[5.1][Runtime] Fix swift_conformsToProtocol crashing on conformances to unavailable classes.

include/swift/ABI/Metadata.h

@@ -2333,6 +2333,12 @@ struct TargetProtocolConformanceDescriptor final
     return TypeRef.getTypeDescriptor(getTypeKind());
   }
 
+  const TargetContextDescriptor<Runtime> **_getTypeDescriptorLocation() const {
+    if (getTypeKind() != TypeReferenceKind::IndirectTypeDescriptor)
+      return nullptr;
+    return TypeRef.IndirectTypeDescriptor.get();
+  }
+
   /// Retrieve the context of a retroactive conformance.
   const TargetContextDescriptor<Runtime> *getRetroactiveContext() const {
     if (!Flags.isRetroactive()) return nullptr;

stdlib/public/runtime/ProtocolConformance.cpp

@@ -145,14 +145,15 @@ ProtocolConformanceDescriptor::getCanonicalTypeMetadata() const {
 
   case TypeReferenceKind::DirectTypeDescriptor:
   case TypeReferenceKind::IndirectTypeDescriptor: {
-    auto anyType = getTypeDescriptor();
-    if (auto type = dyn_cast<TypeContextDescriptor>(anyType)) {
-      if (!type->isGeneric()) {
-        if (auto accessFn = type->getAccessFunction())
-          return accessFn(MetadataState::Abstract).Value;
+    if (auto anyType = getTypeDescriptor()) {
+      if (auto type = dyn_cast<TypeContextDescriptor>(anyType)) {
+        if (!type->isGeneric()) {
+          if (auto accessFn = type->getAccessFunction())
+            return accessFn(MetadataState::Abstract).Value;
+        }
+      } else if (auto protocol = dyn_cast<ProtocolDescriptor>(anyType)) {
+        return _getSimpleProtocolTypeMetadata(protocol);
       }
-    } else if (auto protocol = dyn_cast<ProtocolDescriptor>(anyType)) {
-      return _getSimpleProtocolTypeMetadata(protocol);
     }
 
     return nullptr;

stdlib/toolchain/Compatibility50/ProtocolConformance.cpp

@@ -20,10 +20,22 @@
 #include "Overrides.h"
 #include "../../public/runtime/Private.h"
 #include "swift/Basic/Lazy.h"
+#include <mach-o/dyld.h>
+#include <mach-o/getsect.h>
 #include <objc/runtime.h>
 
 using namespace swift;
 
+#if __POINTER_WIDTH__ == 64
+using mach_header_platform = mach_header_64;
+#else
+using mach_header_platform = mach_header;
+#endif
+
+/// The Mach-O section name for the section containing protocol conformances.
+/// This lives within SEG_TEXT.
+constexpr const char ProtocolConformancesSection[] = "__swift5_proto";
+
 // Clone of private function getRootSuperclass. This returns the SwiftObject
 // class in the ABI-stable dylib, regardless of what the local runtime build
 // does, since we're always patching an ABI-stable dylib.
@@ -33,6 +45,50 @@ const ClassMetadata *swift::getRootSuperclass() {
   return (const ClassMetadata *)theClass;
 }
 
+// A dummy target context descriptor to use in conformance records which point
+// to a NULL descriptor. It doesn't have to be completely valid, just something
+// that code reading conformance descriptors will ignore.
+struct {
+  ContextDescriptorFlags flags;
+  int32_t offset;
+} DummyTargetContextDescriptor = {
+  ContextDescriptorFlags().withKind(ContextDescriptorKind::Extension),
+  0
+};
+
+// Search for any protocol conformance descriptors with a NULL type descriptor
+// and rewrite those to point to the dummy descriptor. This occurs when an
+// extension is used to declare a conformance on a weakly linked type and that
+// type is not present at runtime.
+static void addImageCallback(const mach_header *mh, intptr_t vmaddr_slide) {
+  unsigned long size;
+  const uint8_t *section =
+    getsectiondata(reinterpret_cast<const mach_header_platform *>(mh),
+                   SEG_TEXT, ProtocolConformancesSection,
+                   &size);
+  if (!section)
+    return;
+
+  auto recordsBegin
+    = reinterpret_cast<const ProtocolConformanceRecord*>(section);
+  auto recordsEnd
+    = reinterpret_cast<const ProtocolConformanceRecord*>
+                                          (section + size);
+  for (auto record = recordsBegin; record != recordsEnd; record++) {
+    auto descriptor = record->get();
+    if (auto typePtr = descriptor->_getTypeDescriptorLocation()) {
+      if (*typePtr == nullptr)
+        *typePtr = reinterpret_cast<TargetContextDescriptor<InProcess> *>(
+          &DummyTargetContextDescriptor);
+    }
+  }
+}
+
+// Register the add image callback with dyld.
+static void registerAddImageCallback(void *) {
+  _dyld_register_func_for_add_image(addImageCallback);
+}
+
 // Clone of private helper swift::_swiftoverride_class_getSuperclass
 // for use in the override implementation.
 static const Metadata *_swift50override_class_getSuperclass(
@@ -56,6 +112,10 @@ swift::swift50override_conformsToProtocol(const Metadata *type,
   const ProtocolDescriptor *protocol,
   ConformsToProtocol_t *original_conformsToProtocol)
 {
+  // Register our add image callback if necessary.
+  static OnceToken_t token;
+  SWIFT_ONCE_F(token, registerAddImageCallback, nullptr);
+
   // The implementation of swift_conformsToProtocol in Swift 5.0 would return
   // a false negative answer when asking whether a subclass conforms using
   // a conformance from a superclass. Work around this by walking up the

