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GeezerVison is showing github.com — gh-160253: Fix test_c_stack_unwind manual unwinding on sparc64 by shalseth · Pull Request #160255 · python/cpython

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@shalseth

@shalseth shalseth commented Oct 22, 2026 •
edited by bedevere-app Bot
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Teach the manual frame pointer unwinder in _testinternalcapi the SPARC V9 frame layout. There's no frame record on SPARC: the caller's %fp (biased by 2047) and its return address are in slots 14 and 15 of the register window save area at fp, and they're only in memory after a flushw.

Tested on a SPARC T7-1 and a T4-1 (Linux, GCC 16): ManualStackUnwindTests fails without the change and passes with it, and the unwinder walks all the way down to _start. No change on x86_64.

The GNU backtrace test still fails on sparc64, that's the missing unwind tables from the issue (GCC PR 128091), not this code.

  • Issue: test_c_stack_unwind fails on Linux sparc64 #160253

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@shalseth
pythongh-160253: Fix test_c_stack_unwind manual unwinding on sparc64
d8083e7 
SPARC V9 has no frame record. The caller's %fp (biased by 2047) and return
address are in slots 14 and 15 of the register window save area at fp, and
are only there after the windows have been flushed to the stack.
@python-cla-bot

python-cla-bot Bot commented Oct 22, 2026 •
edited
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@bedevere-app bedevere-app Bot mentioned this pull request Oct 22, 2026
test_c_stack_unwind fails on Linux sparc64 #160253
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@bedevere-app bedevere-app Bot added awaiting review tests Tests in the Lib/test dir labels Oct 22, 2026
@bedevere-app

bedevere-app Bot commented Oct 22, 2026

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.
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@shalseth shalseth mentioned this pull request Oct 22, 2026
gcc sparc64: Python 3.15 test failure in test_c_stack_unwind (requires -fasynchronous-unwind-tables) sparclinux/issues#120
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@shalseth

shalseth commented Oct 22, 2026

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If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

Please apply skip news to this one.
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@shalseth

shalseth commented Oct 24, 2026

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A patch for the related GCC bug in #160626 is now merged: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128091

If this PR is merged, SPARC will have a fully clean test suite on 3.15.
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@encukou encukou added the skip news label Oct 30, 2026
@encukou

encukou commented Oct 30, 2026

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Thank you. I have no way to test this, but for #ifdef blocks in test-only code, I'n inclined to just trust you.
Note that per PEP 11, we don't do backports for unsupported platforms: I can merge for 3.16 but ask you to keep a 3.15 patch.

If you'd like to provide/coordinate support for CPython on SPARC, you might want to add yourself here: https://devguide.python.org/developer-workflow/porting/#ports

@kulikjak, do you want to test this? (Assuming you have access to a SPARC box, from #78952 (comment))
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@shalseth shalseth mentioned this pull request Oct 30, 2026
Add SPARC/Linux to the ports and contacts table python/devguide#1955
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@shalseth

shalseth commented Oct 30, 2026

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Thank you. I have no way to test this, but for #ifdef blocks in test-only code, I'n inclined to just trust you. Note that per PEP 11, we don't do backports for unsupported platforms: I can merge for 3.16 but ask you to keep a 3.15 patch.

Thanks! 3.16 is fine. It's tested on Linux, haven't touched Solaris.

If you'd like to provide/coordinate support for CPython on SPARC, you might want to add yourself here: https://devguide.python.org/developer-workflow/porting/#ports

Yes, sent PR: python/devguide#1955
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@encukou

encukou commented Nov 2, 2026

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Thanks!
I'll merge ~Friday if there are no objections.
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@kulikjak

kulikjak commented Nov 2, 2026

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Thanks for the ping and for the fix - I tested it on Solaris SPARC and the test failure is gone here as well.
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3 participants

@shalseth @encukou @kulikjak
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