mold/macho/output-chunks.cc

#include "mold.h"

#include <shared_mutex>
#include <sys/mman.h>

#ifdef __APPLE__
#  define COMMON_DIGEST_FOR_OPENSSL
#  include <CommonCrypto/CommonDigest.h>
#  define SHA256(data, len, md) CC_SHA256(data, len, md)
#else
#  include <openssl/sha.h>
#endif

namespace mold::macho {

template <typename E>
std::ostream &operator<<(std::ostream &out, const Chunk<E> &chunk) {
  out << chunk.hdr.get_segname() << "," << chunk.hdr.get_sectname();
  return out;
}

template <typename E>
static std::vector<u8> create_pagezero_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(SegmentCommand));
  SegmentCommand &cmd = *(SegmentCommand *)buf.data();

  cmd.cmd = LC_SEGMENT_64;
  cmd.cmdsize = buf.size();
  strcpy(cmd.segname, "__PAGEZERO");
  cmd.vmsize = ctx.arg.pagezero_size;
  return buf;
}

template <typename E>
static std::vector<u8> create_dyld_info_only_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(DyldInfoCommand));
  DyldInfoCommand &cmd = *(DyldInfoCommand *)buf.data();

  cmd.cmd = LC_DYLD_INFO_ONLY;
  cmd.cmdsize = buf.size();

  cmd.rebase_off = ctx.rebase.hdr.offset;
  cmd.rebase_size = ctx.rebase.hdr.size;

  cmd.bind_off = ctx.bind.hdr.offset;
  cmd.bind_size = ctx.bind.hdr.size;

  cmd.lazy_bind_off = ctx.lazy_bind.hdr.offset;
  cmd.lazy_bind_size = ctx.lazy_bind.hdr.size;

  cmd.export_off = ctx.export_.hdr.offset;
  cmd.export_size = ctx.export_.hdr.size;
  return buf;
}

template <typename E>
static std::vector<u8> create_symtab_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(SymtabCommand));
  SymtabCommand &cmd = *(SymtabCommand *)buf.data();

  cmd.cmd = LC_SYMTAB;
  cmd.cmdsize = buf.size();
  cmd.symoff = ctx.symtab.hdr.offset;
  cmd.nsyms = ctx.symtab.hdr.size / sizeof(MachSym);
  cmd.stroff = ctx.strtab.hdr.offset;
  cmd.strsize = ctx.strtab.hdr.size;
  return buf;
}

template <typename E>
static std::vector<u8> create_dysymtab_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(DysymtabCommand));
  DysymtabCommand &cmd = *(DysymtabCommand *)buf.data();

  cmd.cmd = LC_DYSYMTAB;
  cmd.cmdsize = buf.size();

  i64 locals = ctx.symtab.locals.size();
  i64 globals = ctx.symtab.globals.size();
  i64 undefs = ctx.symtab.undefs.size();

  cmd.ilocalsym = 0;
  cmd.nlocalsym = locals;
  cmd.iextdefsym = locals;
  cmd.nextdefsym = globals;
  cmd.iundefsym = locals + globals;
  cmd.nundefsym = undefs;

  cmd.indirectsymoff = ctx.indir_symtab.hdr.offset;
  cmd.nindirectsyms =
    ctx.indir_symtab.hdr.size / OutputIndirectSymtabSection<E>::ENTRY_SIZE;
  return buf;
}

template <typename E>
static std::vector<u8> create_dylinker_cmd(Context<E> &ctx) {
  static constexpr char path[] = "/usr/lib/dyld";

  std::vector<u8> buf(align_to(sizeof(DylinkerCommand) + sizeof(path), 8));
  DylinkerCommand &cmd = *(DylinkerCommand *)buf.data();

  cmd.cmd = LC_LOAD_DYLINKER;
  cmd.cmdsize = buf.size();
  cmd.nameoff = sizeof(cmd);
  memcpy(buf.data() + sizeof(cmd), path, sizeof(path));
  return buf;
}

template <typename E>
static std::vector<u8> create_uuid_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(UUIDCommand));
  UUIDCommand &cmd = *(UUIDCommand *)buf.data();

  cmd.cmd = LC_UUID;
  cmd.cmdsize = buf.size();
  return buf;
}

template <typename E>
static std::vector<u8> create_build_version_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(BuildVersionCommand) + sizeof(BuildToolVersion));
  BuildVersionCommand &cmd = *(BuildVersionCommand *)buf.data();

  cmd.cmd = LC_BUILD_VERSION;
  cmd.cmdsize = buf.size();
  cmd.platform = ctx.arg.platform;
  cmd.minos = ctx.arg.platform_min_version;
  cmd.sdk = ctx.arg.platform_sdk_version;
  cmd.ntools = 1;

  BuildToolVersion &tool = *(BuildToolVersion *)(buf.data() + sizeof(cmd));
  tool.tool = 3;
  tool.version = 0x28a0900;
  return buf;
}

template <typename E>
static std::vector<u8> create_source_version_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(SourceVersionCommand));
  SourceVersionCommand &cmd = *(SourceVersionCommand *)buf.data();

  cmd.cmd = LC_SOURCE_VERSION;
  cmd.cmdsize = buf.size();
  return buf;
}

template <typename E>
static std::vector<u8> create_main_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(EntryPointCommand));
  EntryPointCommand &cmd = *(EntryPointCommand *)buf.data();

  cmd.cmd = LC_MAIN;
  cmd.cmdsize = buf.size();
  cmd.entryoff = get_symbol(ctx, ctx.arg.entry)->get_addr(ctx) - ctx.arg.pagezero_size;
  return buf;
}

template <typename E>
static std::vector<u8>
create_load_dylib_cmd(Context<E> &ctx, std::string_view name) {
  i64 size = sizeof(DylibCommand) + name.size() + 1; // +1 for NUL
  std::vector<u8> buf(align_to(size, 8));
  DylibCommand &cmd = *(DylibCommand *)buf.data();

