Fix profiler ELT callbacks for Runtime Async suspension by tommcdon · Pull Request #131985 · dotnet/runtime

tommcdon · 2026-08-07T04:00:19Z

Summary

Emit profiler Leave callbacks when Runtime Async methods suspend, pairing the existing Enter callbacks emitted on initial invocation and resume. This makes ELT callbacks consistently represent physical execution segments.

Preserves the continuation across profiler callbacks on all supported ABIs and adds Windows/Linux regression coverage for Task, Task<long>, and Task<double> methods.

Fixes #122488.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-08-07T04:01:10Z

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azure-pipelines · 2026-08-07T04:01:13Z

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Copilot

Pull request overview

This PR updates CoreCLR JIT codegen for Runtime Async suspension points to emit profiler Leave callbacks on suspend (to match the existing Enter callbacks that occur on initial invocation and resume), while preserving the async continuation value across the profiler helper call. It also adds a new profiler-based regression test to validate the callback pairing behavior.

Changes:

Update CodeGen::genReturnSuspend to call the profiling leave helper on GT_RETURN_SUSPEND, with target-specific handling to preserve the async continuation register across the callback.
Add a new native profiler (RuntimeAsyncELTProfiler) that counts and validates enter/leave sequencing for a runtime-async method.
Add a new managed profilee (runtimeasyncelt) and wire the new profiler into the native profiler test build/activation.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/coreclr/jit/codegencommon.cpp	Emit profiling `Leave` callback on runtime-async suspend while preserving the continuation across the helper call.
src/tests/profiler/native/runtimeasyncelt/runtimeasynceltprofiler.h	Declares a new native profiler test type tracking enter/leave counts and sequencing.
src/tests/profiler/native/runtimeasyncelt/runtimeasynceltprofiler.cpp	Implements the enter/leave hooks, target method selection, and pass/fail reporting.
src/tests/profiler/native/CMakeLists.txt	Adds the new profiler source to the native profiler test build.
src/tests/profiler/native/classfactory.cpp	Registers the new profiler CLSID in the native class factory.
src/tests/profiler/elt/runtimeasyncelt.csproj	Adds the new managed profilee project configured for `runtime-async`.
src/tests/profiler/elt/runtimeasyncelt.cs	Managed profilee that exercises runtime-async suspension/resume patterns.

tommcdon · 2026-08-07T17:16:44Z

+    if (FAILED(hrStatus) || GetFunctionIDName(functionId) != WCHAR("Work"))
+    {
+        return S_OK;
+    }


Addressed in 58c682a. The profiler now tracks Work, WorkVoid, and WorkDouble independently and requires exact paired callback counts of 25, 3, and 3 respectively, with balanced depth and no sequence failures. The expanded test passes on Windows x64 and Linux x64.

jakobbotsch · 2026-08-07T11:29:50Z

+#ifdef PROFILING_SUPPORTED
+    if (m_compiler->compIsProfilerHookNeeded())
+    {
+#ifdef TARGET_ARM
+        // The ARM32 Leave helper preserves REG_PROFILER_RET_SCRATCH, which is also the dedicated
+        // Runtime Async continuation register. For integer/soft-float returns it preserves R0 by
+        // moving it through this scratch register; for void and hard-float returns R0 is overwritten
+        // and the scratch register itself is preserved.
+        static_assert(REG_ASYNC_CONTINUATION_RET == REG_PROFILER_RET_SCRATCH);
+        bool r0InUse;
+        if (m_compiler->info.compRetType == TYP_VOID)
+        {
+            r0InUse = false;
+        }
+        else if (varTypeIsFloating(m_compiler->info.compRetType) ||
+                 m_compiler->IsHfa(m_compiler->info.compMethodInfo->args.retTypeClass))
+        {
+            r0InUse = m_compiler->info.compIsVarArgs || m_compiler->opts.compUseSoftFP;
+        }
+        else
+        {
+            r0InUse = true;
+        }
+        if (r0InUse)
+        {
+            inst_Mov(TYP_REF, REG_INTRET, reg, /* canSkip */ true);
+            gcInfo.gcMarkRegPtrVal(REG_INTRET, TYP_REF);
+            genProfilingLeaveCallback(CORINFO_HELP_PROF_FCN_LEAVE);
+            inst_Mov(TYP_REF, REG_ASYNC_CONTINUATION_RET, REG_INTRET, /* canSkip */ true);
+            gcInfo.gcMarkRegSetNpt(genRegMask(REG_INTRET));
+        }
+        else
+        {
+            inst_Mov(TYP_REF, REG_ASYNC_CONTINUATION_RET, reg, /* canSkip */ true);
+            gcInfo.gcMarkRegPtrVal(REG_ASYNC_CONTINUATION_RET, TYP_REF);
+            genProfilingLeaveCallback(CORINFO_HELP_PROF_FCN_LEAVE);
+        }
+#else
+        // The Leave helper preserves the normal return register, but may overwrite the dedicated
+        // Runtime Async continuation register because it is an argument register on supported
+        // ABIs. Temporarily use the normal return register to carry the continuation across the
+        // callback, then restore the dedicated register.
+        inst_Mov(TYP_REF, REG_INTRET, reg, /* canSkip */ true);
+        gcInfo.gcMarkRegPtrVal(REG_INTRET, TYP_REF);
+        genProfilingLeaveCallback(CORINFO_HELP_PROF_FCN_LEAVE);
+        inst_Mov(TYP_REF, REG_ASYNC_CONTINUATION_RET, REG_INTRET, /* canSkip */ true);
+        gcInfo.gcMarkRegSetNpt(genRegMask(REG_INTRET));
+#endif
+    }
+    else
+#endif


