[browser][coreCLR] no COM, no swift by pavelsavara · Pull Request #125083 · dotnet/runtime

pavelsavara · 2026-03-02T23:23:43Z

Trim dead interop/COM code from browser-WASM CoreCLR builds

Summary

This PR reduces the browser-WASM CoreCLR native binary size by excluding COM interop, SEH exception, and Swift interop code that cannot run on the browser platform.

Changes

1. Guard COM/Interop exception types with FEATURE_COMINTEROP (

excep.h)

Move InvalidOleVariantTypeException into the existing FEATURE_COMINTEROP block alongside InvalidComObjectException
Wrap ExternalException, and SEHException definitions with #ifdef FEATURE_COMINTEROP — these types only exist for COM interop scenarios

2. Guard SEHException handling block with TARGET_WASM (clrex.cpp)

Wrap the entire SEHException branch in CLRException::GetThrowableFromException with #ifndef TARGET_WASM. WASM has no hardware exception (signal) support, so SEHException objects are never produced on that platform.

3. Fix MapWin32FaultToCOMPlusException default case (�xcep.cpp)

The default case returned kSEHException, which is only defined under FEATURE_COMINTEROP. Guard the return with #ifdef FEATURE_COMINTEROP, falling back to kException on non-COM platforms.

4. Guard ComVariant references with FEATURE_COMINTEROP

corelib.h: Wrap DEFINE_CLASS(COMVARIANT, ...) with #if defined(FEATURE_COMINTEROP)
metasig.h: Wrap 3 COMVARIANT metasig entries with #ifdef FEATURE_COMINTEROP
olevariant.cpp: Wrap the VT_VARIANT → CLASS__COMVARIANT case with #ifdef FEATURE_COMINTEROP

5. Restrict Swift interop types to Apple platforms (corelib.h)

Guard SwiftSelf, SwiftSelf, SwiftError, and SwiftIndirectResult with #if defined(TARGET_APPLE). Swift interop is not supported on WASM or other non-Apple platforms.

6. Add [UnsupportedOSPlatform("browser")] to ComActivator

File: ComActivator.PlatformNotSupported.cs

Annotate ComActivator with [UnsupportedOSPlatform("browser")] so its [UnmanagedCallersOnly] methods are excluded from generated reverse P/Invoke stubs on browser builds.

7. Filter [UnsupportedOSPlatform("browser")] types from reverse P/Invoke stubs

File: PInvokeCollector.cs

Add IsUnsupportedOnBrowser() helper to DoesMethodHaveCallbacks() — skips generating reverse P/Invoke callback stubs for methods on types annotated with [UnsupportedOSPlatform("browser")].

8. Regenerated callhelpers files

Files: callhelpers-pinvoke.cpp, callhelpers-reverse.cpp, callhelpers-interp-to-managed.cpp

Regenerated to reflect the ComActivator exclusion and upstream changes.

Testing

Build verified with .\build.cmd -bl -os browser -subset clr -c Release /p:RuntimeFlavor=CoreCLR.

dotnet-policy-service · 2026-03-02T23:24:49Z

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Copilot

Pull request overview

This PR aims to reduce trimmed size for browser-WASM CoreCLR builds by removing/gating roots and native support code for features that aren’t supported in the browser (COM/interop-related pieces, DynamicInterfaceCastable, Swift interop, and intrinsics metadata rooting).

Changes:

Filters reverse P/Invoke stub generation for types marked [UnsupportedOSPlatform("browser")] and annotates ComActivator accordingly.
Gates ILLink rooting for ComponentActivator.GetFunctionPointer behind the existing native-hosting feature switch.
Adds TARGET_WASM guards to exclude DynamicInterfaceCastable native support on WASM and trims related ILLink roots / metadata retention paths.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/tasks/WasmAppBuilder/generate-coreclr-helpers.cmd	Updates helper generation script used for CoreCLR WASM callhelper regeneration.
src/tasks/WasmAppBuilder/coreclr/PInvokeCollector.cs	Skips generating reverse P/Invoke callback stubs for types unsupported on browser.
src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/CompExactlyDependsOnAttribute.cs	Removes `CompExactlyDependsOnAttribute` metadata for browser/WASI builds to improve trimming.
src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.Shared.xml	Gates `ComponentActivator.GetFunctionPointer` rooting behind the native-hosting feature switch.
src/coreclr/vm/wasm/callhelpers-reverse.cpp	Regenerated reverse thunk table reflecting removed callbacks.
src/coreclr/vm/wasm/callhelpers-pinvoke.cpp	Regenerated P/Invoke table reflecting upstream removals.
src/coreclr/vm/virtualcallstub.cpp	Removes DynamicInterfaceCastable resolver path from WASM builds.
src/coreclr/vm/rexcep.h	Attempts to exclude interop exception types from WASM ILLink descriptor generation.
src/coreclr/vm/methodtable.cpp	Removes IDynamicInterfaceCastable special method resolution on WASM.
src/coreclr/vm/jithelpers.cpp	Removes IDynamicInterfaceCastable cast path on WASM.
src/coreclr/vm/dynamicinterfacecastable.h	Wraps DynamicInterfaceCastable API surface out of WASM builds.
src/coreclr/vm/dynamicinterfacecastable.cpp	Wraps DynamicInterfaceCastable implementation out of WASM builds.
src/coreclr/vm/corelib.h	Attempts to exclude Swift interop and ComVariant from WASM ILLink descriptor generation; removes DynamicInterfaceCastableHelpers from WASM.
src/coreclr/System.Private.CoreLib/src/Internal/Runtime/InteropServices/ComActivator.PlatformNotSupported.cs	Marks `ComActivator` as unsupported on browser to suppress reverse stub generation.

