Enable building a stubbed NativeAOT WASM CoreLib by jtschuster · Pull Request #134210 · dotnet/runtime

jtschuster · 2026-09-18T18:33:09Z

Building the repro project requires a number of helper methods in CoreLib, but stack unwinding, GC, and EH designs haven't been determined, so in the meantime we could just stub all of these out. This will enable ilc to at compile a WASM module (or at least moves one blocker), though it won't link or run yet.

Enable the managed NativeAOT CoreLib build for single-threaded browser WASM and provide shape-compatible stubs for runtime functionality that is not implemented yet. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 6cdcf8df-1e43-462e-b0a7-b4cea297b576

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 6cdcf8df-1e43-462e-b0a7-b4cea297b576

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Copilot

🟡 Changes recommended

The WASM exception helpers have an ABI mismatch and are missing the required RhpThrowExact export.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Adds browser-WASM NativeAOT CoreLib stubs and build configuration to unblock compilation while exception handling, stack unwinding, GC, and dynamic thunks remain unsupported.

Changes:

Adds WASM-specific source selection and platform definitions.
Stubs thunk allocation, stack tracing, frozen-object memory, and exception handling.
Removes unsupported native WASM imports and exports placeholder EH helpers.

File summaries

File	Summary
`src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/ThunkPool.NotSupported.cs`	Stubs dynamic thunk operations.
`src/coreclr/nativeaot/System.Private.CoreLib/src/System/Diagnostics/StackTrace.NativeAot.Browser.cs`	Disables browser-WASM stack traces.
`src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj`	Selects WASM-specific implementations.
`src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/FrozenObjectHeapManager.Wasm.cs`	Stubs virtual memory operations.
`src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/RuntimeExports.cs`	Omits native stack-trace exports on WASM.
`src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/InternalCalls.cs`	Omits unsupported EH and stack-walking imports.
`src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ExceptionHandling.wasm.cs`	Adds placeholder exception-handling exports.
`src/coreclr/nativeaot/Directory.Build.props`	Adds WASM platform definitions.

Review details

Files reviewed: 8/8 changed files
Comments generated: 2
Review effort level: Lite

… twice into one

Copilot

🟡 Changes recommended

Critical WASI build inconsistencies remain, and the NativeAOT support change belongs in the Arcade-managed source.

Get a fresh assessment by requesting another Copilot review.

Review details

Files reviewed: 10/11 changed files
Comments generated: 4
Review effort level: Lite

jkotas · 2026-09-19T04:10:26Z

    <_NativeAotSupportedOS Condition="
-      '$(TargetOS)' != 'browser' and
      '$(TargetOS)' != 'haiku' and


Valid feedback

We can create additional PR upstream so overwriting doesn’t revert it, without dropping the changes here. It’s not exactly prohibited.

…ining from Rhp* helpers

Copilot

Copilot review overview

🟡 Changes recommended

The WASI TARGET_UNIX definition must be corrected, and the browser-specific source should be renamed.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 3 · 1

Open (4)

Define TARGET_UNIX for WASI builds · New
TARGET_WASM is also defined for WASI (eng/OSArch.props:23-24), but this project only…
eng/common is explicitly managed by automation from dotnet/arcade, and…
Rename browser-specific stack trace source for shared WASM · New

Resolved since last review (2)

The new support predicate also enables wasi/wasm, but the rest of this patch only supplies…
This removal is browser-only, but the preceding NativeAOT support change now enables every…

Copilot

Copilot review overview

🔵 Needs a closer look

Broad runtime stubs and WASM/WASI build changes require final human review.

Review effort: Lite
Findings: 1 · 2

Open (3)

eng/common is explicitly managed by automation from dotnet/arcade, and…
Use WASM instead of browser-WASM in ABI description · New
Update stale Browser-WASM qualifier in comment · New

Resolved since last review (3)

Define TARGET_UNIX for WASI builds
TARGET_WASM is also defined for WASI (eng/OSArch.props:23-24), but this project only…
Rename browser-specific stack trace source for shared WASM

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Copilot review overview

🟡 Changes recommended

The WASM EH stub omits a required member, and WASM perf-tracing configuration remains inconsistent.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

Add missing WASM stub for GetClasslibExceptionFromEEType · New
eng/common is explicitly managed by automation from dotnet/arcade, and…

Resolved since last review (2)

Update stale Browser-WASM qualifier in comment
Use WASM instead of browser-WASM in ABI description

Previously missed (1)

In code that hasn't changed since last review

Clarify comment applies to all WASM targets, including WASI

src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/InternalCalls.cs:147

This guard applies to every TARGET_WASM build, including WASI, but the new comment limits the rationale to Browser-WASM. Since the surrounding project now explicitly enables both browser and WASI NativeAOT, the comment is inaccurate and can mislead future changes; describe the shared WASM limitation instead.

