llvm-capstone/lld/COFF/Chunks.cpp

//===- Chunks.cpp ---------------------------------------------------------===//
//
// 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 "Chunks.h"
#include "InputFiles.h"
#include "Symbols.h"
#include "Writer.h"
#include "SymbolTable.h"
#include "lld/Common/ErrorHandler.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/Object/COFF.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>

using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::COFF;
using llvm::support::ulittle32_t;

namespace lld {
namespace coff {

SectionChunk::SectionChunk(ObjFile *F, const coff_section *H)
    : Chunk(SectionKind), File(F), Header(H), Repl(this) {
  // Initialize Relocs.
  setRelocs(File->getCOFFObj()->getRelocations(Header));

  // Initialize SectionName.
  StringRef SectionName;
  if (Expected<StringRef> E = File->getCOFFObj()->getSectionName(Header))
    SectionName = *E;
  SectionNameData = SectionName.data();
  SectionNameSize = SectionName.size();

  setAlignment(Header->getAlignment());

  HasData = !(Header->Characteristics & IMAGE_SCN_CNT_UNINITIALIZED_DATA);

  // If linker GC is disabled, every chunk starts out alive.  If linker GC is
  // enabled, treat non-comdat sections as roots. Generally optimized object
  // files will be built with -ffunction-sections or /Gy, so most things worth
  // stripping will be in a comdat.
  Live = !Config->DoGC || !isCOMDAT();
}

// SectionChunk is one of the most frequently allocated classes, so it is
// important to keep it as compact as possible. As of this writing, the number
// below is the size of this class on x64 platforms.
static_assert(sizeof(SectionChunk) <= 88, "SectionChunk grew unexpectedly");

static void add16(uint8_t *P, int16_t V) { write16le(P, read16le(P) + V); }
static void add32(uint8_t *P, int32_t V) { write32le(P, read32le(P) + V); }
static void add64(uint8_t *P, int64_t V) { write64le(P, read64le(P) + V); }
static void or16(uint8_t *P, uint16_t V) { write16le(P, read16le(P) | V); }
static void or32(uint8_t *P, uint32_t V) { write32le(P, read32le(P) | V); }

// Verify that given sections are appropriate targets for SECREL
// relocations. This check is relaxed because unfortunately debug
// sections have section-relative relocations against absolute symbols.
static bool checkSecRel(const SectionChunk *Sec, OutputSection *OS) {
  if (OS)
    return true;
  if (Sec->isCodeView())
    return false;
  error("SECREL relocation cannot be applied to absolute symbols");
  return false;
}

static void applySecRel(const SectionChunk *Sec, uint8_t *Off,
                        OutputSection *OS, uint64_t S) {
  if (!checkSecRel(Sec, OS))
    return;
  uint64_t SecRel = S - OS->getRVA();
  if (SecRel > UINT32_MAX) {
    error("overflow in SECREL relocation in section: " + Sec->getSectionName());
    return;
  }
  add32(Off, SecRel);
}

static void applySecIdx(uint8_t *Off, OutputSection *OS) {
  // Absolute symbol doesn't have section index, but section index relocation
  // against absolute symbol should be resolved to one plus the last output
  // section index. This is required for compatibility with MSVC.
  if (OS)
    add16(Off, OS->SectionIndex);
  else
    add16(Off, DefinedAbsolute::NumOutputSections + 1);
}

void SectionChunk::applyRelX64(uint8_t *Off, uint16_t Type, OutputSection *OS,
                               uint64_t S, uint64_t P) const {
  switch (Type) {
  case IMAGE_REL_AMD64_ADDR32:   add32(Off, S + Config->ImageBase); break;
  case IMAGE_REL_AMD64_ADDR64:   add64(Off, S + Config->ImageBase); break;
  case IMAGE_REL_AMD64_ADDR32NB: add32(Off, S); break;
  case IMAGE_REL_AMD64_REL32:    add32(Off, S - P - 4); break;
  case IMAGE_REL_AMD64_REL32_1:  add32(Off, S - P - 5); break;
  case IMAGE_REL_AMD64_REL32_2:  add32(Off, S - P - 6); break;
  case IMAGE_REL_AMD64_REL32_3:  add32(Off, S - P - 7); break;
  case IMAGE_REL_AMD64_REL32_4:  add32(Off, S - P - 8); break;
  case IMAGE_REL_AMD64_REL32_5:  add32(Off, S - P - 9); break;
  case IMAGE_REL_AMD64_SECTION:  applySecIdx(Off, OS); break;
  case IMAGE_REL_AMD64_SECREL:   applySecRel(this, Off, OS, S); break;
  default:
    error("unsupported relocation type 0x" + Twine::utohexstr(Type) + " in " +
          toString(File));
  }
}

