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GH-126910: Allow native profilers and debuggers to unwind through JIT frames #143548

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GH-126910: Allow native profilers and debuggers to unwind through JIT frames #143548

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@brandtbucher brandtbucher commented Jan 8, 2026 •
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Most unwinders will optimistically fall back to frame pointers if DWARF unwind info isn't present for a given frame. This patch enables frame pointers in JIT code on x86-64 Linux, by setting them in the "shim" frame and reserving the frame pointer register in the rest of the JIT code. @Fidget-Spinner can confirm that this works for the unwinders in https://github.com/pablogsal/cpython-unwind.

Perf impact is neutral.

@brandtbucher brandtbucher requested a review from pablogsal January 8, 2026 07:03
@brandtbucher brandtbucher changed the title Allow native profilers and debuggers to unwind through JIT frames GH-126910: Allow native profilers and debuggers to unwind through JIT frames Jan 8, 2026
@bedevere-app bedevere-app bot mentioned this pull request Jan 8, 2026
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pablogsal commented Jan 8, 2026

This patch enables frame pointers in JIT code on x86-64 Linux

What's the situation in aarch64?

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Fidget-Spinner commented Jan 8, 2026

Can confirm this works for everything except GNU backtrace, and for that one I think we're just missing debug info.

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pablogsal commented Jan 9, 2026

BTW we should check gdb and lldb as well but my guess is that those have the biggest set of tricks under the sleeve so I assume this won't be a problem....

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Fidget-Spinner commented Jan 13, 2026

PYTHON_JIT=0

[GNU backtrace]
Total frames: 56
Showing first 10 frames:
  # 0  /home/ken/Documents/GitHub/cpython-unwind/stackunwind.cpython-315-x86_64-linux-gnu.so(+0x23f4) [0x7b3bfc4bc3f4]
  # 1  ./python(PyObject_Vectorcall+0x43) [0x5706adb32893]
  # 2  ./python(_Py_VectorCallInstrumentation_StackRefSteal+0x176) [0x5706adc5d8e6]
  # 3  ./python(_PyEval_EvalFrameDefault+0x23be) [0x5706adc60a9e]
  # 4  ./python(+0x2223c6) [0x5706adc5d3c6]
  # 5  ./python(PyObject_Vectorcall+0x43) [0x5706adb32893]
  # 6  ./python(_Py_BuiltinCallFastWithKeywords_StackRefSteal+0x146) [0x5706adc5dd46]
  # 7  ./python(_PyEval_EvalFrameDefault+0x2e5c) [0x5706adc6153c]
  # 8  ./python(+0x2223c6) [0x5706adc5d3c6]
  # 9  ./python(PyObject_Vectorcall+0x43) [0x5706adb32893]
  ... (46 more frames)

[libunwind]
Total frames: 54
Showing first 10 frames:
  # 0  PyObject_Vectorcall+0x43
  # 1  _Py_VectorCall_StackRefSteal+0x15d
  # 2  _PyEval_EvalFrameDefault+0x4a89
  # 3  _PyEval_Vector+0x276
  # 4  PyObject_Vectorcall+0x43
  # 5  _Py_BuiltinCallFastWithKeywords_StackRefSteal+0x146
  # 6  _PyEval_EvalFrameDefault+0x2e5c
  # 7  _PyEval_Vector+0x276
  # 8  PyObject_Vectorcall+0x43
  # 9  _Py_BuiltinCallFastWithKeywords_StackRefSteal+0x146
  ... (44 more frames)

[libdw (DWARF)]
Total frames: 54
Showing first 10 frames:
  # 0  PyObject_Vectorcall
  # 1  _Py_VectorCall_StackRefSteal
  # 2  _PyEval_EvalFrameDefault
  # 3  _PyEval_Vector
  # 4  PyObject_Vectorcall
  # 5  _Py_BuiltinCallFastWithKeywords_StackRefSteal
  # 6  _PyEval_EvalFrameDefault
  # 7  _PyEval_Vector
  # 8  PyObject_Vectorcall
  # 9  _Py_BuiltinCallFastWithKeywords_StackRefSteal
  ... (44 more frames)

[Manual frame pointers]
Total frames: 2
Showing first 2 frames:
  # 0  0x5706adb32893
  # 1  0x7ffeb5887bc8

======================================================================
  Remote Stack Unwinding Test (libunwind-ptrace)
======================================================================

[Parent] Attaching to child process (PID: 50223)...
[Child 50223] Ready for sampling

