[Wasm] Add missing return buffer argument in wasm import thunks

[kg]

Fixes errors like

Failed to construct WebAssembly module for Webcil image: {
  wasmPath: '/Users/kg/AppData/Local/Temp/wasm-ryujit-runner/sandbox/IL/test-module.wasm',
  errorMessage: 'WebAssembly.Module(): Compiling function #39 failed: not enough arguments on the stack for call_indirect (need 3, got 2) @+8418'
}
Unhandled exception. System.BadImageFormatException: Bad IL format. The format of the file '/Users/kg/AppData/Local/Temp/wasm-ryujit-runner/sandbox/IL/test-module.wasm' is invalid.

#39 WasmDelayLoadHelper->EagerImports->SignaturePointer_ReadyToRunHelper_DelayLoad_MethodCall(ImportSection:MethodImports,Kind:DelayLoadHelper,Sig:S16p) ( i32, i32, i32 ) -> none (75 byte(s))

cc @davidwrighton @AndyAyersMS

[Copilot]

Pull request overview

This PR updates the WebAssembly import thunk emitter in the ReadyToRun AOT toolchain to account for signatures that require a hidden return-buffer (struct return) argument, preventing invalid wasm codegen at indirect call sites.

Changes:

• Detect struct-return signatures that require a hidden return buffer argument.
• Attempt to push the return buffer argument before the final call_indirect dispatch in the import thunk.

[davidwrighton]

LGTM, just remove the FIXME.

[Copilot]

Pull request overview

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

[kg]

/ba-g os x flakes