Emit Async Methods in crossgen2 #124203

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.

Code for async methods and resumption stubs are emitted in the InstanceMethod table, with an additional ENCODE_METHOD_SIG_ResumptionStub (0x100) or ENCODE_METHOD_SIG_ResumptionStub (0x200) flag, respectively. Aside from the flags, the encoded signatures should be identical so that searching for a resumption stub can be done with the async variant. They also have identical VersionResilient hash codes for this purpose.

Resumption stubs are not the subject of any fixups, so in order to create MethodDescs and resolve GC info, the resumption stubs are searched for when an async variant method is resolved by GetEntryPoint(). It's not trivial to use existing fixup mechanisms for resumption stubs because the jit expects the entrypoint address in the resumption stub table (which resides in the .text section), while fixups require an additional level of indirection. We could work around this in crossgen or the jit.

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

Copilot · 2026-02-09T23:35:31Z

src/coreclr/vm/methodtable.cpp

+    if (asyncVariantLookup == AsyncVariantLookup::AsyncResumptionStub)
+    {
+        mdMethodDef tkMethod = pDefMD->GetMemberDef();
+        Module* mod = pDefMD->GetModule();
+        bool isAsyncVariantMethod = pDefMD->IsAsyncVariantMethod();


The new AsyncResumptionStub branch duplicates the existing slow-path lookup later in this method (both linearly scan for the method with the opposite IsAsyncVariantMethod() value). This makes the new enum value effectively redundant and adds maintenance overhead; consider removing the branch or making it resumption-stub-specific.

Copilot · 2026-02-09T23:35:32Z

src/coreclr/vm/zapsig.cpp

    bool isAsyncVariant = (methodFlags & ENCODE_METHOD_SIG_AsyncVariant) != 0;
+    bool isResumptionStub =  (methodFlags & ENCODE_METHOD_SIG_ResumptionStub) != 0;



isResumptionStub is computed but never used. If the ResumptionStub flag is intended to affect method decoding, the flag currently has no effect and will also trigger unused-local warnings in builds that treat warnings as errors. Either remove the local or incorporate the flag into the FindOrCreateAssociatedMethodDesc lookup (e.g., select an appropriate AsyncVariantLookup value when the signature requests a resumption stub).

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

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

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

…o runtime16

jtschuster · 2026-02-09T23:49:16Z

/azp run runtime-coreclr crossgen2

azure-pipelines · 2026-02-09T23:49:29Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 32 out of 33 changed files in this pull request and generated 6 comments.

Copilot · 2026-02-09T23:51:46Z

src/coreclr/vm/jitinterface.cpp

                default:
                    STRESS_LOG1(LF_ZAP, LL_WARNING, "Unknown READYTORUN_HELPER %d\n", helperNum);
+                    printf("Unknown READYTORUN_HELPER %d", helperNum);
                    _ASSERTE(!"Unknown READYTORUN_HELPER");
                    return FALSE;


Avoid calling printf from the VM here. This will write to stdout in production builds and can interfere with test output/logging. Prefer existing runtime logging mechanisms (e.g., STRESS_LOG, LOG, or EEMessageBox/DbgAssertDialog depending on intent) and let the _ASSERTE remain the debug-time signal.

Copilot · 2026-02-09T23:51:46Z

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunTableManager.cs

                    Debug.Assert(!_sortedMethods);
                    MethodDesc method = methodNode.Method;
-                    EcmaModule module = (EcmaModule)((EcmaMethod)method.GetTypicalMethodDefinition().GetPrimaryMethodDesc()).Module;
+                    EcmaModule module = (EcmaModule)((EcmaMethod)method.GetPrimaryMethodDesc().GetTypicalMethodDefinition().GetTypicalMethodDefinition()).Module;


This expression redundantly calls GetTypicalMethodDefinition() twice. It’s clearer (and avoids implying different semantics) to call it once before casting to EcmaMethod/getting the module.

Suggested change

EcmaModule module = (EcmaModule)((EcmaMethod)method.GetPrimaryMethodDesc().GetTypicalMethodDefinition().GetTypicalMethodDefinition()).Module;

MethodDesc typicalMethodDefinition = method.GetPrimaryMethodDesc().GetTypicalMethodDefinition();

EcmaModule module = (EcmaModule)((EcmaMethod)typicalMethodDefinition).Module;

Copilot · 2026-02-09T23:51:47Z

src/coreclr/vm/ilstubcache.h

+    static MethodDesc* CreateR2RBackedILStub(
+        LoaderAllocator* pAllocator,
+        MethodTable* pMT,
+        PCODE r2rEntryPoint,
+        DWORD stubType,         // DynamicMethodDesc::ILStubType
+        PCCOR_SIGNATURE pSig,
+        DWORD cbSig,
+        BOOL isAsync,
+        AllocMemTracker* pamTracker);


stubType is declared as a DWORD even though the comment says it must be a DynamicMethodDesc::ILStubType. Consider changing the parameter type to the actual enum to make invalid values impossible at compile time and avoid accidental misuse at call sites.

