lib/ExecutionEngine/Orc/MachOPlatform.cpp - llvm-project/llvm - Git at Google

 //===------ MachOPlatform.cpp - Utilities for executing MachO in Orc ------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/ExecutionEngine/Orc/MachOPlatform.h"

 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/ExecutionEngine/Orc/DebugUtils.h"
 #include "llvm/Support/BinaryByteStream.h"
 #include "llvm/Support/Debug.h"

 #define DEBUG_TYPE "orc"

 namespace {

 struct objc_class;
 struct objc_image_info;
 struct objc_object;
 struct objc_selector;

 using Class = objc_class *;
 using id = objc_object *;
 using SEL = objc_selector *;

 using ObjCMsgSendTy = id (*)(id, SEL, ...);
 using ObjCReadClassPairTy = Class (*)(Class, const objc_image_info *);
 using SelRegisterNameTy = SEL (*)(const char *);

 enum class ObjCRegistrationAPI { Uninitialized, Unavailable, Initialized };

 ObjCRegistrationAPI ObjCRegistrationAPIState =
     ObjCRegistrationAPI::Uninitialized;
 ObjCMsgSendTy objc_msgSend = nullptr;
 ObjCReadClassPairTy objc_readClassPair = nullptr;
 SelRegisterNameTy sel_registerName = nullptr;

 } // end anonymous namespace

 namespace llvm {
 namespace orc {

 template <typename FnTy>
 static Error setUpObjCRegAPIFunc(FnTy &Target, sys::DynamicLibrary &LibObjC,
                                  const char *Name) {
   if (void *Addr = LibObjC.getAddressOfSymbol(Name))
     Target = reinterpret_cast<FnTy>(Addr);
   else
     return make_error<StringError>(
         (Twine("Could not find address for ") + Name).str(),
         inconvertibleErrorCode());
   return Error::success();
 }

 Error enableObjCRegistration(const char *PathToLibObjC) {
   // If we've already tried to initialize then just bail out.
   if (ObjCRegistrationAPIState != ObjCRegistrationAPI::Uninitialized)
     return Error::success();

   ObjCRegistrationAPIState = ObjCRegistrationAPI::Unavailable;

   std::string ErrMsg;
   auto LibObjC =
       sys::DynamicLibrary::getPermanentLibrary(PathToLibObjC, &ErrMsg);

   if (!LibObjC.isValid())
     return make_error<StringError>(std::move(ErrMsg), inconvertibleErrorCode());

   if (auto Err = setUpObjCRegAPIFunc(objc_msgSend, LibObjC, "objc_msgSend"))
     return Err;
   if (auto Err = setUpObjCRegAPIFunc(objc_readClassPair, LibObjC,
                                      "objc_readClassPair"))
     return Err;
   if (auto Err =
           setUpObjCRegAPIFunc(sel_registerName, LibObjC, "sel_registerName"))
     return Err;

   ObjCRegistrationAPIState = ObjCRegistrationAPI::Initialized;
   return Error::success();
 }

 bool objCRegistrationEnabled() {
   return ObjCRegistrationAPIState == ObjCRegistrationAPI::Initialized;
 }

 void MachOJITDylibInitializers::runModInits() const {
   for (const auto &ModInit : ModInitSections) {
     for (uint64_t I = 0; I != ModInit.NumPtrs; ++I) {
       auto *InitializerAddr = jitTargetAddressToPointer<uintptr_t *>(
           ModInit.Address + (I * sizeof(uintptr_t)));
       auto *Initializer =
           jitTargetAddressToFunction<void (*)()>(*InitializerAddr);
       Initializer();
     }
   }
 }

 void MachOJITDylibInitializers::registerObjCSelectors() const {
   assert(objCRegistrationEnabled() && "ObjC registration not enabled.");

   for (const auto &ObjCSelRefs : ObjCSelRefsSections) {
     for (uint64_t I = 0; I != ObjCSelRefs.NumPtrs; ++I) {
       auto SelEntryAddr = ObjCSelRefs.Address + (I * sizeof(uintptr_t));
       const auto *SelName =
           *jitTargetAddressToPointer<const char **>(SelEntryAddr);
       auto Sel = sel_registerName(SelName);
       *jitTargetAddressToPointer<SEL *>(SelEntryAddr) = Sel;
     }
   }
 }

 Error MachOJITDylibInitializers::registerObjCClasses() const {
   assert(objCRegistrationEnabled() && "ObjC registration not enabled.");

   struct ObjCClassCompiled {
     void *Metaclass;
     void *Parent;
     void *Cache1;
     void *Cache2;
     void *Data;
   };

   auto *ImageInfo =
       jitTargetAddressToPointer<const objc_image_info *>(ObjCImageInfoAddr);
   auto ClassSelector = sel_registerName("class");

   for (const auto &ObjCClassList : ObjCClassListSections) {
     for (uint64_t I = 0; I != ObjCClassList.NumPtrs; ++I) {
       auto ClassPtrAddr = ObjCClassList.Address + (I * sizeof(uintptr_t));
       auto Cls = *jitTargetAddressToPointer<Class *>(ClassPtrAddr);
       auto *ClassCompiled =
           *jitTargetAddressToPointer<ObjCClassCompiled **>(ClassPtrAddr);
       objc_msgSend(reinterpret_cast<id>(ClassCompiled->Parent), ClassSelector);
       auto Registered = objc_readClassPair(Cls, ImageInfo);

