Fix generic lookups and thunks by davidwrighton · Pull Request #129825 · dotnet/runtime

davidwrighton · 2026-06-24T22:42:10Z

Add support for generic lookups to Wasm R2R code by following the DynamicHelper pattern we use on other platforms. This looks like a quite suitable implementation for Wasm, so I expect that this will remain for the long term.

Add support for WebAssembly .S files, as it was difficult to implement the helpers in inline assembly due to clang limitations.
Tweak Crossgen2 into generating uses of the DynamicHelper logic.

Also add support for precomputed thunks for various runtime helpers which were missing them, and add an assert that will fire even in interpreted runs for missing cases.

Fixes (most) of #129622
Fixes#129821

…e debuggable

Copilot

Pull request overview

This PR extends the WebAssembly ReadyToRun (R2R) pipeline to support generic dictionary lookups and related delay-load helper paths using the “DynamicHelper” pattern already used on other architectures, including adding dedicated Wasm .S helpers and updating Crossgen2’s Wasm thunk/signature plumbing accordingly.

Changes:

Add new Wasm dynamic helper stubs (in .S) for generic dictionary lookup variants and supporting VM glue to allocate the corresponding portable-entrypoint stub data.
Update Wasm delay-load/import thunk generation to support generic lookups via portable entrypoints (signature updates + always generating a thunk).
Add missing Wasm portable-entrypoint interpreter-call thunks for additional signatures (e.g., double arg + i32/i64 return, and S8 payload).

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/coreclr/vm/wasm/helpers.cpp	Adds additional portable-entrypoint interpreter-call thunks and updates the portable-entrypoint thunk table; removes Wasm placeholder DelayLoad_Helper stubs.
src/coreclr/vm/wasm/dynamichelpers.S	New Wasm assembly implementations of generic dictionary lookup dynamic helpers (incl. size-check / null-test variants and small constant-offset fast paths).
src/coreclr/vm/wasm/dynamichelpers.cpp	Implements Wasm `DelayLoad_Helper` entry and creates portable-entrypoint data for generic dictionary lookup helpers on Wasm.
src/coreclr/vm/wasm/asmconstants.h	Introduces Wasm-specific asm constants/offsets needed by `dynamichelpers.S` (with debug/fre handling and static-assert hooks).
src/coreclr/vm/readytoruninfo.h	Adds `GenericDictionaryDynamicHelperStubData_PortableEntryPoint` layout used by Wasm helper stubs.
src/coreclr/vm/prestub.cpp	Allows resolving import sections by RVA when `sectionIndex == (DWORD)-1` (used by Wasm delay-load helper), and excludes non-Wasm fixup kinds under `TARGET_WASM`.
src/coreclr/vm/jitinterface.cpp	Adds a debug assert ensuring portable-entrypoint targets have actual code under R2R (helps catch missing cases).
src/coreclr/vm/CMakeLists.txt	Wires new Wasm `.S` and `.cpp` sources (and asmconstants header) into the VM build.
src/coreclr/vm/cgensys.h	Adjusts `DelayLoad_Helper` declaration for Wasm to match the new calling convention/signature.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/.../WasmImportThunkPortableEntrypoint.cs	Updates generic-lookup thunk signature shape/string to include the portable-entrypoint parameter.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/.../DelayLoadHelperImport.cs	Always generates a Wasm import-thunk portable entrypoint (including for generic lookups).
eng/native/configurecompiler.cmake	Enables ASM for Browser/WASI toolchains so preprocessed Wasm `.S` files can be assembled by clang-based toolchains.

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

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

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

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 7 comments.

…ricLookupsAndThunks

AndyAyersMS · 2026-06-25T22:57:24Z

Have been testing this locally and it looks good from that standpoint. Still some possibly related failures but it will take me a bit longer to isolate those.

AndyAyersMS

Changes look reasonable to me, but I confess I didn't dig through all the wasm in detail. From a testing standpoint things are definitely better.

dotnet-policy-service · 2026-06-26T08:04:33Z

Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara
See info in area-owners.md if you want to be subscribed.

AndyAyersMS · 2026-06-26T17:48:51Z

Remaining generics-related Pri-1 failures look like a jit issue, we are not passing the instantiation parameter for some calls. PR for this up soon.

…/runtime into FixGenericLookupsAndThunks

Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 7 comments.

AndyAyersMS

re-approving

davidwrighton · 2026-06-26T23:52:45Z

/ba-g Infra and unrelated failures

Add support for generic lookups to Wasm R2R code by following the DynamicHelper pattern we use on other platforms. This looks like a quite suitable implementation for Wasm, so I expect that this will remain for the long term. Add support for WebAssembly .S files, as it was difficult to implement the helpers in inline assembly due to clang limitations. Tweak Crossgen2 into generating uses of the DynamicHelper logic. Also add support for precomputed thunks for various runtime helpers which were missing them, and add an assert that will fire even in interpreted runs for missing cases. Fixes (most) of #129622Fixes#129821 --------- Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

davidwrighton added 5 commits June 24, 2026 15:38

Changes to fix corinfo helper calls, and to make the failure case mor…
23282f9
…e debuggable

Basic support for Generic Lookups
18d8ed4

Add handling for the more optimized generic lookups
c30152c

Implement fallback ultra-slow path
f52b69c

Refactor dynamichelpers code into a new file.
4a5eefd

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Comment threadsrc/coreclr/vm/wasm/helpers.cpp
Comment threadsrc/coreclr/vm/wasm/helpers.cpp
Comment threadsrc/coreclr/vm/wasm/dynamichelpers.cpp Outdated

Potential fix for pull request finding
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Comment threadsrc/coreclr/vm/wasm/helpers.cpp Outdated
Comment threadsrc/coreclr/vm/cgensys.h
Comment threadsrc/coreclr/vm/wasm/dynamichelpers.cpp

Potential fix for pull request finding
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AndyAyersMS mentioned this pull request Jun 25, 2026
Running wasm with R2R'd System.Private.CoreLib #129850
Open

Merge branch 'main' ofhttps://github.com/dotnet/runtimeinto FixGene…
2097af3
…ricLookupsAndThunks

AndyAyersMS approved these changes Jun 25, 2026
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AaronRobinsonMSFT reviewed Jun 26, 2026
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Comment threadsrc/coreclr/vm/prestub.cpp
Comment threadsrc/coreclr/vm/prestub.cpp Outdated
Comment threadsrc/coreclr/vm/wasm/dynamichelpers.cpp
Comment threadsrc/coreclr/vm/wasm/dynamichelpers.cpp
Comment threadsrc/coreclr/vm/wasm/dynamichelpers.cpp

pavelsavara added the arch-wasm WebAssembly architecture label Jun 26, 2026

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Merge branch 'FixGenericLookupsAndThunks' of github.com:davidwrighton…
5012a92
…/runtime into FixGenericLookupsAndThunks

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davidwrighton merged commit 0bc7eda into dotnet:mainJun 26, 2026
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The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008
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[main] Source code updates from dotnet/runtime dotnet/dotnet#7441
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dotnet-milestone-botBot added this to the 11.0-preview7 milestone Jun 28, 2026

github-actionsBot mentioned this pull request Jul 13, 2026
[ccr-loop] CCR Improvement Loop — dotnet/runtime (2026-06) JennyPng/gh-aw-trial#29
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pavelsavara mentioned this pull request Jul 15, 2026
[Wasm R2R]: crossgen seems to be missing some thunk signatures #129622
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davidwrighton commented Jun 24, 2026•
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