--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lld/MachO/UnwindInfoSection.cpp	Tue Jun 08 06:07:14 2021 +0900
@@ -0,0 +1,556 @@
+//===- UnwindInfoSection.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 "UnwindInfoSection.h"
+#include "ConcatOutputSection.h"
+#include "Config.h"
+#include "InputSection.h"
+#include "OutputSection.h"
+#include "OutputSegment.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "SyntheticSections.h"
+#include "Target.h"
+
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/BinaryFormat/MachO.h"
+
+using namespace llvm;
+using namespace llvm::MachO;
+using namespace lld;
+using namespace lld::macho;
+
+#define COMMON_ENCODINGS_MAX 127
+#define COMPACT_ENCODINGS_MAX 256
+
+#define SECOND_LEVEL_PAGE_BYTES 4096
+#define SECOND_LEVEL_PAGE_WORDS (SECOND_LEVEL_PAGE_BYTES / sizeof(uint32_t))
+#define REGULAR_SECOND_LEVEL_ENTRIES_MAX                                       \
+  ((SECOND_LEVEL_PAGE_BYTES -                                                  \
+    sizeof(unwind_info_regular_second_level_page_header)) /                    \
+   sizeof(unwind_info_regular_second_level_entry))
+#define COMPRESSED_SECOND_LEVEL_ENTRIES_MAX                                    \
+  ((SECOND_LEVEL_PAGE_BYTES -                                                  \
+    sizeof(unwind_info_compressed_second_level_page_header)) /                 \
+   sizeof(uint32_t))
+
+#define COMPRESSED_ENTRY_FUNC_OFFSET_BITS 24
+#define COMPRESSED_ENTRY_FUNC_OFFSET_MASK                                      \
+  UNWIND_INFO_COMPRESSED_ENTRY_FUNC_OFFSET(~0)
+
+// Compact Unwind format is a Mach-O evolution of DWARF Unwind that
+// optimizes space and exception-time lookup.  Most DWARF unwind
+// entries can be replaced with Compact Unwind entries, but the ones
+// that cannot are retained in DWARF form.
+//
+// This comment will address macro-level organization of the pre-link
+// and post-link compact unwind tables. For micro-level organization
+// pertaining to the bitfield layout of the 32-bit compact unwind
+// entries, see libunwind/include/mach-o/compact_unwind_encoding.h
+//
+// Important clarifying factoids:
+//
+// * __LD,__compact_unwind is the compact unwind format for compiler
+// output and linker input. It is never a final output. It could be
+// an intermediate output with the `-r` option which retains relocs.
+//
+// * __TEXT,__unwind_info is the compact unwind format for final
+// linker output. It is never an input.
+//
+// * __TEXT,__eh_frame is the DWARF format for both linker input and output.
+//
+// * __TEXT,__unwind_info entries are divided into 4 KiB pages (2nd
+// level) by ascending address, and the pages are referenced by an
+// index (1st level) in the section header.
+//
+// * Following the headers in __TEXT,__unwind_info, the bulk of the
+// section contains a vector of compact unwind entries
+// `{functionOffset, encoding}` sorted by ascending `functionOffset`.
+// Adjacent entries with the same encoding can be folded to great
+// advantage, achieving a 3-order-of-magnitude reduction in the
+// number of entries.
+//
+// * The __TEXT,__unwind_info format can accommodate up to 127 unique
+// encodings for the space-efficient compressed format. In practice,
+// fewer than a dozen unique encodings are used by C++ programs of
+// all sizes. Therefore, we don't even bother implementing the regular
+// non-compressed format. Time will tell if anyone in the field ever
+// overflows the 127-encodings limit.
+//
+// Refer to the definition of unwind_info_section_header in
+// compact_unwind_encoding.h for an overview of the format we are encoding
+// here.
+
+// TODO(gkm): prune __eh_frame entries superseded by __unwind_info, PR50410
+// TODO(gkm): how do we align the 2nd-level pages?