       // FIXME: Improve diagnostic by reporting the failed class's name.
       if (Registered != Cls)
         return make_error<StringError>("Unable to register Objective-C class",
                                        inconvertibleErrorCode());
     }
   }
   return Error::success();
 }

 MachOPlatform::MachOPlatform(
     ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
     std::unique_ptr<MemoryBuffer> StandardSymbolsObject)
     : ES(ES), ObjLinkingLayer(ObjLinkingLayer),
       StandardSymbolsObject(std::move(StandardSymbolsObject)) {
   ObjLinkingLayer.addPlugin(std::make_unique<InitScraperPlugin>(*this));
 }

 Error MachOPlatform::setupJITDylib(JITDylib &JD) {
   auto ObjBuffer = MemoryBuffer::getMemBuffer(
       StandardSymbolsObject->getMemBufferRef(), false);
   return ObjLinkingLayer.add(JD, std::move(ObjBuffer));
 }

 Error MachOPlatform::notifyAdding(ResourceTracker &RT,
                                   const MaterializationUnit &MU) {
   auto &JD = RT.getJITDylib();
   const auto &InitSym = MU.getInitializerSymbol();
   if (!InitSym)
     return Error::success();

   RegisteredInitSymbols[&JD].add(InitSym,
                                  SymbolLookupFlags::WeaklyReferencedSymbol);
   LLVM_DEBUG({
     dbgs() << "MachOPlatform: Registered init symbol " << *InitSym << " for MU "
            << MU.getName() << "\n";
   });
   return Error::success();
 }

 Error MachOPlatform::notifyRemoving(ResourceTracker &RT) {
   llvm_unreachable("Not supported yet");
 }

 Expected<MachOPlatform::InitializerSequence>
 MachOPlatform::getInitializerSequence(JITDylib &JD) {

   LLVM_DEBUG({
     dbgs() << "MachOPlatform: Building initializer sequence for "
            << JD.getName() << "\n";
   });

   std::vector<JITDylibSP> DFSLinkOrder;

   while (true) {

     DenseMap<JITDylib *, SymbolLookupSet> NewInitSymbols;

     ES.runSessionLocked([&]() {
       DFSLinkOrder = JD.getDFSLinkOrder();

       for (auto &InitJD : DFSLinkOrder) {
         auto RISItr = RegisteredInitSymbols.find(InitJD.get());
         if (RISItr != RegisteredInitSymbols.end()) {
           NewInitSymbols[InitJD.get()] = std::move(RISItr->second);
           RegisteredInitSymbols.erase(RISItr);
         }
       }
     });

     if (NewInitSymbols.empty())
       break;

     LLVM_DEBUG({
       dbgs() << "MachOPlatform: Issuing lookups for new init symbols: "
                 "(lookup may require multiple rounds)\n";
       for (auto &KV : NewInitSymbols)
         dbgs() << "  \"" << KV.first->getName() << "\": " << KV.second << "\n";
     });

     // Outside the lock, issue the lookup.
     if (auto R = lookupInitSymbols(JD.getExecutionSession(), NewInitSymbols))
       ; // Nothing to do in the success case.
     else
       return R.takeError();
   }

   LLVM_DEBUG({
     dbgs() << "MachOPlatform: Init symbol lookup complete, building init "
               "sequence\n";
   });

   // Lock again to collect the initializers.
   InitializerSequence FullInitSeq;
   {
     std::lock_guard<std::mutex> Lock(InitSeqsMutex);
     for (auto &InitJD : reverse(DFSLinkOrder)) {
       LLVM_DEBUG({
         dbgs() << "MachOPlatform: Appending inits for \"" << InitJD->getName()
                << "\" to sequence\n";
       });
       auto ISItr = InitSeqs.find(InitJD.get());
       if (ISItr != InitSeqs.end()) {
         FullInitSeq.emplace_back(InitJD.get(), std::move(ISItr->second));
         InitSeqs.erase(ISItr);
       }
     }
   }

   return FullInitSeq;
 }

 Expected<MachOPlatform::DeinitializerSequence>
 MachOPlatform::getDeinitializerSequence(JITDylib &JD) {
   std::vector<JITDylibSP> DFSLinkOrder = JD.getDFSLinkOrder();

