GOFFObjectWriter.cpp

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//===- lib/MC/GOFFObjectWriter.cpp - GOFF File Writer ---------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements GOFF object file writer information.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/BinaryFormat/GOFF.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCGOFFAttributes.h"
#include "llvm/MC/MCGOFFObjectWriter.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionGOFF.h"
#include "llvm/MC/MCSymbolGOFF.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/ConvertEBCDIC.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/raw_ostream.h"
 
using namespace llvm;
 
#define DEBUG_TYPE "goff-writer"
 
namespace {
// Common flag values on records.
 
// Flag: This record is continued.
constexpr uint8_t RecContinued = GOFF::Flags(7, 1, 1);
 
// Flag: This record is a continuation.
constexpr uint8_t RecContinuation = GOFF::Flags(6, 1, 1);
 
// The GOFFOstream is responsible to write the data into the fixed physical
// records of the format. A user of this class announces the begin of a new
// logical record. While writing the payload, the physical records are created
// for the data. Possible fill bytes at the end of a physical record are written
// automatically. In principle, the GOFFOstream is agnostic of the endianness of
// the payload. However, it also supports writing data in big endian byte order.
//
// The physical records use the flag field to indicate if the there is a
// successor and predecessor record. To be able to set these flags while
// writing, the basic implementation idea is to always buffer the last seen
// physical record.
class GOFFOstream {
  /// The underlying raw_pwrite_stream.
  raw_pwrite_stream &OS;
 
  /// The number of logical records emitted so far.
  uint32_t LogicalRecords = 0;
 
  /// The number of physical records emitted so far.
  uint32_t PhysicalRecords = 0;
 
  /// The size of the buffer. Same as the payload size of a physical record.
  static constexpr uint8_t BufferSize = GOFF::PayloadLength;
 
  /// Current position in buffer.
  char *BufferPtr = Buffer;
 
  /// Static allocated buffer for the stream.
  char Buffer[BufferSize];
 
  /// The type of the current logical record, and the flags (aka continued and
  /// continuation indicators) for the previous (physical) record.
  uint8_t TypeAndFlags = 0;
 
public:
  GOFFOstream(raw_pwrite_stream &OS);
  ~GOFFOstream();
 
  raw_pwrite_stream &getOS() { return OS; }
  size_t getWrittenSize() const { return PhysicalRecords * GOFF::RecordLength; }
  uint32_t getNumLogicalRecords() { return LogicalRecords; }
 
  /// Write the specified bytes.
  void write(const char *Ptr, size_t Size);
 
  /// Write zeroes, up to a maximum of 16 bytes.
  void write_zeros(unsigned NumZeros);
 
  /// Support for endian-specific data.
  template <typename value_type> void writebe(value_type Value) {
    Value =
        support::endian::byte_swap<value_type>(Value, llvm::endianness::big);
    write((const char *)&Value, sizeof(value_type));
  }
 
  /// Begin a new logical record. Implies finalizing the previous record.
  void newRecord(GOFF::RecordType Type);
 
  /// Ends a logical record.
  void finalizeRecord();
 
private:
  /// Updates the continued/continuation flags, and writes the record prefix of
  /// a physical record.
  void updateFlagsAndWritePrefix(bool IsContinued);
 
  /// Returns the remaining size in the buffer.
  size_t getRemainingSize();
};
} // namespace
 
GOFFOstream::GOFFOstream(raw_pwrite_stream &OS) : OS(OS) {}
 
GOFFOstream::~GOFFOstream() { finalizeRecord(); }
 
void GOFFOstream::updateFlagsAndWritePrefix(bool IsContinued) {
  // Update the flags based on the previous state and the flag IsContinued.
  if (TypeAndFlags & RecContinued)
    TypeAndFlags |= RecContinuation;
  if (IsContinued)
    TypeAndFlags |= RecContinued;
  else
    TypeAndFlags &= ~RecContinued;
 
  OS << static_cast<unsigned char>(GOFF::PTVPrefix) // Record Type
     << static_cast<unsigned char>(TypeAndFlags)    // Continuation
     << static_cast<unsigned char>(0);              // Version
 
  ++PhysicalRecords;
}
 
size_t GOFFOstream::getRemainingSize() {
  return size_t(&Buffer[BufferSize] - BufferPtr);
}
 
void GOFFOstream::write(const char *Ptr, size_t Size) {
  size_t RemainingSize = getRemainingSize();
 
  // Data fits into the buffer.
  if (LLVM_LIKELY(Size <= RemainingSize)) {
    memcpy(BufferPtr, Ptr, Size);
    BufferPtr += Size;
    return;
  }
 
