[wasm] Fix reverse P/Invoke thunk key for nested [UnmanagedCallersOnly] types (CoreCLR + Mono) by lewing · Pull Request #130740 · dotnet/runtime

lewing · 2026-07-14T23:02:26Z

Why

On wasm, the first cold ldftn of a nested [UnmanagedCallersOnly] callback failed to resolve its native-to-interp / reverse-thunk entry:

CoreCLR asserted at precode_portable.cpp:35.
Mono trapped as MONO_WASM: null function.

Both native-to-interp tables are keyed by "{Method}#{argCount}:{Assembly}:{Namespace}:{Type}", and on both runtimes the two sides of that key disagreed for nested types:

The generators (PInvokeCollector, one per runtime) used reflection's Type.Namespace, which for a nested type returns the enclosing namespace.
The runtime lookups read the metadata namespace, which is empty for nested types:
- CoreCLR: helpers.cpp GetHashCode -> GetFullyQualifiedNameInfo
- Mono: browser/runtime/runtime.c get_native_to_interp -> mono_class_get_namespace

Because the keys never matched, the lookup returned null and the callback had no code.

Note the Mono token+name fallback in wasm_dl_get_native_to_interp does not recover this: bsearch compares the key first, so a key mismatch defeats both the (key, token) and key-only lookups. The token only disambiguates within a matching key (the trimmed case).

Fix

Emit the metadata namespace (empty for nested types) in both generators so the generated key matches what each runtime computes at lookup time:

Namespace = t.IsNested ? string.Empty : t.Namespace;

Tests

UnmanagedCallersOnly_Nested (new Wasm.Build.Tests case + UnmanagedCallbackNested.cs asset): cold-ldftns and invokes [UnmanagedCallersOnly] callbacks on nested (and doubly-nested) types inside a namespace, asserting they run. It executes on browser-wasm for both the Mono and CoreCLR generators (the wasi WBT leg is build-only in CI). This test is what surfaced the Mono half of the bug (no prior test exercised nested UCO). The only pre-existing execution coverage was incidental and wasi/CoreCLR-only (a nested UCO helper in TimeZoneInfoTests, compiled out on browser).
UnmanagedCallersOnly_NestedConflict (new, [ActiveIssue(#130739)], skipped): documents the residual limitation where two nested types sharing a simple name under different enclosing types collide because the key drops the enclosing-type chain. It encodes the desired behavior so the attribute can be removed once [wasm] reverse P/Invoke thunk key drops enclosing type for nested [UnmanagedCallersOnly] methods #130739 is fixed.

Notes

The key still drops the enclosing-type chain, so nested types sharing a simple name in different enclosing types collide. Tracked by #130739 (which also records the proven Mono remedy: key+token lookup with a name-only fallback, per #107113). Related: #130129.

Files changed

src/tasks/WasmAppBuilder/coreclr/PInvokeCollector.cs and src/tasks/WasmAppBuilder/mono/PInvokeCollector.cs (the fix, one per runtime)
src/mono/wasm/Wasm.Build.Tests/PInvokeTableGeneratorTests.cs and two src/mono/wasm/testassets/EntryPoints/PInvoke/*.cs assets (tests)

Note

This PR description was generated with the assistance of GitHub Copilot.

…y] types The CoreCLR wasm reverse-P/Invoke thunk table is keyed by "{Method}#{argCount}:{Assembly}:{Namespace}:{Type}". The generator (PInvokeCollector) used Type.Namespace, which for a nested type returns the enclosing namespace (e.g. "System.Tests" for System.Tests.TimeZoneInfoTests+WindowsUILanguageHelper). The runtime lookup (src/coreclr/vm/wasm/helpers.cpp GetHashCode -> GetFullyQualifiedNameInfo) reports an empty namespace for nested types, so the emitted key never matched at lookup time: LookupThunk returned null, EnsureCodeForUnmanagedCallersOnly left the portable entry point without code, and GetActualCode asserted (precode_portable.cpp:35) on the first cold ldftn of a nested UnmanagedCallersOnly callback. Match the runtime by emitting an empty namespace for nested types. With this, a nested [UnmanagedCallersOnly] callback (e.g. the EnumUILanguages callback used by globalization/culture code) resolves its reverse thunk and the interpreter runs it instead of asserting. Contributes to CoreCLR-WASI library test bring-up (dotnet#130129). Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea71f7e7-5477-4e58-bf1a-ca27d4b23d74

Add a reference to dotnet#130739 documenting that the nested-type reverse-thunk key drops the enclosing-type chain (collisions are caught as a build-time duplicate-key error). The generator is expected to be superseded once R2R generates the reverse thunks directly. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea71f7e7-5477-4e58-bf1a-ca27d4b23d74

azure-pipelines · 2026-07-14T23:03:02Z

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dotnet-policy-service · 2026-07-14T23:03:47Z

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Copilot

Pull request overview

This PR updates the CoreCLR Wasm WasmAppBuilder reverse P/Invoke callback key generation so nested [UnmanagedCallersOnly] methods use an empty namespace (matching the runtime’s metadata-based namespace for nested types), preventing lookup misses at runtime.