  cmd.cmd = LC_LOAD_DYLIB;
  cmd.cmdsize = buf.size();
  cmd.nameoff = sizeof(cmd);
  cmd.timestamp = 2;
  cmd.current_version = 0x50c6405;
  cmd.compatibility_version = 0x10000;
  write_string(buf.data() + sizeof(cmd), name);
  return buf;
}

template <typename E>
static std::vector<u8> create_rpath_cmd(Context<E> &ctx, std::string_view name) {
  i64 size = sizeof(RpathCommand) + name.size() + 1; // +1 for NUL
  std::vector<u8> buf(align_to(size, 8));
  RpathCommand &cmd = *(RpathCommand *)buf.data();

  cmd.cmd = LC_RPATH;
  cmd.cmdsize = buf.size();
  cmd.path_off = sizeof(cmd);
  write_string(buf.data() + sizeof(cmd), name);
  return buf;
}

template <typename E>
static std::vector<u8> create_function_starts_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(LinkEditDataCommand));
  LinkEditDataCommand &cmd = *(LinkEditDataCommand *)buf.data();

  cmd.cmd = LC_FUNCTION_STARTS;
  cmd.cmdsize = buf.size();
  cmd.dataoff = ctx.function_starts.hdr.offset;
  cmd.datasize = ctx.function_starts.hdr.size;
  return buf;
}

template <typename E>
static std::vector<u8> create_data_in_code_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(LinkEditDataCommand));
  LinkEditDataCommand &cmd = *(LinkEditDataCommand *)buf.data();

  cmd.cmd = LC_DATA_IN_CODE;
  cmd.cmdsize = buf.size();
  cmd.dataoff = ctx.data_in_code.hdr.offset;
  cmd.datasize = ctx.data_in_code.hdr.size;
  return buf;
}

template <typename E>
static std::vector<u8> create_id_dylib_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(DylibCommand) + ctx.arg.output.size() + 1);
  DylibCommand &cmd = *(DylibCommand *)buf.data();

  cmd.cmd = LC_ID_DYLIB;
  cmd.cmdsize = buf.size();
  cmd.nameoff = sizeof(cmd);
  write_string(buf.data() + sizeof(cmd), ctx.arg.output);
  return buf;
}

template <typename E>
static std::vector<u8> create_code_signature_cmd(Context<E> &ctx) {
  std::vector<u8> buf(sizeof(LinkEditDataCommand));
  LinkEditDataCommand &cmd = *(LinkEditDataCommand *)buf.data();

  cmd.cmd = LC_CODE_SIGNATURE;
  cmd.cmdsize = buf.size();
  cmd.dataoff = ctx.code_sig.hdr.offset;
  cmd.datasize = ctx.code_sig.hdr.size;
  return buf;
}

template <typename E>
static std::pair<i64, std::vector<u8>> create_load_commands(Context<E> &ctx) {
  std::vector<std::vector<u8>> vec;

  if (ctx.arg.pagezero_size)
    vec.push_back(create_pagezero_cmd(ctx));

  auto append = [&](std::vector<u8> &buf, auto x) {
    i64 off = buf.size();
    buf.resize(buf.size() + sizeof(x));
    memcpy(buf.data() + off, &x, sizeof(x));
  };

  // Add LC_SEGMENT_64 comamnds
  for (std::unique_ptr<OutputSegment<E>> &seg : ctx.segments) {
    std::vector<u8> &buf = vec.emplace_back();

    i64 nsects = 0;
    for (Chunk<E> *sec : seg->chunks)
      if (!sec->is_hidden)
        nsects++;

    SegmentCommand cmd = seg->cmd;
    cmd.cmdsize = sizeof(SegmentCommand) + sizeof(MachSection) * nsects;
    cmd.nsects = nsects;
    append(buf, cmd);

    for (Chunk<E> *sec : seg->chunks) {
      if (!sec->is_hidden) {
        sec->hdr.set_segname(cmd.segname);
        append(buf, sec->hdr);
      }
    }
  }

  vec.push_back(create_dyld_info_only_cmd(ctx));
  vec.push_back(create_symtab_cmd(ctx));
  vec.push_back(create_dysymtab_cmd(ctx));
  vec.push_back(create_uuid_cmd(ctx));
  vec.push_back(create_build_version_cmd(ctx));
  vec.push_back(create_source_version_cmd(ctx));
  vec.push_back(create_function_starts_cmd(ctx));

  for (DylibFile<E> *dylib : ctx.dylibs)
    vec.push_back(create_load_dylib_cmd(ctx, dylib->install_name));

  for (std::string_view rpath : ctx.arg.rpath)
    vec.push_back(create_rpath_cmd(ctx, rpath));

  if (!ctx.data_in_code.contents.empty())
    vec.push_back(create_data_in_code_cmd(ctx));

  switch (ctx.output_type) {
  case MH_EXECUTE:
    vec.push_back(create_dylinker_cmd(ctx));
    vec.push_back(create_main_cmd(ctx));
    break;
  case MH_DYLIB:
    vec.push_back(create_id_dylib_cmd(ctx));
    break;
  case MH_BUNDLE:
    break;
  default:
    unreachable();
  }

  if (ctx.arg.adhoc_codesign)
    vec.push_back(create_code_signature_cmd(ctx));

  return {vec.size(), flatten(vec)};
}

template <typename E>
void OutputMachHeader<E>::compute_size(Context<E> &ctx) {
  std::vector<u8> cmds;
  std::tie(std::ignore, cmds) = create_load_commands(ctx);
  this->hdr.size = sizeof(MachHeader) + cmds.size() + ctx.arg.headerpad;
}

template <typename E>
static bool has_tlv(Context<E> &ctx) {
  for (std::unique_ptr<OutputSegment<E>> &seg : ctx.segments)
    for (Chunk<E> *chunk : seg->chunks)
      if (chunk->hdr.type == S_THREAD_LOCAL_VARIABLES)
        return true;
  return false;
}

template <typename E>
void OutputMachHeader<E>::copy_buf(Context<E> &ctx) {
  u8 *buf = ctx.buf + this->hdr.offset;

  i64 ncmds;
  std::vector<u8> cmds;
  std::tie(ncmds, cmds) = create_load_commands(ctx);

