ELFDebugObjectPlugin.cpp

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//===--------- ELFDebugObjectPlugin.cpp - JITLink debug objects -----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// FIXME: Update Plugin to poke the debug object into a new JITLink section,
//        rather than creating a new allocation.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/ExecutionEngine/Orc/Debugging/ELFDebugObjectPlugin.h"
 
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/ExecutionEngine/JITLink/JITLinkDylib.h"
#include "llvm/ExecutionEngine/JITLink/JITLinkMemoryManager.h"
#include "llvm/ExecutionEngine/Orc/Shared/OrcRTBridge.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/MSVCErrorWorkarounds.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Process.h"
#include "llvm/Support/raw_ostream.h"
 
#include <set>
 
#define DEBUG_TYPE "orc"
 
using namespace llvm::jitlink;
using namespace llvm::object;
 
namespace llvm {
namespace orc {
 
class DebugObjectSection {
public:
  virtual void setTargetMemoryRange(SectionRange Range) = 0;
  virtual void dump(raw_ostream &OS, StringRef Name) {}
  virtual ~DebugObjectSection() = default;
};
 
template <typename ELFT>
class ELFDebugObjectSection : public DebugObjectSection {
public:
  // BinaryFormat ELF is not meant as a mutable format. We can only make changes
  // that don't invalidate the file structure.
  ELFDebugObjectSection(const typename ELFT::Shdr *Header)
      : Header(const_cast<typename ELFT::Shdr *>(Header)) {}
 
  void setTargetMemoryRange(SectionRange Range) override;
  void dump(raw_ostream &OS, StringRef Name) override;
 
  Error validateInBounds(StringRef Buffer, const char *Name) const;
 
private:
  typename ELFT::Shdr *Header;
};
 
template <typename ELFT>
void ELFDebugObjectSection<ELFT>::setTargetMemoryRange(SectionRange Range) {
  // All recorded sections are candidates for load-address patching.
  Header->sh_addr =
      static_cast<typename ELFT::uint>(Range.getStart().getValue());
}
 
template <typename ELFT>
Error ELFDebugObjectSection<ELFT>::validateInBounds(StringRef Buffer,
                                                    const char *Name) const {
  const uint8_t *Start = Buffer.bytes_begin();
  const uint8_t *End = Buffer.bytes_end();
  const uint8_t *HeaderPtr = reinterpret_cast<uint8_t *>(Header);
  if (HeaderPtr < Start || HeaderPtr + sizeof(typename ELFT::Shdr) > End)
    return make_error<StringError>(
        formatv("{0} section header at {1:x16} not within bounds of the "
                "given debug object buffer [{2:x16} - {3:x16}]",
                Name, &Header->sh_addr, Start, End),
        inconvertibleErrorCode());
  if (Header->sh_offset + Header->sh_size > Buffer.size())
    return make_error<StringError>(
        formatv("{0} section data [{1:x16} - {2:x16}] not within bounds of "
                "the given debug object buffer [{3:x16} - {4:x16}]",
                Name, Start + Header->sh_offset,
                Start + Header->sh_offset + Header->sh_size, Start, End),
        inconvertibleErrorCode());
  return Error::success();
}
 
template <typename ELFT>
void ELFDebugObjectSection<ELFT>::dump(raw_ostream &OS, StringRef Name) {
  if (uint64_t Addr = Header->sh_addr) {
    OS << formatv("  {0:x16} {1}\n", Addr, Name);
  } else {
    OS << formatv("                     {0}\n", Name);
  }
}
 
enum DebugObjectFlags : int {
  // Request final target memory load-addresses for all sections.
  ReportFinalSectionLoadAddresses = 1 << 0,
 
  // We found sections with debug information when processing the input object.
  HasDebugSections = 1 << 1,
};
 
/// The plugin creates a debug object from when JITLink starts processing the
/// corresponding LinkGraph. It provides access to the pass configuration of
/// the LinkGraph and calls the finalization function, once the resulting link
/// artifact was emitted.
///
class DebugObject {
public:
  DebugObject(JITLinkMemoryManager &MemMgr, const JITLinkDylib *JD,
              ExecutionSession &ES)
      : MemMgr(MemMgr), JD(JD), ES(ES), Flags(DebugObjectFlags{}) {
    FinalizeFuture = FinalizePromise.get_future();
  }
 
  bool hasFlags(DebugObjectFlags F) const { return Flags & F; }
  void setFlags(DebugObjectFlags F) {
    Flags = static_cast<DebugObjectFlags>(Flags | F);
  }
  void clearFlags(DebugObjectFlags F) {
    Flags = static_cast<DebugObjectFlags>(Flags & ~F);
  }
 
  using FinalizeContinuation = std::function<void(Expected<ExecutorAddrRange>)>;
  void finalizeAsync(FinalizeContinuation OnAsync);
 
  void failMaterialization(Error Err) {
    FinalizePromise.set_value(std::move(Err));
  }
 
  void reportTargetMem(ExecutorAddrRange TargetMem) {
    FinalizePromise.set_value(TargetMem);
  }
 