[libunwind-ptrace (remote)]
Total frames: 16
Showing first 15 frames:
  # 0  0x00007b3bfc0eca7a in __clock_nanosleep + 0x5a (sp=0x00007ffeb5887180)
  # 1  0x00005706add904cc in time_sleep + 0x9c (sp=0x00007ffeb5887200)
  # 2  0x00005706adb32893 in PyObject_Vectorcall + 0x43 (sp=0x00007ffeb5887240)
  # 3  0x00005706adc5d8e6 in _Py_VectorCallInstrumentation_StackRefSteal + 0x176 (sp=0x00007ffeb5887260)
  # 4  0x00005706adc60a9e in _PyEval_EvalFrameDefault + 0x23be (sp=0x00007ffeb5887310)
  # 5  0x00005706adc5d0f6 in PyEval_EvalCode + 0x156 (sp=0x00007ffeb5887550)
  # 6  0x00005706add05bc6 in run_mod + 0x3f6 (sp=0x00007ffeb5887610)
  # 7  0x00005706add0325e in _PyRun_SimpleFileObject + 0x35e (sp=0x00007ffeb5887670)
  # 8  0x00005706add02cb3 in _PyRun_AnyFileObject + 0x73 (sp=0x00007ffeb58876e0)
  # 9  0x00005706add2a3f1 in pymain_run_file + 0x171 (sp=0x00007ffeb5887710)
  #10  0x00005706add29d09 in Py_RunMain + 0x689 (sp=0x00007ffeb58877d0)
  #11  0x00005706add29ffa in pymain_main + 0x14a (sp=0x00007ffeb5887850)
  #12  0x00005706add2a04d in Py_BytesMain + 0x2d (sp=0x00007ffeb5887ac0)
  #13  0x00007b3bfc02a1ca in __libc_start_call_main + 0x7a (sp=0x00007ffeb5887af0)
  #14  0x00007b3bfc02a28b in __libc_start_main_alias_2 + 0x8b (sp=0x00007ffeb5887b90)
  ... (1 more frames)

[elfutils native (remote)]
Total frames: 16
Showing first 15 frames:
  # 0  clock_nanosleep@GLIBC_2.2.5 (clock_nanosleep.c:78)
  # 1  time_sleep (0x5706add904cb)
  # 2  PyObject_Vectorcall (0x5706adb32892)
  # 3  _Py_VectorCallInstrumentation_StackRefSteal (0x5706adc5d8e5)
  # 4  _PyEval_EvalFrameDefault (0x5706adc60a9d)
  # 5  PyEval_EvalCode (0x5706adc5d0f5)
  # 6  run_mod (0x5706add05bc5)
  # 7  _PyRun_SimpleFileObject (0x5706add0325d)
  # 8  _PyRun_AnyFileObject (0x5706add02cb2)
  # 9  pymain_run_file (0x5706add2a3f0)
  #10  Py_RunMain (0x5706add29d08)
  #11  pymain_main (0x5706add29ff9)
  #12  Py_BytesMain (0x5706add2a04c)
  #13  __libc_start_call_main (libc_start_call_main.h:58)
  #14  __libc_start_main@@GLIBC_2.34 (libc-start.c:360)
  ... (1 more frames)

[Parent] Detaching and terminating child...

======================================================================
  Tests Complete
======================================================================

PYTHON_JIT=1

======================================================================
  Local Stack Unwinding Tests
======================================================================

Testing various unwinding methods on the same deep call stack...

[GNU backtrace]
Total frames: 8
Showing first 8 frames:
  # 0  /home/ken/Documents/GitHub/cpython-unwind/stackunwind.cpython-315-x86_64-linux-gnu.so(+0x23f4) [0x7ed57fec43f4]
  # 1  ./python(PyObject_Vectorcall+0x43) [0x5999ea29e893]
  # 2  ./python(_Py_VectorCallInstrumentation_StackRefSteal+0x176) [0x5999ea3c98e6]
  # 3  ./python(_PyEval_EvalFrameDefault+0x23be) [0x5999ea3cca9e]
  # 4  ./python(+0x2223c6) [0x5999ea3c93c6]
  # 5  ./python(PyObject_Vectorcall+0x43) [0x5999ea29e893]
  # 6  ./python(_Py_BuiltinCallFastWithKeywords_StackRefSteal+0x146) [0x5999ea3c9d46]
  # 7  [0x7ed57febf61d]

[libunwind]
Total frames: 64
Showing first 10 frames:
  # 0  PyObject_Vectorcall+0x43
  # 1  _Py_VectorCall_StackRefSteal+0x15d
  # 2  _PyEval_EvalFrameDefault+0x4a89
  # 3  _PyEval_Vector+0x276
  # 4  PyObject_Vectorcall+0x43
  # 5  _Py_BuiltinCallFastWithKeywords_StackRefSteal+0x146
  # 6  <unknown>
  # 7  _PyEval_EvalFrameDefault+0x6a4b
  # 8  _PyEval_Vector+0x276
  # 9  PyObject_Vectorcall+0x43
  ... (54 more frames)

