Emit Async Methods in crossgen2 by jtschuster · Pull Request #124203 · dotnet/runtime

jtschuster · 2026-02-09T23:25:04Z

Emit async methods, and their resumption stubs into ReadyToRun images. Also compiles and emits async thunks for task-returning methods.

Signatures for async methods are emitted in the InstanceMethod table, with an additional ENCODE_METHOD_SIG_AsyncVariant (0x100) flag.

Resumption stubs are encoded as precode fixups for the async method with the "signature" being the RVA of the start point of the code. When the fixups are resolved, a DynamicMethodDesc / ILStub is created to represent the resumption and enable GC and unwind info to be resolved. Async methods which do not await and do not need resumption stubs won't have a resumption stub fixup.

The resumption stub MethodDescs are created following the existing pattern for ILStubs, but set the code to the R2R code rather than a precode thunk.

…itialize

…ating

…c method.

- Add UseRuntimeAsync property for source projects - Add TestRuntimeAsync property for test projects - Enable RuntimeAsync with crossgen2 - Add pipeline leg for runtimeasync tests with crossgen2

jtschuster · 2026-02-09T23:30:31Z

/azp run runtime-coreclr crossgen2

azure-pipelines · 2026-02-09T23:30:42Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

This PR adds initial support for emitting and consuming runtime-async-related methods in crossgen2 ReadyToRun (R2R) images, including new signature flags and runtime-side lookup/GC-walk plumbing for async variants and resumption stubs.

Changes:

Enables runtime-async=on feature flagging for selected source and test projects, and adds a dedicated CI leg to run R2R + runtime-async library tests.
Extends R2R method signature encoding/decoding to represent async variants and resumption stubs, and updates crossgen2 tooling/readers to surface these modifiers.
Adds runtime support for locating and registering resumption stub entrypoints so stack walking/GC can associate R2R resumption stubs with a MethodDesc.

Reviewed changes

Copilot reviewed 35 out of 36 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/libraries/Directory.Build.targets	Enables preview features + `runtime-async=on` for source projects when `UseRuntimeAsync=true`.
eng/testing/tests.targets	Adjusts runtime-async enablement for tests and adds `TestRuntimeAsync` override knob.
eng/pipelines/coreclr/crossgen2.yml	Adds a new CI test matrix leg for R2R + runtime-async libraries testing.
src/coreclr/inc/corcompile.h	Adds `ENCODE_METHOD_SIG_ResumptionStub` flag for method signature encoding.
src/coreclr/tools/Common/Internal/Runtime/ReadyToRunConstants.cs	Adds managed enum flag `READYTORUN_METHOD_SIG_ResumptionStub`.
src/coreclr/vm/zapsig.cpp	Reads new ResumptionStub flag during method sig decode (currently unused in logic).
src/coreclr/vm/stackwalk.cpp	Relaxes a debug assert for unwind table registration to accommodate async R2R scenarios.
src/coreclr/vm/readytoruninfo.h	Declares runtime API to look up resumption stub entrypoints for async variants.
src/coreclr/vm/readytoruninfo.cpp	Implements resumption stub lookup and registers R2R-backed stub `MethodDesc` for GC stack walks.
src/coreclr/vm/method.hpp	Extends async lookup enum and dynamic IL stub types to represent R2R resumption stubs.
src/coreclr/vm/methodtable.cpp	Adds an `AsyncResumptionStub` lookup path (currently duplicative of the existing slow path).
src/coreclr/vm/ilstubcache.h	Declares helper to create a DynamicMethodDesc wrapper around precompiled (R2R) stub code.
src/coreclr/vm/ilstubcache.cpp	Implements creation of an R2R-backed IL-stub `MethodDesc` with native entrypoint set directly.
src/coreclr/vm/jitinterface.cpp	Tweaks READYTORUN_HELPER handling (includes an unexpected `printf`).
src/coreclr/inc/readytorunhelpers.h	Adds mapping for `READYTORUN_HELPER_ThrowExact`.
src/coreclr/inc/readytorun.h	Clarifies formatting/commenting for async continuation helpers.
src/coreclr/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunSignature.cs	Shows `[RESUME]` in method display and improves `BadImageFormatException` message.
src/coreclr/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunReader.cs	Tracks async/resume modifiers when parsing instance method + PGO sections.
src/coreclr/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunMethod.cs	Stores/display method modifiers (async/resume) in signature string.
src/coreclr/tools/aot/ILCompiler.Reflection.ReadyToRun/PgoInfoKey.cs	Includes modifiers in PGO key signature string generation.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj	Adds `AsyncMethodVariant.Mangling.cs` to the build.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/IL/ReadyToRunILProvider.cs	Broadens IL provisioning to handle async variants and resumption stubs.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunTableManager.cs	Categorizes async variants/resumption stubs with instantiated methods for table emission.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilation.cs	Avoids inlining async call/thunk methods and force-adds required async metadata references once.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs	Minor whitespace/style fix.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/SignatureBuilder.cs	Emits ResumptionStub flag and hashes resumption stubs with their async variant method signature.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/ModuleTokenResolver.cs	Adjusts method token resolution and adds field token resolution helper.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/MethodFixupSignature.cs	Ensures async variants/resumption stubs aren’t incorrectly optimized as ordinary defs.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/InstanceEntryPointTableNode.cs	Handles async variants/resumption stubs in instantiated entrypoint table emission.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/InliningInfoNode.cs	Skips emitting inlining info for async thunks and avoids work for methods with no inlinees.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/ExceptionInfoLookupTableNode.cs	Skips EH-info table processing for resumption stubs.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeFixupSignature.cs	Adjusts GC map encoding size computation (currently incorrect for non-64-bit pointer sizes).
src/coreclr/tools/Common/TypeSystem/IL/Stubs/AsyncResumptionStub.cs	Updates diagnostic naming and hashing; marks token generation on emit.
src/coreclr/tools/Common/TypeSystem/IL/InstantiatedMethodIL.cs	Relaxes a Debug.Assert to accommodate non-standard owning method relationships.
src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs	Enables READYTORUN path to provide an async resumption stub and relaxes a debug assert for async variants.
src/coreclr/tools/Common/Compiler/CompilerTypeSystemContext.Async.cs	Tracks continuation types as valid types.
src/coreclr/tools/Common/Compiler/AsyncMethodVariant.cs	Treats resumption stubs as async thunks for compilation decisions.