  Expected<ExecutorAddrRange> awaitTargetMem() { return FinalizeFuture.get(); }
 
  virtual ~DebugObject() {
    if (Alloc) {
      std::vector<FinalizedAlloc> Allocs;
      Allocs.push_back(std::move(Alloc));
      if (Error Err = MemMgr.deallocate(std::move(Allocs)))
        ES.reportError(std::move(Err));
    }
  }
 
  virtual void reportSectionTargetMemoryRange(StringRef Name,
                                              SectionRange TargetMem) {}
 
protected:
  using InFlightAlloc = JITLinkMemoryManager::InFlightAlloc;
  using FinalizedAlloc = JITLinkMemoryManager::FinalizedAlloc;
 
  virtual Expected<SimpleSegmentAlloc> finalizeWorkingMemory() = 0;
 
  JITLinkMemoryManager &MemMgr;
  const JITLinkDylib *JD = nullptr;
  ExecutionSession &ES;
 
  std::promise<MSVCPExpected<ExecutorAddrRange>> FinalizePromise;
  std::future<MSVCPExpected<ExecutorAddrRange>> FinalizeFuture;
 
private:
  DebugObjectFlags Flags;
  FinalizedAlloc Alloc;
};
 
// Finalize working memory and take ownership of the resulting allocation. Start
// copying memory over to the target and pass on the result once we're done.
// Ownership of the allocation remains with us for the rest of our lifetime.
void DebugObject::finalizeAsync(FinalizeContinuation OnFinalize) {
  assert(!this->Alloc && "Cannot finalize more than once");
  if (auto SimpleSegAlloc = finalizeWorkingMemory()) {
    auto ROSeg = SimpleSegAlloc->getSegInfo(MemProt::Read);
    ExecutorAddrRange DebugObjRange(ROSeg.Addr, ROSeg.WorkingMem.size());
    SimpleSegAlloc->finalize(
        [this, DebugObjRange,
         OnFinalize = std::move(OnFinalize)](Expected<FinalizedAlloc> FA) {
          if (FA) {
            // Note: FA->getAddress() is supposed to be the address of the
            // memory range on the target, but InProcessMemoryManager returns
            // the address of a FinalizedAllocInfo helper instead.
            this->Alloc = std::move(*FA);
            OnFinalize(DebugObjRange);
          } else
            OnFinalize(FA.takeError());
        });
  } else {
    // We could report this error synchronously, but it's easier this way,
    // because the FinalizePromise will be triggered unconditionally.
    OnFinalize(SimpleSegAlloc.takeError());
  }
}
 
/// The current implementation of ELFDebugObject replicates the approach used in
/// RuntimeDyld: It patches executable and data section headers in the given
/// object buffer with load-addresses of their corresponding sections in target
/// memory.
///
class ELFDebugObject : public DebugObject {
public:
  static Expected<std::unique_ptr<DebugObject>>
  Create(MemoryBufferRef Buffer, JITLinkContext &Ctx, ExecutionSession &ES);
 
  void reportSectionTargetMemoryRange(StringRef Name,
                                      SectionRange TargetMem) override;
 
  StringRef getBuffer() const { return Buffer->getMemBufferRef().getBuffer(); }
 
protected:
  Expected<SimpleSegmentAlloc> finalizeWorkingMemory() override;
 
  template <typename ELFT>
  Error recordSection(StringRef Name,
                      std::unique_ptr<ELFDebugObjectSection<ELFT>> Section);
  DebugObjectSection *getSection(StringRef Name);
 
private:
  template <typename ELFT>
  static Expected<std::unique_ptr<ELFDebugObject>>
  CreateArchType(MemoryBufferRef Buffer, JITLinkMemoryManager &MemMgr,
                 const JITLinkDylib *JD, ExecutionSession &ES);
 
  static std::unique_ptr<WritableMemoryBuffer>
  CopyBuffer(MemoryBufferRef Buffer, Error &Err);
 