void SectionChunk::applyRelX86(uint8_t *Off, uint16_t Type, OutputSection *OS,
                               uint64_t S, uint64_t P) const {
  switch (Type) {
  case IMAGE_REL_I386_ABSOLUTE: break;
  case IMAGE_REL_I386_DIR32:    add32(Off, S + Config->ImageBase); break;
  case IMAGE_REL_I386_DIR32NB:  add32(Off, S); break;
  case IMAGE_REL_I386_REL32:    add32(Off, S - P - 4); break;
  case IMAGE_REL_I386_SECTION:  applySecIdx(Off, OS); break;
  case IMAGE_REL_I386_SECREL:   applySecRel(this, Off, OS, S); break;
  default:
    error("unsupported relocation type 0x" + Twine::utohexstr(Type) + " in " +
          toString(File));
  }
}

static void applyMOV(uint8_t *Off, uint16_t V) {
  write16le(Off, (read16le(Off) & 0xfbf0) | ((V & 0x800) >> 1) | ((V >> 12) & 0xf));
  write16le(Off + 2, (read16le(Off + 2) & 0x8f00) | ((V & 0x700) << 4) | (V & 0xff));
}

static uint16_t readMOV(uint8_t *Off, bool MOVT) {
  uint16_t Op1 = read16le(Off);
  if ((Op1 & 0xfbf0) != (MOVT ? 0xf2c0 : 0xf240))
    error("unexpected instruction in " + Twine(MOVT ? "MOVT" : "MOVW") +
          " instruction in MOV32T relocation");
  uint16_t Op2 = read16le(Off + 2);
  if ((Op2 & 0x8000) != 0)
    error("unexpected instruction in " + Twine(MOVT ? "MOVT" : "MOVW") +
          " instruction in MOV32T relocation");
  return (Op2 & 0x00ff) | ((Op2 >> 4) & 0x0700) | ((Op1 << 1) & 0x0800) |
         ((Op1 & 0x000f) << 12);
}

void applyMOV32T(uint8_t *Off, uint32_t V) {
  uint16_t ImmW = readMOV(Off, false);    // read MOVW operand
  uint16_t ImmT = readMOV(Off + 4, true); // read MOVT operand
  uint32_t Imm = ImmW | (ImmT << 16);
  V += Imm;                         // add the immediate offset
  applyMOV(Off, V);           // set MOVW operand
  applyMOV(Off + 4, V >> 16); // set MOVT operand
}

static void applyBranch20T(uint8_t *Off, int32_t V) {
  if (!isInt<21>(V))
    error("relocation out of range");
  uint32_t S = V < 0 ? 1 : 0;
  uint32_t J1 = (V >> 19) & 1;
  uint32_t J2 = (V >> 18) & 1;
  or16(Off, (S << 10) | ((V >> 12) & 0x3f));
  or16(Off + 2, (J1 << 13) | (J2 << 11) | ((V >> 1) & 0x7ff));
}

void applyBranch24T(uint8_t *Off, int32_t V) {
  if (!isInt<25>(V))
    error("relocation out of range");
  uint32_t S = V < 0 ? 1 : 0;
  uint32_t J1 = ((~V >> 23) & 1) ^ S;
  uint32_t J2 = ((~V >> 22) & 1) ^ S;
  or16(Off, (S << 10) | ((V >> 12) & 0x3ff));
  // Clear out the J1 and J2 bits which may be set.
  write16le(Off + 2, (read16le(Off + 2) & 0xd000) | (J1 << 13) | (J2 << 11) | ((V >> 1) & 0x7ff));
}

void SectionChunk::applyRelARM(uint8_t *Off, uint16_t Type, OutputSection *OS,
                               uint64_t S, uint64_t P) const {
  // Pointer to thumb code must have the LSB set.
  uint64_t SX = S;
  if (OS && (OS->Header.Characteristics & IMAGE_SCN_MEM_EXECUTE))
    SX |= 1;
  switch (Type) {
  case IMAGE_REL_ARM_ADDR32:    add32(Off, SX + Config->ImageBase); break;
  case IMAGE_REL_ARM_ADDR32NB:  add32(Off, SX); break;
  case IMAGE_REL_ARM_MOV32T:    applyMOV32T(Off, SX + Config->ImageBase); break;
  case IMAGE_REL_ARM_BRANCH20T: applyBranch20T(Off, SX - P - 4); break;
  case IMAGE_REL_ARM_BRANCH24T: applyBranch24T(Off, SX - P - 4); break;
  case IMAGE_REL_ARM_BLX23T:    applyBranch24T(Off, SX - P - 4); break;
  case IMAGE_REL_ARM_SECTION:   applySecIdx(Off, OS); break;
  case IMAGE_REL_ARM_SECREL:    applySecRel(this, Off, OS, S); break;
  case IMAGE_REL_ARM_REL32:     add32(Off, SX - P - 4); break;
  default:
    error("unsupported relocation type 0x" + Twine::utohexstr(Type) + " in " +
          toString(File));
  }
}