src/tasks/WasmAppBuilder/generate-coreclr-helpers.cmd

src/coreclr/vm/corelib.h

src/coreclr/vm/rexcep.h

src/tasks/WasmAppBuilder/coreclr/PInvokeCollector.cs

src/coreclr/vm/corelib.h

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

src/coreclr/vm/rexcep.h

src/coreclr/vm/corelib.h

.../System.Private.CoreLib/src/System/Runtime/CompilerServices/CompExactlyDependsOnAttribute.cs

src/coreclr/vm/wasm/callhelpers-pinvoke.cpp

radekdoulik

Beside the 2 comments it LGTM, thank you!

src/coreclr/vm/corelib.h

src/coreclr/vm/rexcep.h

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.Shared.xml

jkotas · 2026-03-18T16:00:38Z

PR reduces the trimmed size of browser-WASM CoreCLR apps

Do you have any numbers for the size improvement?

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

src/coreclr/vm/corelib.h

- fallback to kException when not FEATURE_COMINTEROP instead of kSEHException and kCOMException - revert of CompExactlyDependsOnAttribute, GetFunctionPointer - regenerated helpers

src/coreclr/vm/clrex.cpp

src/coreclr/vm/rexcep.h

src/coreclr/vm/clrex.cpp

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

src/coreclr/vm/clrex.cpp

src/tasks/WasmAppBuilder/coreclr/PInvokeCollector.cs

src/coreclr/vm/rexcep.h

pavelsavara added this to the 11.0.0 milestone Mar 2, 2026

pavelsavara self-assigned this Mar 2, 2026

Copilot AI review requested due to automatic review settings March 2, 2026 23:23

pavelsavara added arch-wasm WebAssembly architecture area-VM-coreclr size-reduction Issues impacting final app size primary for size sensitive workloads os-browser Browser variant of arch-wasm labels Mar 2, 2026

dotnet-policy-service bot added the linkable-framework Issues associated with delivering a linker friendly framework label Mar 2, 2026

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pavelsavara force-pushed the browser_trim_COM branch from c066985 to 77b2da7 Compare March 3, 2026 07:37

rebase

cb5be74

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pavelsavara force-pushed the browser_trim_COM branch from 77b2da7 to cb5be74 Compare March 13, 2026 15:29

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pavelsavara marked this pull request as ready for review March 18, 2026 08:53

pavelsavara requested a review from maraf as a code owner March 18, 2026 08:53

Copilot AI mentioned this pull request Mar 18, 2026

Cache IsUnsupportedOnBrowser result per Type in PInvokeCollector #125722

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pavelsavara added 2 commits March 18, 2026 12:11

feedback

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Merge branch 'main' into browser_trim_COM

68792a5

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Merge branch 'main' into browser_trim_COM

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- feedback

8b8f562

- fallback to kException when not FEATURE_COMINTEROP instead of kSEHException and kCOMException - revert of CompExactlyDependsOnAttribute, GetFunctionPointer - regenerated helpers

pavelsavara changed the title ~~[browser][coreCLR] no COM, no swift, no x86 intrinsics~~ [browser][coreCLR] no COM, no swift Mar 20, 2026

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pavelsavara commented Mar 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Trim dead interop/COM code from browser-WASM CoreCLR builds

Summary

Changes

1. Guard COM/Interop exception types with FEATURE_COMINTEROP (

2. Guard SEHException handling block with TARGET_WASM (clrex.cpp)

3. Fix MapWin32FaultToCOMPlusException default case (�xcep.cpp)

4. Guard ComVariant references with FEATURE_COMINTEROP

5. Restrict Swift interop types to Apple platforms (corelib.h)

6. Add [UnsupportedOSPlatform("browser")] to ComActivator

7. Filter [UnsupportedOSPlatform("browser")] types from reverse P/Invoke stubs

8. Regenerated callhelpers files

Testing

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pavelsavara commented Mar 2, 2026 •

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