  MachHeader &mhdr = *(MachHeader *)buf;
  mhdr.magic = 0xfeedfacf;
  mhdr.cputype = E::cputype;
  mhdr.cpusubtype = E::cpusubtype;
  mhdr.filetype = ctx.output_type;
  mhdr.ncmds = ncmds;
  mhdr.sizeofcmds = cmds.size();
  mhdr.flags = MH_TWOLEVEL | MH_NOUNDEFS | MH_DYLDLINK | MH_PIE;

  if (has_tlv(ctx))
    mhdr.flags |= MH_HAS_TLV_DESCRIPTORS;

  if (ctx.output_type == MH_DYLIB)
    mhdr.flags |= MH_NO_REEXPORTED_DYLIBS;

  write_vector(buf + sizeof(mhdr), cmds);
}

template <typename E>
OutputSection<E> *
OutputSection<E>::get_instance(Context<E> &ctx, std::string_view segname,
                               std::string_view sectname) {
  static std::shared_mutex mu;

  auto find = [&]() -> OutputSection<E> * {
    for (Chunk<E> *chunk : ctx.chunks) {
      if (chunk->hdr.match(segname, sectname)) {
        if (!chunk->is_regular)
          Fatal(ctx) << ": reserved name is used: " << segname << "," << sectname;
        return (OutputSection<E> *)chunk;
      }
    }
    return nullptr;
  };

  {
    std::shared_lock lock(mu);
    if (OutputSection<E> *osec = find())
      return osec;
  }

  std::unique_lock lock(mu);
  if (OutputSection<E> *osec = find())
    return osec;

  OutputSection<E> *osec = new OutputSection<E>(ctx, segname, sectname);
  ctx.osec_pool.push_back(std::unique_ptr<OutputSection<E>>(osec));
  return osec;
}

template <typename E>
void OutputSection<E>::compute_size(Context<E> &ctx) {
  u64 addr = this->hdr.addr;

  if (this == ctx.data) {
    // As a special case, we need a word-size padding at the beginning
    // of __data for dyld. It is located by __dyld_private symbol.
    addr += 8;
  }

  for (Subsection<E> *subsec : members) {
    addr = align_to(addr, 1 << subsec->p2align);
    subsec->raddr = addr - ctx.arg.pagezero_size;
    addr += subsec->input_size;
  }
  this->hdr.size = addr - this->hdr.addr;
}

template <typename E>
void OutputSection<E>::copy_buf(Context<E> &ctx) {
  u8 *buf = ctx.buf + this->hdr.offset;
  assert(this->hdr.type != S_ZEROFILL);

  for (Subsection<E> *subsec : members) {
    std::string_view data = subsec->get_contents();
    u8 *loc = buf + subsec->get_addr(ctx) - this->hdr.addr;
    memcpy(loc, data.data(), data.size());
    subsec->apply_reloc(ctx, loc);
  }
}

template <typename E>
OutputSegment<E> *
OutputSegment<E>::get_instance(Context<E> &ctx, std::string_view name) {
  static std::shared_mutex mu;

  auto find = [&]() -> OutputSegment<E> *{
    for (std::unique_ptr<OutputSegment<E>> &seg : ctx.segments)
      if (seg->cmd.get_segname() == name)
        return seg.get();
    return nullptr;
  };

  {
    std::shared_lock lock(mu);
    if (OutputSegment<E> *seg = find())
      return seg;
  }

  std::unique_lock lock(mu);
  if (OutputSegment<E> *seg = find())
    return seg;

  OutputSegment<E> *seg = new OutputSegment<E>(name);
  ctx.segments.push_back(std::unique_ptr<OutputSegment<E>>(seg));
  return seg;
}

template <typename E>
OutputSegment<E>::OutputSegment(std::string_view name) {
  cmd.cmd = LC_SEGMENT_64;
  memcpy(cmd.segname, name.data(), name.size());

  if (name == "__PAGEZERO")
    cmd.initprot = cmd.maxprot = 0;
  else if (name == "__TEXT")
    cmd.initprot = cmd.maxprot = VM_PROT_READ | VM_PROT_EXECUTE;
  else if (name == "__LINKEDIT")
    cmd.initprot = cmd.maxprot = VM_PROT_READ;
  else
    cmd.initprot = cmd.maxprot = VM_PROT_READ | VM_PROT_WRITE;

  if (name == "__DATA_CONST")
    cmd.flags = SG_READ_ONLY;
}

template <typename E>
void OutputSegment<E>::set_offset(Context<E> &ctx, i64 fileoff, u64 vmaddr) {
  cmd.fileoff = fileoff;
  cmd.vmaddr = vmaddr;

  i64 i = 0;

  while (i < chunks.size() && chunks[i]->hdr.type != S_ZEROFILL) {
    Chunk<E> &sec = *chunks[i++];
    fileoff = align_to(fileoff, 1 << sec.hdr.p2align);
    vmaddr = align_to(vmaddr, 1 << sec.hdr.p2align);

    sec.hdr.offset = fileoff;
    sec.hdr.addr = vmaddr;

    sec.compute_size(ctx);
    fileoff += sec.hdr.size;
    vmaddr += sec.hdr.size;
  }

  while (i < chunks.size()) {
    Chunk<E> &sec = *chunks[i++];
    assert(sec.hdr.type == S_ZEROFILL);
    vmaddr = align_to(vmaddr, 1 << sec.hdr.p2align);
    sec.hdr.addr = vmaddr;
    sec.compute_size(ctx);
    vmaddr += sec.hdr.size;
  }

  cmd.vmsize = align_to(vmaddr - cmd.vmaddr, COMMON_PAGE_SIZE);

  if (this == ctx.segments.back().get())
    cmd.filesize = fileoff - cmd.fileoff;
  else
    cmd.filesize = align_to(fileoff - cmd.fileoff, COMMON_PAGE_SIZE);
}

template <typename E>
void OutputSegment<E>::copy_buf(Context<E> &ctx) {
  // Fill text segment paddings with NOPs
  if (cmd.get_segname() == "__TEXT")
    memset(ctx.buf + cmd.fileoff, 0x90, cmd.filesize);

  for (Chunk<E> *sec : chunks)
    if (sec->hdr.type != S_ZEROFILL)
      sec->copy_buf(ctx);
}