   DeinitializerSequence FullDeinitSeq;
   {
     std::lock_guard<std::mutex> Lock(InitSeqsMutex);
     for (auto &DeinitJD : DFSLinkOrder) {
       FullDeinitSeq.emplace_back(DeinitJD.get(), MachOJITDylibDeinitializers());
     }
   }

   return FullDeinitSeq;
 }

 void MachOPlatform::registerInitInfo(
     JITDylib &JD, JITTargetAddress ObjCImageInfoAddr,
     MachOJITDylibInitializers::SectionExtent ModInits,
     MachOJITDylibInitializers::SectionExtent ObjCSelRefs,
     MachOJITDylibInitializers::SectionExtent ObjCClassList) {
   std::lock_guard<std::mutex> Lock(InitSeqsMutex);

   auto &InitSeq = InitSeqs[&JD];

   InitSeq.setObjCImageInfoAddr(ObjCImageInfoAddr);

   if (ModInits.Address)
     InitSeq.addModInitsSection(std::move(ModInits));

   if (ObjCSelRefs.Address)
     InitSeq.addObjCSelRefsSection(std::move(ObjCSelRefs));

   if (ObjCClassList.Address)
     InitSeq.addObjCClassListSection(std::move(ObjCClassList));
 }

 static Expected<MachOJITDylibInitializers::SectionExtent>
 getSectionExtent(jitlink::LinkGraph &G, StringRef SectionName) {
   auto *Sec = G.findSectionByName(SectionName);
   if (!Sec)
     return MachOJITDylibInitializers::SectionExtent();
   jitlink::SectionRange R(*Sec);
   if (R.getSize() % G.getPointerSize() != 0)
     return make_error<StringError>(SectionName + " section size is not a "
                                                  "multiple of the pointer size",
                                    inconvertibleErrorCode());
   return MachOJITDylibInitializers::SectionExtent(
       R.getStart(), R.getSize() / G.getPointerSize());
 }

 void MachOPlatform::InitScraperPlugin::modifyPassConfig(
     MaterializationResponsibility &MR, jitlink::LinkGraph &LG,
     jitlink::PassConfiguration &Config) {

   if (!MR.getInitializerSymbol())
     return;

   Config.PrePrunePasses.push_back([this, &MR](jitlink::LinkGraph &G) -> Error {
     JITLinkSymbolVector InitSectionSymbols;
     preserveInitSectionIfPresent(InitSectionSymbols, G, "__mod_init_func");
     preserveInitSectionIfPresent(InitSectionSymbols, G, "__objc_selrefs");
     preserveInitSectionIfPresent(InitSectionSymbols, G, "__objc_classlist");

     if (!InitSectionSymbols.empty()) {
       std::lock_guard<std::mutex> Lock(InitScraperMutex);
       InitSymbolDeps[&MR] = std::move(InitSectionSymbols);
     }

     if (auto Err = processObjCImageInfo(G, MR))
       return Err;

     return Error::success();
   });

   Config.PostFixupPasses.push_back([this, &JD = MR.getTargetJITDylib()](
                                        jitlink::LinkGraph &G) -> Error {
     MachOJITDylibInitializers::SectionExtent ModInits, ObjCSelRefs,
         ObjCClassList;

     JITTargetAddress ObjCImageInfoAddr = 0;
     if (auto *ObjCImageInfoSec = G.findSectionByName("__objc_image_info")) {
       if (auto Addr = jitlink::SectionRange(*ObjCImageInfoSec).getStart())
         ObjCImageInfoAddr = Addr;
     }

     // Record __mod_init_func.
     if (auto ModInitsOrErr = getSectionExtent(G, "__mod_init_func"))
       ModInits = std::move(*ModInitsOrErr);
     else
       return ModInitsOrErr.takeError();

     // Record __objc_selrefs.
     if (auto ObjCSelRefsOrErr = getSectionExtent(G, "__objc_selrefs"))
       ObjCSelRefs = std::move(*ObjCSelRefsOrErr);
     else
       return ObjCSelRefsOrErr.takeError();

     // Record __objc_classlist.
     if (auto ObjCClassListOrErr = getSectionExtent(G, "__objc_classlist"))
       ObjCClassList = std::move(*ObjCClassListOrErr);
     else
       return ObjCClassListOrErr.takeError();

     // Dump the scraped inits.
     LLVM_DEBUG({
       dbgs() << "MachOPlatform: Scraped " << G.getName() << " init sections:\n";
       dbgs() << "  __objc_selrefs: ";
       if (ObjCSelRefs.NumPtrs)
         dbgs() << ObjCSelRefs.NumPtrs << " pointer(s) at "
                << formatv("{0:x16}", ObjCSelRefs.Address) << "\n";
       else
         dbgs() << "none\n";

       dbgs() << "  __objc_classlist: ";
       if (ObjCClassList.NumPtrs)
         dbgs() << ObjCClassList.NumPtrs << " pointer(s) at "
                << formatv("{0:x16}", ObjCClassList.Address) << "\n";
       else
         dbgs() << "none\n";

       dbgs() << "  __mod_init_func: ";
       if (ModInits.NumPtrs)
         dbgs() << ModInits.NumPtrs << " pointer(s) at "
                << formatv("{0:x16}", ModInits.Address) << "\n";
       else
         dbgs() << "none\n";
     });