  // Otherwise the buffer is partially filled or full, and data does not fit
  // into it.
  updateFlagsAndWritePrefix(/*IsContinued=*/true);
  OS.write(Buffer, size_t(BufferPtr - Buffer));
  if (RemainingSize > 0) {
    OS.write(Ptr, RemainingSize);
    Ptr += RemainingSize;
    Size -= RemainingSize;
  }
 
  while (Size > BufferSize) {
    updateFlagsAndWritePrefix(/*IsContinued=*/true);
    OS.write(Ptr, BufferSize);
    Ptr += BufferSize;
    Size -= BufferSize;
  }
 
  // The remaining bytes fit into the buffer.
  memcpy(Buffer, Ptr, Size);
  BufferPtr = &Buffer[Size];
}
 
void GOFFOstream::write_zeros(unsigned NumZeros) {
  assert(NumZeros <= 16 && "Range for zeros too large");
 
  // Handle the common case first: all fits in the buffer.
  size_t RemainingSize = getRemainingSize();
  if (LLVM_LIKELY(RemainingSize >= NumZeros)) {
    memset(BufferPtr, 0, NumZeros);
    BufferPtr += NumZeros;
    return;
  }
 
  // Otherwise some field value is cleared.
  static char Zeros[16] = {
      0,
  };
  write(Zeros, NumZeros);
}
 
void GOFFOstream::newRecord(GOFF::RecordType Type) {
  finalizeRecord();
  TypeAndFlags = Type << 4;
  ++LogicalRecords;
}
 
void GOFFOstream::finalizeRecord() {
  if (Buffer == BufferPtr)
    return;
  updateFlagsAndWritePrefix(/*IsContinued=*/false);
  OS.write(Buffer, size_t(BufferPtr - Buffer));
  OS.write_zeros(getRemainingSize());
  BufferPtr = Buffer;
}
 
namespace {
// A GOFFSymbol holds all the data required for writing an ESD record.
class GOFFSymbol {
public:
  std::string Name;
  uint32_t EsdId;
  uint32_t ParentEsdId;
  uint64_t Offset = 0; // Offset of the symbol into the section. LD only.
                       // Offset is only 32 bit, the larger type is used to
                       // enable error checking.
  GOFF::ESDSymbolType SymbolType;
  GOFF::ESDNameSpaceId NameSpace = GOFF::ESD_NS_ProgramManagementBinder;
 
  GOFF::BehavioralAttributes BehavAttrs;
  GOFF::SymbolFlags SymbolFlags;
  uint32_t SortKey = 0;
  uint32_t SectionLength = 0;
  uint32_t ADAEsdId = 0;
  uint32_t EASectionEDEsdId = 0;
  uint32_t EASectionOffset = 0;
  uint8_t FillByteValue = 0;
 
  GOFFSymbol() : EsdId(0), ParentEsdId(0) {}
 
  GOFFSymbol(StringRef Name, uint32_t EsdID, const GOFF::SDAttr &Attr)
      : Name(Name.data(), Name.size()), EsdId(EsdID), ParentEsdId(0),
        SymbolType(GOFF::ESD_ST_SectionDefinition) {
    BehavAttrs.setTaskingBehavior(Attr.TaskingBehavior);
    BehavAttrs.setBindingScope(Attr.BindingScope);
  }
 
  GOFFSymbol(StringRef Name, uint32_t EsdID, uint32_t ParentEsdID,
             const GOFF::EDAttr &Attr, GOFF::ESDAlignment Alignment)
      : Name(Name.data(), Name.size()), EsdId(EsdID), ParentEsdId(ParentEsdID),
        SymbolType(GOFF::ESD_ST_ElementDefinition) {
    this->NameSpace = Attr.NameSpace;
    // We always set a fill byte value.
    this->FillByteValue = Attr.FillByteValue;
    SymbolFlags.setFillBytePresence(1);
    SymbolFlags.setReservedQwords(Attr.ReservedQwords);
    // TODO Do we need/should set the "mangled" flag?
    BehavAttrs.setReadOnly(Attr.IsReadOnly);
    BehavAttrs.setRmode(Attr.Rmode);
    BehavAttrs.setTextStyle(Attr.TextStyle);
    BehavAttrs.setBindingAlgorithm(Attr.BindAlgorithm);
    BehavAttrs.setLoadingBehavior(Attr.LoadBehavior);
    BehavAttrs.setAlignment(Alignment);
  }
 
  GOFFSymbol(StringRef Name, uint32_t EsdID, uint32_t ParentEsdID,
             GOFF::ESDNameSpaceId NameSpace, const GOFF::LDAttr &Attr)
      : Name(Name.data(), Name.size()), EsdId(EsdID), ParentEsdId(ParentEsdID),
        SymbolType(GOFF::ESD_ST_LabelDefinition), NameSpace(NameSpace) {
    SymbolFlags.setRenameable(Attr.IsRenamable);
    BehavAttrs.setExecutable(Attr.Executable);
    BehavAttrs.setBindingStrength(Attr.BindingStrength);
    BehavAttrs.setLinkageType(Attr.Linkage);
    BehavAttrs.setAmode(Attr.Amode);
    BehavAttrs.setBindingScope(Attr.BindingScope);
  }
 