// Interpret the existing immediate value as a byte offset to the
// target symbol, then update the instruction with the immediate as
// the page offset from the current instruction to the target.
void applyArm64Addr(uint8_t *Off, uint64_t S, uint64_t P, int Shift) {
  uint32_t Orig = read32le(Off);
  uint64_t Imm = ((Orig >> 29) & 0x3) | ((Orig >> 3) & 0x1FFFFC);
  S += Imm;
  Imm = (S >> Shift) - (P >> Shift);
  uint32_t ImmLo = (Imm & 0x3) << 29;
  uint32_t ImmHi = (Imm & 0x1FFFFC) << 3;
  uint64_t Mask = (0x3 << 29) | (0x1FFFFC << 3);
  write32le(Off, (Orig & ~Mask) | ImmLo | ImmHi);
}

// Update the immediate field in a AARCH64 ldr, str, and add instruction.
// Optionally limit the range of the written immediate by one or more bits
// (RangeLimit).
void applyArm64Imm(uint8_t *Off, uint64_t Imm, uint32_t RangeLimit) {
  uint32_t Orig = read32le(Off);
  Imm += (Orig >> 10) & 0xFFF;
  Orig &= ~(0xFFF << 10);
  write32le(Off, Orig | ((Imm & (0xFFF >> RangeLimit)) << 10));
}

// Add the 12 bit page offset to the existing immediate.
// Ldr/str instructions store the opcode immediate scaled
// by the load/store size (giving a larger range for larger
// loads/stores). The immediate is always (both before and after
// fixing up the relocation) stored scaled similarly.
// Even if larger loads/stores have a larger range, limit the
// effective offset to 12 bit, since it is intended to be a
// page offset.
static void applyArm64Ldr(uint8_t *Off, uint64_t Imm) {
  uint32_t Orig = read32le(Off);
  uint32_t Size = Orig >> 30;
  // 0x04000000 indicates SIMD/FP registers
  // 0x00800000 indicates 128 bit
  if ((Orig & 0x4800000) == 0x4800000)
    Size += 4;
  if ((Imm & ((1 << Size) - 1)) != 0)
    error("misaligned ldr/str offset");
  applyArm64Imm(Off, Imm >> Size, Size);
}

static void applySecRelLow12A(const SectionChunk *Sec, uint8_t *Off,
                              OutputSection *OS, uint64_t S) {
  if (checkSecRel(Sec, OS))
    applyArm64Imm(Off, (S - OS->getRVA()) & 0xfff, 0);
}

static void applySecRelHigh12A(const SectionChunk *Sec, uint8_t *Off,
                               OutputSection *OS, uint64_t S) {
  if (!checkSecRel(Sec, OS))
    return;
  uint64_t SecRel = (S - OS->getRVA()) >> 12;
  if (0xfff < SecRel) {
    error("overflow in SECREL_HIGH12A relocation in section: " +
          Sec->getSectionName());
    return;
  }
  applyArm64Imm(Off, SecRel & 0xfff, 0);
}

static void applySecRelLdr(const SectionChunk *Sec, uint8_t *Off,
                           OutputSection *OS, uint64_t S) {
  if (checkSecRel(Sec, OS))
    applyArm64Ldr(Off, (S - OS->getRVA()) & 0xfff);
}

void applyArm64Branch26(uint8_t *Off, int64_t V) {
  if (!isInt<28>(V))
    error("relocation out of range");
  or32(Off, (V & 0x0FFFFFFC) >> 2);
}

static void applyArm64Branch19(uint8_t *Off, int64_t V) {
  if (!isInt<21>(V))
    error("relocation out of range");
  or32(Off, (V & 0x001FFFFC) << 3);
}

static void applyArm64Branch14(uint8_t *Off, int64_t V) {
  if (!isInt<16>(V))
    error("relocation out of range");
  or32(Off, (V & 0x0000FFFC) << 3);
}