+
+using EncodingMap = llvm::DenseMap<compact_unwind_encoding_t, size_t>;
+
+struct SecondLevelPage {
+  uint32_t kind;
+  size_t entryIndex;
+  size_t entryCount;
+  size_t byteCount;
+  std::vector<compact_unwind_encoding_t> localEncodings;
+  EncodingMap localEncodingIndexes;
+};
+
+template <class Ptr> class UnwindInfoSectionImpl : public UnwindInfoSection {
+public:
+  void prepareRelocations(InputSection *) override;
+  void finalize() override;
+  void writeTo(uint8_t *buf) const override;
+
+private:
+  std::vector<std::pair<compact_unwind_encoding_t, size_t>> commonEncodings;
+  EncodingMap commonEncodingIndexes;
+  // Indices of personality functions within the GOT.
+  std::vector<uint32_t> personalities;
+  SmallDenseMap<std::pair<InputSection *, uint64_t /* addend */>, Symbol *>
+      personalityTable;
+  std::vector<unwind_info_section_header_lsda_index_entry> lsdaEntries;
+  // Map of function offset (from the image base) to an index within the LSDA
+  // array.
+  llvm::DenseMap<uint32_t, uint32_t> functionToLsdaIndex;
+  std::vector<CompactUnwindEntry<Ptr>> cuVector;
+  std::vector<CompactUnwindEntry<Ptr> *> cuPtrVector;
+  std::vector<SecondLevelPage> secondLevelPages;
+  uint64_t level2PagesOffset = 0;
+};
+
+// Compact unwind relocations have different semantics, so we handle them in a
+// separate code path from regular relocations. First, we do not wish to add
+// rebase opcodes for __LD,__compact_unwind, because that section doesn't
+// actually end up in the final binary. Second, personality pointers always
+// reside in the GOT and must be treated specially.
+template <class Ptr>
+void UnwindInfoSectionImpl<Ptr>::prepareRelocations(InputSection *isec) {
+  assert(isec->segname == segment_names::ld &&
+         isec->name == section_names::compactUnwind);
+  assert(!isec->shouldOmitFromOutput() &&
+         "__compact_unwind section should not be omitted");
+
+  // FIXME: This could skip relocations for CompactUnwindEntries that
+  // point to dead-stripped functions. That might save some amount of
+  // work. But since there are usually just few personality functions
+  // that are referenced from many places, at least some of them likely
+  // live, it wouldn't reduce number of got entries.
+  for (Reloc &r : isec->relocs) {
+    assert(target->hasAttr(r.type, RelocAttrBits::UNSIGNED));
+    if (r.offset % sizeof(CompactUnwindEntry<Ptr>) !=
+        offsetof(CompactUnwindEntry<Ptr>, personality))
+      continue;
+
+    if (auto *s = r.referent.dyn_cast<Symbol *>()) {
+      if (auto *undefined = dyn_cast<Undefined>(s)) {
+        treatUndefinedSymbol(*undefined);
+        // treatUndefinedSymbol() can replace s with a DylibSymbol; re-check.
+        if (isa<Undefined>(s))
+          continue;
+      }
+      if (auto *defined = dyn_cast<Defined>(s)) {
+        // Check if we have created a synthetic symbol at the same address.
+        Symbol *&personality =
+            personalityTable[{defined->isec, defined->value}];
+        if (personality == nullptr) {
+          personality = defined;
+          in.got->addEntry(defined);
+        } else if (personality != defined) {
+          r.referent = personality;
+        }
+        continue;
+      }
+      assert(isa<DylibSymbol>(s));
+      in.got->addEntry(s);
+      continue;
+    }
+
+    if (auto *referentIsec = r.referent.dyn_cast<InputSection *>()) {
+      assert(!referentIsec->isCoalescedWeak());
+
+      // Personality functions can be referenced via section relocations
+      // if they live in the same object file. Create placeholder synthetic
+      // symbols for them in the GOT.
+      Symbol *&s = personalityTable[{referentIsec, r.addend}];
+      if (s == nullptr) {
+        // This runs after dead stripping, so the noDeadStrip argument does not
+        // matter.