  GOFFSymbol(StringRef Name, uint32_t EsdID, uint32_t ParentEsdID,
             const GOFF::EDAttr &EDAttr, GOFF::ESDAlignment Alignment,
             const GOFF::PRAttr &Attr)
      : Name(Name.data(), Name.size()), EsdId(EsdID), ParentEsdId(ParentEsdID),
        SymbolType(GOFF::ESD_ST_PartReference), NameSpace(EDAttr.NameSpace) {
    SymbolFlags.setRenameable(Attr.IsRenamable);
    BehavAttrs.setExecutable(Attr.Executable);
    BehavAttrs.setBindingStrength(Attr.BindingStrength);
    BehavAttrs.setLinkageType(Attr.Linkage);
    // See
    // https://www.ibm.com/docs/en/hla-and-tf/1.6.0?topic=statements-amode-instruction#amode__modcomb,
    // Table 2. HLASM sets the AMODE based on the RMODE if no AMODE is given.
    GOFF::ESDAmode Amode;
    switch (EDAttr.Rmode) {
    case GOFF::ESD_RMODE_24:
      Amode = GOFF::ESD_AMODE_24;
      break;
    case GOFF::ESD_RMODE_31:
      Amode = GOFF::ESD_AMODE_31;
      break;
    case GOFF::ESD_RMODE_64:
      Amode = GOFF::ESD_AMODE_64;
      break;
    default:
      Amode = GOFF::ESD_AMODE_None;
      break;
    }
    BehavAttrs.setAmode(Amode);
    BehavAttrs.setBindingScope(Attr.BindingScope);
    BehavAttrs.setAlignment(Alignment);
  }
 
  GOFFSymbol(StringRef Name, uint32_t EsdID, uint32_t ParentEsdID,
             const GOFF::ERAttr &Attr)
      : Name(Name.data(), Name.size()), EsdId(EsdID), ParentEsdId(ParentEsdID),
        SymbolType(GOFF::ESD_ST_ExternalReference),
        NameSpace(GOFF::ESD_NS_NormalName) {
    BehavAttrs.setExecutable(Attr.Executable);
    BehavAttrs.setBindingStrength(Attr.BindingStrength);
    BehavAttrs.setLinkageType(Attr.Linkage);
    BehavAttrs.setAmode(Attr.Amode);
    BehavAttrs.setBindingScope(Attr.BindingScope);
    BehavAttrs.setIndirectReference(Attr.IsIndirectReference);
  }
};
 
class GOFFWriter {
  GOFFOstream OS;
  MCAssembler &Asm;
  MCSectionGOFF *RootSD;
 
  /// Saved relocation data collected in recordRelocations().
  std::vector<GOFFRelocationEntry> &Relocations;
 
public:
  enum DwoMode {
    AllSections,
    NonDwoOnly,
    DwoOnly,
  };
 
private:
  const DwoMode Mode;
 
  void writeHeader();
  void writeSymbol(const GOFFSymbol &Symbol);
  void writeText(const MCSectionGOFF *MC);
  void writeRelocations();
  void writeEnd();
 
  void defineSectionSymbols(const MCSectionGOFF &Section);
  void defineLabel(const MCSymbolGOFF &Symbol);
  void defineExtern(const MCSymbolGOFF &Symbol);
  void defineSymbols();
 
public:
  GOFFWriter(raw_pwrite_stream &OS, MCAssembler &Asm, MCSectionGOFF *RootSD,
             std::vector<GOFFRelocationEntry> &Relocations, DwoMode Mode);
  uint64_t writeObject();
};
} // namespace
 
GOFFWriter::GOFFWriter(raw_pwrite_stream &OS, MCAssembler &Asm,
                       MCSectionGOFF *RootSD,
                       std::vector<GOFFRelocationEntry> &Relocations,
                       DwoMode Mode)
    : OS(OS), Asm(Asm), RootSD(RootSD), Relocations(Relocations), Mode(Mode) {}
 
namespace {
bool isDwoSection(const MCSection &Section) {
  StringRef Name = Section.getName();
  return (Name.ends_with(".dwo") && Name.starts_with(".debug_")) ||
         (Name.ends_with("_DWO") && Name.starts_with("D_"));
}
 