void SectionChunk::applyRelARM64(uint8_t *Off, uint16_t Type, OutputSection *OS,
                                 uint64_t S, uint64_t P) const {
  switch (Type) {
  case IMAGE_REL_ARM64_PAGEBASE_REL21: applyArm64Addr(Off, S, P, 12); break;
  case IMAGE_REL_ARM64_REL21:          applyArm64Addr(Off, S, P, 0); break;
  case IMAGE_REL_ARM64_PAGEOFFSET_12A: applyArm64Imm(Off, S & 0xfff, 0); break;
  case IMAGE_REL_ARM64_PAGEOFFSET_12L: applyArm64Ldr(Off, S & 0xfff); break;
  case IMAGE_REL_ARM64_BRANCH26:       applyArm64Branch26(Off, S - P); break;
  case IMAGE_REL_ARM64_BRANCH19:       applyArm64Branch19(Off, S - P); break;
  case IMAGE_REL_ARM64_BRANCH14:       applyArm64Branch14(Off, S - P); break;
  case IMAGE_REL_ARM64_ADDR32:         add32(Off, S + Config->ImageBase); break;
  case IMAGE_REL_ARM64_ADDR32NB:       add32(Off, S); break;
  case IMAGE_REL_ARM64_ADDR64:         add64(Off, S + Config->ImageBase); break;
  case IMAGE_REL_ARM64_SECREL:         applySecRel(this, Off, OS, S); break;
  case IMAGE_REL_ARM64_SECREL_LOW12A:  applySecRelLow12A(this, Off, OS, S); break;
  case IMAGE_REL_ARM64_SECREL_HIGH12A: applySecRelHigh12A(this, Off, OS, S); break;
  case IMAGE_REL_ARM64_SECREL_LOW12L:  applySecRelLdr(this, Off, OS, S); break;
  case IMAGE_REL_ARM64_SECTION:        applySecIdx(Off, OS); break;
  case IMAGE_REL_ARM64_REL32:          add32(Off, S - P - 4); break;
  default:
    error("unsupported relocation type 0x" + Twine::utohexstr(Type) + " in " +
          toString(File));
  }
}

static void maybeReportRelocationToDiscarded(const SectionChunk *FromChunk,
                                             Defined *Sym,
                                             const coff_relocation &Rel) {
  // Don't report these errors when the relocation comes from a debug info
  // section or in mingw mode. MinGW mode object files (built by GCC) can
  // have leftover sections with relocations against discarded comdat
  // sections. Such sections are left as is, with relocations untouched.
  if (FromChunk->isCodeView() || FromChunk->isDWARF() || Config->MinGW)
    return;

  // Get the name of the symbol. If it's null, it was discarded early, so we
  // have to go back to the object file.
  ObjFile *File = FromChunk->File;
  StringRef Name;
  if (Sym) {
    Name = Sym->getName();
  } else {
    COFFSymbolRef COFFSym =
        check(File->getCOFFObj()->getSymbol(Rel.SymbolTableIndex));
    File->getCOFFObj()->getSymbolName(COFFSym, Name);
  }

  error("relocation against symbol in discarded section: " + Name +
        getSymbolLocations(File, Rel.SymbolTableIndex));
}

void SectionChunk::writeTo(uint8_t *Buf) const {
  if (!hasData())
    return;
  // Copy section contents from source object file to output file.
  ArrayRef<uint8_t> A = getContents();
  if (!A.empty())
    memcpy(Buf, A.data(), A.size());

  // Apply relocations.
  size_t InputSize = getSize();
  for (size_t I = 0, E = RelocsSize; I < E; I++) {
    const coff_relocation &Rel = RelocsData[I];

    // Check for an invalid relocation offset. This check isn't perfect, because
    // we don't have the relocation size, which is only known after checking the
    // machine and relocation type. As a result, a relocation may overwrite the
    // beginning of the following input section.
    if (Rel.VirtualAddress >= InputSize) {
      error("relocation points beyond the end of its parent section");
      continue;
    }

    uint8_t *Off = Buf + Rel.VirtualAddress;

    auto *Sym =
        dyn_cast_or_null<Defined>(File->getSymbol(Rel.SymbolTableIndex));

    // Get the output section of the symbol for this relocation.  The output
    // section is needed to compute SECREL and SECTION relocations used in debug
    // info.
    Chunk *C = Sym ? Sym->getChunk() : nullptr;
    OutputSection *OS = C ? C->getOutputSection() : nullptr;

    // Skip the relocation if it refers to a discarded section, and diagnose it
    // as an error if appropriate. If a symbol was discarded early, it may be
    // null. If it was discarded late, the output section will be null, unless
    // it was an absolute or synthetic symbol.
    if (!Sym ||
        (!OS && !isa<DefinedAbsolute>(Sym) && !isa<DefinedSynthetic>(Sym))) {
      maybeReportRelocationToDiscarded(this, Sym, Rel);
      continue;
    }

    uint64_t S = Sym->getRVA();

    // Compute the RVA of the relocation for relative relocations.
    uint64_t P = RVA + Rel.VirtualAddress;
    switch (Config->Machine) {
    case AMD64:
      applyRelX64(Off, Rel.Type, OS, S, P);
      break;
    case I386:
      applyRelX86(Off, Rel.Type, OS, S, P);
      break;
    case ARMNT:
      applyRelARM(Off, Rel.Type, OS, S, P);
      break;
    case ARM64:
      applyRelARM64(Off, Rel.Type, OS, S, P);
      break;
    default:
      llvm_unreachable("unknown machine type");
    }
  }
}

void SectionChunk::addAssociative(SectionChunk *Child) {
  // Insert this child at the head of the list.
  assert(Child->AssocChildren == nullptr &&
         "associated sections cannot have their own associated children");
  Child->AssocChildren = AssocChildren;
  AssocChildren = Child;
}