+        s = make<Defined>("<internal>", /*file=*/nullptr, referentIsec,
+                          r.addend, /*size=*/0, /*isWeakDef=*/false,
+                          /*isExternal=*/false, /*isPrivateExtern=*/false,
+                          /*isThumb=*/false, /*isReferencedDynamically=*/false,
+                          /*noDeadStrip=*/false);
+        in.got->addEntry(s);
+      }
+      r.referent = s;
+      r.addend = 0;
+    }
+  }
+}
+
+// Unwind info lives in __DATA, and finalization of __TEXT will occur before
+// finalization of __DATA. Moreover, the finalization of unwind info depends on
+// the exact addresses that it references. So it is safe for compact unwind to
+// reference addresses in __TEXT, but not addresses in any other segment.
+static void checkTextSegment(InputSection *isec) {
+  if (isec->segname != segment_names::text)
+    error("compact unwind references address in " + toString(isec) +
+          " which is not in segment __TEXT");
+}
+
+// We need to apply the relocations to the pre-link compact unwind section
+// before converting it to post-link form. There should only be absolute
+// relocations here: since we are not emitting the pre-link CU section, there
+// is no source address to make a relative location meaningful.
+template <class Ptr>
+static void
+relocateCompactUnwind(ConcatOutputSection *compactUnwindSection,
+                      std::vector<CompactUnwindEntry<Ptr>> &cuVector) {
+  for (const InputSection *isec : compactUnwindSection->inputs) {
+    assert(isec->parent == compactUnwindSection);
+
+    uint8_t *buf =
+        reinterpret_cast<uint8_t *>(cuVector.data()) + isec->outSecFileOff;
+    memcpy(buf, isec->data.data(), isec->data.size());
+
+    for (const Reloc &r : isec->relocs) {
+      uint64_t referentVA = 0;
+      if (auto *referentSym = r.referent.dyn_cast<Symbol *>()) {
+        if (!isa<Undefined>(referentSym)) {
+          assert(referentSym->isInGot());
+          if (auto *defined = dyn_cast<Defined>(referentSym))
+            checkTextSegment(defined->isec);
+          // At this point in the link, we may not yet know the final address of
+          // the GOT, so we just encode the index. We make it a 1-based index so
+          // that we can distinguish the null pointer case.
+          referentVA = referentSym->gotIndex + 1;
+        }
+      } else if (auto *referentIsec = r.referent.dyn_cast<InputSection *>()) {
+        checkTextSegment(referentIsec);
+        if (referentIsec->shouldOmitFromOutput())
+          referentVA = UINT64_MAX; // Tombstone value
+        else
+          referentVA = referentIsec->getVA() + r.addend;
+      }
+
+      writeAddress(buf + r.offset, referentVA, r.length);
+    }
+  }
+}
+
+// There should only be a handful of unique personality pointers, so we can
+// encode them as 2-bit indices into a small array.
+template <class Ptr>
+void encodePersonalities(
+    const std::vector<CompactUnwindEntry<Ptr> *> &cuPtrVector,
+    std::vector<uint32_t> &personalities) {
+  for (CompactUnwindEntry<Ptr> *cu : cuPtrVector) {
+    if (cu->personality == 0)
+      continue;
+    // Linear search is fast enough for a small array.
+    auto it = find(personalities, cu->personality);
+    uint32_t personalityIndex; // 1-based index
+    if (it != personalities.end()) {
+      personalityIndex = std::distance(personalities.begin(), it) + 1;
+    } else {
+      personalities.push_back(cu->personality);
+      personalityIndex = personalities.size();
+    }
+    cu->encoding |=
+        personalityIndex << countTrailingZeros(
+            static_cast<compact_unwind_encoding_t>(UNWIND_PERSONALITY_MASK));
+  }
+  if (personalities.size() > 3)
+    error("too many personalities (" + std::to_string(personalities.size()) +
+          ") for compact unwind to encode");
+}
+
+// Scan the __LD,__compact_unwind entries and compute the space needs of
+// __TEXT,__unwind_info and __TEXT,__eh_frame
+template <class Ptr> void UnwindInfoSectionImpl<Ptr>::finalize() {
+  if (compactUnwindSection == nullptr)
+    return;
+
+  // At this point, the address space for __TEXT,__text has been
+  // assigned, so we can relocate the __LD,__compact_unwind entries
+  // into a temporary buffer. Relocation is necessary in order to sort
+  // the CU entries by function address. Sorting is necessary so that
+  // we can fold adjacent CU entries with identical
+  // encoding+personality+lsda. Folding is necessary because it reduces
+  // the number of CU entries by as much as 3 orders of magnitude!
