It's possible to trigger an assertion failure in a JIT build by running the code below:
python: Python/optimizer.c:759: int _PyJit_translate_single_bytecode_to_trace(PyThreadState *, _PyInterpreterFrame *, _Py_CODEUNIT *, int): Assertion `jump_happened == (target_instr[1].cache & 1)' failed.
Program received signal SIGABRT, Aborted.
#0 __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=0) at ./nptl/pthread_kill.c:44
#1 __pthread_kill_internal (threadid=<optimized out>, signo=6) at ./nptl/pthread_kill.c:89
#2 __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=6) at ./nptl/pthread_kill.c:100
#3 0x00007ffff7c45e2e in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4 0x00007ffff7c28888 in __GI_abort () at ./stdlib/abort.c:77
#5 0x00007ffff7c287f0 in __assert_fail_base (fmt=<optimized out>, assertion=<optimized out>, file=<optimized out>, line=<optimized out>, function=<optimized out>) at ./assert/assert.c:118
#6 0x00007ffff7c3c19f in __assert_fail (assertion=<optimized out>, file=<optimized out>, line=<optimized out>, function=<optimized out>) at ./assert/assert.c:127
#7 0x0000555556129d8a in _PyJit_translate_single_bytecode_to_trace (tstate=0x555556aead00 <_PyRuntime+358304>, frame=frame@entry=0x7e8ff6de5280, next_instr=next_instr@entry=0x7d2ff6dfd4d6,
stop_tracing_opcode=0) at Python/optimizer.c:759
#8 0x0000555555e5d06d in _PyEval_EvalFrameDefault (tstate=<optimized out>, frame=<optimized out>, throwflag=<optimized out>) at Python/generated_cases.c.h:12266
#9 0x0000555555e49d1b in _PyEval_EvalFrame (tstate=0x555556aead00 <_PyRuntime+358304>, frame=0x7e8ff6de5220, throwflag=0) at ./Include/internal/pycore_ceval.h:121
#10 _PyEval_Vector (tstate=<optimized out>, func=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=<optimized out>, kwnames=0x0) at Python/ceval.c:2104
#11 0x0000555555e49735 in PyEval_EvalCode (co=<optimized out>, globals=<optimized out>, locals=0x7c7ff6e872c0) at Python/ceval.c:944
#12 0x00005555561bb04f in run_eval_code_obj (tstate=tstate@entry=0x555556aead00 <_PyRuntime+358304>, co=co@entry=0x7d1ff6e1bbd0, globals=globals@entry=0x7c7ff6e872c0,
locals=locals@entry=0x7c7ff6e872c0) at Python/pythonrun.c:1372
#13 0x00005555561ba21c in run_mod (mod=<optimized out>, filename=<optimized out>, globals=<optimized out>, locals=<optimized out>, flags=<optimized out>, arena=<optimized out>,
interactive_src=<optimized out>, generate_new_source=<optimized out>) at Python/pythonrun.c:1475
Python 3.15.0a2+ (heads/main:b1558b6d3e2, Nov 20 2025, 13:04:18) [Clang 21.1.2 (2ubuntu6)]
Crash report
What happened?
It's possible to trigger an assertion failure in a JIT build by running the code below:
Backtrace:
Output from running with
PYTHON_LLTRACE=4:6_abort_lltrace.txt
Running with
PYTHON_OPT_DEBUG=4generates no output.Found using lafleur.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.15.0a2+ (heads/main:b1558b6d3e2, Nov 20 2025, 13:04:18) [Clang 21.1.2 (2ubuntu6)]