RebaseEncoder::RebaseEncoder() {
  buf.push_back(REBASE_OPCODE_SET_TYPE_IMM | REBASE_TYPE_POINTER);
}

void RebaseEncoder::add(i64 seg_idx, i64 offset) {
  assert(seg_idx < 16);

  // Accumulate consecutive base relocations
  if (seg_idx == cur_seg && offset == cur_off) {
    cur_off += 8;
    times++;
    return;
  }

  // Flush the accumulated base relocations
  flush();

  // Advance the cursor
  if (seg_idx != cur_seg || offset < cur_off) {
    buf.push_back(REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | seg_idx);
    encode_uleb(buf, offset);
  } else {
    i64 dist = offset - cur_off;
    assert(dist >= 0);

    if (dist % 8 == 0 && dist < 128) {
      buf.push_back(REBASE_OPCODE_ADD_ADDR_IMM_SCALED | (dist >> 3));
    } else {
      buf.push_back(REBASE_OPCODE_ADD_ADDR_ULEB);
      encode_uleb(buf, dist);
    }
  }

  cur_seg = seg_idx;
  cur_off = offset + 8;
  times = 1;
}

void RebaseEncoder::flush() {
  if (times == 0)
    return;

  if (times < 16) {
    buf.push_back(REBASE_OPCODE_DO_REBASE_IMM_TIMES | times);
  } else {
    buf.push_back(REBASE_OPCODE_DO_REBASE_ULEB_TIMES);
    encode_uleb(buf, times);
  }

  times = 0;
}

void RebaseEncoder::finish() {
  flush();
  buf.push_back(REBASE_OPCODE_DONE);
}

template <typename E>
void OutputRebaseSection<E>::compute_size(Context<E> &ctx) {
  RebaseEncoder enc;

  for (i64 i = 0; i < ctx.stubs.syms.size(); i++)
    enc.add(ctx.data_seg->seg_idx,
            ctx.lazy_symbol_ptr.hdr.addr + i * E::word_size -
            ctx.data_seg->cmd.vmaddr);

  for (Symbol<E> *sym : ctx.got.syms)
    if (!sym->file->is_dylib)
      enc.add(ctx.data_const_seg->seg_idx,
              sym->get_got_addr(ctx) - ctx.data_const_seg->cmd.vmaddr);

  for (Symbol<E> *sym : ctx.thread_ptrs.syms)
    if (!sym->file->is_dylib)
      enc.add(ctx.data_seg->seg_idx,
              sym->get_tlv_addr(ctx) - ctx.data_seg->cmd.vmaddr);

  for (std::unique_ptr<OutputSegment<E>> &seg : ctx.segments)
    for (Chunk<E> *chunk : seg->chunks)
      if (chunk->is_regular)
        for (Subsection<E> *subsec : ((OutputSection<E> *)chunk)->members)
          for (Relocation<E> &rel : subsec->get_rels())
            if (!rel.is_pcrel && rel.type == E::abs_rel)
              enc.add(seg->seg_idx,
                      subsec->get_addr(ctx) + rel.offset - seg->cmd.vmaddr);

  enc.finish();
  contents = std::move(enc.buf);
  this->hdr.size = align_to(contents.size(), 8);
}

template <typename E>
void OutputRebaseSection<E>::copy_buf(Context<E> &ctx) {
  write_vector(ctx.buf + this->hdr.offset, contents);
}

BindEncoder::BindEncoder() {
  buf.push_back(BIND_OPCODE_SET_TYPE_IMM | BIND_TYPE_POINTER);
}

void BindEncoder::add(i64 dylib_idx, std::string_view sym, i64 flags,
                      i64 seg_idx, i64 offset) {
  if (last_dylib != dylib_idx) {
    if (dylib_idx < 16) {
      buf.push_back(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM | dylib_idx);
    } else {
      buf.push_back(BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB);
      encode_uleb(buf, dylib_idx);
    }
  }

  if (last_sym != sym || last_flags != flags) {
    assert(flags < 16);
    buf.push_back(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM | flags);
    buf.insert(buf.end(), (u8 *)sym.data(), (u8 *)(sym.data() + sym.size()));
    buf.push_back('\0');
  }

  if (last_seg != seg_idx || last_off != offset) {
    assert(seg_idx < 16);
    buf.push_back(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | seg_idx);
    encode_uleb(buf, offset);
  }

  buf.push_back(BIND_OPCODE_DO_BIND);

  last_dylib = dylib_idx;
  last_sym = sym;
  last_flags = flags;
  last_seg = seg_idx;
  last_off = offset;
}

void BindEncoder::finish() {
  buf.push_back(BIND_OPCODE_DONE);
}

template <typename E>
void OutputBindSection<E>::compute_size(Context<E> &ctx) {
  BindEncoder enc;

  for (Symbol<E> *sym : ctx.got.syms)
    if (sym->file->is_dylib)
      enc.add(((DylibFile<E> *)sym->file)->dylib_idx, sym->name, 0,
              ctx.data_const_seg->seg_idx,
              sym->get_got_addr(ctx) - ctx.data_const_seg->cmd.vmaddr);

