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[wasm][R2R] GC/API/GC/GetGeneration: objects stay in generation 0 after GC.Collect #134803

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Closed as not planned
[wasm][R2R] GC/API/GC/GetGeneration: objects stay in generation 0 after GC.Collect#134803
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arch-wasmWebAssembly architecturearea-GC-coreclros-browserBrowser variant of arch-wasm

Description

@lewing
lewing
opened on Sep 28, 2026

Description

On browser-wasm CoreCLR with ReadyToRun (RunCrossGen2=1), GC/API/GC/GetGeneration fails. After GC.Collect() the tested objects are still reported as generation 0, so ObjectTest and arrayTest fail:

Running test: GC/API/GC/GetGeneration/GetGeneration.dll
0 0
ObjectTest Failed!
0 0
arrayTest Failed!
failTest Passed!
Test for GetGeneration() FAILED!
Expected: 100
Actual:   1

That matches the reason the test already skips under the interpreter ("Interpreter reports locals as pinned, causing generation demotion that this test does not expect"). The test used to be skipped on every wasm run, because the runtime-test InterpreterActive mode was always true on wasm. #134767 changes InterpreterActive to mean "code runs in the interpreter" (no JIT and not ReadyToRun-compiled), so wasm R2R now runs it.

Configuration

  • Fails: browser-wasm CoreCLR Checked, ReadyToRun (TEST_READY_TO_RUN_MODE=1).
  • Skipped (interpreter): browser-wasm CoreCLR without R2R.
  • Passes: maccatalyst-arm64 CoreCLR Release ReadyToRun (no JIT), android-arm64 CoreCLR, and desktop CoreCLR.

The root cause isn't known. Candidates are part of the call path still running in the interpreter under wasm R2R, or conservative or pinned stack reporting for wasm R2R frames.

Note

This issue was drafted with GitHub Copilot.

Activity

  1. lewing
    added
    arch-wasmWebAssembly architecture
    area-GC-coreclr
    os-browserBrowser variant of arch-wasm
    on Sep 28, 2026
  2. github-project-automation
    added this to AppModelon Sep 28, 2026
  3. dotnet-policy-service
    added
    untriagedNew issue has not been triaged by the area owner
    on Sep 28, 2026

  4. dotnet-policy-service commented on Sep 28, 2026

    @dotnet-policy-service
    dotnet-policy-servicebot
    on Sep 28, 2026 – with Dotnet Policy Service
    Contributor

    Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara
    See info in area-owners.md if you want to be subscribed.

  5. dotnet-policy-service commented on Sep 28, 2026

    @dotnet-policy-service
    dotnet-policy-servicebot
    on Sep 28, 2026 – with Dotnet Policy Service
    Contributor

    Tagging subscribers to this area: @anicka-net, @dotnet/gc
    See info in area-owners.md if you want to be subscribed.

  6. AndyAyersMS commented on Sep 28, 2026

    @AndyAyersMS
    AndyAyersMS
    on Sep 28, 2026
    Member

    Likely because all stack roots are reported as pinned.

  7. lewing
    added 2 commits that reference this issue on Sep 28, 2026

    Make InterpreterActive mean code runs in the interpreter

    c4e410a

    Keep the meaning of IsCoreClrInterpreter and fix GetGeneration's skip…

    db3c2ff

  8. lewing commented on Sep 28, 2026

    @lewing
    lewing
    on Sep 28, 2026
    MemberAuthor

    Closing as expected behavior. As @AndyAyersMS noted, WebAssembly reports stack roots as pinned, so GetGeneration's generation-promotion checks can't hold there, with or without ReadyToRun. #134767 now skips the test on Browser/Wasi permanently (SkipOnPlatform, linking here for context) instead of quarantining it. It keeps running where the test's own code is compiled, including Apple mobile ReadyToRun.

    Note

    This comment was generated with GitHub Copilot.

  9. lewing
    closed this as not plannedon Sep 28, 2026
  10. dotnet-policy-service
    removed
    untriagedNew issue has not been triaged by the area owner
    on Sep 28, 2026
  11. lewing
    added 3 commits that reference this issue on Sep 28, 2026

    [Apple][Android][CoreCLR] Don't pass the program path as managed args…

    47a2e6d

    Make the wasm R2R GC-lifetime skips permanent

    e1f4044

    [wasm][CoreCLR] Add browser_wasm R2R_CG2 leg to runtime-coreclr outer…

    ed08972
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