Merge pull request #31256 from jckarter/backport-conformance-cache-51

Compatibility51: Backport the 5.2 implementation of the conformance cache.

Author: jckarter

include/swift/Runtime/Config.h

@@ -154,6 +154,14 @@
 # elif SWIFT_BNI_XCODE_BUILD
 #  define SWIFT_CLASS_IS_SWIFT_MASK 1ULL
 
+// Compatibility hook libraries cannot rely on the "is swift" bit being either
+// value, since they must work with both OS and Xcode versions of the libraries.
+// Generate a reference to a nonexistent symbol so that we get obvious linker
+// errors if we try.
+# elif SWIFT_COMPATIBILITY_LIBRARY
+extern uintptr_t __COMPATIBILITY_LIBRARIES_CANNOT_CHECK_THE_IS_SWIFT_BIT_DIRECTLY__;
+#  define SWIFT_CLASS_IS_SWIFT_MASK __COMPATIBILITY_LIBRARIES_CANNOT_CHECK_THE_IS_SWIFT_BIT_DIRECTLY__
+
 // Other builds (such as local builds on developers' computers)
 // dynamically choose the bit at runtime based on the current OS
 // version.

stdlib/toolchain/CMakeLists.txt

@@ -56,6 +56,10 @@ else()
   add_compile_definitions(LLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING=1)
 endif()
 
+# Compatibility libraries build in a special alternate universe that can't
+# directly link to most OS runtime libraries, and have to access the
+# runtime being patched only through public ABI.
+list(APPEND CXX_COMPILE_FLAGS "-DSWIFT_COMPATIBILITY_LIBRARY=1")
 
 add_subdirectory(legacy_layouts)
 add_subdirectory(Compatibility50)

stdlib/toolchain/Compatibility50/Overrides.cpp

@@ -15,6 +15,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Overrides.h"
+#include "../Compatibility51/Overrides.h"
 #include "../../public/runtime/CompatibilityOverride.h"
 
 #include <dlfcn.h>
@@ -34,6 +35,11 @@ OverrideSection Swift50Overrides
 __attribute__((used, section("__DATA,__swift_hooks"))) = {
   .version = 0,
   .conformsToProtocol = swift50override_conformsToProtocol,
+  // We use the same hook for conformsToSwiftProtocol as we do for a 5.1
+  // runtime, so reference the override from the Compatibility51 library.
+  // If we're back deploying to Swift 5.0, we also have to support 5.1, so
+  // the Compatibility51 library is always linked when the 50 library is.
+  .conformsToSwiftProtocol = swift51override_conformsToSwiftProtocol,
 };
 
 // Allow this library to get force-loaded by autolinking

stdlib/toolchain/Compatibility50/Overrides.h

@@ -1,8 +1,8 @@
-//===--- Overrides.cpp - Compat overrides for Swift 5.0 runtime ----s------===//
+//===--- Overrides.h --- Compat overrides for Swift 5.0 runtime ----s------===//
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2020 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

stdlib/toolchain/Compatibility50/ProtocolConformance.cpp

@@ -37,15 +37,6 @@ using mach_header_platform = mach_header;
 /// 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.
-__attribute__((visibility("hidden"), weak))
-const ClassMetadata *swift::getRootSuperclass() {
-  auto theClass = SWIFT_LAZY_CONSTANT(objc_getClass("_TtCs12_SwiftObject"));
-  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.
@@ -90,35 +81,9 @@ static void registerAddImageCallback(void *) {
   _dyld_register_func_for_add_image(addImageCallback);
 }
 
-static const Metadata *getObjCClassMetadata(const ClassMetadata *c) {
-  // Look up swift_getObjCClassMetadata dynamically. This handles the case
-  // where the main executable can't link against libswiftCore.dylib because
-  // it will be loaded dynamically from a location that isn't known at build
-  // time.
-  using FPtr = const Metadata *(*)(const ClassMetadata *);
-  FPtr func = SWIFT_LAZY_CONSTANT(
-    reinterpret_cast<FPtr>(dlsym(RTLD_DEFAULT, "swift_getObjCClassMetadata")));
-
-  return func(c);
-}
-
-// Clone of private helper swift::_swiftoverride_class_getSuperclass
-// for use in the override implementation.
-static const Metadata *_swift50override_class_getSuperclass(
-                                                    const Metadata *theClass) {
-  if (const ClassMetadata *classType = theClass->getClassObject()) {
-    if (classHasSuperclass(classType))
-      return getObjCClassMetadata(classType->Superclass);
-  }
-  
-  if (const ForeignClassMetadata *foreignClassType
-      = dyn_cast<ForeignClassMetadata>(theClass)) {
-    if (const Metadata *superclass = foreignClassType->Superclass)
-      return superclass;
-  }
-  
-  return nullptr;
-}
+// Defined in libswiftCompatibility51, which is always linked if we link against
+// libswiftCompatibility50
+const Metadata *_swiftoverride_class_getSuperclass(const Metadata *theClass);
 
 const WitnessTable *
 swift::swift50override_conformsToProtocol(const Metadata *type,
@@ -138,7 +103,7 @@ swift::swift50override_conformsToProtocol(const Metadata *type,
     auto result = original_conformsToProtocol(type, protocol);
     if (result)
       return result;
-  } while ((type = _swift50override_class_getSuperclass(type)));
+  } while ((type = _swiftoverride_class_getSuperclass(type)));
 
   return nullptr;
 }

stdlib/toolchain/Compatibility51/CMakeLists.txt

@@ -3,6 +3,7 @@ set(library_name "swiftCompatibility51")
 
 add_swift_target_library("${library_name}" STATIC
   Overrides.cpp
+  ProtocolConformance.cpp
 
   TARGET_SDKS ${SWIFT_APPLE_PLATFORMS}