bool isSectionToSkip(const MCSection &Section, GOFFWriter::DwoMode Mode) {
  if (Mode == GOFFWriter::DwoOnly) {
    if (!isDwoSection(Section))
      return true;
  } else if (Mode == GOFFWriter::NonDwoOnly) {
    if (isDwoSection(Section))
      return true;
  }
  return false;
}
} // namespace
 
void GOFFWriter::defineSectionSymbols(const MCSectionGOFF &Section) {
  if (isSectionToSkip(Section, Mode))
    return;
 
  if (Section.isSD()) {
    GOFFSymbol SD(Section.getExternalName(), Section.getOrdinal(),
                  Section.getSDAttributes());
    writeSymbol(SD);
  }
 
  if (Section.isED()) {
    GOFFSymbol ED(Section.getExternalName(), Section.getOrdinal(),
                  Section.getParent()->getOrdinal(), Section.getEDAttributes(),
                  Section.getEDAlignment());
    ED.SectionLength = Asm.getSectionAddressSize(Section);
    writeSymbol(ED);
  }
 
  if (Section.isPR()) {
    MCSectionGOFF *Parent = Section.getParent();
    GOFFSymbol PR(Section.getExternalName(), Section.getOrdinal(),
                  Parent->getOrdinal(), Parent->getEDAttributes(),
                  Parent->getEDAlignment(), Section.getPRAttributes());
    PR.SectionLength = Asm.getSectionAddressSize(Section);
    if (Section.requiresNonZeroLength()) {
      // We cannot have a zero-length section for data.  If we do,
      // artificially inflate it. Use 2 bytes to avoid odd alignments. Note:
      // if this is ever changed, you will need to update the code in
      // SystemZAsmPrinter::emitCEEMAIN and SystemZAsmPrinter::emitCELQMAIN to
      // generate -1 if there is no ADA
      if (!PR.SectionLength)
        PR.SectionLength = 2;
    }
    writeSymbol(PR);
  }
}
 
void GOFFWriter::defineLabel(const MCSymbolGOFF &Symbol) {
  MCSectionGOFF &Section = static_cast<MCSectionGOFF &>(Symbol.getSection());
  GOFFSymbol LD(Symbol.getExternalName(), Symbol.getIndex(),
                Section.getOrdinal(), Section.getEDAttributes().NameSpace,
                GOFF::LDAttr{false, Symbol.getCodeData(),
                             Symbol.getBindingStrength(), Symbol.getLinkage(),
                             GOFF::ESD_AMODE_64, Symbol.getBindingScope()});
  if (Symbol.getADA())
    LD.ADAEsdId = Symbol.getADA()->getOrdinal();
  LD.Offset = Asm.getSymbolOffset(Symbol);
  writeSymbol(LD);
}
 
void GOFFWriter::defineExtern(const MCSymbolGOFF &Symbol) {
  if (Symbol.getCodeData() == GOFF::ESD_EXE_DATA) {
    MCSectionGOFF *ED = Symbol.getADA()->getParent();
    GOFFSymbol PR(Symbol.getExternalName(), Symbol.getIndex(), ED->getOrdinal(),
                  ED->getEDAttributes(), ED->getEDAlignment(),
                  GOFF::PRAttr{/*IsRenamable*/ false, Symbol.getCodeData(),
                               Symbol.getBindingStrength(), Symbol.getLinkage(),
                               Symbol.getBindingScope(), 0});
    writeSymbol(PR);
  } else {
    GOFFSymbol ER(Symbol.getExternalName(), Symbol.getIndex(),
                  RootSD->getOrdinal(),
                  GOFF::ERAttr{Symbol.isIndirect(), Symbol.getCodeData(),
                               Symbol.getBindingStrength(), Symbol.getLinkage(),
                               GOFF::ESD_AMODE_64, Symbol.getBindingScope()});
    writeSymbol(ER);
  }
}
 
void GOFFWriter::defineSymbols() {
  unsigned Ordinal = 0;
  // Process all sections.
  for (MCSection &S : Asm) {
    auto &Section = static_cast<MCSectionGOFF &>(S);
    Section.setOrdinal(++Ordinal);
    defineSectionSymbols(Section);
  }
 
  // Process all symbols
  for (const MCSymbol &Sym : Asm.symbols()) {
    if (Sym.isTemporary())
      continue;
    auto &Symbol = static_cast<const MCSymbolGOFF &>(Sym);
    if (!Symbol.isDefined()) {
      if (Mode != DwoOnly) {
        Symbol.setIndex(++Ordinal);
        defineExtern(Symbol);
      }
    } else {
      if (isSectionToSkip(Symbol.getSection(), Mode))
        continue;
      if (Symbol.isInEDSection()) {
        Symbol.setIndex(++Ordinal);
        defineLabel(Symbol);
      } else {
        // Symbol is in PR section, the symbol refers to the section.
        Symbol.setIndex(Symbol.getSection().getOrdinal());
      }
    }
  }
}
 