  for (Symbol<E> *sym : ctx.thread_ptrs.syms)
    if (sym->file->is_dylib)
      enc.add(((DylibFile<E> *)sym->file)->dylib_idx, sym->name, 0,
              ctx.data_seg->seg_idx,
              sym->get_tlv_addr(ctx) - ctx.data_seg->cmd.vmaddr);

  enc.finish();

  contents = enc.buf;
  this->hdr.size = align_to(contents.size(), 8);
}

template <typename E>
void OutputBindSection<E>::copy_buf(Context<E> &ctx) {
  write_vector(ctx.buf + this->hdr.offset, contents);
}

template <typename E>
void OutputLazyBindSection<E>::add(Context<E> &ctx, Symbol<E> &sym, i64 flags) {
  auto emit = [&](u8 byte) {
    contents.push_back(byte);
  };

  i64 dylib_idx = ((DylibFile<E> *)sym.file)->dylib_idx;
  if (dylib_idx < 16) {
    emit(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM | dylib_idx);
  } else {
    emit(BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB);
    encode_uleb(contents, dylib_idx);
  }

  assert(flags < 16);
  emit(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM | flags);
  contents.insert(contents.end(), (u8 *)sym.name.data(),
                  (u8 *)(sym.name.data() + sym.name.size()));
  emit('\0');

  i64 seg_idx = ctx.data_seg->seg_idx;
  emit(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | seg_idx);

  i64 offset = ctx.lazy_symbol_ptr.hdr.addr + sym.stub_idx * E::word_size -
               ctx.data_seg->cmd.vmaddr;
  encode_uleb(contents, offset);

  emit(BIND_OPCODE_DO_BIND);
  emit(BIND_OPCODE_DONE);
}

template <typename E>
void OutputLazyBindSection<E>::compute_size(Context<E> &ctx) {
  ctx.stubs.bind_offsets.clear();

  for (Symbol<E> *sym : ctx.stubs.syms) {
    ctx.stubs.bind_offsets.push_back(contents.size());
    add(ctx, *sym, 0);
  }

  this->hdr.size = align_to(contents.size(), 1 << this->hdr.p2align);
}

template <typename E>
void OutputLazyBindSection<E>::copy_buf(Context<E> &ctx) {
  write_vector(ctx.buf + this->hdr.offset, contents);
}

void ExportEncoder::add(std::string_view name, u32 flags, u64 addr) {
  entries.push_back({name, flags, addr});
}

i64 ExportEncoder::finish() {
  sort(entries, [](const Entry &a, const Entry &b) {
    return a.name < b.name;
  });

  TrieNode trie = construct_trie(entries, 0);

  if (trie.prefix.empty())
    root = std::move(trie);
  else
    root.children.push_back(std::move(trie));

  i64 size = set_offset(root, 0);
  for (;;) {
    i64 sz = set_offset(root, 0);
    if (sz == size)
      return sz;
    size = sz;
  }
}

i64 ExportEncoder::common_prefix_len(std::span<Entry> entries, i64 len) {
  for (; len < entries[0].name.size(); len++)
    for (Entry &ent : entries.subspan(1))
      if (ent.name.size() == len || ent.name[len] != entries[0].name[len])
        return len;
  return len;
}

ExportEncoder::TrieNode
ExportEncoder::construct_trie(std::span<Entry> entries, i64 len) {
  TrieNode node;

  i64 new_len = common_prefix_len(entries, len);
  if (new_len > len) {
    node.prefix = entries[0].name.substr(len, new_len - len);
    if (entries[0].name.size() == new_len) {
      node.is_leaf = true;
      node.flags = entries[0].flags;
      node.addr = entries[0].addr;
      entries = entries.subspan(1);
    }
  }

  for (i64 i = 0; i < entries.size();) {
    i64 j = i + 1;
    u8 c = entries[i].name[new_len];
    while (j < entries.size() && c == entries[j].name[new_len])
      j++;
    node.children.push_back(construct_trie(entries.subspan(i, j - i), new_len));
    i = j;
  }
  return node;
}

i64 ExportEncoder::set_offset(TrieNode &node, i64 offset) {
  node.offset = offset;

  i64 size = 0;
  if (node.is_leaf) {
    size = uleb_size(node.flags) + uleb_size(node.addr);
    size += uleb_size(size);
  } else {
    size = 1;
  }

  size++; // # of children

  for (TrieNode &child : node.children) {
    // +1 for NUL byte
    size += child.prefix.size() + 1 + uleb_size(child.offset);
  }

  for (TrieNode &child : node.children)
    size += set_offset(child, offset + size);
  return size;
}

void ExportEncoder::write_trie(u8 *start, TrieNode &node) {
  u8 *buf = start + node.offset;

  if (node.is_leaf) {
    buf += write_uleb(buf, uleb_size(node.flags) + uleb_size(node.addr));
    buf += write_uleb(buf, node.flags);
    buf += write_uleb(buf, node.addr);
  } else {
    *buf++ = 0;
  }

  *buf++ = node.children.size();

  for (TrieNode &child : node.children) {
    buf += write_string(buf, child.prefix);
    buf += write_uleb(buf, child.offset);
  }

  for (TrieNode &child : node.children)
    write_trie(start, child);
}

template <typename E>
void OutputExportSection<E>::compute_size(Context<E> &ctx) {
  for (ObjectFile<E> *file : ctx.objs)
    for (Symbol<E> *sym : file->syms)
      if (sym && sym->is_extern && sym->file == file)
        enc.add(sym->name, 0, sym->get_addr(ctx) - ctx.arg.pagezero_size);

  this->hdr.size = align_to(enc.finish(), 8);
}

template <typename E>
void OutputExportSection<E>::copy_buf(Context<E> &ctx) {
  enc.write_trie(ctx.buf + this->hdr.offset);
}

template <typename E>
void OutputFunctionStartsSection<E>::compute_size(Context<E> &ctx) {
  std::vector<u64> addrs;

  for (ObjectFile<E> *file : ctx.objs)
    for (Symbol<E> *sym : file->syms)
      if (sym && sym->file == file && sym->subsec &&
          &sym->subsec->isec.osec == ctx.text)
        addrs.push_back(sym->get_addr(ctx));

