Logic to load R2R files on WebAssembly by davidwrighton · Pull Request #127229 · dotnet/runtime

davidwrighton · 2026-04-21T16:34:09Z

Add better error checking to libCorerun.js
Add handling of relocs/tableBase to WebCIL v1 images
Actually handle PortableEntryPoint correctly in the ReadyToRun code
Generate WASM_TABLE_INDEX_I32 relocs in the the RuntimeFunctionsTableNode
Adjust DoesSlotCallPrestub to return false and not assert all the time on Wasm. In the absence of code versioning, returning false appears to be adequate.

- Add better error checking to libCorerun.js - Add handling of relocs/tableBase to WebCIL v1 images - Actually handle PortableEntryPoint correctly in the ReadyToRun code - Generate WASM_TABLE_INDEX_I32 relocs in the the RuntimeFunctionsTableNode - Adjust DoesSlotCallPrestub to return false and not assert all the time on Wasm. In the absence of code versioning, returning false appears to be adequate.

dotnet-policy-service · 2026-04-21T16:36:41Z

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Copilot

Pull request overview

This PR enables loading and executing ReadyToRun (R2R) code from WebAssembly/Webcil images by extending Webcil decoding/relocation support and wiring portable entrypoints + runtime function table relocs for Wasm.

Changes:

Extend Webcil decoding and PEImageLayout dispatch so Webcil images can expose R2R headers, manifest metadata, and apply base/table relocs.
Update R2R runtime entrypoint lookup to correctly use portable entrypoints (temporary entrypoint + “actual code”).
Emit Wasm table-index relocations for the runtime functions table and improve libCorerun.js error handling around module compile/table growth.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/coreclr/vm/readytoruninfo.cpp	Uses portable entrypoints to route R2R entrypoint resolution via temporary entrypoints.
src/coreclr/vm/precode_portable.cpp	Makes `DoesSlotCallPrestub` return false under portable entrypoints (Wasm scenario).
src/coreclr/vm/peimagelayout.inl	Adds Webcil `GetTableBaseOffset` forwarding + changes Webcil dispatch behavior for R2R header queries.
src/coreclr/vm/peimagelayout.h	Removes legacy table-base setter/getter in favor of decoder-derived offset.
src/coreclr/vm/peimagelayout.cpp	Applies relocations for Webcil at init time and adds Wasm-specific relocation parsing logic.
src/coreclr/utilcode/webcildecoder.cpp	Adds R2R header discovery + manifest metadata access for Webcil.
src/coreclr/inc/webcildecoder.h	Exposes new Webcil R2R surface area and table-base offset from Webcil v1 header.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/.../RuntimeFunctionsTableNode.cs	Emits `WASM_TABLE_INDEX_I32` relocs for Wasm runtime function BeginAddress values.
src/coreclr/hosts/corerun/wasm/libCorerun.js	Adds error handling for Wasm module compilation and table growth failures.

Comments suppressed due to low confidence (1)

src/coreclr/utilcode/webcildecoder.cpp:92

WebcilDecoder::Reset() doesn't reset the new ReadyToRun header caches (m_hasNoReadyToRunHeader and m_pReadyToRunHeader). If the decoder instance is reused (e.g., via Reset/Init), stale cached state can incorrectly force HasReadyToRunHeader() to return false or return a pointer from a previous image. Reset should clear these fields (and any other R2R-related cached state) to the same defaults as the constructor.

void WebcilDecoder::Reset()
{
    LIMITED_METHOD_CONTRACT;
    m_base = 0;
    m_size = 0;
    m_hasContents = false;
    m_pHeader = NULL;
    m_sections = NULL;
    m_pCorHeader = NULL;
    m_relocated = FALSE;
}

    COUNT_T dirPos = 0;
+#ifdef TARGET_WASM
+    // WASM will padd out the reloc size to the next 16 byte boundary, so we need to validate we can safely read the IMAGE_BASE_RELOCATION struct before processing each entry.
+    while (dirPos < (dirSize - sizeof(IMAGE_BASE_RELOCATION)))
+#else
    while (dirPos < dirSize)
+#endif


+                        if (_nodeFactory.Target.Architecture == TargetArchitecture.Wasm32)
                        {
-                            // On Amd64, the 2nd word contains the EndOffset of the runtime function
-                            Debug.Assert(frameInfo.StartOffset != frameInfo.EndOffset);
-                            runtimeFunctionsBuilder.EmitReloc(symbol, RelocType.IMAGE_REL_BASED_ADDR32NB, delta: frameInfo.EndOffset);
+                            runtimeFunctionsBuilder.EmitReloc(symbol, RelocType.WASM_TABLE_INDEX_I32, frameIndex);
+                        }
+                        else
+                        {
+                            runtimeFunctionsBuilder.EmitReloc(symbol, RelocType.IMAGE_REL_BASED_ADDR32NB, delta: frameInfo.StartOffset + _nodeFactory.Target.CodeDelta);
+                            if (!relocsOnly && _nodeFactory.Target.Architecture == TargetArchitecture.X64)
+                            {
+                                // On Amd64, the 2nd word contains the EndOffset of the runtime function
+                                Debug.Assert(frameInfo.StartOffset != frameInfo.EndOffset);
+                                runtimeFunctionsBuilder.EmitReloc(symbol, RelocType.IMAGE_REL_BASED_ADDR32NB, delta: frameInfo.EndOffset);
+                            }
                        }