Changes:

Emit Namespace = string.Empty for nested callback declaring types when constructing PInvokeCallback keys.
Add explanatory comments documenting why nested namespaces must be empty and the existing collision behavior.

Address PR review feedback for the nested reverse-P/Invoke thunk key fix: - Add a dedicated positive Wasm.Build.Tests case (UnmanagedCallersOnly_Nested) that cold-ldftns and invokes [UnmanagedCallersOnly] callbacks declared on nested types inside a namespace, asserting they run. This covers the empty-metadata-namespace path the fix enables on both browser and wasi (unlike the incidental, wasi-only TimeZoneInfoTests coverage). - Clarify the PInvokeCollector comment: the duplicate-key check lives in PInvokeTableGenerator.EmitNativeToInterp, not below the constructor line. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 5abc3144-1f18-4321-98b4-d7b5c0627e9e

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

Encode the residual reverse-P/Invoke thunk key limitation as executable documentation: two nested types sharing a simple name under different enclosing types collide because the key drops the enclosing-type chain. The test asserts the desired behavior (both callbacks resolve and run) and is marked [ActiveIssue(dotnet#130739)] so it is skipped until the limitation is removed, at which point the attribute can be dropped to lock the fix. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 5abc3144-1f18-4321-98b4-d7b5c0627e9e

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

… issue link Copilot PR review flagged leftover comments from the earlier prebuilt-corerun approach. CoreCLR-WASI now relinks the corerun host per-app; update the comments in WasiApp.InTree.props/.targets and sendtohelix-wasi.targets accordingly. Also fix the CI template to reference dotnet#130740 (the nested-type thunk-key fix) instead of dotnet#130739 (which tracks the remaining enclosing-type collision limitation). Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea71f7e7-5477-4e58-bf1a-ca27d4b23d74

The new UnmanagedCallersOnly_Nested test caught the same bug on Mono: the native-to-interp key mismatched for nested [UnmanagedCallersOnly] types, producing a "null function" trap. The Mono runtime computes the lookup key with mono_class_get_namespace (browser/runtime/runtime.c get_native_to_interp), which is empty for nested types, but the generator emitted the reflection (enclosing) namespace. The token+name fallback in wasm_dl_get_native_to_interp cannot recover this because bsearch compares the key first. Emit the metadata namespace (empty for nested) to match, mirroring the CoreCLR fix. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 5abc3144-1f18-4321-98b4-d7b5c0627e9e

Copilot

Pull request overview

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

The Wasm.Build.Tests run path (RunForPublishWithWebServer + BrowserRunOptions) executes on browser-wasm only; the wasi leg is build-only in CI. Note the execution boundary in the test comment so it does not imply wasi run coverage. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 5abc3144-1f18-4321-98b4-d7b5c0627e9e

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

… issue link Copilot PR review flagged leftover comments from the earlier prebuilt-corerun approach. CoreCLR-WASI now relinks the corerun host per-app; update the comments in WasiApp.InTree.props/.targets and sendtohelix-wasi.targets accordingly. Also fix the CI template to reference dotnet#130740 (the nested-type thunk-key fix) instead of dotnet#130739 (which tracks the remaining enclosing-type collision limitation). Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea71f7e7-5477-4e58-bf1a-ca27d4b23d74

