Implement struct return thunks in CoreCLR WASM InterpToNativeGenerator by lewing · Pull Request #130379 · dotnet/runtime

lewing · 2026-07-08T21:43:05Z

Summary

Implements struct return support in the CoreCLR WASM interp-to-native thunk generator, fixing #120897.

Problem

InterpToNativeGenerator.cs emitted a PORTABILITY_ASSERT("Indirect struct return is not yet implemented.") for any PInvoke signature with a struct return type. This caused a runtime crash when CoreCLR WASM apps called native functions returning structs.

Fix

Collect unique struct return sizes from all signatures during code generation
Emit C typedefs (typedef struct { char d[N]; } wasm_ret_SN;) for each unique size
Use those typedefs as the return type in generated CallFunc_* thunks instead of asserting
emcc automatically lowers struct returns to the sret pointer convention — no special ABI handling needed

The fix works for both browser-wasm and wasi-wasm (same generator, same wasm32 ABI).

Test Changes

Removed native-mono test category from EnsureWasmAbiRulesAreFollowedInInterpreter — this test now passes on CoreCLR too

Note

This PR was generated with the assistance of GitHub Copilot.

Remove the PORTABILITY_ASSERT for indirect struct returns in the CoreCLR WASM interp-to-native thunk generator. For struct return types (S<N> tokens), emit C typedefs of the correct size so emcc generates the proper sret ABI calling convention. This fixes the runtime crash when CoreCLR WASM code calls native functions that return structs. Also remove the native-mono test category filter from EnsureWasmAbiRulesAreFollowedInInterpreter since it now works on CoreCLR. Fixes dotnet#120897 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This pull request updates the CoreCLR WASM interp-to-native thunk generator to support P/Invokes that return structs, removing the prior assert-only behavior and enabling CoreCLR interpreter scenarios that involve indirect struct returns. It also updates a WASM build test to run on CoreCLR now that this ABI shape is supported.

Changes:

Collect unique S<N> struct return sizes up-front and emit corresponding typedef struct { char d[N]; } wasm_ret_S<N>; definitions in generated code.
Generate call-thunks that use the emitted typedef as the native function’s return type (instead of asserting), allowing the toolchain to apply the correct hidden-return-buffer calling convention.
Remove the native-mono test category restriction from EnsureWasmAbiRulesAreFollowedInInterpreter, allowing the interpreter ABI test to run on CoreCLR.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/tasks/WasmAppBuilder/coreclr/InterpToNativeGenerator.cs	Adds struct-return typedef emission and uses those types for `S<N>` return thunks to avoid the previous portability assert.
src/mono/wasm/Wasm.Build.Tests/PInvokeTableGeneratorTests.cs	Enables the interpreter ABI validation test to run on CoreCLR by removing the mono-only category gate.

dotnet-policy-service · 2026-07-08T22:21:28Z

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

The CoreCLR WASM pipeline generates callhelpers-pinvoke.cpp, not pinvoke-table.cpp. This was already fixed in the workload PR but needs to be included here since the test now runs on CoreCLR after removing the native-mono category. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

pavelsavara · 2026-07-09T12:45:00Z

/azp run runtime-wasm

azure-pipelines · 2026-07-09T12:45:19Z

Azure Pipelines successfully started running 1 pipeline(s).

pavelsavara · 2026-07-09T12:47:35Z

Log

System.DllNotFoundException: Unable to load shared library 'wasm-abi' or one of its dependencies.

The EnsureWasmAbiRulesAreFollowedInInterpreter test requires the native build pipeline (NativeFileReference for wasm-abi.c) which is only available in the workload enablement PR. Re-add native-mono category so this test is skipped on CoreCLR until the pipeline is available. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

lewing · 2026-07-09T13:09:50Z

Log

System.DllNotFoundException: Unable to load shared library 'wasm-abi' or one of its dependencies.

The change is correct, it needs the native build changes in the workload pr to go green #130380 I've added back the active issue for now

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

pavelsavara · 2026-07-09T13:16:30Z

/azp run runtime-wasm

azure-pipelines · 2026-07-09T13:16:41Z

Azure Pipelines successfully started running 1 pipeline(s).

lewing · 2026-07-13T20:54:02Z

/azp run runtime-wasm

azure-pipelines · 2026-07-13T20:54:20Z

Azure Pipelines successfully started running 1 pipeline(s).

maraf · 2026-07-15T10:11:52Z

        [Theory]
        [BuildAndRun(aot: false)]
-        [TestCategory("native-mono")] // coreclr ActiveIssue: https://github.com/dotnet/runtime/issues/120897
+        [TestCategory("native-mono")]


The native-mono runs only on mono. The native runs on both.

@copilot create new PR and make this change

Copilot AI review requested due to automatic review settings July 8, 2026 21:43

github-actions Bot added the area-Infrastructure-coreclr Only use for closed issues label Jul 8, 2026

github-project-automation Bot added this to Runtime Infra Jul 8, 2026

Copilot started reviewing on behalf of lewing July 8, 2026 21:43 View session

lewing mentioned this pull request Jul 8, 2026

Enable wasm-tools workload for CoreCLR WASM targets #130380

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lewing marked this pull request as ready for review July 8, 2026 22:20

lewing requested review from akoeplinger, ilonatommy and maraf as code owners July 8, 2026 22:20

lewing added the arch-wasm WebAssembly architecture label Jul 8, 2026

lewing mentioned this pull request Jul 8, 2026

[WIP] Enable wasm-tools workload for CoreCLR WASM targets #130226

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Copilot AI review requested due to automatic review settings July 9, 2026 03:57

Copilot started reviewing on behalf of lewing July 9, 2026 03:57 View session

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build-analysis Bot mentioned this pull request Jul 9, 2026

Unable to pull image from mcr.microsoft.com #117164

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Copilot AI review requested due to automatic review settings July 9, 2026 13:08

Copilot started reviewing on behalf of lewing July 9, 2026 13:09 View session

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Comment thread src/tasks/WasmAppBuilder/coreclr/InterpToNativeGenerator.cs

Comment thread src/mono/wasm/Wasm.Build.Tests/PInvokeTableGeneratorTests.cs

lewing enabled auto-merge (squash) July 13, 2026 20:53

build-analysis Bot mentioned this pull request Jul 13, 2026

Wasm.Build.NativeRebuild.Tests.ReferenceNewAssemblyRebuildTest.ReferenceNewAssembly failure: Expected changed file: driver-gen.c #130540

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lewing requested review from pavelsavara and radekdoulik July 14, 2026 02:43

steveisok approved these changes Jul 14, 2026

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lewing merged commit c0a703f into dotnet:main Jul 14, 2026
56 of 61 checks passed

github-project-automation Bot moved this to Done in Runtime Infra Jul 14, 2026

This was referenced Jul 15, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#7749

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[main] Source code updates from dotnet/runtime dotnet/dotnet#7752

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maraf reviewed Jul 15, 2026

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dotnet-milestone-bot Bot added this to the 11.0-preview7 milestone Jul 15, 2026

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lewing commented Jul 8, 2026

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