+#ifndef FEATURE_PORTABLE_ENTRYPOINTS
    pEntryPoint = dac_cast<TADDR>(GetImage()->GetBase()) + m_pRuntimeFunctions[id].BeginAddress;
+#else
+    // When we have portable entrypoints enable, the R2R image contains actual entrypoints.


+READYTORUN_HEADER * WebcilDecoder::GetReadyToRunHeader() const
+{
+    CONTRACT(READYTORUN_HEADER *)
+    {
+        INSTANCE_CHECK;
+        PRECONDITION(CheckNTHeaders());
+        PRECONDITION(HasCorHeader());
+        PRECONDITION(HasReadyToRunHeader());
+        NOTHROW;
+        GC_NOTRIGGER;


+TADDR WebcilDecoder::GetDirectoryData(IMAGE_DATA_DIRECTORY *pDir) const
+{
+    CONTRACT(TADDR)
+    {
+        INSTANCE_CHECK;
+        PRECONDITION(CheckNTHeaders());
+        PRECONDITION(CheckDirectory(pDir, 0, NULL_OK));
+        NOTHROW;
+        GC_NOTRIGGER;
+        SUPPORTS_DAC;
+        POSTCONDITION(CheckPointer((void *)RETVAL, NULL_OK));
+        CANNOT_TAKE_LOCK;
+    }
+    CONTRACT_END;
+
+    RETURN GetRvaData(VAL32(pDir->VirtualAddress));
+}
+
+CHECK WebcilDecoder::CheckDirectory(IMAGE_DATA_DIRECTORY *pDir, int forbiddenFlags, IsNullOK ok) const
+{
+    CONTRACT_CHECK
+    {
+        INSTANCE_CHECK;
+        PRECONDITION(CheckNTHeaders());
+        PRECONDITION(CheckPointer(pDir));
+        NOTHROW;



    COUNT_T dirPos = 0;
+#ifdef TARGET_WASM
+    // WASM will padd out the reloc size to the next 16 byte boundary, so we need to validate we can safely read the IMAGE_BASE_RELOCATION struct before processing each entry.


-#ifdef FEATURE_WEBCIL
-    , m_tableBaseOffset(0)
-#endif
    , m_pOwner(NULL)


+                const errormessage = e instanceof Error ? e.message : String(e);
+                console.error("Failed to compile WebAssembly module for Webcil image:", {wasmPath, errormessage});


adamperlin · 2026-04-21T18:11:56Z

 {
    LIMITED_METHOD_CONTRACT;
-    _ASSERTE(!"DoesSlotCallPrestub is not supported with Portable EntryPoints");
+    /* On WASM slots never directly call the prestub. Instead we have the R2R to interpreter thunks


Does this need to be guarded with a #ifdef TARGET_WASM? I'm just wondering if we could have other platforms with portable entrypoints where this behavior may be different.

pavelsavara · 2026-04-21T20:20:13Z

-    BOOL IsNativeMachineFormat() const { return FALSE; }
-    PTR_CVOID GetNativeManifestMetadata(COUNT_T *pSize = NULL) const;
+    READYTORUN_HEADER *GetReadyToRunHeader() const;
+    BOOL IsNativeMachineFormat() const { return TRUE; }


TRUE only when you found R2R ?

davidwrighton requested review from adamperlin, Copilot and pavelsavara April 21, 2026 16:34

github-actions Bot added the area-VM-coreclr label Apr 21, 2026

dotnet-policy-service Bot assigned davidwrighton Apr 21, 2026

Copilot started reviewing on behalf of davidwrighton April 21, 2026 16:35 View session

Copilot AI reviewed Apr 21, 2026

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adamperlin reviewed Apr 21, 2026

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pavelsavara reviewed Apr 21, 2026

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build-analysis Bot mentioned this pull request Apr 21, 2026

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Logic to load R2R files on WebAssembly#127229

Logic to load R2R files on WebAssembly#127229
davidwrighton wants to merge 1 commit intodotnet:mainfrom
davidwrighton:LoadR2R_Core

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		const errormessage = e instanceof Error ? e.message : String(e);
		console.error("Failed to compile WebAssembly module for Webcil image:", {wasmPath, errormessage});

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davidwrighton commented Apr 21, 2026

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Pull request overview

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adamperlin Apr 21, 2026

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