Merge pull request #62619 from aschwaighofer/dyn_repl_weak

Fix dynamic replacement of weakly linked symbols

Author: aschwaighofer

stdlib/public/runtime/MetadataLookup.cpp

@@ -2732,6 +2732,10 @@ static InitializeDynamicReplacementLookup initDynamicReplacements;
 SWIFT_ALLOWED_RUNTIME_GLOBAL_CTOR_END
 
 void DynamicReplacementDescriptor::enableReplacement() const {
+  // Weakly linked symbols can be zero.
+  if (replacedFunctionKey.get() == nullptr)
+    return;
+
   auto *chainRoot = const_cast<DynamicReplacementChainEntry *>(
       replacedFunctionKey->root.get());
 

test/Interpreter/Inputs/dynamic_replacement_ReplacementA.swift

@@ -0,0 +1,8 @@
+@_weakLinked import LibA
+
+extension A {
+  @_dynamicReplacement(for: printThis())
+  func _replacementForPrintThis() {
+    Swift.print("replacement")
+  }
+}

test/Interpreter/Inputs/dynamic_replacement_libA.swift

@@ -0,0 +1,25 @@
+public struct A {
+    public var x : Int = 0
+    public var y : Int = 1
+    public init() {}
+#if BEFORE
+    public func print() {
+        printThis()
+    }
+
+    public dynamic func printThis() {
+        Swift.print(x)
+        Swift.print(y)
+    }
+#else
+    public func print() {
+        printThis2()
+    }
+
+    public dynamic func printThis2() {
+        Swift.print(x)
+        Swift.print(y)
+    }
+
+#endif
+}

test/Interpreter/dynamic_replacement_weak_linked.swift

@@ -0,0 +1,25 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift-dylib(%t/%target-library-name(LibA)) -DBEFORE -module-name LibA -emit-module -emit-module-path %t/LibA.swiftmodule -swift-version 5 %S/Inputs/dynamic_replacement_libA.swift
+// RUN: %target-build-swift-dylib(%t/%target-library-name(ReplacementA)) -I%t -L%t -lLibA -module-name ReplacementA -swift-version 5 %S/Inputs/dynamic_replacement_ReplacementA.swift
+// RUN: %target-build-swift-dylib(%t/%target-library-name(LibA)) -module-name LibA -emit-module -emit-module-path %t/LibA.swiftmodule -swift-version 5 %S/Inputs/dynamic_replacement_libA.swift
+// RUN: %target-build-swift -I%t -L%t -lLibA -o %t/main %target-rpath(%t) %s -swift-version 5
+// RUN: %target-codesign %t/main %t/%target-library-name(LibA) %t/%target-library-name(ReplacementA)
+// RUN: %target-run %t/main %t/%target-library-name(LibA) %t/%target-library-name(ReplacementA)
+
+// REQUIRES: executable_test
+// REQUIRES: OS=macosx
+// REQUIRES: swift_test_mode_optimize_none
+
+import Darwin
+
+import LibA
+
+private func target_library_name(_ name: String) -> String {
+  return "lib\(name).dylib"
+}
+
+var executablePath = CommandLine.arguments[0]
+executablePath.removeLast(4)
+_ = dlopen(executablePath + target_library_name("ReplacementA"), RTLD_NOW)
+
+A().print()