Comments suppressed due to low confidence (1)

src/coreclr/vm/jitinterface.cpp:14153

Avoid calling printf from the VM here. This will write to stdout in production and can interfere with host output; it also bypasses existing logging/diagnostics patterns already present in this block (STRESS_LOG + _ASSERTE). Please remove the printf and rely on the existing logging/assertion mechanisms (or route through the runtime logging infrastructure if an additional message is needed).

                    result = (size_t)GetEEFuncEntryPoint(DelayLoad_Helper_Obj);
                    break;

                case READYTORUN_HELPER_DelayLoad_Helper_ObjObj:

src/coreclr/vm/methodtable.cpp

src/coreclr/vm/zapsig.cpp

...tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/TypeFixupSignature.cs

src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs

Co-authored-by: Copilot <[email protected]>

azure-pipelines · 2026-03-06T22:50:28Z

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azure-pipelines · 2026-03-06T22:50:53Z

Azure Pipelines successfully started running 1 pipeline(s).

src/coreclr/jit/async.cpp

1. ARM Thumb bit (emit.cpp): Add codeDelta to emitRecordRelocationWithAddlDelta for CORINFO_AsyncResumeInfo.Resume and DiagnosticIP. On ARM32, CorInfoReloc::DIRECT maps to IMAGE_REL_BASED_HIGHLOW which doesn't add the Thumb bit, causing SIGILL when DispatchContinuations calls the resume stub. 2. Tiered compilation init (ilstubcache.cpp): Call DetermineAndSetIsEligibleForTieredCompilation() on the MethodDescChunk in CreateR2RBackedILStub. Without this, GC stack walks through R2R-backed IL stubs assert on IsEligibleForTieredCompilation(). Co-authored-by: Copilot <[email protected]>

Copilot

Pull request overview

Copilot reviewed 39 out of 40 changed files in this pull request and generated no new comments.

jtschuster · 2026-03-09T18:03:50Z

Looks like all failures are unrelated

davidwrighton

I see a need for minor changes only.