static uint8_t getBaserelType(const coff_relocation &Rel) {
  switch (Config->Machine) {
  case AMD64:
    if (Rel.Type == IMAGE_REL_AMD64_ADDR64)
      return IMAGE_REL_BASED_DIR64;
    return IMAGE_REL_BASED_ABSOLUTE;
  case I386:
    if (Rel.Type == IMAGE_REL_I386_DIR32)
      return IMAGE_REL_BASED_HIGHLOW;
    return IMAGE_REL_BASED_ABSOLUTE;
  case ARMNT:
    if (Rel.Type == IMAGE_REL_ARM_ADDR32)
      return IMAGE_REL_BASED_HIGHLOW;
    if (Rel.Type == IMAGE_REL_ARM_MOV32T)
      return IMAGE_REL_BASED_ARM_MOV32T;
    return IMAGE_REL_BASED_ABSOLUTE;
  case ARM64:
    if (Rel.Type == IMAGE_REL_ARM64_ADDR64)
      return IMAGE_REL_BASED_DIR64;
    return IMAGE_REL_BASED_ABSOLUTE;
  default:
    llvm_unreachable("unknown machine type");
  }
}

// Windows-specific.
// Collect all locations that contain absolute addresses, which need to be
// fixed by the loader if load-time relocation is needed.
// Only called when base relocation is enabled.
void SectionChunk::getBaserels(std::vector<Baserel> *Res) {
  for (size_t I = 0, E = RelocsSize; I < E; I++) {
    const coff_relocation &Rel = RelocsData[I];
    uint8_t Ty = getBaserelType(Rel);
    if (Ty == IMAGE_REL_BASED_ABSOLUTE)
      continue;
    Symbol *Target = File->getSymbol(Rel.SymbolTableIndex);
    if (!Target || isa<DefinedAbsolute>(Target))
      continue;
    Res->emplace_back(RVA + Rel.VirtualAddress, Ty);
  }
}

// MinGW specific.
// Check whether a static relocation of type Type can be deferred and
// handled at runtime as a pseudo relocation (for references to a module
// local variable, which turned out to actually need to be imported from
// another DLL) This returns the size the relocation is supposed to update,
// in bits, or 0 if the relocation cannot be handled as a runtime pseudo
// relocation.
static int getRuntimePseudoRelocSize(uint16_t Type) {
  // Relocations that either contain an absolute address, or a plain
  // relative offset, since the runtime pseudo reloc implementation
  // adds 8/16/32/64 bit values to a memory address.
  //
  // Given a pseudo relocation entry,
  //
  // typedef struct {
  //   DWORD sym;
  //   DWORD target;
  //   DWORD flags;
  // } runtime_pseudo_reloc_item_v2;
  //
  // the runtime relocation performs this adjustment:
  //     *(base + .target) += *(base + .sym) - (base + .sym)
  //
  // This works for both absolute addresses (IMAGE_REL_*_ADDR32/64,
  // IMAGE_REL_I386_DIR32, where the memory location initially contains
  // the address of the IAT slot, and for relative addresses (IMAGE_REL*_REL32),
  // where the memory location originally contains the relative offset to the
  // IAT slot.
  //
  // This requires the target address to be writable, either directly out of
  // the image, or temporarily changed at runtime with VirtualProtect.
  // Since this only operates on direct address values, it doesn't work for
  // ARM/ARM64 relocations, other than the plain ADDR32/ADDR64 relocations.
  switch (Config->Machine) {
  case AMD64:
    switch (Type) {
    case IMAGE_REL_AMD64_ADDR64:
      return 64;
    case IMAGE_REL_AMD64_ADDR32:
    case IMAGE_REL_AMD64_REL32:
    case IMAGE_REL_AMD64_REL32_1:
    case IMAGE_REL_AMD64_REL32_2:
    case IMAGE_REL_AMD64_REL32_3:
    case IMAGE_REL_AMD64_REL32_4:
    case IMAGE_REL_AMD64_REL32_5:
      return 32;
    default:
      return 0;
    }
  case I386:
    switch (Type) {
    case IMAGE_REL_I386_DIR32:
    case IMAGE_REL_I386_REL32:
      return 32;
    default:
      return 0;
    }
  case ARMNT:
    switch (Type) {
    case IMAGE_REL_ARM_ADDR32:
      return 32;
    default:
      return 0;
    }
  case ARM64:
    switch (Type) {
    case IMAGE_REL_ARM64_ADDR64:
      return 64;
    case IMAGE_REL_ARM64_ADDR32:
      return 32;
    default:
      return 0;
    }
  default:
    llvm_unreachable("unknown machine type");
  }
}