[!NOTE] This review comment was generated by GitHub Copilot.

MichalStrehovsky · 2026-09-24T01:36:36Z

    <FeatureComWrappers>true</FeatureComWrappers>
    <DefineConstants Condition="'$(FeatureComWrappers)' == 'true'">FEATURE_COMWRAPPERS;$(DefineConstants)</DefineConstants>


CoreCLR disables FeatureComWrappers on non-Windows/non-Unix, this is the first such target.

Also cc @dotnet/interop-contrib just in case - not sure if ComWrappers being disabled on Browser/WASI is intentional. We disable the tests with no tracking bug and the disablement was done in one of those "let's just bulk disable everything that doesn't work" PRs so not clear if this is intentional.

not sure if ComWrappers being disabled on Browser/WASI is intentional

I see no reason to add support for ComWrappers on Browser/WASI at this point. If we get it "for free" that might be okay, but investigating COM scenarios on that platform sounds painful. I'm also suspicious of anyone using COM there for interop or API design. My guidance would be avoid enabling it for now since it is already disabled and if someone squeeks we can have the conversation.

I would like to ifdef out and IL trim any COM code that still remains there.

…ot-wasm-runtime-pack

…huster/runtime into nativeaot-wasm-runtime-pack

- Use Unix implementations instead of separate wasm implementations for StackTrace.NativeAot.cs and FrozenObjectHeap.cs - Remove useless Feature defines - Disable ComWrappers support - Don't define TARGET_UNIX for WASM and add || TARGET_WASM to TARGET_UNIX where necessary.

Copilot

Copilot review overview

🟡 Changes recommended

Unresolved critical WASI ABI and COM-wrapper feature-definition issues block approval.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 3

Open (3)

Define TARGET_UNIX for WASI builds · New
Apply FeatureComWrappers override before defining feature constant · New
eng/common is explicitly managed by automation from dotnet/arcade, and…

Resolved since last review (1)

Add missing WASM stub for GetClasslibExceptionFromEEType

MichalStrehovsky · 2026-09-25T04:44:53Z

    <DefineConstants Condition="'$(TargetsUnix)'=='true'">TARGET_UNIX;$(DefineConstants)</DefineConstants>
+    <DefineConstants Condition="'$(TargetsBrowser)'=='true'">TARGET_BROWSER;$(DefineConstants)</DefineConstants>
+    <DefineConstants Condition="'$(TargetsWasi)'=='true'">TARGET_WASI;$(DefineConstants)</DefineConstants>


I don't see us setting TARGET_UNIX on WASI with CoreCLR corelib. I assume we're just getting the lobotomized copilot review agent.

+  <PropertyGroup Condition="'$(TargetsWasm)' == 'true'">
+    <FeatureThunkPool>false</FeatureThunkPool>
+    <FeatureComWrappers>false</FeatureComWrappers>


jkotas · 2026-09-25T04:38:37Z

        // StackFrameIterator
        //

+        // Browser-WASM does not have the native register context required by this iterator.


Suggested change

// Browser-WASM does not have the native register context required by this iterator.

// WASM does not have the native register context required by this iterator.

jkotas · 2026-09-25T04:44:14Z

        internal static unsafe void FreeLibrary(IntPtr hModule)
        {
-#if !TARGET_UNIX
+#if !(TARGET_UNIX || TARGET_WASM)


Suggested change

#if !(TARGET_UNIX || TARGET_WASM)

#if TARGET_WINDOWS

MichalStrehovsky · 2026-09-25T04:41:43Z

        internal static unsafe void FreeLibrary(IntPtr hModule)
        {
-#if !TARGET_UNIX
+#if !(TARGET_UNIX || TARGET_WASM)


The original already wasn't great but this is making it even worse.