     MP.registerInitInfo(JD, ObjCImageInfoAddr, std::move(ModInits),
                         std::move(ObjCSelRefs), std::move(ObjCClassList));

     return Error::success();
   });
 }

 ObjectLinkingLayer::Plugin::LocalDependenciesMap
 MachOPlatform::InitScraperPlugin::getSyntheticSymbolLocalDependencies(
     MaterializationResponsibility &MR) {
   std::lock_guard<std::mutex> Lock(InitScraperMutex);
   auto I = InitSymbolDeps.find(&MR);
   if (I != InitSymbolDeps.end()) {
     LocalDependenciesMap Result;
     Result[MR.getInitializerSymbol()] = std::move(I->second);
     InitSymbolDeps.erase(&MR);
     return Result;
   }
   return LocalDependenciesMap();
 }

 void MachOPlatform::InitScraperPlugin::preserveInitSectionIfPresent(
     JITLinkSymbolVector &Symbols, jitlink::LinkGraph &G,
     StringRef SectionName) {
   if (auto *Sec = G.findSectionByName(SectionName)) {
     auto SecBlocks = Sec->blocks();
     if (!llvm::empty(SecBlocks))
       Symbols.push_back(
           &G.addAnonymousSymbol(**SecBlocks.begin(), 0, 0, false, true));
   }
 }

 Error MachOPlatform::InitScraperPlugin::processObjCImageInfo(
     jitlink::LinkGraph &G, MaterializationResponsibility &MR) {

   // If there's an ObjC imagine info then either
   //   (1) It's the first __objc_imageinfo we've seen in this JITDylib. In
   //       this case we name and record it.
   // OR
   //   (2) We already have a recorded __objc_imageinfo for this JITDylib,
   //       in which case we just verify it.
   auto *ObjCImageInfo = G.findSectionByName("__objc_imageinfo");
   if (!ObjCImageInfo)
     return Error::success();

   auto ObjCImageInfoBlocks = ObjCImageInfo->blocks();

   // Check that the section is not empty if present.
   if (llvm::empty(ObjCImageInfoBlocks))
     return make_error<StringError>("Empty __objc_imageinfo section in " +
                                        G.getName(),
                                    inconvertibleErrorCode());

   // Check that there's only one block in the section.
   if (std::next(ObjCImageInfoBlocks.begin()) != ObjCImageInfoBlocks.end())
     return make_error<StringError>("Multiple blocks in __objc_imageinfo "
                                    "section in " +
                                        G.getName(),
                                    inconvertibleErrorCode());

   // Check that the __objc_imageinfo section is unreferenced.
   // FIXME: We could optimize this check if Symbols had a ref-count.
   for (auto &Sec : G.sections()) {
     if (&Sec != ObjCImageInfo)
       for (auto *B : Sec.blocks())
         for (auto &E : B->edges())
           if (E.getTarget().isDefined() &&
               &E.getTarget().getBlock().getSection() == ObjCImageInfo)
             return make_error<StringError>("__objc_imageinfo is referenced "
                                            "within file " +
                                                G.getName(),
                                            inconvertibleErrorCode());
   }

   auto &ObjCImageInfoBlock = **ObjCImageInfoBlocks.begin();
   auto *ObjCImageInfoData = ObjCImageInfoBlock.getContent().data();
   auto Version = support::endian::read32(ObjCImageInfoData, G.getEndianness());
   auto Flags =
       support::endian::read32(ObjCImageInfoData + 4, G.getEndianness());

   // Lock the mutex while we verify / update the ObjCImageInfos map.
   std::lock_guard<std::mutex> Lock(InitScraperMutex);

   auto ObjCImageInfoItr = ObjCImageInfos.find(&MR.getTargetJITDylib());
   if (ObjCImageInfoItr != ObjCImageInfos.end()) {
     // We've already registered an __objc_imageinfo section. Verify the
     // content of this new section matches, then delete it.
     if (ObjCImageInfoItr->second.first != Version)
       return make_error<StringError>(
           "ObjC version in " + G.getName() +
               " does not match first registered version",
           inconvertibleErrorCode());
     if (ObjCImageInfoItr->second.second != Flags)
       return make_error<StringError>("ObjC flags in " + G.getName() +
                                          " do not match first registered flags",
                                      inconvertibleErrorCode());

     // __objc_imageinfo is valid. Delete the block.
     for (auto *S : ObjCImageInfo->symbols())
       G.removeDefinedSymbol(*S);
     G.removeBlock(ObjCImageInfoBlock);
   } else {
     // We haven't registered an __objc_imageinfo section yet. Register and
     // move on. The section should already be marked no-dead-strip.
     ObjCImageInfos[&MR.getTargetJITDylib()] = std::make_pair(Version, Flags);
   }

   return Error::success();
 }

 } // End namespace orc.
 } // End namespace llvm.
	//===------ MachOPlatform.cpp - Utilities for executing MachO in Orc ------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/ExecutionEngine/Orc/MachOPlatform.h"