// MinGW specific.
// Append information to the provided vector about all relocations that
// need to be handled at runtime as runtime pseudo relocations (references
// to a module local variable, which turned out to actually need to be
// imported from another DLL).
void SectionChunk::getRuntimePseudoRelocs(
    std::vector<RuntimePseudoReloc> &Res) {
  for (const coff_relocation &Rel : getRelocs()) {
    auto *Target =
        dyn_cast_or_null<Defined>(File->getSymbol(Rel.SymbolTableIndex));
    if (!Target || !Target->IsRuntimePseudoReloc)
      continue;
    int SizeInBits = getRuntimePseudoRelocSize(Rel.Type);
    if (SizeInBits == 0) {
      error("unable to automatically import from " + Target->getName() +
            " with relocation type " +
            File->getCOFFObj()->getRelocationTypeName(Rel.Type) + " in " +
            toString(File));
      continue;
    }
    // SizeInBits is used to initialize the Flags field; currently no
    // other flags are defined.
    Res.emplace_back(
        RuntimePseudoReloc(Target, this, Rel.VirtualAddress, SizeInBits));
  }
}

bool SectionChunk::isCOMDAT() const {
  return Header->Characteristics & IMAGE_SCN_LNK_COMDAT;
}

void SectionChunk::printDiscardedMessage() const {
  // Removed by dead-stripping. If it's removed by ICF, ICF already
  // printed out the name, so don't repeat that here.
  if (Sym && this == Repl)
    message("Discarded " + Sym->getName());
}

StringRef SectionChunk::getDebugName() const {
  if (Sym)
    return Sym->getName();
  return "";
}

ArrayRef<uint8_t> SectionChunk::getContents() const {
  ArrayRef<uint8_t> A;
  cantFail(File->getCOFFObj()->getSectionContents(Header, A));
  return A;
}

ArrayRef<uint8_t> SectionChunk::consumeDebugMagic() {
  assert(isCodeView());
  return consumeDebugMagic(getContents(), getSectionName());
}

ArrayRef<uint8_t> SectionChunk::consumeDebugMagic(ArrayRef<uint8_t> Data,
                                                  StringRef SectionName) {
  if (Data.empty())
    return {};

  // First 4 bytes are section magic.
  if (Data.size() < 4)
    fatal("the section is too short: " + SectionName);

  if (!SectionName.startswith(".debug$"))
    fatal("invalid section: " + SectionName);

  unsigned Magic = support::endian::read32le(Data.data());
  unsigned ExpectedMagic = SectionName == ".debug$H"
                               ? DEBUG_HASHES_SECTION_MAGIC
                               : DEBUG_SECTION_MAGIC;
  if (Magic != ExpectedMagic)
    fatal("section: " + SectionName + " has an invalid magic: " + Twine(Magic));
  return Data.slice(4);
}

SectionChunk *SectionChunk::findByName(ArrayRef<SectionChunk *> Sections,
                                       StringRef Name) {
  for (SectionChunk *C : Sections)
    if (C->getSectionName() == Name)
      return C;
  return nullptr;
}

void SectionChunk::replace(SectionChunk *Other) {
  P2Align = std::max(P2Align, Other->P2Align);
  Other->Repl = Repl;
  Other->Live = false;
}

uint32_t SectionChunk::getSectionNumber() const {
  DataRefImpl R;
  R.p = reinterpret_cast<uintptr_t>(Header);
  SectionRef S(R, File->getCOFFObj());
  return S.getIndex() + 1;
}

CommonChunk::CommonChunk(const COFFSymbolRef S) : Sym(S) {
  // The value of a common symbol is its size. Align all common symbols smaller
  // than 32 bytes naturally, i.e. round the size up to the next power of two.
  // This is what MSVC link.exe does.
  setAlignment(std::min(32U, uint32_t(PowerOf2Ceil(Sym.getValue()))));
  HasData = false;
}

uint32_t CommonChunk::getOutputCharacteristics() const {
  return IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ |
         IMAGE_SCN_MEM_WRITE;
}

void StringChunk::writeTo(uint8_t *Buf) const {
  memcpy(Buf, Str.data(), Str.size());
  Buf[Str.size()] = '\0';
}

ImportThunkChunkX64::ImportThunkChunkX64(Defined *S) : ImportThunkChunk(S) {
  // Intel Optimization Manual says that all branch targets
  // should be 16-byte aligned. MSVC linker does this too.
  setAlignment(16);
}

void ImportThunkChunkX64::writeTo(uint8_t *Buf) const {
  memcpy(Buf, ImportThunkX86, sizeof(ImportThunkX86));
  // The first two bytes is a JMP instruction. Fill its operand.
  write32le(Buf + 2, ImpSymbol->getRVA() - RVA - getSize());
}

void ImportThunkChunkX86::getBaserels(std::vector<Baserel> *Res) {
  Res->emplace_back(getRVA() + 2);
}

