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CI should run Undefined Behavior Sanitizer (UBSAN), as already done for ASAN #111758

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CI should run Undefined Behavior Sanitizer (UBSAN), as already done for ASAN#111758
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buildThe build process and cross-buildinfraCI, GitHub Actions, buildbots, Dependabot, etc.type-featureA feature request or enhancement

Description

@thesamesam
thesamesam
opened on Nov 5, 2023

Feature or enhancement

Proposal:

cpython's CI should run Undefined Behavior Sanitizer (UBSAN), like it already does for Address Sanitizer (ASAN).

It already has support in configure for this with ./configure --with-undefined-behavior-sanitizer.

This is important for portability, future proofing (keeping CPython working with a range of compilers), and avoiding confusing bug reports later when UB manifests.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

Activity

  1. thesamesam
    added
    type-featureA feature request or enhancement
    on Nov 5, 2023

  2. thesamesam commented on Nov 5, 2023

    @thesamesam
    thesamesam
    on Nov 5, 2023
    ContributorAuthor

    Note that --with-undefined-behavior-sanitizer does not set export UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1 right now.

    By default, UBSAN will not abort on errors, which might mean errors are being missed by the fuzzer right now which does seem to use UBSAN? Not sure how the configuration works for that job:

    $ grep -rsin undefined .github/
.github/workflows/build.yml:467:        sanitizer: [address, undefined, memory]

  3. thesamesam commented on Nov 5, 2023

    @thesamesam
    thesamesam
    on Nov 5, 2023
    ContributorAuthor

    cc @gpshead as we've discussed build issues before and this feels like it's in your wheelhouse

  4. gpshead commented on Nov 5, 2023

    @gpshead
    gpshead
    on Nov 5, 2023
    Member

    Overall in favor. Doing this in CI is predicated on if we actually pass UBSAN today and which things we need to categorize and disable in order to do so.

  5. gpshead commented on Nov 5, 2023

    @gpshead
    gpshead
    on Nov 5, 2023
    Member

    Note that there have been some UB reports in the past that may be technically correct from a C++ compiler spec perspective (read: clang, and note that C and C++ have different defined behavior definitions) but not actually undefined from a "giant swath of C code in the world has depended on the implemented behavior for 30+ years" perspective so the implemented behavior won't actually ever be changed. (see us passing -fwrapv to the compiler all over the place? defining that behavior in our build is one reason why)

    Work to be done there (if any) is mostly around categorization and how to tell UBSAN which things we know and are okay with, the goal being not to introduce more.

  6. gpshead commented on Nov 5, 2023

    @gpshead
    gpshead
    on Nov 5, 2023
    Member

    For example, clang 17 ubsan gives triggers a build failure trying to run _freeze_module:

    ../cpython/Objects/object.c:2858:5: runtime error: call to function list_dealloc through pointer to incorrect function type 'void (*)(struct _o
bject *)'
../cpython/Objects/listobject.c:347: note: list_dealloc defined here

    (*)(PyObject *) vs (*)(PyListObject *) is "undefined"? CPython casts things to PyObject* all over the place as a standard practice by design as a common C idiom for structure extension.

  7. thesamesam commented on Nov 5, 2023

    @thesamesam
    thesamesam
    on Nov 5, 2023
    ContributorAuthor

    Yeah, see #111178 for that one. I'm not sure that this use as it stands is compatible with CFI which is a useful exploit mitigation.

    But yeah, categorising existing errors sounds fine, sorting them into "things we should fix" and "things we want to make defined in CPython".

  8. iritkatriel
    added
    buildThe build process and cross-build
    on Dec 1, 2023

  9. encukou commented on Jun 16, 2025

    @encukou
    encukou
    on Jun 16, 2025
    Member

    Undefined behavior is now gone (#111178, #133157), thanks to @picnixz and many others.

  10. encukou
    added a commit that references this issue on Jun 19, 2025

    gh-111758: Run UBSan in GitHub Actions (GH-135578)

    7a20c72

  11. encukou commented on Jun 19, 2025

    @encukou
    encukou
    on Jun 19, 2025
    Member

    The CI run is in. But, as Hugo pointed out, the workflow definitions are now somewhat repetitive.

    I'll watch the job for about a week before consolidating.

  12. picnixz
    added
    infraCI, GitHub Actions, buildbots, Dependabot, etc.
    on Jun 19, 2025
  13. lkollar
    added a commit that references this issue on Jun 19, 2025

    pythongh-111758: Run UBSan in GitHub Actions (pythonGH-135578)

    a8d54c9
  14. Pranjal095
    added a commit that references this issue on Jul 12, 2025

    pythongh-111758: Run UBSan in GitHub Actions (pythonGH-135578)

    e288c17

  15. webknjaz commented on Jul 20, 2025

    @webknjaz
    webknjaz
    on Jul 20, 2025
    Member

    I'll watch the job for about a week before consolidating.

    Now that it's passed, #136820 does this thanks to the EuroPython collab ;)

  16. thesamesam commented on Jul 20, 2025

    @thesamesam
    thesamesam
    on Jul 20, 2025
    ContributorAuthor

    Thanks for the efforts on this, all.

  17. hugovk
    added a commit that references this issue on Jul 20, 2025

    GH-111758: Merge TSan and UBSan reusable GHA workflows (#136820)

    65d2c51
  18. miss-islington
    added a commit that references this issue on Jul 20, 2025

    pythonGH-111758: Merge TSan and UBSan reusable GHA workflows (pythonG…

    1e3d1a8
  19. hugovk
    added a commit that references this issue on Jul 20, 2025

    [3.14] GH-111758: Merge TSan and UBSan reusable GHA workflows (GH-136820

    2f7684c

  20. webknjaz commented on Jul 22, 2025

    @webknjaz
    webknjaz
    on Jul 22, 2025
    Member

    @thesamesam I think this issue can be considered resolved.

  21. thesamesam commented on Jul 22, 2025

    @thesamesam
    thesamesam
    on Jul 22, 2025
    ContributorAuthor

    Indeed.

  22. thesamesam
    closed this as completedon Jul 22, 2025
  23. webknjaz
    added 2 commits that reference this issue on Jul 23, 2025

    [3.13] pythonGH-111758: Merge TSan and UBSan reusable GHA workflows (p…

    8876f0a

    [3.13] pythonGH-111758: Merge TSan and UBSan reusable GHA workflows (p…

    96da074
  24. encukou
    added a commit that references this issue on Aug 1, 2025

    [3.13] GH-111758: Merge TSan and UBSan reusable GHA workflows (#136820)…

    6a217ce
  25. taegyunkim
    added 2 commits that reference this issue on Aug 4, 2025

    pythongh-111758: Run UBSan in GitHub Actions (pythonGH-135578)

    78a9778

    pythonGH-111758: Merge TSan and UBSan reusable GHA workflows (python#…

    ad8bc56
  26. Agent-Hellboy
    added 2 commits that reference this issue on Aug 19, 2025

    pythongh-111758: Run UBSan in GitHub Actions (pythonGH-135578)

    b4cff88

    pythonGH-111758: Merge TSan and UBSan reusable GHA workflows (python#…

    a14be76
  27. kumaraditya303
    added a commit that references this issue on Sep 9, 2025

    [3.14] pythonGH-111758: Merge TSan and UBSan reusable GHA workflows (p…

    f740369
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