Suggested change

#if !(TARGET_UNIX || TARGET_WASM)

#if TARGET_WINDOWS

MichalStrehovsky · 2026-09-25T04:44:53Z

    <DefineConstants Condition="'$(TargetsUnix)'=='true'">TARGET_UNIX;$(DefineConstants)</DefineConstants>
+    <DefineConstants Condition="'$(TargetsBrowser)'=='true'">TARGET_BROWSER;$(DefineConstants)</DefineConstants>
+    <DefineConstants Condition="'$(TargetsWasi)'=='true'">TARGET_WASI;$(DefineConstants)</DefineConstants>


I don't see us setting TARGET_UNIX on WASI with CoreCLR corelib. I assume we're just getting the lobotomized copilot review agent.

jtschuster added 4 commits September 18, 2026 10:59

remove extra stuff

9cfab06

Tighten browser WASM CoreLib stubs

f87741c

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 6cdcf8df-1e43-462e-b0a7-b4cea297b576

Simplify browser WASM CoreLib configuration

b71f149

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 6cdcf8df-1e43-462e-b0a7-b4cea297b576

jtschuster added this to the 12.0.0 milestone Sep 18, 2026

jtschuster requested a review from agocke September 18, 2026 18:33

jtschuster self-assigned this Sep 18, 2026

Copilot AI lite review requested due to automatic review settings September 18, 2026 18:33

jtschuster added the arch-wasm WebAssembly architecture label Sep 18, 2026

jtschuster requested a review from MichalStrehovsky as a code owner September 18, 2026 18:33

jtschuster added the area-NativeAOT-coreclr label Sep 18, 2026

github-project-automation Bot added this to AppModel Sep 18, 2026

Copilot started reviewing on behalf of jtschuster September 18, 2026 18:33 View session

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Comment thread src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ExceptionHandling.wasm.cs Outdated

Comment thread src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ExceptionHandling.wasm.cs Outdated

jkotas reviewed Sep 18, 2026

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/ThunkPool.NotSupported.cs Outdated

jkotas reviewed Sep 18, 2026

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Comment thread src/coreclr/nativeaot/Directory.Build.props Outdated

jkotas reviewed Sep 18, 2026

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj

jkotas reviewed Sep 18, 2026

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj Outdated

jtschuster added 3 commits September 18, 2026 14:39

Enable clr.nativeaotlibs subset for browser-wasm

9d47d3b

Fix RhpThrow* helpers and remove unnecessary comment

da4f8bb

Match clr.featuredefines.props and coalesce setting the same property…

0159f79

… twice into one

Copilot AI review requested due to automatic review settings September 18, 2026 21:40

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jkotas reviewed Sep 19, 2026

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Comment thread src/coreclr/nativeaot/Test.CoreLib/src/Test.CoreLib.csproj Outdated

jkotas reviewed Sep 19, 2026

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Comment thread src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ExceptionHandling.wasm.cs Outdated

Remove Browser filter on shared wasm msbuild confitions, remove NoInl…

e33dd4d

…ining from Rhp* helpers

Copilot AI review requested due to automatic review settings September 22, 2026 22:27

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Comment thread src/coreclr/nativeaot/Directory.Build.props Outdated

Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj Outdated

Add TARGET_WASI, rename *.Browser.cs to *.Wasm.cs

0926af3

Copilot AI review requested due to automatic review settings September 23, 2026 18:20

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Comment thread src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ExceptionHandling.wasm.cs Outdated

Comment thread src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/InternalCalls.cs Outdated

Update comments to remove 'Browser-' prefix for WASM

7c1dc98

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings September 23, 2026 18:30

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Comment thread src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/ExceptionHandling.wasm.cs

build-analysis Bot mentioned this pull request Sep 24, 2026

System.Security.Cryptography.Tests.HpkeImplementationTests.InvalidEncapsulation_Rejected fails in CI #134528

Open

MichalStrehovsky reviewed Sep 24, 2026

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jtschuster added 3 commits September 24, 2026 10:35

Merge branch 'main' of https://github.com/dotnet/runtime into nativea…

b1069b0

…ot-wasm-runtime-pack

Merge branch 'nativeaot-wasm-runtime-pack' of https://github.com/jtsc…

8d2cb42

…huster/runtime into nativeaot-wasm-runtime-pack

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This was referenced Sep 24, 2026

8.0: Http2_IncorrectServerPreface_RequestFailsWithAppropriateHttpProtocolException failed #118906

Open

Async2TaskAdapters.TestValueTaskOfTaskValueVersusAsync fails with SanityCheck() in Wasm R2R test #133953

Open

jkotas reviewed Sep 25, 2026

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MichalStrehovsky reviewed Sep 25, 2026

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		<FeatureComWrappers>true</FeatureComWrappers>
		<DefineConstants Condition="'$(FeatureComWrappers)' == 'true'">FEATURE_COMWRAPPERS;$(DefineConstants)</DefineConstants>

	// Browser-WASM does not have the native register context required by this iterator.
	// WASM does not have the native register context required by this iterator.

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am11 Sep 20, 2026 •

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