void ImportThunkChunkX86::writeTo(uint8_t *Buf) const {
  memcpy(Buf, ImportThunkX86, sizeof(ImportThunkX86));
  // The first two bytes is a JMP instruction. Fill its operand.
  write32le(Buf + 2,
            ImpSymbol->getRVA() + Config->ImageBase);
}

void ImportThunkChunkARM::getBaserels(std::vector<Baserel> *Res) {
  Res->emplace_back(getRVA(), IMAGE_REL_BASED_ARM_MOV32T);
}

void ImportThunkChunkARM::writeTo(uint8_t *Buf) const {
  memcpy(Buf, ImportThunkARM, sizeof(ImportThunkARM));
  // Fix mov.w and mov.t operands.
  applyMOV32T(Buf, ImpSymbol->getRVA() + Config->ImageBase);
}

void ImportThunkChunkARM64::writeTo(uint8_t *Buf) const {
  int64_t Off = ImpSymbol->getRVA() & 0xfff;
  memcpy(Buf, ImportThunkARM64, sizeof(ImportThunkARM64));
  applyArm64Addr(Buf, ImpSymbol->getRVA(), RVA, 12);
  applyArm64Ldr(Buf + 4, Off);
}

// A Thumb2, PIC, non-interworking range extension thunk.
const uint8_t ArmThunk[] = {
    0x40, 0xf2, 0x00, 0x0c, // P:  movw ip,:lower16:S - (P + (L1-P) + 4)
    0xc0, 0xf2, 0x00, 0x0c, //     movt ip,:upper16:S - (P + (L1-P) + 4)
    0xe7, 0x44,             // L1: add  pc, ip
};

size_t RangeExtensionThunkARM::getSize() const {
  assert(Config->Machine == ARMNT);
  return sizeof(ArmThunk);
}

void RangeExtensionThunkARM::writeTo(uint8_t *Buf) const {
  assert(Config->Machine == ARMNT);
  uint64_t Offset = Target->getRVA() - RVA - 12;
  memcpy(Buf, ArmThunk, sizeof(ArmThunk));
  applyMOV32T(Buf, uint32_t(Offset));
}

// A position independent ARM64 adrp+add thunk, with a maximum range of
// +/- 4 GB, which is enough for any PE-COFF.
const uint8_t Arm64Thunk[] = {
    0x10, 0x00, 0x00, 0x90, // adrp x16, Dest
    0x10, 0x02, 0x00, 0x91, // add  x16, x16, :lo12:Dest
    0x00, 0x02, 0x1f, 0xd6, // br   x16
};

size_t RangeExtensionThunkARM64::getSize() const {
  assert(Config->Machine == ARM64);
  return sizeof(Arm64Thunk);
}

void RangeExtensionThunkARM64::writeTo(uint8_t *Buf) const {
  assert(Config->Machine == ARM64);
  memcpy(Buf, Arm64Thunk, sizeof(Arm64Thunk));
  applyArm64Addr(Buf + 0, Target->getRVA(), RVA, 12);
  applyArm64Imm(Buf + 4, Target->getRVA() & 0xfff, 0);
}

void LocalImportChunk::getBaserels(std::vector<Baserel> *Res) {
  Res->emplace_back(getRVA());
}

size_t LocalImportChunk::getSize() const { return Config->Wordsize; }

void LocalImportChunk::writeTo(uint8_t *Buf) const {
  if (Config->is64()) {
    write64le(Buf, Sym->getRVA() + Config->ImageBase);
  } else {
    write32le(Buf, Sym->getRVA() + Config->ImageBase);
  }
}

void RVATableChunk::writeTo(uint8_t *Buf) const {
  ulittle32_t *Begin = reinterpret_cast<ulittle32_t *>(Buf);
  size_t Cnt = 0;
  for (const ChunkAndOffset &CO : Syms)
    Begin[Cnt++] = CO.InputChunk->getRVA() + CO.Offset;
  std::sort(Begin, Begin + Cnt);
  assert(std::unique(Begin, Begin + Cnt) == Begin + Cnt &&
         "RVA tables should be de-duplicated");
}

// MinGW specific, for the "automatic import of variables from DLLs" feature.
size_t PseudoRelocTableChunk::getSize() const {
  if (Relocs.empty())
    return 0;
  return 12 + 12 * Relocs.size();
}

// MinGW specific.
void PseudoRelocTableChunk::writeTo(uint8_t *Buf) const {
  if (Relocs.empty())
    return;

  ulittle32_t *Table = reinterpret_cast<ulittle32_t *>(Buf);
  // This is the list header, to signal the runtime pseudo relocation v2
  // format.
  Table[0] = 0;
  Table[1] = 0;
  Table[2] = 1;

  size_t Idx = 3;
  for (const RuntimePseudoReloc &RPR : Relocs) {
    Table[Idx + 0] = RPR.Sym->getRVA();
    Table[Idx + 1] = RPR.Target->getRVA() + RPR.TargetOffset;
    Table[Idx + 2] = RPR.Flags;
    Idx += 3;
  }
}