  std::sort(addrs.begin(), addrs.end());

  contents.resize(addrs.size() * 5);

  u8 *p = contents.data();
  u64 last = ctx.arg.pagezero_size;

  for (u64 val : addrs) {
    p += write_uleb(p, val - last);
    last = val;
  }

  this->hdr.size = p - contents.data();
  contents.resize(this->hdr.size);
}

template <typename E>
void OutputFunctionStartsSection<E>::copy_buf(Context<E> &ctx) {
  write_vector(ctx.buf + this->hdr.offset, contents);
}

template <typename E>
void OutputSymtabSection<E>::compute_size(Context<E> &ctx) {
  for (ObjectFile<E> *file : ctx.objs)
    for (Symbol<E> *sym : file->syms)
      if (sym && sym->file == file)
        globals.push_back({sym, ctx.strtab.add_string(sym->name)});

  i64 idx = globals.size();

  for (DylibFile<E> *dylib : ctx.dylibs) {
    for (Symbol<E> *sym : dylib->syms) {
      if (sym && sym->file == dylib &&
          (sym->stub_idx != -1 || sym->got_idx != -1)) {
        undefs.push_back({sym, ctx.strtab.add_string(sym->name)});

        if (sym->stub_idx != -1)
          ctx.indir_symtab.stubs.push_back({sym, idx});
        else
          ctx.indir_symtab.gots.push_back({sym, idx});
        idx++;
      }
    }
  }

  this->hdr.size = idx * sizeof(MachSym);
}

template <typename E>
void OutputSymtabSection<E>::copy_buf(Context<E> &ctx) {
  MachSym *buf = (MachSym *)(ctx.buf + this->hdr.offset);
  memset(buf, 0, this->hdr.size);

  auto write = [&](Entry &ent) {
    MachSym &msym = *buf++;
    Symbol<E> &sym = *ent.sym;

    msym.stroff = ent.stroff;
    msym.type = (sym.file->is_dylib ? N_UNDF : N_SECT);
    msym.ext = sym.is_extern;

    if (!sym.file->is_dylib)
      msym.value = sym.get_addr(ctx);
    if (sym.subsec)
      msym.sect = sym.subsec->isec.osec.sect_idx;

    if (sym.file->is_dylib)
      msym.desc = ((DylibFile<E> *)sym.file)->dylib_idx << 8;
    else if (sym.referenced_dynamically)
      msym.desc = REFERENCED_DYNAMICALLY;
  };

  for (Entry &ent : locals)
    write(ent);
  for (Entry &ent : globals)
    write(ent);
  for (Entry &ent : undefs)
    write(ent);
}

template <typename E>
i64 OutputStrtabSection<E>::add_string(std::string_view str) {
  i64 off = contents.size();
  contents += str;
  contents += '\0';
  return off;
}

template <typename E>
void OutputStrtabSection<E>::compute_size(Context<E> &ctx) {
  this->hdr.size = align_to(contents.size(), 1 << this->hdr.p2align);
}

template <typename E>
void OutputStrtabSection<E>::copy_buf(Context<E> &ctx) {
  memcpy(ctx.buf + this->hdr.offset, &contents[0], contents.size());
}

template <typename E>
void OutputIndirectSymtabSection<E>::compute_size(Context<E> &ctx) {
  ctx.stubs.hdr.reserved1 = 0;
  ctx.got.hdr.reserved1 = stubs.size();
  ctx.lazy_symbol_ptr.hdr.reserved1 = stubs.size() + gots.size();

  i64 nsyms = stubs.size() * 2 + gots.size();
  this->hdr.size = nsyms * ENTRY_SIZE;
}

template <typename E>
void OutputIndirectSymtabSection<E>::copy_buf(Context<E> &ctx) {
  u32 *buf = (u32 *)(ctx.buf + this->hdr.offset);

  for (Entry &ent : stubs)
    buf[ent.sym->stub_idx] = ent.symtab_idx;
  buf += stubs.size();

  for (Entry &ent : gots)
    buf[ent.sym->got_idx] = ent.symtab_idx;
  buf += gots.size();

  for (Entry &ent : stubs)
    buf[ent.sym->stub_idx] = ent.symtab_idx;
}

template <typename E>
void CodeSignatureSection<E>::compute_size(Context<E> &ctx) {
  std::string filename = filepath(ctx.arg.output).filename();
  i64 filename_size = align_to(filename.size() + 1, 16);
  i64 num_blocks = align_to(this->hdr.offset, BLOCK_SIZE) / BLOCK_SIZE;
  this->hdr.size = sizeof(CodeSignatureHeader) + sizeof(CodeSignatureBlobIndex) +
                   sizeof(CodeSignatureDirectory) + filename_size +
                   num_blocks * SHA256_SIZE;
}

template <typename E>
void CodeSignatureSection<E>::write_signature(Context<E> &ctx) {
  u8 *buf = ctx.buf + this->hdr.offset;

  std::string filename = filepath(ctx.arg.output).filename();
  i64 filename_size = align_to(filename.size() + 1, 16);
  i64 num_blocks = align_to(this->hdr.offset, BLOCK_SIZE) / BLOCK_SIZE;

  CodeSignatureHeader &sighdr = *(CodeSignatureHeader *)buf;
  buf += sizeof(sighdr);

  sighdr.magic = CSMAGIC_EMBEDDED_SIGNATURE;
  sighdr.length = this->hdr.size;
  sighdr.count = 1;

  CodeSignatureBlobIndex &idx = *(CodeSignatureBlobIndex *)buf;
  buf += sizeof(idx);

  idx.type = CSSLOT_CODEDIRECTORY;
  idx.offset = sizeof(sighdr) + sizeof(idx);