void GOFFWriter::writeHeader() {
  OS.newRecord(GOFF::RT_HDR);
  OS.write_zeros(1);       // Reserved
  OS.writebe<uint32_t>(0); // Target Hardware Environment
  OS.writebe<uint32_t>(0); // Target Operating System Environment
  OS.write_zeros(2);       // Reserved
  OS.writebe<uint16_t>(0); // CCSID
  OS.write_zeros(16);      // Character Set name
  OS.write_zeros(16);      // Language Product Identifier
  OS.writebe<uint32_t>(1); // Architecture Level
  OS.writebe<uint16_t>(0); // Module Properties Length
  OS.write_zeros(6);       // Reserved
}
 
void GOFFWriter::writeSymbol(const GOFFSymbol &Symbol) {
  if (Symbol.Offset >= (((uint64_t)1) << 31))
    report_fatal_error("ESD offset out of range");
 
  // All symbol names are in EBCDIC.
  SmallString<256> Name;
  ConverterEBCDIC::convertToEBCDIC(Symbol.Name, Name);
 
  // Check length here since this number is technically signed but we need uint
  // for writing to records.
  if (Name.size() >= GOFF::MaxDataLength)
    report_fatal_error("Symbol max name length exceeded");
  uint16_t NameLength = Name.size();
 
  OS.newRecord(GOFF::RT_ESD);
  OS.writebe<uint8_t>(Symbol.SymbolType);   // Symbol Type
  OS.writebe<uint32_t>(Symbol.EsdId);       // ESDID
  OS.writebe<uint32_t>(Symbol.ParentEsdId); // Parent or Owning ESDID
  OS.writebe<uint32_t>(0);                  // Reserved
  OS.writebe<uint32_t>(
      static_cast<uint32_t>(Symbol.Offset));     // Offset or Address
  OS.writebe<uint32_t>(0);                       // Reserved
  OS.writebe<uint32_t>(Symbol.SectionLength);    // Length
  OS.writebe<uint32_t>(Symbol.EASectionEDEsdId); // Extended Attribute ESDID
  OS.writebe<uint32_t>(Symbol.EASectionOffset);  // Extended Attribute Offset
  OS.writebe<uint32_t>(0);                       // Reserved
  OS.writebe<uint8_t>(Symbol.NameSpace);         // Name Space ID
  OS.writebe<uint8_t>(Symbol.SymbolFlags);       // Flags
  OS.writebe<uint8_t>(Symbol.FillByteValue);     // Fill-Byte Value
  OS.writebe<uint8_t>(0);                        // Reserved
  OS.writebe<uint32_t>(Symbol.ADAEsdId);         // ADA ESDID
  OS.writebe<uint32_t>(Symbol.SortKey);          // Sort Priority
  OS.writebe<uint64_t>(0);                       // Reserved
  for (auto F : Symbol.BehavAttrs.Attr)
    OS.writebe<uint8_t>(F);          // Behavioral Attributes
  OS.writebe<uint16_t>(NameLength);  // Name Length
  OS.write(Name.data(), NameLength); // Name
}
 
namespace {
/// Adapter stream to write a text section.
class TextStream : public raw_ostream {
  /// The underlying GOFFOstream.
  GOFFOstream &OS;
 
  /// The buffer size is the maximum number of bytes in a TXT section.
  static constexpr size_t BufferSize = GOFF::MaxDataLength;
 
  /// Static allocated buffer for the stream, used by the raw_ostream class. The
  /// buffer is sized to hold the payload of a logical TXT record.
  char Buffer[BufferSize];
 
  /// The offset for the next TXT record. This is equal to the number of bytes
  /// written.
  size_t Offset;
 
  /// The Esdid of the GOFF section.
  const uint32_t EsdId;
 
  /// The record style.
  const GOFF::ESDTextStyle RecordStyle;
 
  /// See raw_ostream::write_impl.
  void write_impl(const char *Ptr, size_t Size) override;
 
  uint64_t current_pos() const override { return Offset; }
 
public:
  explicit TextStream(GOFFOstream &OS, uint32_t EsdId,
                      GOFF::ESDTextStyle RecordStyle)
      : OS(OS), Offset(0), EsdId(EsdId), RecordStyle(RecordStyle) {
    SetBuffer(Buffer, sizeof(Buffer));
  }
 
  ~TextStream() override { flush(); }
};
} // namespace
 
void TextStream::write_impl(const char *Ptr, size_t Size) {
  size_t WrittenLength = 0;
 
  // We only have signed 32bits of offset.
  if (Offset + Size > std::numeric_limits<int32_t>::max())
    report_fatal_error("TXT section too large");
 
  while (WrittenLength < Size) {
    size_t ToWriteLength =
        std::min(Size - WrittenLength, size_t(GOFF::MaxDataLength));
 