#130745) Draft. Stands up a CoreCLR-WASI library-test leg (smoke scope: `System.Runtime.Tests`), addressing part of #130129. Builds on the CoreCLR-WASI `wasihost` corehost (#130816, merged), which ships `libWasiHost.a` in the runtime pack. This PR generates each test's own reverse P/Invoke thunks and links them into that host per-app. ## What this does Adds a per-app native link of the shipping `wasihost` corehost (`libWasiHost.a`) so a test's own `[UnmanagedCallersOnly]` reverse P/Invoke thunks are covered — mirroring the browser-CoreCLR relink. The baked callhelpers table (`libcoreclr_gen_static.a`) only covers framework top-level UCO callbacks; library/test callbacks (e.g. a nested `WindowsUILanguageHelper.EnumUiLanguagesCallback`) are unknown to it and trap at first use without the per-app link. - **Host**: consumes `libWasiHost.a` from the `wasihost` corehost (#130816) — the leg does not manufacture its own host. - **Per-app link** (`src/mono/wasi/build/WasiApp.CoreCLR.targets`): `ManagedToNativeGenerator` (TargetOS=wasi) → compile the generated callhelpers with the wasi-sdk clang → link `libWasiHost.a` from the runtime-pack static archives + the app callhelper `.o` (replacing `libcoreclr_gen_static.a`) via `wasm-component-ld`. The `wasi:http` import that `System.Net.*` pulls in is declared with `-Wl,--component-type` (`WasiHttpWorld_component_type.wit`, as Mono does); wasmtime is given `-S http` by the test targets. - **Generator** (`ManagedToNativeGenerator.cs` / `PInvokeTableGenerator.cs`): a `WarnOnUnresolvedPInvokeModules` flag downgrades `WASM0066` to a message for untrimmed library-test closures (whose foreign-platform P/Invokes are unresolved on wasm and never called), so they don't fail the build under warn-as-error. - **Test/CI wiring**: `tests.wasi.targets`, `sendtohelix-wasi.targets`, `tests.proj` smoke set, and a `wasi-wasm-coreclr-library-tests` CI template (non-gating, rolling). The leg runs with full ICU globalization (non-invariant): the `wasihost` corehost preloads `icudt.dat` from `CORE_ROOT`. ## Validation Locally (macOS arm64, wasi-sdk + wasmtime): the baseline (`clr+libs+host+packs -os wasi -c Release`) builds green and stages `libWasiHost.a` from the `wasihost` corehost into the runtime pack. The `System.Runtime.Tests` bundle links the host per-app and discovers + runs the full suite: ``` Discovered: managed/System.Runtime.Tests.dll (found 9966 of 9966 test cases) Starting: managed/System.Runtime.Tests.dll ``` Managed exception dispatch through the interpreter EH + reverse UCO thunks works with no precode assert. A `System.Tests.VersionTests` subset ran 251/251 passing (`WASM EXIT 0`). ## Relationship to other work - **#130816** (merged) — the `wasihost` corehost this leg links. - **#130740** (merged) — the nested-UCO thunk-key generator fix the interpreter needs to resolve nested reverse thunks. - **#130634** stays scoped to the R2R `call_indirect` path (not this pure-interpreter leg). ## Tracked follow-ups (not in this PR) - **#130742** — build-switchable `wasi:http` capability (no-http vs http-capable host), and the longer-term "statify the app-declared imports" direction. - **#130739** — token-based reverse-thunk key robustness. - **#128362** — relocate `coreclr_compat.h` to a neutral shared location + stage the vm/minipal headers and the wit for out-of-tree/Helix runs (the per-app link currently uses in-repo fallbacks in-tree). - Polish: `-Wl,-u,__main_void` in place of `--whole-archive`, and incremental `Inputs`/`Outputs` on the link target. > [!NOTE] > This pull request was authored with GitHub Copilot. --------- Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

lewing and others added 2 commits July 14, 2026 17:59

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[wasm] reverse P/Invoke thunk key drops enclosing type for nested [UnmanagedCallersOnly] methods #130739

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[wasi] Stand up CoreCLR-WASI library-test leg (per-app corerun relink) #130745

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[wasm][coreclr] GetUnmanagedCallersOnlyThunk: unknown thunk for unmanaged callers only method #124219

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lewing changed the title ~~[wasm] Fix reverse P/Invoke thunk key for nested [UnmanagedCallersOnly] types~~ [wasm] Fix reverse P/Invoke thunk key for nested [UnmanagedCallersOnly] types (CoreCLR + Mono) Jul 15, 2026

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Comment thread src/mono/wasm/Wasm.Build.Tests/PInvokeTableGeneratorTests.cs

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lewing merged commit 8b10904 into dotnet:main Jul 15, 2026
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[main] Source code updates from dotnet/runtime dotnet/dotnet#7778

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[wasm] Fix reverse P/Invoke thunk key for nested [UnmanagedCallersOnly] types (CoreCLR + Mono)#130740

[wasm] Fix reverse P/Invoke thunk key for nested [UnmanagedCallersOnly] types (CoreCLR + Mono)#130740
lewing merged 6 commits into
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lewing:lewing-wasm-nested-uco-thunk-key-fix

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lewing commented Jul 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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lewing commented Jul 14, 2026 •

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