  CodeSignatureDirectory &dir = *(CodeSignatureDirectory *)buf;
  buf += sizeof(dir);

  dir.magic = CSMAGIC_CODEDIRECTORY;
  dir.length = sizeof(dir) + filename_size + num_blocks * SHA256_SIZE;
  dir.version = CS_SUPPORTSEXECSEG;
  dir.flags = CS_ADHOC | CS_LINKER_SIGNED;
  dir.hash_offset = sizeof(dir) + filename_size;
  dir.ident_offset = sizeof(dir);
  dir.n_code_slots = num_blocks;
  dir.code_limit = this->hdr.offset;
  dir.hash_size = SHA256_SIZE;
  dir.hash_type = CS_HASHTYPE_SHA256;
  dir.page_size = __builtin_ctz(BLOCK_SIZE);
  dir.exec_seg_base = ctx.text_seg->cmd.fileoff;
  dir.exec_seg_limit = ctx.text_seg->cmd.filesize;
  if (ctx.output_type == MH_EXECUTE)
    dir.exec_seg_flags = CS_EXECSEG_MAIN_BINARY;

  memcpy(buf, filename.data(), filename.size());
  buf += filename_size;

  for (i64 i = 0; i < num_blocks; i++) {
    u8 *start = ctx.buf + i * BLOCK_SIZE;
    u8 *end = ctx.buf + std::min<i64>((i + 1) * BLOCK_SIZE, this->hdr.offset);
    SHA256(start, end - start, buf);
    buf += SHA256_SIZE;
  }

  // A hack borrowed from lld.
  msync(ctx.buf, ctx.output_file->filesize, MS_INVALIDATE);
}

template <typename E>
void DataInCodeSection<E>::compute_size(Context<E> &ctx) {
  assert(contents.empty());

  for (ObjectFile<E> *file : ctx.objs) {
    std::span<DataInCodeEntry> entries = file->data_in_code_entries;

    for (std::unique_ptr<Subsection<E>> &subsec : file->subsections) {
      if (entries.empty())
        break;

      DataInCodeEntry &ent = entries[0];
      if (subsec->input_addr + subsec->input_size < ent.offset)
        continue;

      if (ent.offset < subsec->input_addr + subsec->input_size) {
        u32 offset = subsec->get_addr(ctx) + subsec->input_addr - ent.offset -
                     ctx.text_seg->cmd.vmaddr;
        contents.push_back({offset, ent.length, ent.kind});
      }

      entries = entries.subspan(1);
    }
  }

  this->hdr.size = contents.size() * sizeof(contents[0]);
}

template <typename E>
void DataInCodeSection<E>::copy_buf(Context<E> &ctx) {
  write_vector(ctx.buf + this->hdr.offset, contents);
}

template <typename E>
void StubsSection<E>::add(Context<E> &ctx, Symbol<E> *sym) {
  assert(sym->stub_idx == -1);
  sym->stub_idx = syms.size();

  syms.push_back(sym);

  i64 nsyms = syms.size();
  this->hdr.size = nsyms * E::stub_size;

  ctx.stub_helper.hdr.size =
    E::stub_helper_hdr_size + nsyms * E::stub_helper_size;
  ctx.lazy_symbol_ptr.hdr.size = nsyms * E::word_size;
}

template <typename E>
std::vector<u8>
UnwindEncoder<E>::encode(Context<E> &ctx, std::span<UnwindRecord<E>> records) {
  i64 num_lsda = 0;

  for (UnwindRecord<E> &rec : records) {
    if (rec.personality)
      rec.encoding |= encode_personality(ctx, rec.personality);
    if (rec.lsda)
      num_lsda++;
  }

  std::vector<std::span<UnwindRecord<E>>> pages = split_records(ctx, records);

  // Allocate a buffer that is more than large enough to hold the
  // entire section.
  std::vector<u8> buf(4096 * 1024);

  // Write the section header.
  UnwindSectionHeader &uhdr = *(UnwindSectionHeader *)buf.data();
  uhdr.version = UNWIND_SECTION_VERSION;
  uhdr.encoding_offset = sizeof(uhdr);
  uhdr.encoding_count = 0;
  uhdr.personality_offset = sizeof(uhdr);
  uhdr.personality_count = personalities.size();
  uhdr.page_offset = sizeof(uhdr) + personalities.size() * 4;
  uhdr.page_count = pages.size() + 1;

  // Write the personalities
  u32 *per = (u32 *)(buf.data() + sizeof(uhdr));
  for (Symbol<E> *sym : personalities) {
    assert(sym->got_idx != -1);
    *per++ = sym->get_got_addr(ctx);
  }

  // Write first level pages, LSDA and second level pages
  UnwindFirstLevelPage *page1 = (UnwindFirstLevelPage *)per;
  UnwindLsdaEntry *lsda = (UnwindLsdaEntry *)(page1 + (pages.size() + 1));
  UnwindSecondLevelPage *page2 = (UnwindSecondLevelPage *)(lsda + num_lsda);

  for (std::span<UnwindRecord<E>> span : pages) {
    page1->func_addr = span[0].get_func_raddr(ctx);
    page1->page_offset = (u8 *)page2 - buf.data();
    page1->lsda_offset = (u8 *)lsda - buf.data();

    for (UnwindRecord<E> &rec : span) {
      if (rec.lsda) {
        lsda->func_addr = rec.get_func_raddr(ctx);
        lsda->lsda_addr = rec.lsda->raddr + rec.lsda_offset;
        lsda++;
      }
    }

    std::unordered_map<u32, u32> map;
    for (UnwindRecord<E> &rec : span)
      map.insert({rec.encoding, map.size()});

    page2->kind = UNWIND_SECOND_LEVEL_COMPRESSED;
    page2->page_offset = sizeof(UnwindSecondLevelPage);
    page2->page_count = span.size();

