but my interpretation is an error value of "Invalid argument". ``` 116876 get_thread_area(0x00000001) = 989882672 116876 116876 get_thread_area(0x00000001)get_thread_area(0x00000018) = 989882672 = 1065219744 116876 get_thread_area(0x00000000) = 1065219744 116876 futex(0x3f5003fa,FUTEX_PRIVATE_FLAG|FUTEX_WAIT116876 ,2,116876 NULL,0x3fffda10,get_thread_area(0xffffffff) = 1065219744 futex(0x3f5003fa,1073732112)FUTEX_PRIVATE_FLAG|FUTEX_WAIT = ,2,NULL,-1 errno=22 (Invalid argument)116876 get_thread_area(0x00000000) = 1065219744 0x3fffda10,116876 get_thread_area(0x00000000)1073732112 = )1065219744 116876 futex(0x3f7d4c34,FUTEX_PRIVATE_FLAG|FUTEX_WAKE,1,NULL,NULL, = 0)-1 errno=22 (Invalid argument) = 0 = 116876 get_thread_area(0x3f7d4c34)1 = 116876 get_thread_area(0x00000000) = 1065219744 926968112 116876 get_thread_area(0x00000016) = 926968112 116876 get_thread_area(0x00000000) = 1065219744 116876 get_thread_area(0x00000000) = 1065219744 116876 get_thread_area(0x00000001)116876 = futex(116876 0x3f5003fa,get_thread_area(0x00000000)FUTEX_PRIVATE_FLAG| = 926968112 116876 get_thread_area(0x00000000) = 926968112FUTEX_WAKE ,1,116876 NULL,0x3fffda10,get_thread_area(0x00000000) = 926968112 1065219744 116876 get_thread_area(0x00000001)116876 = 1065219744 1073732112) = 116876 -1 errno=22 (Invalid argument) futex(0x3ba005fc,FUTEX_PRIVATE_FLAG|FUTEX_CLOCK_REALTIME|FUTEX_WAIT_BITSET,0,NULL,NULL,get_thread_area(0x00000000)0 = 926968112) 116876 get_thread_area(0x00000000) = 926968112 116876 futex(0x3f7d4c38,FUTEX_PRIVATE_FLAG|FUTEX_WAKE,1,NULL,0x40007bf8,1073773560) = 0 116876 futex(0x40053a8c,FUTEX_PRIVATE_FLAG|FUTEX_WAKE,1,NULL,NULL,0) = 1 = 0 116876 get_thread_area(0x40053a8c) = 885025072 116876 get_thread_area(0x00000001) = 885025072 116876 get_thread_area(0x00b4b456) = 885025072 116876 get_thread_area(0x00000000) = 885025072 116876 get_thread_area(0x00000000) = 885025072 116876 Unknown syscall 403 116876 get_thread_area(0x00000000) = 885025072 116876 get_thread_area(0x00003baa) = 885025072 116876 get_thread_area(0x00003b01) = 885025072 116876 get_thread_area(0x00003b01) = 885025072 116876 116876 futex(get_thread_area(0x00b4b456)0x3f7d4c30,FUTEX_PRIVATE_FLAG|FUTEX_WAIT_BITSET,0,0x34bfe62c,NULL,0) = 926968112 116876 get_thread_area(0x00000018) = 926968112 116876 get_thread_area(0x3ed5b9c8) = 926968112 116876 get_thread_area(0x00000000) = 926968112 116876 get_thread_area(0x00000000) = 926968112 116876 get_thread_area(0x00000000) = 926968112 116876 get_thread_area(0x00000000) = 926968112 116876 get_thread_area(0x00000000) = 926968112 116876 futex(0x3f7d4c30,FUTEX_PRIVATE_FLAG|FUTEX_WAKE,1,NULL,NULL,0) = 1 116876 get_thread_area(0x00000000) = 926968112 116876 get_thread_area(0x00000001) = 926968112 116876 get_thread_area(0x0000000f) = 926968112116876 = 0 116876 get_thread_area(0x00000001) = 926968112 116876 get_thread_area(0x00000001) = 926968112 116876 get_thread_area(0x00000001)writev(2,0x3affed88,0x1) = 926968112 The futex facility returned an unexpected error code. 116876 get_thread_area(0x3f7d4c30) = 885025072 ``` Advice on how to do further debuggging is appreciated.