MachOPlatform.cpp

//===------ 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/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(JITDylib &JD, const MaterializationUnit &MU) {
  const auto &InitSym = MU.getInitializerSymbol();
  if (!InitSym)
    return Error::success();

  std::lock_guard<std::mutex> Lock(PlatformMutex);
  RegisteredInitSymbols[&JD].add(InitSym);
  LLVM_DEBUG({
    dbgs() << "MachOPlatform: Registered init symbol " << *InitSym << " for MU "
           << MU.getName() << "\n";
  });
  return Error::success();
}

Error MachOPlatform::notifyRemoving(JITDylib &JD, VModuleKey K) {
  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<JITDylib *> DFSLinkOrder;

  while (true) {
    // Lock the platform while we search for any initializer symbols to
    // look up.
    DenseMap<JITDylib *, SymbolLookupSet> NewInitSymbols;
    {
      std::lock_guard<std::mutex> Lock(PlatformMutex);
      DFSLinkOrder = getDFSLinkOrder(JD);

      for (auto *InitJD : DFSLinkOrder) {
        auto RISItr = RegisteredInitSymbols.find(InitJD);
        if (RISItr != RegisteredInitSymbols.end()) {
          NewInitSymbols[InitJD] = 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(PlatformMutex);
    for (auto *InitJD : reverse(DFSLinkOrder)) {
      LLVM_DEBUG({
        dbgs() << "MachOPlatform: Appending inits for \"" << InitJD->getName()
               << "\" to sequence\n";
      });
      auto ISItr = InitSeqs.find(InitJD);
      if (ISItr != InitSeqs.end()) {
        FullInitSeq.emplace_back(InitJD, std::move(ISItr->second));
        InitSeqs.erase(ISItr);
      }
    }
  }

  return FullInitSeq;
}

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

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

  return FullDeinitSeq;
}

std::vector<JITDylib *> MachOPlatform::getDFSLinkOrder(JITDylib &JD) {
  std::vector<JITDylib *> Result, WorkStack({&JD});
  DenseSet<JITDylib *> Visited;

  while (!WorkStack.empty()) {
    auto *NextJD = WorkStack.back();
    WorkStack.pop_back();
    if (Visited.count(NextJD))
      continue;
    Visited.insert(NextJD);
    Result.push_back(NextJD);
    NextJD->withSearchOrderDo([&](const JITDylibSearchOrder &SO) {
      for (auto &KV : SO)
        WorkStack.push_back(KV.first);
    });
  }

  return Result;
}

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

  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, const Triple &TT,
    jitlink::PassConfiguration &Config) {

  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 (!InitSymbolDeps.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;
        dbgs() << "Recorded __objc_imageinfo @ " << formatv("{0:x16}", 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.