[Reflection] Add an utility to stress test the metadata reader.

lldb now uses this quite extensively so we want to make sure
we don't crash on invalid.

<rdar://problem/49043621>

Author: Davide Italiano

tools/CMakeLists.txt

@@ -37,6 +37,7 @@ endif()
 
 if(LLVM_USE_SANITIZE_COVERAGE)
 add_swift_tool_subdirectory(swift-demangle-fuzzer)
+add_swift_tool_subdirectory(swift-reflection-fuzzer)
 endif()
 
 if(SWIFT_BUILD_STDLIB AND SWIFT_BUILD_SDK_OVERLAY)

tools/swift-reflection-fuzzer/CMakeLists.txt

@@ -0,0 +1,8 @@
+add_swift_fuzzer_host_tool(swift-reflection-fuzzer
+  swift-reflection-fuzzer.cpp
+  LLVM_COMPONENT_DEPENDS support
+  SWIFT_COMPONENT tools 
+  )
+target_link_libraries(swift-reflection-fuzzer
+                      PRIVATE
+                        swiftReflection)

tools/swift-reflection-fuzzer/swift-reflection-fuzzer.cpp

@@ -0,0 +1,97 @@
+//===--- swift-reflection-fuzzer.cpp - Swift reflection fuzzer ------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This program tries to fuzz the metadata reader shipped as part of the swift
+// runtime and used by the debugger.
+// For this to work you need to pass --enable-sanitizer-coverage to build-script
+// otherwise the fuzzer doesn't have coverage information to make progress
+// (making the whole fuzzing operation really ineffective).
+// It is recommended to use the tool together with another sanitizer to expose
+// more bugs (asan, lsan, etc...)
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/Reflection/ReflectionContext.h"
+#include "swift/Reflection/TypeRef.h"
+#include "swift/Reflection/TypeRefBuilder.h"
+#include "llvm/Object/Archive.h"
+#include "llvm/Object/ELF.h"
+#include "llvm/Object/ELFObjectFile.h"
+#include "llvm/Object/MachOUniversal.h"
+#include "llvm/Support/CommandLine.h"
+#include <stddef.h>
+#include <stdint.h>
+
+using namespace llvm::object;
+
+using namespace swift;
+using namespace swift::reflection;
+using namespace swift::remote;
+
+using NativeReflectionContext = swift::reflection::ReflectionContext<
+    External<RuntimeTarget<sizeof(uintptr_t)>>>;
+
+template <typename T> static T unwrap(llvm::Expected<T> value) {
+  if (value)
+    return std::move(value.get());
+  return T();
+}
+
+class ObjectMemoryReader : public MemoryReader {
+public:
+  ObjectMemoryReader() {}
+
+  bool queryDataLayout(DataLayoutQueryType type, void *inBuffer,
+                       void *outBuffer) override {
+    switch (type) {
+    case DLQ_GetPointerSize: {
+      auto result = static_cast<uint8_t *>(outBuffer);
+      *result = sizeof(void *);
+      return true;
+    }
+    case DLQ_GetSizeSize: {
+      auto result = static_cast<uint8_t *>(outBuffer);
+      *result = sizeof(size_t);
+      return true;
+    }
+    }
+
+    return false;
+  }
+
+  RemoteAddress getSymbolAddress(const std::string &name) override {
+    return RemoteAddress(nullptr);
+  }
+
+  bool isAddressValid(RemoteAddress addr, uint64_t size) const { return true; }
+
+  ReadBytesResult readBytes(RemoteAddress address, uint64_t size) override {
+    return ReadBytesResult((const void *)address.getAddressData(),
+                           [](const void *) {});
+  }
+
+  bool readString(RemoteAddress address, std::string &dest) override {
+    if (!isAddressValid(address, 1))
+      return false;
+    auto cString = StringRef((const char *)address.getAddressData());
+    dest.append(cString.begin(), cString.end());
+    return true;
+  }
+};
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  auto reader = std::make_shared<ObjectMemoryReader>();
+  NativeReflectionContext context(std::move(reader));
+  context.addImage(RemoteAddress(Data));
+  context.getBuilder().dumpAllSections(std::cout);
+  return 0; // Non-zero return values are reserved for future use.
+}