[wasm][coreCLR] Dispatch R2R-compiled methods from reflection and UnmanagedCallersOnly paths by pavelsavara · Pull Request #129766 · dotnet/runtime

pavelsavara · 2026-06-23T19:53:00Z

Summary

On wasm (CoreCLR interpreter, FEATURE_PORTABLE_ENTRYPOINTS), invoking a method that was compiled to native R2R code crashed at xUnit discovery with:

Unimplemented or invalid interpreter opcode

followed by a secondary m_crawl.GetCodeInfo()->IsValid() stackwalk assert.

Root cause

The wasm invoke paths resolve a method's interpreter byte code via MethodDesc::GetInterpreterCode() and pass the pointer to the interpreter. When the target method has no interpreter byte code because it was compiled to native (R2R) code, GetInterpreterCode() returns NULL. On wasm a NULL pointer reads zeroed low linear memory instead of faulting, so the interpreter set startIp = NULL, fetched ip[0] == 0, and dispatched it as INTOP_INVALID — aborting the process.

This only reproduced with R2R builds (native methods have no interpreter byte code). Pure-IL builds give every method interpreter byte code, so the byte code pointer was never NULL.

Two distinct entry paths reach a native (R2R) method without interpreter byte code:

Reflection / CallDescr (e.g. xUnit discovery and invoke) → CallDescrWorkerInternal.
UnmanagedCallersOnly reverse calls from native code → GetUnmanagedCallersOnlyThunk / ExecuteInterpretedMethodFromUnmanaged.

Fix

Reflection / CallDescr path (calldescrworkerwasm.cpp): when the resolved interpreter byte code is NULL, fall back to InvokeManagedMethod (the interpreter → R2R thunk), mirroring the established pattern in ExecuteInterpretedMethodWithArgs_PortableEntryPoint_Complex and the CALL_INTERP_METHOD path in InterpExecMethod.

UnmanagedCallersOnly path (wasm/helpers.cpp): resolve the method's code first and, if it has native (R2R) code, return that R2R entrypoint directly. An UnmanagedCallersOnly method compiled by crossgen2 is emitted with the native calling convention, so its R2R code is itself the directly-callable unmanaged entrypoint. The g_ReverseThunks interpreter fallback is only needed for interpreted methods, so R2R methods are now dispatched directly and never go through the interpreter reverse thunk.

Because the UnmanagedCallersOnly path is fixed at the source, the downstream interpreter helpers now assert instead of silently dispatching a NULL:

ExecuteInterpretedMethodFromUnmanaged asserts a non-NULL byte code pointer (R2R methods no longer reach it).
ExecuteInterpretedMethodWithArgs asserts a non-NULL targetIp, so any future misuse fails loudly at the actual point of error instead of as a cryptic INTOP_INVALID.

Contract widening: resolving an UnmanagedCallersOnly entrypoint may now run the prestub to publish R2R native code, which can throw and trigger a GC. Contracts are widened accordingly:

MethodDesc::GetSingleCallableAddrOfCodeForUnmanagedCallersOnly is GC_TRIGGERS under FEATURE_PORTABLE_ENTRYPOINTS.
PortableEntryPoint::EnsureCodeForUnmanagedCallersOnly is THROWS; GC_TRIGGERS; MODE_PREEMPTIVE.

Validation

System.Drawing.Primitives tests built with R2R, run under V8:

Tests run: 2441  Passed: 2439  Failed: 0  Skipped: 2
WASM EXIT 0

Identical to the IL baseline.

Note

This pull request was authored with the assistance of GitHub Copilot.

…thods CallDescrWorkerInternal (the wasm reflection/CallDescr invoke path) resolved the interpreter byte code via MethodDesc::GetInterpreterCode() and, after a DoPrestub retry, passed the pointer straight to ExecuteInterpretedMethodWithArgs. When the target method has no interpreter byte code because it was compiled to native (R2R) code, GetInterpreterCode() returns NULL. On wasm a NULL pointer reads zeroed low linear memory instead of faulting, so the interpreter dispatched the NULL byte code as INTOP_INVALID and aborted with Unimplemented or invalid interpreter opcode plus a secondary stackwalk assert. Add the InvokeManagedMethod fallback (the interpreter->R2R thunk) when there is no interpreter code, mirroring the existing pattern in ExecuteInterpretedMethodWithArgs_PortableEntryPoint_Complex and the CALL_INTERP_METHOD path in InterpExecMethod. Also harden the sibling entry points: ExecuteInterpretedMethodFromUnmanaged now takes the same fallback, and ExecuteInterpretedMethodWithArgs asserts a non-NULL targetIp so future misuse fails loudly at the point of error.

dotnet-policy-service · 2026-06-23T19:54:16Z

Tagging subscribers to this area: @JulieLeeMSFT, @BrzVlad, @janvorli, @kg
See info in area-owners.md if you want to be subscribed.

