GH-126910: Allow native profilers and debuggers to unwind through JIT frames by brandtbucher · Pull Request #143548 · python/cpython · GitHub

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.

Issue: Supporting stack unwinding in the JIT compiler #126910

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

What's the situation in aarch64?

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

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....

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
======================================================================

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

What's the situation in aarch64?

Replied here: #126910 (comment)

Can we get this enabled for AArch64 as well?

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

This would also work for Windows 32bit. I've done successful experiments with @diegorusso's #144137 back then.

I just don't know how much we're willing to do wrt jit and Windows 32bit?

@diegorusso I think you can make a follow-up PR for AArch64. We don't need to hold up this PR because of that.

We can make a follow-up PR for AArch64.

…through JIT frames (pythonGH-143548)

brandtbucher added 4 commits January 7, 2026 18:50

Reserve the frame pointer in JIT code

d76d264

shim -> trampoline

c214c07

trampoline -> shim

8cfff6f

Clean up

766d404

brandtbucher requested a review from pablogsal January 8, 2026 07:03

brandtbucher requested review from diegorusso and savannahostrowski as code owners January 8, 2026 07:03

bedevere-app Bot added the awaiting core review label Jan 8, 2026

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 Bot mentioned this pull request Jan 8, 2026

Supporting stack unwinding in the JIT compiler #126910

Open

blurb add

ae8649f

diegorusso previously requested changes Mar 13, 2026

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bedevere-app Bot added awaiting changes and removed awaiting core review labels Mar 13, 2026

Merge branch 'main' into jit-unwind

8c038c8

Fidget-Spinner approved these changes Mar 24, 2026

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bedevere-app Bot added awaiting merge and removed awaiting changes labels Mar 24, 2026

Fidget-Spinner merged commit 535b09c into python:main Mar 24, 2026
77 of 78 checks passed

bedevere-app Bot removed the awaiting merge label Mar 24, 2026

diegorusso mentioned this pull request Mar 27, 2026

GH-126910: reserve FP on AArch64 when generating JIT stencils #146520

Merged

pablogsal mentioned this pull request Apr 4, 2026

gh-130273: Fix traceback color output with unicode characters #142529

Merged

clin1234 pushed a commit to clin1234/cpython that referenced this pull request Apr 16, 2026

pythonGH-126910 : Allow most native profilers and debuggers to unwind …

3d04df6

…through JIT frames (pythonGH-143548)

ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026

pythonGH-126910 : Allow most native profilers and debuggers to unwind …

5db3b69

…through JIT frames (pythonGH-143548)

GH-126910: Allow native profilers and debuggers to unwind through JIT frames by brandtbucher · Pull Request #143548 · python/cpython · GitHub

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

GH-126910: Allow native profilers and debuggers to unwind through JIT frames#143548
Fidget-Spinner merged 6 commits into
python:mainfrom
brandtbucher:jit-unwind

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GH-126910: Allow native profilers and debuggers to unwind through JIT frames by brandtbucher · Pull Request #143548 · python/cpython · GitHub

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

GH-126910: Allow native profilers and debuggers to unwind through JIT frames#143548Fidget-Spinner merged 6 commits intopython:mainpython/cpython:mainfrom brandtbucher:jit-unwindbrandtbucher/cpython:jit-unwindCopy head branch name to clipboard

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GH-126910: Allow native profilers and debuggers to unwind through JIT frames#143548
Fidget-Spinner merged 6 commits into
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