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GeezerVison is showing github.com — gh-148286: Fail on new UB in CI by StanFromIreland · Pull Request #148168 · python/cpython

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@StanFromIreland

@StanFromIreland StanFromIreland commented Apr 6, 2026 •
edited by bedevere-app Bot
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Trying to debug a bit, it should be detecting #148166 (and also screaming about it), but it isn't. Mirroring what we do for the TSan job.

Just chucked everything in suppressions for now, they should be reviewed as it may have actual bugs.

  • Issue: Various UB warnings found by UBSan #148286

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@StanFromIreland
Fail on new UB
38ae0c1
@StanFromIreland StanFromIreland changed the title Fail on new UB Fail on new UB in CI Apr 6, 2026
@StanFromIreland StanFromIreland added skip issue skip news labels Apr 6, 2026
StanFromIreland added 3 commits April 6, 2026 15:49
@StanFromIreland
Don't waste CI resources
d1a9414
@StanFromIreland
wrong branch:-/
a2a444d
@StanFromIreland
Run --with-strict-overflow
46f0582
@StanFromIreland

StanFromIreland commented Apr 6, 2026

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I've never been so happy to see the CI fail :-)

[3](https://github.com/python/cpython/actions/runs/24037637122/job/70101135069?pr=148168#step:11:144)
==> /home/runner/work/cpython/cpython/san_log.26255 <==
Modules/binascii.c:1243:42: runtime error: left shift of 129 by 24 places cannot be represented in type 'int'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior Modules/binascii.c:1243:42
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@thesamesam

thesamesam commented Apr 6, 2026

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We got there in the end: #111758 (comment) :)

I'd assumed that #135578 or #136820 included that but I didn't check.
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thesamesam
thesamesam reviewed Apr 6, 2026
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Comment thread .github/workflows/reusable-san.yml Resolved

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thesamesam
thesamesam reviewed Apr 6, 2026
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Comment thread .github/workflows/reusable-san.yml Resolved

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@StanFromIreland
Populate suppressions.txt, fix test_capi fails
cdebb42
@StanFromIreland
StanFromIreland marked this pull request as ready for review April 6, 2026 16:16
@StanFromIreland
StanFromIreland requested review from AA-Turner, ezio-melotti, hugovk and webknjaz as code owners April 6, 2026 16:16
@bedevere-app bedevere-app Bot added the awaiting core review label Apr 6, 2026
@StanFromIreland
StanFromIreland marked this pull request as draft April 6, 2026 16:19
@bedevere-app bedevere-app Bot removed the awaiting core review label Apr 6, 2026
StanFromIreland added 4 commits April 6, 2026 17:22
@StanFromIreland
Just skip test_capi
1e92881
@StanFromIreland
Move halt on error to fix configure
00c6488
@StanFromIreland
Fix suppressions
b67defe
@StanFromIreland
Add another suppression
a1a0e7f
@StanFromIreland
StanFromIreland marked this pull request as ready for review April 6, 2026 17:19
@bedevere-app bedevere-app Bot added the awaiting core review label Apr 6, 2026
@StanFromIreland
Skip test_faulthandler too, and oh hey, I fixed that one!
8c423e0
@encukou

encukou commented Apr 9, 2026

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LGTM, thank you!
Consider opening an issue, which we could use to track the fixes too.
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@StanFromIreland StanFromIreland changed the title Fail on new UB in CI gh-148286: Fail on new UB in CI Apr 9, 2026
@StanFromIreland

StanFromIreland commented Apr 9, 2026

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Created #148286.
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@StanFromIreland
StanFromIreland requested a review from encukou April 9, 2026 08:47
@StanFromIreland
Merge branch 'main' into san-ubsan
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@StanFromIreland
StanFromIreland merged commit ade914b into python:main Apr 9, 2026
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@StanFromIreland
StanFromIreland deleted the san-ubsan branch April 9, 2026 09:30
@bedevere-app bedevere-app Bot removed the awaiting core review label Apr 9, 2026
@StanFromIreland

StanFromIreland commented Apr 9, 2026

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Thanks for the reviews!
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ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
@StanFromIreland @ljfp
pythongh-148286: Fail when new UB is found by CI UBSan (python#148168)
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@vstinner vstinner mentioned this pull request Jun 10, 2026
gh-148286: Run test_capi and test_faulthandler on GHA UBSan #151274
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@vstinner vstinner removed the skip issue label Jun 10, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Jun 10, 2026
Various UB warnings found by UBSan #148286
Open
@matthiasgoergens matthiasgoergens mentioned this pull request Aug 5, 2026
gh-148286: Fix undefined behaviour in io.StringIO.read() after an overseek #154913
Open
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@ezio-melotti ezio-melotti Awaiting requested review from ezio-melotti ezio-melotti is a code owner
@hugovk hugovk Awaiting requested review from hugovk hugovk is a code owner
@AA-Turner AA-Turner Awaiting requested review from AA-Turner AA-Turner is a code owner
@webknjaz webknjaz Awaiting requested review from webknjaz webknjaz is a code owner
@encukou encukou Awaiting requested review from encukou
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@thesamesam thesamesam thesamesam left review comments
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@StanFromIreland @thesamesam @encukou @vstinner
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