Address PR dotnet#129766 review feedback: resolve R2R-compiled native code for UnmanagedCallersOnly methods directly instead of going through the interpreter reverse-thunk fallback. - GetUnmanagedCallersOnlyThunk (wasm/helpers.cpp): run DoPrestub under GCX_PREEMP to publish code, then return the native (R2R) entrypoint via PortableEntryPoint when present; the g_ReverseThunks fallback is only for interpreted methods. - ExecuteInterpretedMethodFromUnmanaged (prestub.cpp): R2R methods are now dispatched directly and never reach this path, so replace the InvokeManagedMethod fallback with an assert that the interpreter byte code exists. - Widen contracts for the prestub-on-resolve path: EnsureCodeForUnmanagedCallersOnly (precode_portable.cpp) is THROWS/GC_TRIGGERS/MODE_PREEMPTIVE; GetSingleCallableAddrOfCodeForUnmanagedCallersOnly (method.cpp) is GC_TRIGGERS under FEATURE_PORTABLE_ENTRYPOINTS.

AndyAyersMS · 2026-06-24T19:26:34Z

UCO -> R2R seems to be needed to run against an R2R'd SPC, something in the shutdown path calls back into the runtime this way.

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

pavelsavara · 2026-06-25T22:18:35Z

I'm OOO till Wed, whoever is blocked by this, feel free to take over.

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Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

jkotas · 2026-06-26T04:06:11Z

+    if (targetIp == NULL)
+    {
+        // The target method has no interpreter code because it was compiled to native (R2R) code.
+        // Invoke it as a compiled managed method through the interpreter->R2R thunk, mirroring the
+        // fallback already present in ExecuteInterpretedMethodWithArgs_PortableEntryPoint_Complex and
+        // the CALL_INTERP_METHOD path in InterpExecMethod. Without this, the NULL bytecode pointer
+        // would be handed to the interpreter and dispatched as INTOP_INVALID.
+        ManagedMethodParam param = { pMethod, args, (int8_t*)retBuff, (PCODE)NULL, nullptr };
+        InvokeManagedMethod(&param);
+        return;
+    }


Yes, the whole CallDescrWorker is not setup correctly wrt GC on wasm. Our plan is to delete it.

Copilot

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

+    if (targetIp == NULL)
+    {
+        // The target method has no interpreter code because it was compiled to native (R2R) code.
+        // Invoke it as a compiled managed method through the interpreter->R2R thunk, mirroring the
+        // fallback already present in ExecuteInterpretedMethodWithArgs_PortableEntryPoint_Complex and
+        // the CALL_INTERP_METHOD path in InterpExecMethod. Without this, the NULL bytecode pointer
+        // would be handed to the interpreter and dispatched as INTOP_INVALID.
+        ManagedMethodParam param = { pMethod, args, (int8_t*)retBuff, (PCODE)NULL, nullptr };
+        InvokeManagedMethod(&param);
+        return;


Copilot

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

+        ManagedMethodParam param = { pMethod, args, (int8_t*)retBuff, (PCODE)NULL, nullptr };
+        InvokeManagedMethod(&param);
+        return;


Copilot AI review requested due to automatic review settings June 23, 2026 19:53

github-actions Bot added the area-CodeGen-Interpreter-coreclr label Jun 23, 2026

dotnet-policy-service Bot assigned pavelsavara Jun 23, 2026

Copilot started reviewing on behalf of pavelsavara June 23, 2026 19:53 View session

pavelsavara added arch-wasm WebAssembly architecture os-browser Browser variant of arch-wasm labels Jun 23, 2026

pavelsavara changed the title ~~[wasm] Fix interpreter dispatch of NULL byte code for R2R-compiled methods~~ [wasm][coreCLR] Fix interpreter dispatch of NULL byte code for R2R-compiled methods Jun 23, 2026

pavelsavara requested review from davidwrighton, janvorli and radekdoulik June 23, 2026 19:54

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Flaky timeout in CreateFileChangeToken_RootDeletedAndRecreated_TokenFiresWhenFileCreated #129691

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pavelsavara added 3 commits June 24, 2026 12:04

Merge branch 'main' into fix/wasm-interp-r2r-null-bytecode

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Merge branch 'main' into fix/wasm-interp-r2r-null-bytecode

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pavelsavara changed the title ~~[wasm][coreCLR] Fix interpreter dispatch of NULL byte code for R2R-compiled methods~~ [wasm][coreCLR] Dispatch R2R-compiled methods from reflection and UnmanagedCallersOnly paths Jun 24, 2026

AndyAyersMS mentioned this pull request Jun 24, 2026

[wasm] Fix reflection invoke of R2R-compiled methods #129808

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pavelsavara mentioned this pull request Jun 24, 2026

[wasm][coreCLR] R2R generic dictionary lookup traps with null function (zero import cell for GenericLookupSignature) #129821

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AndyAyersMS mentioned this pull request Jun 25, 2026

Running wasm with R2R'd System.Private.CoreLib #129850

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[wasm][coreCLR] R2R delegate* unmanaged<> call to [UnmanagedCallersOnly] method traps with indirect call signature mismatch #129857

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Co-authored-by: Jan Kotas <jkotas@microsoft.com>

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Merge branch 'main' into fix/wasm-interp-r2r-null-bytecode

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Assertion failed: new_time >= loop->time in Component Governance Detection dotnet/dnceng#6510

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Comment thread src/coreclr/vm/wasm/calldescrworkerwasm.cpp

Comment on lines +48 to +50

ManagedMethodParam param = { pMethod, args, (int8_t*)retBuff, (PCODE)NULL, nullptr };

InvokeManagedMethod(&param);

return;

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pavelsavara commented Jun 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

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Fix

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pavelsavara commented Jun 25, 2026

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pavelsavara commented Jun 23, 2026 •

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