  ELFDebugObject(std::unique_ptr<WritableMemoryBuffer> Buffer,
                 JITLinkMemoryManager &MemMgr, const JITLinkDylib *JD,
                 ExecutionSession &ES)
      : DebugObject(MemMgr, JD, ES), Buffer(std::move(Buffer)) {
    setFlags(ReportFinalSectionLoadAddresses);
  }
 
  std::unique_ptr<WritableMemoryBuffer> Buffer;
  StringMap<std::unique_ptr<DebugObjectSection>> Sections;
};
 
static const std::set<StringRef> DwarfSectionNames = {
#define HANDLE_DWARF_SECTION(ENUM_NAME, ELF_NAME, CMDLINE_NAME, OPTION)        \
  ELF_NAME,
#include "llvm/BinaryFormat/Dwarf.def"
#undef HANDLE_DWARF_SECTION
};
 
static bool isDwarfSection(StringRef SectionName) {
  return DwarfSectionNames.count(SectionName) == 1;
}
 
std::unique_ptr<WritableMemoryBuffer>
ELFDebugObject::CopyBuffer(MemoryBufferRef Buffer, Error &Err) {
  ErrorAsOutParameter _(Err);
  size_t Size = Buffer.getBufferSize();
  StringRef Name = Buffer.getBufferIdentifier();
  if (auto Copy = WritableMemoryBuffer::getNewUninitMemBuffer(Size, Name)) {
    memcpy(Copy->getBufferStart(), Buffer.getBufferStart(), Size);
    return Copy;
  }
 
  Err = errorCodeToError(make_error_code(errc::not_enough_memory));
  return nullptr;
}
 
template <typename ELFT>
Expected<std::unique_ptr<ELFDebugObject>>
ELFDebugObject::CreateArchType(MemoryBufferRef Buffer,
                               JITLinkMemoryManager &MemMgr,
                               const JITLinkDylib *JD, ExecutionSession &ES) {
  using SectionHeader = typename ELFT::Shdr;
 
  Error Err = Error::success();
  std::unique_ptr<ELFDebugObject> DebugObj(
      new ELFDebugObject(CopyBuffer(Buffer, Err), MemMgr, JD, ES));
  if (Err)
    return std::move(Err);
 
  Expected<ELFFile<ELFT>> ObjRef = ELFFile<ELFT>::create(DebugObj->getBuffer());
  if (!ObjRef)
    return ObjRef.takeError();
 
  Expected<ArrayRef<SectionHeader>> Sections = ObjRef->sections();
  if (!Sections)
    return Sections.takeError();
 
  for (const SectionHeader &Header : *Sections) {
    Expected<StringRef> Name = ObjRef->getSectionName(Header);
    if (!Name)
      return Name.takeError();
    if (Name->empty())
      continue;
    if (isDwarfSection(*Name))
      DebugObj->setFlags(HasDebugSections);
 
    // Only record text and data sections (i.e. no bss, comments, rel, etc.)
    if (Header.sh_type != ELF::SHT_PROGBITS &&
        Header.sh_type != ELF::SHT_X86_64_UNWIND)
      continue;
    if (!(Header.sh_flags & ELF::SHF_ALLOC))
      continue;
 
    auto Wrapped = std::make_unique<ELFDebugObjectSection<ELFT>>(&Header);
    if (Error Err = DebugObj->recordSection(*Name, std::move(Wrapped)))
      return std::move(Err);
  }
 
  return std::move(DebugObj);
}
 
Expected<std::unique_ptr<DebugObject>>
ELFDebugObject::Create(MemoryBufferRef Buffer, JITLinkContext &Ctx,
                       ExecutionSession &ES) {
  unsigned char Class, Endian;
  std::tie(Class, Endian) = getElfArchType(Buffer.getBuffer());
 
  if (Class == ELF::ELFCLASS32) {
    if (Endian == ELF::ELFDATA2LSB)
      return CreateArchType<ELF32LE>(Buffer, Ctx.getMemoryManager(),
                                     Ctx.getJITLinkDylib(), ES);
    if (Endian == ELF::ELFDATA2MSB)
      return CreateArchType<ELF32BE>(Buffer, Ctx.getMemoryManager(),
                                     Ctx.getJITLinkDylib(), ES);
    return nullptr;
  }
  if (Class == ELF::ELFCLASS64) {
    if (Endian == ELF::ELFDATA2LSB)
      return CreateArchType<ELF64LE>(Buffer, Ctx.getMemoryManager(),
                                     Ctx.getJITLinkDylib(), ES);
    if (Endian == ELF::ELFDATA2MSB)
      return CreateArchType<ELF64BE>(Buffer, Ctx.getMemoryManager(),
                                     Ctx.getJITLinkDylib(), ES);
    return nullptr;
  }
  return nullptr;
}
 