	#include "llvm/BinaryFormat/MachO.h"
	#include "llvm/ExecutionEngine/Orc/DebugUtils.h"
	#include "llvm/Support/BinaryByteStream.h"
	#include "llvm/Support/Debug.h"

	#define DEBUG_TYPE "orc"

	namespace {

	struct objc_class;
	struct objc_image_info;
	struct objc_object;
	struct objc_selector;

	using Class = objc_class *;
	using id = objc_object *;
	using SEL = objc_selector *;

	using ObjCMsgSendTy = id (*)(id, SEL, ...);
	using ObjCReadClassPairTy = Class ()(Class, const objc_image_info );
	using SelRegisterNameTy = SEL ()(const char );

	enum class ObjCRegistrationAPI { Uninitialized, Unavailable, Initialized };

	ObjCRegistrationAPI ObjCRegistrationAPIState =
	ObjCRegistrationAPI::Uninitialized;
	ObjCMsgSendTy objc_msgSend = nullptr;
	ObjCReadClassPairTy objc_readClassPair = nullptr;
	SelRegisterNameTy sel_registerName = nullptr;

	} // end anonymous namespace

	namespace llvm {
	namespace orc {

	template <typename FnTy>
	static Error setUpObjCRegAPIFunc(FnTy &Target, sys::DynamicLibrary &LibObjC,
	const char *Name) {
	if (void *Addr = LibObjC.getAddressOfSymbol(Name))
	Target = reinterpret_cast<FnTy>(Addr);
	else
	return make_error<StringError>(
	(Twine("Could not find address for ") + Name).str(),
	inconvertibleErrorCode());
	return Error::success();
	}

	Error enableObjCRegistration(const char *PathToLibObjC) {
	// If we've already tried to initialize then just bail out.
	if (ObjCRegistrationAPIState != ObjCRegistrationAPI::Uninitialized)
	return Error::success();

	ObjCRegistrationAPIState = ObjCRegistrationAPI::Unavailable;

	std::string ErrMsg;
	auto LibObjC =
	sys::DynamicLibrary::getPermanentLibrary(PathToLibObjC, &ErrMsg);

	if (!LibObjC.isValid())
	return make_error<StringError>(std::move(ErrMsg), inconvertibleErrorCode());

	if (auto Err = setUpObjCRegAPIFunc(objc_msgSend, LibObjC, "objc_msgSend"))
	return Err;
	if (auto Err = setUpObjCRegAPIFunc(objc_readClassPair, LibObjC,
	"objc_readClassPair"))
	return Err;
	if (auto Err =
	setUpObjCRegAPIFunc(sel_registerName, LibObjC, "sel_registerName"))
	return Err;

	ObjCRegistrationAPIState = ObjCRegistrationAPI::Initialized;
	return Error::success();
	}

	bool objCRegistrationEnabled() {
	return ObjCRegistrationAPIState == ObjCRegistrationAPI::Initialized;
	}

	void MachOJITDylibInitializers::runModInits() const {
	for (const auto &ModInit : ModInitSections) {
	for (uint64_t I = 0; I != ModInit.NumPtrs; ++I) {
	auto InitializerAddr = jitTargetAddressToPointer<uintptr_t >(
	ModInit.Address + (I * sizeof(uintptr_t)));
	auto *Initializer =
	jitTargetAddressToFunction<void ()()>(InitializerAddr);
	Initializer();
	}
	}
	}

	void MachOJITDylibInitializers::registerObjCSelectors() const {
	assert(objCRegistrationEnabled() && "ObjC registration not enabled.");

	for (const auto &ObjCSelRefs : ObjCSelRefsSections) {
	for (uint64_t I = 0; I != ObjCSelRefs.NumPtrs; ++I) {
	auto SelEntryAddr = ObjCSelRefs.Address + (I * sizeof(uintptr_t));
	const auto *SelName =
	jitTargetAddressToPointer<const char *>(SelEntryAddr);
	auto Sel = sel_registerName(SelName);
	jitTargetAddressToPointer<SEL >(SelEntryAddr) = Sel;
	}
	}
	}

	Error MachOJITDylibInitializers::registerObjCClasses() const {
	assert(objCRegistrationEnabled() && "ObjC registration not enabled.");

	struct ObjCClassCompiled {
	void *Metaclass;
	void *Parent;
	void *Cache1;
	void *Cache2;
	void *Data;
	};

	auto *ImageInfo =
	jitTargetAddressToPointer<const objc_image_info *>(ObjCImageInfoAddr);
	auto ClassSelector = sel_registerName("class");

	for (const auto &ObjCClassList : ObjCClassListSections) {
	for (uint64_t I = 0; I != ObjCClassList.NumPtrs; ++I) {
	auto ClassPtrAddr = ObjCClassList.Address + (I * sizeof(uintptr_t));
	auto Cls = jitTargetAddressToPointer<Class >(ClassPtrAddr);
	auto *ClassCompiled =
	jitTargetAddressToPointer<ObjCClassCompiled *>(ClassPtrAddr);
	objc_msgSend(reinterpret_cast<id>(ClassCompiled->Parent), ClassSelector);
	auto Registered = objc_readClassPair(Cls, ImageInfo);