[libdw (DWARF)]
Total frames: 64
Showing first 10 frames:
  # 0  PyObject_Vectorcall
  # 1  _Py_VectorCall_StackRefSteal
  # 2  _PyEval_EvalFrameDefault
  # 3  _PyEval_Vector
  # 4  PyObject_Vectorcall
  # 5  _Py_BuiltinCallFastWithKeywords_StackRefSteal
  # 6  <unknown>
  # 7  _PyEval_EvalFrameDefault
  # 8  _PyEval_Vector
  # 9  PyObject_Vectorcall
  ... (54 more frames)

[Manual frame pointers]
Total frames: 2
Showing first 2 frames:
  # 0  0x5999ea29e893
  # 1  0x7ffdfea57f28

======================================================================
  Remote Stack Unwinding Test (libunwind-ptrace)
======================================================================

[Parent] Attaching to child process (PID: 50282)...
[Child 50282] Ready for sampling

[libunwind-ptrace (remote)]
Total frames: 16
Showing first 15 frames:
  # 0  0x00007ed57faeca7a in __clock_nanosleep + 0x5a (sp=0x00007ffdfea574e0)
  # 1  0x00005999ea4fc4cc in time_sleep + 0x9c (sp=0x00007ffdfea57560)
  # 2  0x00005999ea29e893 in PyObject_Vectorcall + 0x43 (sp=0x00007ffdfea575a0)
  # 3  0x00005999ea3c98e6 in _Py_VectorCallInstrumentation_StackRefSteal + 0x176 (sp=0x00007ffdfea575c0)
  # 4  0x00005999ea3cca9e in _PyEval_EvalFrameDefault + 0x23be (sp=0x00007ffdfea57670)
  # 5  0x00005999ea3c90f6 in PyEval_EvalCode + 0x156 (sp=0x00007ffdfea578b0)
  # 6  0x00005999ea471bc6 in run_mod + 0x3f6 (sp=0x00007ffdfea57970)
  # 7  0x00005999ea46f25e in _PyRun_SimpleFileObject + 0x35e (sp=0x00007ffdfea579d0)
  # 8  0x00005999ea46ecb3 in _PyRun_AnyFileObject + 0x73 (sp=0x00007ffdfea57a40)
  # 9  0x00005999ea4963f1 in pymain_run_file + 0x171 (sp=0x00007ffdfea57a70)
  #10  0x00005999ea495d09 in Py_RunMain + 0x689 (sp=0x00007ffdfea57b30)
  #11  0x00005999ea495ffa in pymain_main + 0x14a (sp=0x00007ffdfea57bb0)
  #12  0x00005999ea49604d in Py_BytesMain + 0x2d (sp=0x00007ffdfea57e20)
  #13  0x00007ed57fa2a1ca in __libc_start_call_main + 0x7a (sp=0x00007ffdfea57e50)
  #14  0x00007ed57fa2a28b in __libc_start_main_alias_2 + 0x8b (sp=0x00007ffdfea57ef0)
  ... (1 more frames)

[elfutils native (remote)]
Total frames: 16
Showing first 15 frames:
  # 0  clock_nanosleep@GLIBC_2.2.5 (clock_nanosleep.c:78)
  # 1  time_sleep (0x5999ea4fc4cb)
  # 2  PyObject_Vectorcall (0x5999ea29e892)
  # 3  _Py_VectorCallInstrumentation_StackRefSteal (0x5999ea3c98e5)
  # 4  _PyEval_EvalFrameDefault (0x5999ea3cca9d)
  # 5  PyEval_EvalCode (0x5999ea3c90f5)
  # 6  run_mod (0x5999ea471bc5)
  # 7  _PyRun_SimpleFileObject (0x5999ea46f25d)
  # 8  _PyRun_AnyFileObject (0x5999ea46ecb2)
  # 9  pymain_run_file (0x5999ea4963f0)
  #10  Py_RunMain (0x5999ea495d08)
  #11  pymain_main (0x5999ea495ff9)
  #12  Py_BytesMain (0x5999ea49604c)
  #13  __libc_start_call_main (libc_start_call_main.h:58)
  #14  __libc_start_main@@GLIBC_2.34 (libc-start.c:360)
  ... (1 more frames)

[Parent] Detaching and terminating child...

======================================================================
  Tests Complete
======================================================================

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@brandtbucher @pablogsal @Fidget-Spinner