src/coreclr/jit/async.cpp

.../tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunCodegenNodeFactory.cs

Add comment why we don't emit async methods in composite or ARM32 Use runtime check to avoid setting entrypoint for async helpers in non-r2r scenarios

jakobbotsch

JIT changes LGTM

…tion in async methods Add a TypeDesc case to GetModuleTokenForType to handle InstantiatedType and other non-EcmaType TypeDesc variants by delegating to the existing ModuleTokenResolver.GetModuleTokenForType. Fixes a regression from dotnet#124203 where async resumption stubs referencing generic type instantiations (e.g., CallStruct1M0<T>) crash with NotImplementedException on Apple simulator CoreCLR RuntimeTests. Co-authored-by: Copilot <[email protected]>

…tion in async methods (#125444) Fixes a regression introduced in #124203 where crossgen2 crashes with `NotImplementedException: Unsupported token resolution for Internal.TypeSystem.InstantiatedType` when compiling async methods that reference generic type instantiations (e.g., `CallStruct1M0<T>`) on Apple mobile platforms. ## Problem The `GetModuleTokenForType` local function in `HandleToModuleToken` handles `SignatureMethodVariable`, `ParameterizedType`, and `EcmaType`, but does not handle `InstantiatedType`. When async resumption stubs resolve tokens for instantiated generic types, the code falls through to the `default` case and throws. Affected jobs in `runtime-extra-platforms` pipeline: - `iossimulator-arm64 Release AllSubsets_CoreCLR_RuntimeTests` - `iossimulator-x64 Release AllSubsets_CoreCLR_RuntimeTests` - `tvossimulator-arm64 Release AllSubsets_CoreCLR_RuntimeTests` **Failed build:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1329675&view=results Co-authored-by: Copilot <[email protected]>

Emit async methods and resumption stubs in crossgen2 ReadyToRun images Add support for compiling and emitting runtime-async methods, their async thunks, and resumption stubs into ReadyToRun (R2R) images produced by crossgen2. Async method signatures are emitted in the InstanceMethod table with a new ENCODE_METHOD_SIG_AsyncVariant (0x100) flag. Resumption stubs are encoded as precode fixups using a new READYTORUN_FIXUP_ResumptionStubEntryPoint (0x38) fixup kind, where the "signature" is the RVA of the stub code. At fixup resolution time, a DynamicMethodDesc/ILStub is created to represent the resumption and provide GC and unwind info. Async methods that do not await skip resumption stub emission. Key changes: - Add ResumptionStubEntryPointSignature node and fixup support - Implement getAsyncResumptionStub and getFunctionEntryPoint in crossgen2's CorInfoImpl to enable the JIT to emit async calls - Set R2R entrypoints on JIT-synthesized async helper calls (context capture/restore) via SetCallEntrypointForR2R - Extend ReadyToRunILProvider to handle AsyncMethodVariant and AsyncResumptionStub IL bodies, including cross-module token rewriting through ManifestModuleWrappedMethodIL - Route async variants and resumption stubs through the instance entrypoint table and inlining info emission - Fix PEObjectWriter ARM64 page-relative relocations to support non-zero addends (needed for resumption stub code deltas) - Fix GC pointer map encoding for types whose size is not pointer-aligned (off-by-one in encodedGCRefMap allocation) - Mark CEE_JMP as unsupported in R2R (incorrect indirection cell setup) - Disable hot/cold splitting for async methods (runtime limitation) - Disable async method emission in composite mode and ARM32 (known issues tracked in #125337 and #125338) - Extend crossgen2 CI pipeline to arm64 (linux, osx, windows) - Update r2rdump/ReadyToRunReader to discover resumption stubs - Update ReadyToRun format documentation with new fixup kinds and method signature flag Co-authored-by: Jan Kotas <[email protected]> Co-authored-by: Copilot <[email protected]>