// Windows-specific. This class represents a block in .reloc section.
// The format is described here.
//
// On Windows, each DLL is linked against a fixed base address and
// usually loaded to that address. However, if there's already another
// DLL that overlaps, the loader has to relocate it. To do that, DLLs
// contain .reloc sections which contain offsets that need to be fixed
// up at runtime. If the loader finds that a DLL cannot be loaded to its
// desired base address, it loads it to somewhere else, and add <actual
// base address> - <desired base address> to each offset that is
// specified by the .reloc section. In ELF terms, .reloc sections
// contain relative relocations in REL format (as opposed to RELA.)
//
// This already significantly reduces the size of relocations compared
// to ELF .rel.dyn, but Windows does more to reduce it (probably because
// it was invented for PCs in the late '80s or early '90s.)  Offsets in
// .reloc are grouped by page where the page size is 12 bits, and
// offsets sharing the same page address are stored consecutively to
// represent them with less space. This is very similar to the page
// table which is grouped by (multiple stages of) pages.
//
// For example, let's say we have 0x00030, 0x00500, 0x00700, 0x00A00,
// 0x20004, and 0x20008 in a .reloc section for x64. The uppermost 4
// bits have a type IMAGE_REL_BASED_DIR64 or 0xA. In the section, they
// are represented like this:
//
//   0x00000  -- page address (4 bytes)
//   16       -- size of this block (4 bytes)
//     0xA030 -- entries (2 bytes each)
//     0xA500
//     0xA700
//     0xAA00
//   0x20000  -- page address (4 bytes)
//   12       -- size of this block (4 bytes)
//     0xA004 -- entries (2 bytes each)
//     0xA008
//
// Usually we have a lot of relocations for each page, so the number of
// bytes for one .reloc entry is close to 2 bytes on average.
BaserelChunk::BaserelChunk(uint32_t Page, Baserel *Begin, Baserel *End) {
  // Block header consists of 4 byte page RVA and 4 byte block size.
  // Each entry is 2 byte. Last entry may be padding.
  Data.resize(alignTo((End - Begin) * 2 + 8, 4));
  uint8_t *P = Data.data();
  write32le(P, Page);
  write32le(P + 4, Data.size());
  P += 8;
  for (Baserel *I = Begin; I != End; ++I) {
    write16le(P, (I->Type << 12) | (I->RVA - Page));
    P += 2;
  }
}

void BaserelChunk::writeTo(uint8_t *Buf) const {
  memcpy(Buf, Data.data(), Data.size());
}

uint8_t Baserel::getDefaultType() {
  switch (Config->Machine) {
  case AMD64:
  case ARM64:
    return IMAGE_REL_BASED_DIR64;
  case I386:
  case ARMNT:
    return IMAGE_REL_BASED_HIGHLOW;
  default:
    llvm_unreachable("unknown machine type");
  }
}

MergeChunk *MergeChunk::Instances[Log2MaxSectionAlignment + 1] = {};

MergeChunk::MergeChunk(uint32_t Alignment)
    : Builder(StringTableBuilder::RAW, Alignment) {
  setAlignment(Alignment);
}

void MergeChunk::addSection(SectionChunk *C) {
  assert(isPowerOf2_32(C->getAlignment()));
  uint8_t P2Align = llvm::Log2_32(C->getAlignment());
  assert(P2Align < array_lengthof(Instances));
  auto *&MC = Instances[P2Align];
  if (!MC)
    MC = make<MergeChunk>(C->getAlignment());
  MC->Sections.push_back(C);
}

void MergeChunk::finalizeContents() {
  assert(!Finalized && "should only finalize once");
  for (SectionChunk *C : Sections)
    if (C->Live)
      Builder.add(toStringRef(C->getContents()));
  Builder.finalize();
  Finalized = true;
}

void MergeChunk::assignSubsectionRVAs() {
  for (SectionChunk *C : Sections) {
    if (!C->Live)
      continue;
    size_t Off = Builder.getOffset(toStringRef(C->getContents()));
    C->setRVA(RVA + Off);
  }
}

uint32_t MergeChunk::getOutputCharacteristics() const {
  return IMAGE_SCN_MEM_READ | IMAGE_SCN_CNT_INITIALIZED_DATA;
}

size_t MergeChunk::getSize() const {
  return Builder.getSize();
}

void MergeChunk::writeTo(uint8_t *Buf) const {
  Builder.write(Buf);
}

// MinGW specific.
size_t AbsolutePointerChunk::getSize() const { return Config->Wordsize; }

void AbsolutePointerChunk::writeTo(uint8_t *Buf) const {
  if (Config->is64()) {
    write64le(Buf, Value);
  } else {
    write32le(Buf, Value);
  }
}

} // namespace coff
} // namespace lld