	// FIXME: Improve diagnostic by reporting the failed class's name.
	if (Registered != Cls)
	return make_error<StringError>("Unable to register Objective-C class",
	inconvertibleErrorCode());
	}
	}
	return Error::success();
	}

	MachOPlatform::MachOPlatform(
	ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
	std::unique_ptr<MemoryBuffer> StandardSymbolsObject)
	: ES(ES), ObjLinkingLayer(ObjLinkingLayer),
	StandardSymbolsObject(std::move(StandardSymbolsObject)) {
	ObjLinkingLayer.addPlugin(std::make_unique<InitScraperPlugin>(*this));
	}

	Error MachOPlatform::setupJITDylib(JITDylib &JD) {
	auto ObjBuffer = MemoryBuffer::getMemBuffer(
	StandardSymbolsObject->getMemBufferRef(), false);
	return ObjLinkingLayer.add(JD, std::move(ObjBuffer));
	}

	Error MachOPlatform::notifyAdding(ResourceTracker &RT,
	const MaterializationUnit &MU) {
	auto &JD = RT.getJITDylib();
	const auto &InitSym = MU.getInitializerSymbol();
	if (!InitSym)
	return Error::success();

	RegisteredInitSymbols[&JD].add(InitSym,
	SymbolLookupFlags::WeaklyReferencedSymbol);
	LLVM_DEBUG({
	dbgs() << "MachOPlatform: Registered init symbol " << *InitSym << " for MU "
	<< MU.getName() << "\n";
	});
	return Error::success();
	}

	Error MachOPlatform::notifyRemoving(ResourceTracker &RT) {
	llvm_unreachable("Not supported yet");
	}

	Expected<MachOPlatform::InitializerSequence>
	MachOPlatform::getInitializerSequence(JITDylib &JD) {

	LLVM_DEBUG({
	dbgs() << "MachOPlatform: Building initializer sequence for "
	<< JD.getName() << "\n";
	});

	std::vector<JITDylibSP> DFSLinkOrder;

	while (true) {

	DenseMap<JITDylib *, SymbolLookupSet> NewInitSymbols;

	ES.runSessionLocked([&]() {
	DFSLinkOrder = JD.getDFSLinkOrder();

	for (auto &InitJD : DFSLinkOrder) {
	auto RISItr = RegisteredInitSymbols.find(InitJD.get());
	if (RISItr != RegisteredInitSymbols.end()) {
	NewInitSymbols[InitJD.get()] = std::move(RISItr->second);
	RegisteredInitSymbols.erase(RISItr);
	}
	}
	});

	if (NewInitSymbols.empty())
	break;

	LLVM_DEBUG({
	dbgs() << "MachOPlatform: Issuing lookups for new init symbols: "
	"(lookup may require multiple rounds)\n";
	for (auto &KV : NewInitSymbols)
	dbgs() << " \"" << KV.first->getName() << "\": " << KV.second << "\n";
	});

	// Outside the lock, issue the lookup.
	if (auto R = lookupInitSymbols(JD.getExecutionSession(), NewInitSymbols))
	; // Nothing to do in the success case.
	else
	return R.takeError();
	}

	LLVM_DEBUG({
	dbgs() << "MachOPlatform: Init symbol lookup complete, building init "
	"sequence\n";
	});

	// Lock again to collect the initializers.
	InitializerSequence FullInitSeq;
	{
	std::lock_guard<std::mutex> Lock(InitSeqsMutex);
	for (auto &InitJD : reverse(DFSLinkOrder)) {
	LLVM_DEBUG({
	dbgs() << "MachOPlatform: Appending inits for \"" << InitJD->getName()
	<< "\" to sequence\n";
	});
	auto ISItr = InitSeqs.find(InitJD.get());
	if (ISItr != InitSeqs.end()) {
	FullInitSeq.emplace_back(InitJD.get(), std::move(ISItr->second));
	InitSeqs.erase(ISItr);
	}
	}
	}

	return FullInitSeq;
	}

	Expected<MachOPlatform::DeinitializerSequence>
	MachOPlatform::getDeinitializerSequence(JITDylib &JD) {
	std::vector<JITDylibSP> DFSLinkOrder = JD.getDFSLinkOrder();