    UnwindPageEntry *entry = (UnwindPageEntry *)(page2 + 1);
    for (UnwindRecord<E> &rec : span) {
      entry->func_addr = rec.get_func_raddr(ctx) - page1->func_addr;
      entry->encoding = map[rec.encoding];
      entry++;
    }

    page2->encoding_offset = (u8 *)entry - (u8 *)page2;
    page2->encoding_count = map.size();

    u32 *encoding = (u32 *)entry;
    for (std::pair<u32, u32> kv : map)
      encoding[kv.second] = kv.first;

    page1++;
    page2 = (UnwindSecondLevelPage *)(encoding + map.size());
    break;
  }

  // Write a terminator
  UnwindRecord<E> &last = records[records.size() - 1];
  page1->func_addr = last.subsec->raddr + last.subsec->input_size + 1;
  page1->page_offset = 0;
  page1->lsda_offset = (u8 *)lsda - buf.data();

  buf.resize((u8 *)page2 - buf.data());
  return buf;
}

template <typename E>
u32 UnwindEncoder<E>::encode_personality(Context<E> &ctx, Symbol<E> *sym) {
  assert(sym);

  for (i64 i = 0; i < personalities.size(); i++)
    if (personalities[i] == sym)
      return (i + 1) << __builtin_ctz(UNWIND_PERSONALITY_MASK);

  if (personalities.size() == 3)
    Fatal(ctx) << ": too many personality functions";

  personalities.push_back(sym);
  return personalities.size() << __builtin_ctz(UNWIND_PERSONALITY_MASK);
}

template <typename E>
std::vector<std::span<UnwindRecord<E>>>
UnwindEncoder<E>::split_records(Context<E> &ctx,
                                std::span<UnwindRecord<E>> records) {
  constexpr i64 max_group_size = 4096;

  sort(records, [&](const UnwindRecord<E> &a, const UnwindRecord<E> &b) {
    return a.get_func_raddr(ctx) < b.get_func_raddr(ctx);
  });

  std::vector<std::span<UnwindRecord<E>>> vec;

  for (i64 i = 0; i < records.size();) {
    i64 j = 1;
    u64 end_addr = records[i].get_func_raddr(ctx) + (1 << 24);
    while (j < max_group_size && i + j < records.size() &&
           records[i + j].get_func_raddr(ctx) < end_addr)
      j++;
    vec.push_back(records.subspan(i, j));
    i += j;
  }
  return vec;
}

template <typename E>
static std::vector<u8> construct_unwind_info(Context<E> &ctx) {
  std::vector<UnwindRecord<E>> records;

  for (std::unique_ptr<OutputSegment<E>> &seg : ctx.segments)
    for (Chunk<E> *chunk : seg->chunks)
      if (chunk->is_regular)
        for (Subsection<E> *subsec : ((OutputSection<E> *)chunk)->members)
          for (UnwindRecord<E> &rec : subsec->get_unwind_records())
            if (!ctx.arg.dead_strip || rec.is_alive)
              records.push_back(rec);

  if (records.empty())
    return {};
  return UnwindEncoder<E>().encode(ctx, records);
}

template <typename E>
void UnwindInfoSection<E>::compute_size(Context<E> &ctx) {
  this->hdr.size = construct_unwind_info(ctx).size();
}

template <typename E>
void UnwindInfoSection<E>::copy_buf(Context<E> &ctx) {
  write_vector(ctx.buf + this->hdr.offset, construct_unwind_info(ctx));
}

template <typename E>
void GotSection<E>::add(Context<E> &ctx, Symbol<E> *sym) {
  assert(sym->got_idx == -1);
  sym->got_idx = syms.size();
  syms.push_back(sym);
  this->hdr.size = syms.size() * E::word_size;
}

template <typename E>
void GotSection<E>::copy_buf(Context<E> &ctx) {
  u64 *buf = (u64 *)(ctx.buf + this->hdr.offset);
  for (i64 i = 0; i < syms.size(); i++)
    if (!syms[i]->file->is_dylib)
      buf[i] = syms[i]->get_addr(ctx);
}

template <typename E>
void LazySymbolPtrSection<E>::copy_buf(Context<E> &ctx) {
  u64 *buf = (u64 *)(ctx.buf + this->hdr.offset);

  for (i64 i = 0; i < ctx.stubs.syms.size(); i++)
    buf[i] = ctx.stub_helper.hdr.addr + E::stub_helper_hdr_size +
             i * E::stub_helper_size;
}

template <typename E>
void ThreadPtrsSection<E>::add(Context<E> &ctx, Symbol<E> *sym) {
  assert(sym->tlv_idx == -1);
  sym->tlv_idx = syms.size();
  syms.push_back(sym);
  this->hdr.size = syms.size() * E::word_size;
}

template <typename E>
void ThreadPtrsSection<E>::copy_buf(Context<E> &ctx) {
  u64 *buf = (u64 *)(ctx.buf + this->hdr.offset);
  for (i64 i = 0; i < syms.size(); i++)
    if (!syms[i]->file->is_dylib)
      buf[i] = syms[i]->get_addr(ctx);
}

#define INSTANTIATE(E)                                  \
  template class OutputSegment<E>;                      \
  template class OutputMachHeader<E>;                   \
  template class OutputSection<E>;                      \
  template class OutputRebaseSection<E>;                \
  template class OutputBindSection<E>;                  \
  template class OutputLazyBindSection<E>;              \
  template class OutputExportSection<E>;                \
  template class OutputFunctionStartsSection<E>;        \
  template class OutputSymtabSection<E>;                \
  template class OutputStrtabSection<E>;                \
  template class OutputIndirectSymtabSection<E>;        \
  template class CodeSignatureSection<E>;               \
  template class DataInCodeSection<E>;                  \
  template class StubsSection<E>;                       \
  template class StubHelperSection<E>;                  \
  template class UnwindEncoder<E>;                      \
  template class UnwindInfoSection<E>;                  \
  template class GotSection<E>;                         \
  template class LazySymbolPtrSection<E>;               \
  template class ThreadPtrsSection<E>

INSTANTIATE(ARM64);
INSTANTIATE(X86_64);

} // namespace mold::macho