Expected<SimpleSegmentAlloc> ELFDebugObject::finalizeWorkingMemory() {
  LLVM_DEBUG({
    dbgs() << "Section load-addresses in debug object for \""
           << Buffer->getBufferIdentifier() << "\":\n";
    for (const auto &KV : Sections)
      KV.second->dump(dbgs(), KV.first());
  });
 
  // TODO: This works, but what actual alignment requirements do we have?
  unsigned PageSize = sys::Process::getPageSizeEstimate();
  size_t Size = Buffer->getBufferSize();
 
  // Allocate working memory for debug object in read-only segment.
  auto Alloc = SimpleSegmentAlloc::Create(
      MemMgr, ES.getSymbolStringPool(), ES.getTargetTriple(), JD,
      {{MemProt::Read, {Size, Align(PageSize)}}});
  if (!Alloc)
    return Alloc;
 
  // Initialize working memory with a copy of our object buffer.
  auto SegInfo = Alloc->getSegInfo(MemProt::Read);
  memcpy(SegInfo.WorkingMem.data(), Buffer->getBufferStart(), Size);
  Buffer.reset();
 
  return Alloc;
}
 
void ELFDebugObject::reportSectionTargetMemoryRange(StringRef Name,
                                                    SectionRange TargetMem) {
  if (auto *DebugObjSection = getSection(Name))
    DebugObjSection->setTargetMemoryRange(TargetMem);
}
 
template <typename ELFT>
Error ELFDebugObject::recordSection(
    StringRef Name, std::unique_ptr<ELFDebugObjectSection<ELFT>> Section) {
  if (Error Err = Section->validateInBounds(this->getBuffer(), Name.data()))
    return Err;
  bool Inserted = Sections.try_emplace(Name, std::move(Section)).second;
  if (!Inserted)
    LLVM_DEBUG(dbgs() << "Skipping debug registration for section '" << Name
                      << "' in object " << Buffer->getBufferIdentifier()
                      << " (duplicate name)\n");
  return Error::success();
}
 
DebugObjectSection *ELFDebugObject::getSection(StringRef Name) {
  auto It = Sections.find(Name);
  return It == Sections.end() ? nullptr : It->second.get();
}
 
/// Creates a debug object based on the input object file from
/// ObjectLinkingLayerJITLinkContext.
///
static Expected<std::unique_ptr<DebugObject>>
createDebugObjectFromBuffer(ExecutionSession &ES, LinkGraph &G,
                            JITLinkContext &Ctx, MemoryBufferRef ObjBuffer) {
  switch (G.getTargetTriple().getObjectFormat()) {
  case Triple::ELF:
    return ELFDebugObject::Create(ObjBuffer, Ctx, ES);
 
  default:
    // TODO: Once we add support for other formats, we might want to split this
    // into multiple files.
    return nullptr;
  }
}
 
ELFDebugObjectPlugin::ELFDebugObjectPlugin(ExecutionSession &ES,
                                           bool RequireDebugSections,
                                           bool AutoRegisterCode, Error &Err)
    : ES(ES), RequireDebugSections(RequireDebugSections),
      AutoRegisterCode(AutoRegisterCode) {
  // Pass bootstrap symbol for registration function to enable debugging
  ErrorAsOutParameter _(&Err);
  Err = ES.getExecutorProcessControl().getBootstrapSymbols(
      {{RegistrationAction, rt::RegisterJITLoaderGDBAllocActionName}});
}
 
ELFDebugObjectPlugin::~ELFDebugObjectPlugin() = default;
 
void ELFDebugObjectPlugin::notifyMaterializing(
    MaterializationResponsibility &MR, LinkGraph &G, JITLinkContext &Ctx,
    MemoryBufferRef ObjBuffer) {
  std::lock_guard<std::mutex> Lock(PendingObjsLock);
  assert(PendingObjs.count(&MR) == 0 &&
         "Cannot have more than one pending debug object per "
         "MaterializationResponsibility");
 
