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 <175728472+Copilot@users.noreply.github.com>

The AsyncHelpers prefix made the names too verbose. Revert to the original shorter names (CORINFO_HELP_ALLOC_CONTINUATION, CORINFO_HELP_ASYNC_*, READYTORUN_HELPER_AllocContinuation, READYTORUN_HELPER_Async*) and add a comment above each definition section noting these are helpers for runtime async (System.Runtime.CompilerServices.AsyncHelpers). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The PEObjectWriter previously threw NotSupportedException for ARM64 PAGEBASE_REL21 and PAGEOFFSET_12A/12L relocations with non-zero addends. Async continuation data layouts produce relocations to fields at non-zero offsets within the data node, requiring addend support. Include the addend in the page/offset calculations, matching the approach used by the ELF and Mach-O object writers. The formula is: ADRP: Page(S+A) - Page(P) ADD/LDR: (S+A) & 0xFFF Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 44 out of 45 changed files in this pull request and generated no new comments.

jakobbotsch · 2026-03-03T00:49:49Z

src/coreclr/tools/Common/Compiler/ObjectWriter/PEObjectWriter.cs

-                            {
-                                throw new NotSupportedException();
-                            }
+                            long targetAddress = symbolImageOffset + addend;


Saw your commit about this and I am curious. Can you share some more information about it? Are these relics crossgen2 is using or ones that the JIT ends up using?

From what I can tell, we end up with this pattern for copying the Resume pointer from the resumption table to the continuation. IIRC, the jit calls recordRelocation and points to an offset into the RW data section it requested for the resumption stub, then crossgen converts that to an offset/addend to the MethodReadWriteDataNode.

Ok, it was not totally clear that these were the relocs we were talking about.

For PE there is no need for the JIT to create a read-write data section and emit these relocs, so generally the JIT won't do that when it knows we are targeting Windows. Is this a case where we were generating PE but targeting non-Windows? My understanding was that we had switched to use the native executable formats for each target, but I could be wrong about this.

We probably want to introduce a better mechanism for the EE to tell the JIT that it does not need to create a read-write data section for this case if we are truly still using PE outside Windows.

I believe we do still produce PE files for Linux.

…ection cell register

jtschuster · 2026-03-04T23:15:35Z

/azp run runtime-coreclr crossgen2

azure-pipelines · 2026-03-04T23:15:47Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 41 out of 42 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs:1349

Formatting: else{ is inconsistent with the surrounding style in this file/project and will likely get rewritten by dotnet-format. Use the standard else + brace spacing/newline.

            else{
                throw new RequiresRuntimeJitException(method.ToString());
            }

src/coreclr/vm/ilstubcache.cpp

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs

Copilot

Pull request overview

Copilot reviewed 41 out of 42 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs:1349

Formatting: else{ should follow the prevailing style in this file (else on its own line, { on the next line). This keeps the code consistent and avoids style-only diffs later.

            else{
                throw new RequiresRuntimeJitException(method.ToString());
            }

Copilot · 2026-03-05T00:25:14Z

src/coreclr/tools/aot/ILCompiler.ReadyToRun/IL/ReadyToRunILProvider.cs

            if (method.IsAsync)
            {
-                if (!wrappedMethodIL.Initialize(_manifestMutableModule, GetMethodILForAsyncMethod(method), method, false))
+                Debug.Assert(NeedsTaskReturningThunk(method));
+                if (!wrappedMethodIL.Initialize(_manifestMutableModule, GetMethodILForAsyncMethod(method), (EcmaMethod)method, false))
+                {


CreateCrossModuleInlineableTokensForILBody branches on method.IsAsync before checking IsAsyncVariant(), but AsyncMethodVariant inherits MethodDelegator so IsAsync delegates to the wrapped EcmaMethod. If the wrapped method has IsAsync == true, this path will hit the Debug.Assert(NeedsTaskReturningThunk(method)) (debug) and then throw InvalidCastException on (EcmaMethod)method (release). Consider guarding the async-thunk path with method is EcmaMethod and/or moving the IsAsyncVariant() check before the IsAsync check so variants never flow into the EcmaMethod cast.

jtschuster · 2026-03-05T00:50:57Z

/azp run runtime-coreclr crossgen2

azure-pipelines · 2026-03-05T00:51:08Z

Azure Pipelines successfully started running 1 pipeline(s).

jtschuster · 2026-03-05T16:05:10Z

runtime pipeline failures look unrelated, cDAC failure also happened in the latest build on main, so also seems unrelated.

jtschuster · 2026-03-05T16:34:20Z

src/coreclr/jit/codegenarmarch.cpp

I believe these changes are no longer needed with getFunctionEntrypoint only succeeding on the AsyncHelper methods.

jtschuster · 2026-03-05T16:50:39Z

src/coreclr/inc/readytorun.h

-
    READYTORUN_HELPER_InitClass                 = 0x116,
    READYTORUN_HELPER_InitInstClass             = 0x117,
+


These should be moved back

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

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jtschuster added the runtime-async label Feb 9, 2026

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

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

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Clean up extraneous changes and fix build

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build-analysis bot mentioned this pull request Feb 27, 2026

[android][arm64] System.Net.Sockets.Tests.SendTo_SyncForceNonBlocking.Datagram_UDP_ShouldImplicitlyBindLocalEndpoint fails with NetworkUnreachable #120526

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jtschuster mentioned this pull request Mar 2, 2026

Convert async context helpers from getAsyncInfo method handles to JIT helpers #125079

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jtschuster added 3 commits March 4, 2026 14:53

Remove JIT helpers, only allow getFunctionEntrypoint on AsyncHelper

b8f0768

Add earlier calls to getFunctionEntryPoint so morph can set the indir…

f02f215

…ection cell register

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

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jtschuster added 2 commits March 4, 2026 15:41

JIT format

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Update src/coreclr/vm/ilstubcache.cpp

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build-analysis bot mentioned this pull request Mar 5, 2026

Build error: ilc exited with code 57005 #124976

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Fix ilc, remove dead comments

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build-analysis bot mentioned this pull request Mar 5, 2026

[8.0] System.Exception: Failed to list devices - tvOS, iOS #125135

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jtschuster requested a review from a team March 5, 2026 16:04

jtschuster commented Mar 5, 2026

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		READYTORUN_HELPER_InitClass = 0x116,
		READYTORUN_HELPER_InitInstClass = 0x117,

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jtschuster commented Feb 9, 2026 •

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