.NET 12 wasm: System.OverflowException: Arithmetic operation resulted in an overflow #134015

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1. richlander

   added this to the 12.0.0 milestone on Sep 16, 2026
2. richlander

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   Bug

   issue type on Sep 16, 2026
3. richlander

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   arch-wasmWebAssembly architectureWebAssembly architecture

   os-browserBrowser variant of arch-wasmBrowser variant of arch-wasm

   on Sep 16, 2026
4. dotnet-policy-service commented on Sep 16, 2026

   

   dotnet-policy-serviceBot

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

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   area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMICLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

   on Sep 16, 2026
6. dotnet-policy-service commented on Sep 16, 2026

   

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   Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
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7. richlander commented on Sep 17, 2026

   

   richlander

   on Sep 17, 2026

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   This is how I am installing the wasm SDK:

   richlander/dotnet-inspect#7488
8. richlander commented on Sep 23, 2026

   

   richlander

   on Sep 23, 2026

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   I reduced this to one assembly and bounded the first bad daily.

   Reproduction

   The exact failing dotnet-inspect head is
   469e912b6.
   Publishing its Inspect Web CoreCLR R2R variant with
   12.0.100-alpha.1.26472.116 leaves 96 of 97 expected R2R outputs. The only
   missing output is DotnetInspect.Web.Core.dll.

   Replaying Crossgen2 directly for that linked assembly and the publish reference
   closure reproduces the same exception:

   Emitting R2R Wasm file: DotnetInspect.Web.Core.dll
   Error: Arithmetic operation resulted in an overflow.
   System.OverflowException: Arithmetic operation resulted in an overflow.
      at ILCompiler.DependencyAnalysis.ReadyToRun.InliningInfoNode.GetData(...)
   

   crossgen2 --make-repro-path produced a standalone 14 MB repro bundle, and
   running its generated repro.rsp reproduces the exception independently of
   MSBuild. The bundle SHA-256 is
   eb5a78987847bf04a8a648e095cb00a3a46acba79a4598a4290fb5718621c30b.

   Boundary

   The same generated repro gives:

   Crossgen2	VMR	Result
   12.0.0-alpha.1.26462.105	c8c7ac15e5a07158cc2d5199d25d1840eaadf18e	pass
   12.0.0-alpha.1.26463.105	9da2930951f4498751b02ecf8546f6bde759ef9d	pass
   12.0.0-alpha.1.26464.107	b7e93309a78d453a032ddeb4c13ad57e5e6dffa8	overflow
   12.0.0-alpha.1.26464.120	2577879ab57d812ff130a476b34c717a1276adf3	overflow
   12.0.0-alpha.1.26465.115	b2f96bd7ac75c07fb8067c05c54767d3d5e12e8d	overflow
   12.0.0-alpha.1.26468.106	1c1ae5d3edc93742cdcb2311db6d480723c16033	overflow
   12.0.0-alpha.1.26472.116	0cfd699c3d0ad1d7054f237ccfbbb509b9d1c1e5	overflow

   The first bad VMR is dotnet/dotnet#9263. Its runtime codeflow is
   3d267058...edd70ca5.
   InliningInfoNode.cs itself is unchanged across the last-known-good and failing
   VMRs.

   The repro requires the WebAssembly SDK's --opt-cross-module:* argument:

   • Removing --opt-cross-module:* succeeds and emits the R2R Wasm file.
   • Keeping cross-module optimization but adding --strip-inlining-info also
     succeeds.

   That narrows the failure to cross-module inlining-info construction or
   serialization rather than general Wasm code generation. The first-bad runtime
   range includes #133146, but I have not isolated the regression to
   that PR.

   I have the Crossgen2-generated bundle locally; GitHub's programmatic attachment
   endpoint rejects ZIPs, so I can transfer it through another channel if useful.
9. lewing commented on Sep 26, 2026

   

   lewing

   on Sep 26, 2026

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   I reproduced this locally from the public dotnet-inspect repo at 469e912b6 with 12.0.100-alpha.1.26472.116, so the repro bundle isn't needed. Thanks for narrowing it down to one assembly and the --opt-cross-module:* / --strip-inlining-info behavior; that made it quick to pin down.

   The cause is in crossgen2's cross-module inlining info. When the runtime-async variant of a cross-module generic is compiled into the image and inlines another method (here, the async variant of Task<Completion<...>>.WaitAsync(CancellationToken) inlining TimeProvider.get_System()), the compiler records the Check_IL_Body fixup for the async variant. The inlining info writer then looked up the fixup for the plain EcmaMethod instead. That import was never placed, so its index was unset and the checked cast overflowed.

   It comes from the async inlining change in #125472; #133146 probably just changed codegen enough to produce this case in your app. The bug isn't Wasm-specific, but browser CoreCLR R2R hits it first because it passes --opt-cross-module:* by default.

   Fix and regression test: #134697

   Note

   This comment was generated with GitHub Copilot.
10. lewing

    self-assigned this

    on Sep 26, 2026
11. lewing

    closed this as completedin 56c46fbon Sep 30, 2026
12. pull

    added a commit that references this issue on Sep 30, 2026

    Fix crossgen2 OverflowException emitting inlining info for runtime-as…

    ...

    This issue will close once commit 56c46fb is merged into the 'main' branch.

    56c46fb
13. github-actions

    locked and limited conversation to collaborators on Oct 31, 2026