  if (auto DebugObj = createDebugObjectFromBuffer(ES, G, Ctx, ObjBuffer)) {
    // Not all link artifacts allow debugging.
    if (*DebugObj == nullptr)
      return;
    if (RequireDebugSections && !(**DebugObj).hasFlags(HasDebugSections)) {
      LLVM_DEBUG(dbgs() << "Skipping debug registration for LinkGraph '"
                        << G.getName() << "': no debug info\n");
      return;
    }
    PendingObjs[&MR] = std::move(*DebugObj);
  } else {
    ES.reportError(DebugObj.takeError());
  }
}
 
void ELFDebugObjectPlugin::modifyPassConfig(MaterializationResponsibility &MR,
                                            LinkGraph &G,
                                            PassConfiguration &PassConfig) {
  // Not all link artifacts have associated debug objects.
  std::lock_guard<std::mutex> Lock(PendingObjsLock);
  auto It = PendingObjs.find(&MR);
  if (It == PendingObjs.end())
    return;
 
  DebugObject &DebugObj = *It->second;
  if (DebugObj.hasFlags(ReportFinalSectionLoadAddresses)) {
    PassConfig.PostAllocationPasses.push_back(
        [&DebugObj](LinkGraph &Graph) -> Error {
          for (const Section &GraphSection : Graph.sections())
            DebugObj.reportSectionTargetMemoryRange(GraphSection.getName(),
                                                    SectionRange(GraphSection));
          return Error::success();
        });
 
    PassConfig.PreFixupPasses.push_back(
        [this, &DebugObj, &MR](LinkGraph &G) -> Error {
          DebugObj.finalizeAsync([this, &DebugObj,
                                  &MR](Expected<ExecutorAddrRange> TargetMem) {
            if (!TargetMem) {
              DebugObj.failMaterialization(TargetMem.takeError());
              return;
            }
            // Update tracking info
            Error Err = MR.withResourceKeyDo([&](ResourceKey K) {
              std::lock_guard<std::mutex> LockPending(PendingObjsLock);
              std::lock_guard<std::mutex> LockRegistered(RegisteredObjsLock);
              auto It = PendingObjs.find(&MR);
              RegisteredObjs[K].push_back(std::move(It->second));
              PendingObjs.erase(It);
            });
 
            if (Err)
              DebugObj.failMaterialization(std::move(Err));
 
            // Unblock post-fixup pass
            DebugObj.reportTargetMem(*TargetMem);
          });
          return Error::success();
        });
 
    PassConfig.PostFixupPasses.push_back(
        [this, &DebugObj](LinkGraph &G) -> Error {
          Expected<ExecutorAddrRange> R = DebugObj.awaitTargetMem();
          if (!R)
            return R.takeError();
          if (R->empty())
            return Error::success();
 
          using namespace shared;
          G.allocActions().push_back(
              {cantFail(WrapperFunctionCall::Create<
                        SPSArgList<SPSExecutorAddrRange, bool>>(
                   RegistrationAction, *R, AutoRegisterCode)),
               {/* no deregistration */}});
          return Error::success();
        });
  }
}
 
Error ELFDebugObjectPlugin::notifyFailed(MaterializationResponsibility &MR) {
  std::lock_guard<std::mutex> Lock(PendingObjsLock);
  PendingObjs.erase(&MR);
  return Error::success();
}
 
void ELFDebugObjectPlugin::notifyTransferringResources(JITDylib &JD,
                                                       ResourceKey DstKey,
                                                       ResourceKey SrcKey) {
  // Debug objects are stored by ResourceKey only after registration.
  // Thus, pending objects don't need to be updated here.
  std::lock_guard<std::mutex> Lock(RegisteredObjsLock);
  auto SrcIt = RegisteredObjs.find(SrcKey);
  if (SrcIt != RegisteredObjs.end()) {
    // Resources from distinct MaterializationResponsibilitys can get merged
    // after emission, so we can have multiple debug objects per resource key.
    for (std::unique_ptr<DebugObject> &DebugObj : SrcIt->second)
      RegisteredObjs[DstKey].push_back(std::move(DebugObj));
    RegisteredObjs.erase(SrcIt);
  }
}
 
Error ELFDebugObjectPlugin::notifyRemovingResources(JITDylib &JD,
                                                    ResourceKey Key) {
  // Removing the resource for a pending object fails materialization, so they
  // get cleaned up in the notifyFailed() handler.
  std::lock_guard<std::mutex> Lock(RegisteredObjsLock);
  RegisteredObjs.erase(Key);
 
  // TODO: Implement unregister notifications.
  return Error::success();
}
 
} // namespace orc
} // namespace llvm