Can you factor this into a function? The ifdefs make this quite hard to read now.

Addressed in 58c682a. I factored the target-specific preservation and Leave emission into genProfilingLeaveCallbackForAsyncSuspend, so genReturnSuspend now only selects the profiled versus unprofiled path.

jakobbotsch · 2026-08-07T11:40:13Z

+        // The Leave helper preserves the normal return register, but may overwrite the dedicated
+        // Runtime Async continuation register because it is an argument register on supported
+        // ABIs. Temporarily use the normal return register to carry the continuation across the
+        // callback, then restore the dedicated register.


Are these ELT hooks usually able to look at register state? Does this e.g. break the ability to look at return values from leave callbacks in async functions?

A suspension Leave marks the end of a physical execution segment, not logical method completion, so there is no semantic method return value at that callback. The normal return registers may contain non-semantic state there. The final completion path is unchanged and still uses normal return codegen, so its Leave callback continues to expose the actual return value. I added this distinction to the helper comment in 58c682a.

How is the leave hook expected to detect that it is being called while the return register happens to contain a continuation instead of a return value?

I think this exposes an issue - profilers might not be able to tell the difference between a suspension vs. a synchronous method return. I propose we return CORPROF_E_DATAINCOMPLETE with no return-value range for suspension, and then a synchronous/final return returns S_OK with the real return value. Does that sound reasonable?

Yes, that sounds good. I am not so familiar with this, how do you think we should pass that info through?

FWIW the enter callback similarly will not have arguments available on resumption, so I expect we want to do something similar there.

For Enter, I think we can inspect the Continuation argument, and if it is non-null, GetFunctionEnter3Info would return CORPROF_E_DATAINCOMPLETE.
And for Leave, we can use REG_ASYNC_CONTINUATION_RET to detect suspension and similarly return CORPROF_E_DATAINCOMPLETE if non-null.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

Fix profiler ELT callbacks for Runtime Async suspension

b16fe54

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tommcdon added this to the 11.0.0 milestone Aug 7, 2026

tommcdon requested a review from lateralusX August 7, 2026 04:00

tommcdon self-assigned this Aug 7, 2026

tommcdon added the area-Diagnostics-coreclr label Aug 7, 2026

Copilot AI review requested due to automatic review settings August 7, 2026 04:00

Copilot started reviewing on behalf of tommcdon August 7, 2026 04:02 View session

This was referenced Aug 7, 2026

[Stacked 2/3] Prevent stale managed return values for Runtime Async suspension tommcdon/runtime#1

Closed

[Stacked 3/3] Add Runtime Async profiler API coverage tommcdon/runtime#2

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Copilot AI reviewed Aug 7, 2026

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jakobbotsch reviewed Aug 7, 2026

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Address Runtime Async ELT review feedback

58c682a

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings August 7, 2026 17:16

Copilot started reviewing on behalf of tommcdon August 7, 2026 17:17 View session

Copilot AI reviewed Aug 7, 2026

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This was referenced Aug 8, 2026

[Test] AsnycProfilerV1Tests StateMachineAsync_InlineCompletionClimb Fails #132025

Open

[Test] AsnycProfilerV1Tests StateMachineAsync_ResumeDispatchStack Fails #132026

Open

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Fix profiler ELT callbacks for Runtime Async suspension - #131985

Fix profiler ELT callbacks for Runtime Async suspension#131985
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