	DeinitializerSequence FullDeinitSeq;
	{
	std::lock_guard<std::mutex> Lock(InitSeqsMutex);
	for (auto &DeinitJD : DFSLinkOrder) {
	FullDeinitSeq.emplace_back(DeinitJD.get(), MachOJITDylibDeinitializers());
	}
	}

	return FullDeinitSeq;
	}

	void MachOPlatform::registerInitInfo(
	JITDylib &JD, JITTargetAddress ObjCImageInfoAddr,
	MachOJITDylibInitializers::SectionExtent ModInits,
	MachOJITDylibInitializers::SectionExtent ObjCSelRefs,
	MachOJITDylibInitializers::SectionExtent ObjCClassList) {
	std::lock_guard<std::mutex> Lock(InitSeqsMutex);

	auto &InitSeq = InitSeqs[&JD];

	InitSeq.setObjCImageInfoAddr(ObjCImageInfoAddr);

	if (ModInits.Address)
	InitSeq.addModInitsSection(std::move(ModInits));

	if (ObjCSelRefs.Address)
	InitSeq.addObjCSelRefsSection(std::move(ObjCSelRefs));

	if (ObjCClassList.Address)
	InitSeq.addObjCClassListSection(std::move(ObjCClassList));
	}

	static Expected<MachOJITDylibInitializers::SectionExtent>
	getSectionExtent(jitlink::LinkGraph &G, StringRef SectionName) {
	auto *Sec = G.findSectionByName(SectionName);
	if (!Sec)
	return MachOJITDylibInitializers::SectionExtent();
	jitlink::SectionRange R(*Sec);
	if (R.getSize() % G.getPointerSize() != 0)
	return make_error<StringError>(SectionName + " section size is not a "
	"multiple of the pointer size",
	inconvertibleErrorCode());
	return MachOJITDylibInitializers::SectionExtent(
	R.getStart(), R.getSize() / G.getPointerSize());
	}

	void MachOPlatform::InitScraperPlugin::modifyPassConfig(
	MaterializationResponsibility &MR, jitlink::LinkGraph &LG,
	jitlink::PassConfiguration &Config) {

	if (!MR.getInitializerSymbol())
	return;

	Config.PrePrunePasses.push_back([this, &MR](jitlink::LinkGraph &G) -> Error {
	JITLinkSymbolVector InitSectionSymbols;
	preserveInitSectionIfPresent(InitSectionSymbols, G, "__mod_init_func");
	preserveInitSectionIfPresent(InitSectionSymbols, G, "__objc_selrefs");
	preserveInitSectionIfPresent(InitSectionSymbols, G, "__objc_classlist");

	if (!InitSectionSymbols.empty()) {
	std::lock_guard<std::mutex> Lock(InitScraperMutex);
	InitSymbolDeps[&MR] = std::move(InitSectionSymbols);
	}

	if (auto Err = processObjCImageInfo(G, MR))
	return Err;

	return Error::success();
	});

	Config.PostFixupPasses.push_back([this, &JD = MR.getTargetJITDylib()](
	jitlink::LinkGraph &G) -> Error {
	MachOJITDylibInitializers::SectionExtent ModInits, ObjCSelRefs,
	ObjCClassList;

	JITTargetAddress ObjCImageInfoAddr = 0;
	if (auto *ObjCImageInfoSec = G.findSectionByName("__objc_image_info")) {
	if (auto Addr = jitlink::SectionRange(*ObjCImageInfoSec).getStart())
	ObjCImageInfoAddr = Addr;
	}

	// Record __mod_init_func.
	if (auto ModInitsOrErr = getSectionExtent(G, "__mod_init_func"))
	ModInits = std::move(*ModInitsOrErr);
	else
	return ModInitsOrErr.takeError();

	// Record __objc_selrefs.
	if (auto ObjCSelRefsOrErr = getSectionExtent(G, "__objc_selrefs"))
	ObjCSelRefs = std::move(*ObjCSelRefsOrErr);
	else
	return ObjCSelRefsOrErr.takeError();

	// Record __objc_classlist.
	if (auto ObjCClassListOrErr = getSectionExtent(G, "__objc_classlist"))
	ObjCClassList = std::move(*ObjCClassListOrErr);
	else
	return ObjCClassListOrErr.takeError();

	// Dump the scraped inits.
	LLVM_DEBUG({
	dbgs() << "MachOPlatform: Scraped " << G.getName() << " init sections:\n";
	dbgs() << " __objc_selrefs: ";
	if (ObjCSelRefs.NumPtrs)
	dbgs() << ObjCSelRefs.NumPtrs << " pointer(s) at "
	<< formatv("{0:x16}", ObjCSelRefs.Address) << "\n";
	else
	dbgs() << "none\n";

	dbgs() << " __objc_classlist: ";
	if (ObjCClassList.NumPtrs)
	dbgs() << ObjCClassList.NumPtrs << " pointer(s) at "
	<< formatv("{0:x16}", ObjCClassList.Address) << "\n";
	else
	dbgs() << "none\n";

	dbgs() << " __mod_init_func: ";
	if (ModInits.NumPtrs)
	dbgs() << ModInits.NumPtrs << " pointer(s) at "
	<< formatv("{0:x16}", ModInits.Address) << "\n";
	else
	dbgs() << "none\n";
	});

