runtime, WebAssembly: add ImageInspectionWasm.cpp (#39483)

This change adds a stub for `swift::lookupSymbol` for the WebAssembly platform.

Related to SR-9307.

Author: MaxDesiatov

stdlib/public/runtime/CMakeLists.txt

@@ -53,6 +53,7 @@ set(swift_runtime_sources
     ImageInspectionELF.cpp
     ImageInspectionCOFF.cpp
     ImageInspectionStatic.cpp
+    ImageInspectionWasm.cpp
     KeyPaths.cpp
     KnownMetadata.cpp
     Metadata.cpp

stdlib/public/runtime/ImageInspectionWasm.cpp

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+///
+/// Implementation of ImageInspection for WebAssembly.
+///
+//===----------------------------------------------------------------------===//
+
+#if defined(__wasm__)
+
+#include "../SwiftShims/MetadataSections.h"
+#include "ImageInspection.h"
+
+using namespace swift;
+
+int swift::lookupSymbol(const void *address, SymbolInfo *info) {
+  // Currently, Wasm doesn't have a standard stable ABI for exporting address <->
+  // symbol table, it's work in progress. Also, there is no API to access such
+  // information from Wasm binary side. It's accessible only from host VM. 
+  // See https://github.com/WebAssembly/tool-conventions/blob/main/DynamicLinking.md
+  // Seems reasonable to use a stub for now.
+  return 0;
+}
+
+#endif // defined(__wasm__)