    OS.newRecord(GOFF::RT_TXT);
    OS.writebe<uint8_t>(GOFF::Flags(4, 4, RecordStyle)); // Text Record Style
    OS.writebe<uint32_t>(EsdId);                         // Element ESDID
    OS.writebe<uint32_t>(0);                             // Reserved
    OS.writebe<uint32_t>(static_cast<uint32_t>(Offset)); // Offset
    OS.writebe<uint32_t>(0);                      // Text Field True Length
    OS.writebe<uint16_t>(0);                      // Text Encoding
    OS.writebe<uint16_t>(ToWriteLength);          // Data Length
    OS.write(Ptr + WrittenLength, ToWriteLength); // Data
 
    WrittenLength += ToWriteLength;
    Offset += ToWriteLength;
  }
}
 
void GOFFWriter::writeText(const MCSectionGOFF *Section) {
  // A BSS section contains only zeros, no need to write this.
  if (Section->isBSS())
    return;
 
  TextStream S(OS, Section->getOrdinal(), Section->getTextStyle());
  Asm.writeSectionData(S, Section);
}
 
namespace {
// RelocDataItemBuffer provides a static buffer for relocation data items.
class RelocDataItemBuffer {
  char Buffer[GOFF::MaxDataLength];
  char *Ptr;
 
public:
  RelocDataItemBuffer() : Ptr(Buffer) {}
  const char *data() { return Buffer; }
  size_t size() { return Ptr - Buffer; }
  void reset() { Ptr = Buffer; }
  bool fits(size_t S) { return size() + S < GOFF::MaxDataLength; }
  template <typename T> void writebe(T Val) {
    assert(fits(sizeof(T)) && "Out-of-bounds write");
    support::endian::write<T, llvm::endianness::big>(Ptr, Val);
    Ptr += sizeof(T);
  }
};
} // namespace
 
void GOFFWriter::writeRelocations() {
  // Set the IDs in the relocation entries.
  for (auto &RelocEntry : Relocations) {
    auto GetRptr = [](const MCSymbolGOFF *Sym) -> uint32_t {
      if (Sym->isTemporary())
        return static_cast<MCSectionGOFF &>(Sym->getSection()).getOrdinal();
      return Sym->getIndex();
    };
 
    RelocEntry.PEsdId = RelocEntry.Pptr->getOrdinal();
    RelocEntry.REsdId = GetRptr(RelocEntry.Rptr);
  }
 
  // Sort relocation data items by the P pointer to save space.
  std::sort(
      Relocations.begin(), Relocations.end(),
      [](const GOFFRelocationEntry &Left, const GOFFRelocationEntry &Right) {
        return std::tie(Left.PEsdId, Left.REsdId, Left.POffset) <
               std::tie(Right.PEsdId, Right.REsdId, Right.POffset);
      });
 
  // Construct the compressed relocation data items, and write them out.
  RelocDataItemBuffer Buffer;
  for (auto I = Relocations.begin(), E = Relocations.end(); I != E;) {
    Buffer.reset();
 
    uint32_t PrevResdId = -1;
    uint32_t PrevPesdId = -1;
    uint64_t PrevPOffset = -1;
    for (; I != E; ++I) {
      const GOFFRelocationEntry &Rel = *I;
 
      bool SameREsdId = (Rel.REsdId == PrevResdId);
      bool SamePEsdId = (Rel.PEsdId == PrevPesdId);
      bool SamePOffset = (Rel.POffset == PrevPOffset);
      bool EightByteOffset = ((Rel.POffset >> 32) & 0xffffffff);
 
      // Calculate size of relocation data item, and check if it still fits into
      // the record.
      size_t ItemSize = 8; // Smallest size of a relocation data item.
      if (!SameREsdId)
        ItemSize += 4;
      if (!SamePEsdId)
        ItemSize += 4;
      if (!SamePOffset)
        ItemSize += (EightByteOffset ? 8 : 4);
      if (!Buffer.fits(ItemSize))
        break;
 
      GOFF::Flags RelocFlags[6];
      RelocFlags[0].set(0, 1, SameREsdId);
      RelocFlags[0].set(1, 1, SamePEsdId);
      RelocFlags[0].set(2, 1, SamePOffset);
      RelocFlags[0].set(6, 1, EightByteOffset);
 
      RelocFlags[1].set(0, 4, Rel.ReferenceType);
      RelocFlags[1].set(4, 4, Rel.ReferentType);
 
      RelocFlags[2].set(0, 7, Rel.Action);
      RelocFlags[2].set(7, 1, Rel.FetchStore);
 