…tion in async methods (#125444) Fixes a regression introduced in #124203 where crossgen2 crashes with `NotImplementedException: Unsupported token resolution for Internal.TypeSystem.InstantiatedType` when compiling async methods that reference generic type instantiations (e.g., `CallStruct1M0<T>`) on Apple mobile platforms. ## Problem The `GetModuleTokenForType` local function in `HandleToModuleToken` handles `SignatureMethodVariable`, `ParameterizedType`, and `EcmaType`, but does not handle `InstantiatedType`. When async resumption stubs resolve tokens for instantiated generic types, the code falls through to the `default` case and throws. Affected jobs in `runtime-extra-platforms` pipeline: - `iossimulator-arm64 Release AllSubsets_CoreCLR_RuntimeTests` - `iossimulator-x64 Release AllSubsets_CoreCLR_RuntimeTests` - `tvossimulator-arm64 Release AllSubsets_CoreCLR_RuntimeTests` **Failed build:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1329675&view=results Co-authored-by: Copilot <[email protected]>

jtschuster added 15 commits February 5, 2026 12:57

Passing async tests

db314fe

Undo extra changes

fcf110f

Fix merge issues

e1dec2b

Cleanup ManifestModuleWrappedIL creation

696b6b6

Use correct OwningMethod for ManifestMetadataModuleWrappedMethodIL.In…

d0a228c

…itialize

Merge branch 'main' of https://github.com/dotnet/runtime into runtime16

dea51a8

Undo formatting in CorInfoImpl.ReadyToRun.cs

d37bfc8

Remove duplicated method from merge, remove unnecessary token manipul…

af114a0

…ating

Merge branch 'main' of https://github.com/dotnet/runtime into runtime16

bf8f402

Remove duplicates from merge

435c5d9

Use the same version resilient hash code for resumption stub and asyn…

8465ceb

…c method.

Generalize CreateR2RBackedILStub

49101ed

Allow async methods without resumption stubs

5bcb9b5

Allow using code for methods without resumption stubs in the r2r image

17e3358

Enable RuntimeAsync library tests

c66218c

- Add UseRuntimeAsync property for source projects - Add TestRuntimeAsync property for test projects - Enable RuntimeAsync with crossgen2 - Add pipeline leg for runtimeasync tests with crossgen2

jtschuster requested a review from davidwrighton February 9, 2026 23:25

jtschuster self-assigned this Feb 9, 2026

Copilot AI review requested due to automatic review settings February 9, 2026 23:25

jtschuster added the runtime-async label Feb 9, 2026

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Copilot started reviewing on behalf of jtschuster February 9, 2026 23:26 View session

Merge branch 'main' of https://github.com/dotnet/runtime into runtime16

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Co-authored-by: Copilot <[email protected]>

Copilot AI review requested due to automatic review settings February 9, 2026 23:41

Copilot started reviewing on behalf of jtschuster February 9, 2026 23:42 View session

Clean up extraneous changes and fix build

4dfdfe2

jakobbotsch reviewed Mar 6, 2026

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jtschuster added 2 commits March 6, 2026 16:16

Move method in anon. namespace to static helper

6fe7181

Missed a line when reverting changes

b467dec

build-analysis bot mentioned this pull request Mar 7, 2026

[Android][CoreCLR] System.Security.Cryptography.Tests killed by lowmemorykiller #118603

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jtschuster and others added 2 commits March 8, 2026 17:46

Just skip ARM32 instead of trying to get it all working all at once

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jtschuster mentioned this pull request Mar 9, 2026

Crossgen2 does not emit runtime-async methods in composite mode #125337

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jtschuster requested review from MichalStrehovsky, jakobbotsch and jkotas March 9, 2026 18:30

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PR Feedback:

e3a400c

Add comment why we don't emit async methods in composite or ARM32 Use runtime check to avoid setting entrypoint for async helpers in non-r2r scenarios

jakobbotsch approved these changes Mar 10, 2026

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jtschuster requested a review from davidwrighton March 10, 2026 17:30

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jtschuster merged commit 65b2bc1 into dotnet:main Mar 10, 2026
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jtschuster linked an issue Mar 10, 2026 that may be closed by this pull request

Specific Continuation types for each method need to be encoded in the ready to run image. #122673

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dotnet-maestro bot mentioned this pull request Mar 11, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#5345

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kotlarmilos mentioned this pull request Mar 11, 2026

Fix crossgen2 crash on Apple mobile for InstantiatedType token resolution in async methods #125444

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jtschuster commented Feb 9, 2026 •

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