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gh-151424: Fix impossible stack traces in RemoteUnwinder(..., cache_frames=True) by copying chunks on cache miss #151426

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gh-151424: Fix impossible stack traces in RemoteUnwinder(..., cache_frames=True) by copying chunks on cache miss #151426

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141f623
sync chunks?
maurycy Jun 13, 2026
8b7f97d
news
maurycy Jun 13, 2026
39564f8
better news
maurycy Jun 13, 2026
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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Library/2026-06-13-04-11-00.gh-issue-151426.f2V67e.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Fix impossible stack traces (callers and callees cross called, orphans and
incorrect lines) in the Tachyon profiler when caching frames, by snapshotting
the stack chunks before walking the frame chain on a cache miss. Patch by
Maurycy Pawłowski-Wieroński.
8 changes: 8 additions & 0 deletions Modules/_remote_debugging/frames.c
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Expand Up @@ -580,6 +580,14 @@ collect_frames_with_cache(
return full_hit < 0 ? -1 : 0;
}

assert(ctx->chunks != NULL);

if (ctx->chunks->count == 0) {
if (copy_stack_chunks(unwinder, ctx->thread_state_addr, ctx->chunks) < 0) {
PyErr_Clear();
}
}

Py_ssize_t frames_before = PyList_GET_SIZE(ctx->frame_info);

if (process_frame_chain(unwinder, ctx) < 0) {
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