      RelocFlags[4].set(0, 8, Rel.TargetLength);
 
      for (auto F : RelocFlags)
        Buffer.writebe<uint8_t>(F);
      Buffer.writebe<uint16_t>(0); // Reserved.
      if (!SameREsdId)
        Buffer.writebe<uint32_t>(Rel.REsdId);
      if (!SamePEsdId)
        Buffer.writebe<uint32_t>(Rel.PEsdId);
      if (!SamePOffset) {
        if (EightByteOffset)
          Buffer.writebe<uint64_t>(Rel.POffset);
        else
          Buffer.writebe<uint32_t>(Rel.POffset);
      }
 
      PrevResdId = Rel.REsdId;
      PrevPesdId = Rel.PEsdId;
      PrevPOffset = Rel.POffset;
    }
 
    OS.newRecord(GOFF::RT_RLD);
    OS.writebe<uint8_t>(0);                 // Reserved.
    OS.writebe<uint16_t>(Buffer.size());    // Length (of the relocation data).
    OS.write(Buffer.data(), Buffer.size()); // Relocation Directory Data Items.
  }
}
 
void GOFFWriter::writeEnd() {
  uint8_t F = GOFF::END_EPR_None;
  uint8_t AMODE = 0;
  uint32_t ESDID = 0;
 
  // TODO Set Flags/AMODE/ESDID for entry point.
 
  OS.newRecord(GOFF::RT_END);
  OS.writebe<uint8_t>(GOFF::Flags(6, 2, F)); // Indicator flags
  OS.writebe<uint8_t>(AMODE);                // AMODE
  OS.write_zeros(3);                         // Reserved
  // The record count is the number of logical records. In principle, this value
  // is available as OS.logicalRecords(). However, some tools rely on this field
  // being zero.
  OS.writebe<uint32_t>(0);     // Record Count
  OS.writebe<uint32_t>(ESDID); // ESDID (of entry point)
}
 
uint64_t GOFFWriter::writeObject() {
  writeHeader();
 
  defineSymbols();
 
  for (const MCSection &Section : Asm)
    writeText(static_cast<const MCSectionGOFF *>(&Section));
 
  // Do not write relocations into the dwo file.
  if (Mode != GOFFWriter::DwoOnly)
    writeRelocations();
 
  writeEnd();
 
  // Make sure all records are written.
  OS.finalizeRecord();
 
  LLVM_DEBUG(dbgs() << "Wrote " << OS.getNumLogicalRecords()
                    << " logical records.");
 
  return OS.getWrittenSize();
}
 
GOFFObjectWriter::GOFFObjectWriter(
    std::unique_ptr<MCGOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS)
    : TargetObjectWriter(std::move(MOTW)), OS(OS) {}
 
GOFFObjectWriter::GOFFObjectWriter(
    std::unique_ptr<MCGOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS,
    raw_pwrite_stream &DwoOS)
    : TargetObjectWriter(std::move(MOTW)), OS(OS), DwoOS(&DwoOS) {}
 
GOFFObjectWriter::~GOFFObjectWriter() = default;
 
void GOFFObjectWriter::reset() {
  Relocations.clear();
  RootSD = nullptr;
  MCObjectWriter::reset();
}
 
void GOFFObjectWriter::recordRelocation(const MCFragment &F,
                                        const MCFixup &Fixup, MCValue Target,
                                        uint64_t &FixedValue) {
  const MCFixupKindInfo &FKI =
      Asm->getBackend().getFixupKindInfo(Fixup.getKind());
  const uint32_t Length = FKI.TargetSize / 8;
  assert(FKI.TargetSize % 8 == 0 && "Target Size not multiple of 8");
  const uint64_t FixupOffset = Asm->getFragmentOffset(F) + Fixup.getOffset();
 
  unsigned RelocType = TargetObjectWriter->getRelocType(Target, Fixup);
 
  const MCSectionGOFF *PSection = static_cast<MCSectionGOFF *>(F.getParent());
  const auto &A = *static_cast<const MCSymbolGOFF *>(Target.getAddSym());
  const MCSymbolGOFF *B = static_cast<const MCSymbolGOFF *>(Target.getSubSym());
  if (RelocType == MCGOFFObjectTargetWriter::Reloc_Type_RICon) {
    if (A.isUndefined()) {
      Asm->reportError(
          Fixup.getLoc(),
          Twine("symbol ")
              .concat(A.getExternalName())
              .concat(" must be defined for a relative immediate relocation"));
      return;
    }
    if (&A.getSection() != PSection) {
      MCSectionGOFF &GOFFSection = static_cast<MCSectionGOFF &>(A.getSection());
      Asm->reportError(Fixup.getLoc(),
                       Twine("relative immediate relocation section mismatch: ")
                           .concat(GOFFSection.getExternalName())
                           .concat(" of symbol ")
                           .concat(A.getExternalName())
                           .concat(" <-> ")
                           .concat(PSection->getExternalName()));
      return;
    }
    if (B) {
      Asm->reportError(
          Fixup.getLoc(),
          Twine("subtractive symbol ")
              .concat(B->getExternalName())
              .concat(" not supported for a relative immediate relocation"));
      return;
    }
    FixedValue = Asm->getSymbolOffset(A) - FixupOffset + Target.getConstant();
    return;
  }
  FixedValue = Target.getConstant();
 