test/Interpreter/Inputs/FakeUnavailableSwiftDylib.swift

@@ -0,0 +1,9 @@
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+public protocol UnavailableSwiftProtocol {
+  func someMethod()
+}
+
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+public class UnavailableSwiftClass {
+  func someMethod() {}
+}

test/Interpreter/availability_weak_linking.swift

@@ -2,15 +2,18 @@
 // RUN: cp -R %S/Inputs/FakeUnavailableObjCFramework.framework %t
 // RUN: %target-clang -dynamiclib %S/Inputs/FakeUnavailableObjCFramework.m -fmodules -F %t -framework Foundation -o %t/FakeUnavailableObjCFramework.framework/FakeUnavailableObjCFramework
 // RUN: %target-codesign %t/FakeUnavailableObjCFramework.framework/FakeUnavailableObjCFramework
-// RUN: %target-build-swift -F %t %s -o %t/UseWeaklinkedUnavailableObjCFramework
-// RUN: %target-build-swift -O -F %t %s -o %t/UseWeaklinkedUnavailableObjCFramework.opt
+// RUN: %target-build-swift-dylib(%t/%target-library-name(FakeUnavailableSwiftDylib)) -emit-module -emit-module-path %t/FakeUnavailableSwiftDylib.swiftmodule %S/Inputs/FakeUnavailableSwiftDylib.swift
+// RUN: %target-codesign %t/%target-library-name(FakeUnavailableSwiftDylib)
+// RUN: %target-build-swift %t/%target-library-name(FakeUnavailableSwiftDylib) -I %t -F %t %s -o %t/UseWeaklinkedUnavailableObjCFramework
+// RUN: %target-build-swift -O %t/%target-library-name(FakeUnavailableSwiftDylib) -I %t -F %t %s -o %t/UseWeaklinkedUnavailableObjCFramework.opt
 
 // These tests emulate deploying back to an older OS where newer APIs are not
 // available by linking to an Objective-C framework where APIs have been
 // annotated to only be available in the far future (version 1066.0 of all
 // platforms) and then moving the framework aside so that it can't be found
 // at run time.
 // RUN: mv %t/FakeUnavailableObjCFramework.framework %t/FakeUnavailableObjCFramework-MovedAside.framework
+// RUN: mv %t/%target-library-name(FakeUnavailableSwiftDylib) %t/%target-library-name(FakeUnavailableSwiftDylib)-MovedAside
 
 // RUN: %target-codesign %t/UseWeaklinkedUnavailableObjCFramework
 // RUN: %target-codesign %t/UseWeaklinkedUnavailableObjCFramework.opt
@@ -24,6 +27,7 @@ import StdlibUnittest
 
 
 import FakeUnavailableObjCFramework
+import FakeUnavailableSwiftDylib
 import Foundation
 
 // CHECK: Running
@@ -154,6 +158,59 @@ protocol SomeSwiftProtocol { }
 @available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
 extension UnavailableObjCClass : SomeSwiftProtocol {
 }
+@available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *)
+extension UnavailableSwiftClass : SomeSwiftProtocol {
+}
+
+func checkSwiftProtocolConformance() {
+  // Make sure the runtime doesn't crash in the presence of a conformance
+  // record for a class that doesn't exsit at runtime.
+  let x: Any = 42
+  _blackHole(x as? SomeSwiftProtocol)
+}
+
+checkSwiftProtocolConformance()
+
+class ClassConformingToUnavailableSwiftProtocol : UnavailableSwiftProtocol {
+  func someMethod() {
+    print("Executed ClassConformingToUnavailableSwiftProtocol.someMethod()")
+  }
+}
+
+func useClassConformingToUnavailableSwiftProtocol() {
+  let o = ClassConformingToUnavailableSwiftProtocol()
+  o.someMethod()
+
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+    let oAsUP: UnavailableSwiftProtocol = o as UnavailableSwiftProtocol
+    oAsUP.someMethod()
+  }
+}
+
+// CHECK-NEXT: Executed ClassConformingToUnavailableSwiftProtocol.someMethod()
+useClassConformingToUnavailableSwiftProtocol()
+
+class ClassThatWillBeExtendedToConformToUnavailableSwiftProtocol {
+}
+
+extension ClassThatWillBeExtendedToConformToUnavailableSwiftProtocol : UnavailableSwiftProtocol {
+  func someMethod() {
+    print("Executed ClassThatWillBeExtendedToConformToUnavailableSwiftProtocol.someMethod()")
+  }
+}
+
+func useClassThatWillBeExtendedToConformToUnavailableSwiftProtocol() {
+  let o = ClassThatWillBeExtendedToConformToUnavailableSwiftProtocol()
+  o.someMethod()
+
+  if #available(OSX 1066.0, iOS 1066.0, watchOS 1066.0, tvOS 1066.0, *) {
+    let oAsUP: UnavailableSwiftProtocol = o as UnavailableSwiftProtocol
+    oAsUP.someMethod()
+  }
+}
+
+// CHECK-NEXT: Executed ClassThatWillBeExtendedToConformToUnavailableSwiftProtocol.someMethod()
+useClassThatWillBeExtendedToConformToUnavailableSwiftProtocol()
 
 // CHECK-NEXT: Done
 print("Done")