Copilot · 2026-02-09T23:51:47Z

src/coreclr/vm/readytoruninfo.cpp

+                pMD->GetLoaderAllocator(),
+                pStubMT,
+                stubEntryPoint,
+                DynamicMethodDesc::StubAsyncResume,


This creates an R2R-backed async resumption stub MethodDesc, but it uses DynamicMethodDesc::StubAsyncResume as the stub type. Since a dedicated StubAsyncResumeR2R enum value was introduced, the wrapper should use that value so the runtime can distinguish IL-based stubs from R2R-backed ones (and any future logic keyed off the stub type behaves correctly).

Suggested change

DynamicMethodDesc::StubAsyncResume,

DynamicMethodDesc::StubAsyncResumeR2R,

Copilot · 2026-02-09T23:51:47Z

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilation.cs

 using ILCompiler.DependencyAnalysisFramework;
 using ILCompiler.Reflection.ReadyToRun;
 using Internal.TypeSystem.Ecma;
+using System.Linq;


using System.Linq; appears unused in this file (no LINQ extension methods referenced). If this project treats warnings as errors, this can break the build; please remove the unused using or add the missing LINQ usage if intended.

Suggested change

using System.Linq;

Copilot · 2026-02-09T23:51:47Z

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilation.cs

+                        {
+                            // Keep in sync with CorInfoImpl.getAsyncInfo()
+                            DefType continuation = TypeSystemContext.ContinuationType;
+                            var runtimeHelpers = TypeSystemContext.SystemModule.GetKnownType("System.Runtime.CompilerServices"u8, "RuntimeHelpers"u8);


runtimeHelpers is declared but never used. If this project treats warnings as errors, this will break the build; please remove it or use it as intended.

Suggested change

var runtimeHelpers = TypeSystemContext.SystemModule.GetKnownType("System.Runtime.CompilerServices"u8, "RuntimeHelpers"u8);

This will throw out valid methods that don't await, but I don't think we have the resumption stub resolution perfect yet.

jtschuster · 2026-02-10T18:35:31Z

/azp run runtime-coreclr crossgen2

azure-pipelines · 2026-02-10T18:35:42Z

Azure Pipelines successfully started running 1 pipeline(s).

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

github-project-automation bot added this to AppModel Feb 9, 2026

github-actions bot added the area-crossgen2-coreclr label Feb 9, 2026

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

14973b0

Copilot AI reviewed Feb 9, 2026

View reviewed changes

Apply suggestions from code review

18754ac

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

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

Merge branch 'runtime16' of https://github.com/jtschuster/runtime int…

a887cf6

…o runtime16

Copilot AI reviewed Feb 9, 2026

View reviewed changes

Don't use async method code if we can't find resumption stub

7f36d5a

This will throw out valid methods that don't await, but I don't think we have the resumption stub resolution perfect yet.

		bool isAsyncVariant = (methodFlags & ENCODE_METHOD_SIG_AsyncVariant) != 0;
		bool isResumptionStub = (methodFlags & ENCODE_METHOD_SIG_ResumptionStub) != 0;

	EcmaModule module = (EcmaModule)((EcmaMethod)method.GetPrimaryMethodDesc().GetTypicalMethodDefinition().GetTypicalMethodDefinition()).Module;
	MethodDesc typicalMethodDefinition = method.GetPrimaryMethodDesc().GetTypicalMethodDefinition();
	EcmaModule module = (EcmaModule)((EcmaMethod)typicalMethodDefinition).Module;

	DynamicMethodDesc::StubAsyncResume,
	DynamicMethodDesc::StubAsyncResumeR2R,

Emit Async Methods in crossgen2 #124203

Are you sure you want to change the base?

Emit Async Methods in crossgen2 #124203

Uh oh!

Conversation

jtschuster commented Feb 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

jtschuster commented Feb 9, 2026

Uh oh!

azure-pipelines bot commented Feb 9, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

jtschuster commented Feb 9, 2026

Uh oh!

azure-pipelines bot commented Feb 9, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 9, 2026

Choose a reason for hiding this comment

Uh oh!

jtschuster commented Feb 10, 2026

Uh oh!

azure-pipelines bot commented Feb 10, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

jtschuster commented Feb 9, 2026 •

edited

Loading