  // The symbol only has a section-relative offset if it is a temporary symbol.
  FixedValue += A.isTemporary() ? Asm->getSymbolOffset(A) : 0;
  A.setUsedInReloc();
  if (B) {
    FixedValue -= B->isTemporary() ? Asm->getSymbolOffset(*B) : 0;
    B->setUsedInReloc();
  }
 
  // UseQCon causes class offsets versus absolute addresses to be used. This
  // is analogous to using QCONs in older OBJ object file format.
  bool UseQCon = RelocType == MCGOFFObjectTargetWriter::Reloc_Type_QCon;
 
  GOFF::RLDFetchStore FetchStore =
      (RelocType == MCGOFFObjectTargetWriter::Reloc_Type_RCon ||
       RelocType == MCGOFFObjectTargetWriter::Reloc_Type_VCon)
          ? GOFF::RLDFetchStore::RLD_FS_Store
          : GOFF::RLDFetchStore::RLD_FS_Fetch;
  assert((FetchStore == GOFF::RLDFetchStore::RLD_FS_Fetch || B == nullptr) &&
         "No dependent relocations expected");
 
  enum GOFF::RLDReferenceType ReferenceType = GOFF::RLD_RT_RAddress;
  enum GOFF::RLDReferentType ReferentType = GOFF::RLD_RO_Label;
  if (UseQCon) {
    ReferenceType = GOFF::RLD_RT_ROffset;
    ReferentType = GOFF::RLD_RO_Class;
  }
  if (RelocType == MCGOFFObjectTargetWriter::Reloc_Type_RCon)
    ReferenceType = GOFF::RLD_RT_RTypeConstant;
 
  auto DumpReloc = [&PSection, &ReferenceType, &FixupOffset,
                    &FixedValue](const char *N, const MCSymbolGOFF *Sym) {
    const char *Con;
    switch (ReferenceType) {
    case GOFF::RLDReferenceType::RLD_RT_RAddress:
      Con = "ACon";
      break;
    case GOFF::RLDReferenceType::RLD_RT_ROffset:
      Con = "QCon";
      break;
    case GOFF::RLDReferenceType::RLD_RT_RTypeConstant:
      Con = "VCon";
      break;
    default:
      Con = "(unknown)";
    }
    dbgs() << "Reloc " << N << ": " << Con
           << " Rptr: " << Sym->getExternalName()
           << " Pptr: " << PSection->getExternalName()
           << " Offset: " << FixupOffset << " Fixed Imm: " << FixedValue
           << "\n";
  };
  (void)DumpReloc;
 
  // Save relocation data for later writing.
  LLVM_DEBUG(DumpReloc("A", &A));
  Relocations.emplace_back(PSection, &A, ReferenceType, ReferentType,
                           GOFF::RLD_ACT_Add, FetchStore, FixupOffset, Length);
  if (B) {
    LLVM_DEBUG(DumpReloc("B", B));
    Relocations.emplace_back(
        PSection, B, ReferenceType, ReferentType, GOFF::RLD_ACT_Subtract,
        GOFF::RLDFetchStore::RLD_FS_Fetch, FixupOffset, Length);
  }
}
 
uint64_t GOFFObjectWriter::writeObject() {
  uint64_t Size = 0;
  if (DwoOS)
    Size += GOFFWriter(*DwoOS, *Asm, RootSD, Relocations, GOFFWriter::DwoOnly)
                .writeObject();
  Size += GOFFWriter(OS, *Asm, RootSD, Relocations,
                     DwoOS ? GOFFWriter::NonDwoOnly : GOFFWriter::AllSections)
              .writeObject();
  return Size;
}
 
std::unique_ptr<MCObjectWriter>
llvm::createGOFFObjectWriter(std::unique_ptr<MCGOFFObjectTargetWriter> MOTW,
                             raw_pwrite_stream &OS) {
  return std::make_unique<GOFFObjectWriter>(std::move(MOTW), OS);
}
 
std::unique_ptr<MCObjectWriter>
llvm::createGOFFObjectWriter(std::unique_ptr<MCGOFFObjectTargetWriter> MOTW,
                             raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS) {
  return std::make_unique<GOFFObjectWriter>(std::move(MOTW), OS, DwoOS);
}