	MP.registerInitInfo(JD, ObjCImageInfoAddr, std::move(ModInits),
	std::move(ObjCSelRefs), std::move(ObjCClassList));

	return Error::success();
	});
	}

	ObjectLinkingLayer::Plugin::LocalDependenciesMap
	MachOPlatform::InitScraperPlugin::getSyntheticSymbolLocalDependencies(
	MaterializationResponsibility &MR) {
	std::lock_guard<std::mutex> Lock(InitScraperMutex);
	auto I = InitSymbolDeps.find(&MR);
	if (I != InitSymbolDeps.end()) {
	LocalDependenciesMap Result;
	Result[MR.getInitializerSymbol()] = std::move(I->second);
	InitSymbolDeps.erase(&MR);
	return Result;
	}
	return LocalDependenciesMap();
	}

	void MachOPlatform::InitScraperPlugin::preserveInitSectionIfPresent(
	JITLinkSymbolVector &Symbols, jitlink::LinkGraph &G,
	StringRef SectionName) {
	if (auto *Sec = G.findSectionByName(SectionName)) {
	auto SecBlocks = Sec->blocks();
	if (!llvm::empty(SecBlocks))
	Symbols.push_back(
	&G.addAnonymousSymbol(**SecBlocks.begin(), 0, 0, false, true));
	}
	}

	Error MachOPlatform::InitScraperPlugin::processObjCImageInfo(
	jitlink::LinkGraph &G, MaterializationResponsibility &MR) {

	// If there's an ObjC imagine info then either
	// (1) It's the first __objc_imageinfo we've seen in this JITDylib. In
	// this case we name and record it.
	// OR
	// (2) We already have a recorded __objc_imageinfo for this JITDylib,
	// in which case we just verify it.
	auto *ObjCImageInfo = G.findSectionByName("__objc_imageinfo");
	if (!ObjCImageInfo)
	return Error::success();

	auto ObjCImageInfoBlocks = ObjCImageInfo->blocks();

	// Check that the section is not empty if present.
	if (llvm::empty(ObjCImageInfoBlocks))
	return make_error<StringError>("Empty __objc_imageinfo section in " +
	G.getName(),
	inconvertibleErrorCode());

	// Check that there's only one block in the section.
	if (std::next(ObjCImageInfoBlocks.begin()) != ObjCImageInfoBlocks.end())
	return make_error<StringError>("Multiple blocks in __objc_imageinfo "
	"section in " +
	G.getName(),
	inconvertibleErrorCode());

	// Check that the __objc_imageinfo section is unreferenced.
	// FIXME: We could optimize this check if Symbols had a ref-count.
	for (auto &Sec : G.sections()) {
	if (&Sec != ObjCImageInfo)
	for (auto *B : Sec.blocks())
	for (auto &E : B->edges())
	if (E.getTarget().isDefined() &&
	&E.getTarget().getBlock().getSection() == ObjCImageInfo)
	return make_error<StringError>("__objc_imageinfo is referenced "
	"within file " +
	G.getName(),
	inconvertibleErrorCode());
	}

	auto &ObjCImageInfoBlock = **ObjCImageInfoBlocks.begin();
	auto *ObjCImageInfoData = ObjCImageInfoBlock.getContent().data();
	auto Version = support::endian::read32(ObjCImageInfoData, G.getEndianness());
	auto Flags =
	support::endian::read32(ObjCImageInfoData + 4, G.getEndianness());

	// Lock the mutex while we verify / update the ObjCImageInfos map.
	std::lock_guard<std::mutex> Lock(InitScraperMutex);

	auto ObjCImageInfoItr = ObjCImageInfos.find(&MR.getTargetJITDylib());
	if (ObjCImageInfoItr != ObjCImageInfos.end()) {
	// We've already registered an __objc_imageinfo section. Verify the
	// content of this new section matches, then delete it.
	if (ObjCImageInfoItr->second.first != Version)
	return make_error<StringError>(
	"ObjC version in " + G.getName() +
	" does not match first registered version",
	inconvertibleErrorCode());
	if (ObjCImageInfoItr->second.second != Flags)
	return make_error<StringError>("ObjC flags in " + G.getName() +
	" do not match first registered flags",
	inconvertibleErrorCode());

	// __objc_imageinfo is valid. Delete the block.
	for (auto *S : ObjCImageInfo->symbols())
	G.removeDefinedSymbol(*S);
	G.removeBlock(ObjCImageInfoBlock);
	} else {
	// We haven't registered an __objc_imageinfo section yet. Register and
	// move on. The section should already be marked no-dead-strip.
	ObjCImageInfos[&MR.getTargetJITDylib()] = std::make_pair(Version, Flags);
	}

	return Error::success();
	}

	} // End namespace orc.
	} // End namespace llvm.