+  compactUnwindSection->finalize();
+  assert(compactUnwindSection->getSize() % sizeof(CompactUnwindEntry<Ptr>) ==
+         0);
+  size_t cuCount =
+      compactUnwindSection->getSize() / sizeof(CompactUnwindEntry<Ptr>);
+  cuVector.resize(cuCount);
+  relocateCompactUnwind(compactUnwindSection, cuVector);
+
+  // Rather than sort & fold the 32-byte entries directly, we create a
+  // vector of pointers to entries and sort & fold that instead.
+  cuPtrVector.reserve(cuCount);
+  for (CompactUnwindEntry<Ptr> &cuEntry : cuVector)
+    cuPtrVector.emplace_back(&cuEntry);
+  llvm::sort(cuPtrVector, [](const CompactUnwindEntry<Ptr> *a,
+                             const CompactUnwindEntry<Ptr> *b) {
+    return a->functionAddress < b->functionAddress;
+  });
+
+  // Dead-stripped functions get a functionAddress of UINT64_MAX in
+  // relocateCompactUnwind(). Filter them out here.
+  // FIXME: This doesn't yet collect associated data like LSDAs kept
+  // alive only by a now-removed CompactUnwindEntry or other comdat-like
+  // data (`kindNoneGroupSubordinate*` in ld64).
+  CompactUnwindEntry<Ptr> tombstone;
+  tombstone.functionAddress = static_cast<Ptr>(UINT64_MAX);
+  cuPtrVector.erase(
+      std::lower_bound(cuPtrVector.begin(), cuPtrVector.end(), &tombstone,
+                       [](const CompactUnwindEntry<Ptr> *a,
+                          const CompactUnwindEntry<Ptr> *b) {
+                         return a->functionAddress < b->functionAddress;
+                       }),
+      cuPtrVector.end());
+
+  // Fold adjacent entries with matching encoding+personality+lsda
+  // We use three iterators on the same cuPtrVector to fold in-situ:
+  // (1) `foldBegin` is the first of a potential sequence of matching entries
+  // (2) `foldEnd` is the first non-matching entry after `foldBegin`.
+  // The semi-open interval [ foldBegin .. foldEnd ) contains a range
+  // entries that can be folded into a single entry and written to ...
+  // (3) `foldWrite`
+  auto foldWrite = cuPtrVector.begin();
+  for (auto foldBegin = cuPtrVector.begin(); foldBegin < cuPtrVector.end();) {
+    auto foldEnd = foldBegin;
+    while (++foldEnd < cuPtrVector.end() &&
+           (*foldBegin)->encoding == (*foldEnd)->encoding &&
+           (*foldBegin)->personality == (*foldEnd)->personality &&
+           (*foldBegin)->lsda == (*foldEnd)->lsda)
+      ;
+    *foldWrite++ = *foldBegin;
+    foldBegin = foldEnd;
+  }
+  cuPtrVector.erase(foldWrite, cuPtrVector.end());
+
+  encodePersonalities(cuPtrVector, personalities);
+
+  // Count frequencies of the folded encodings
+  EncodingMap encodingFrequencies;
+  for (const CompactUnwindEntry<Ptr> *cuPtrEntry : cuPtrVector)
+    encodingFrequencies[cuPtrEntry->encoding]++;
+
+  // Make a vector of encodings, sorted by descending frequency
+  for (const auto &frequency : encodingFrequencies)
+    commonEncodings.emplace_back(frequency);
+  llvm::sort(commonEncodings,
+             [](const std::pair<compact_unwind_encoding_t, size_t> &a,
+                const std::pair<compact_unwind_encoding_t, size_t> &b) {
+               if (a.second == b.second)
+                 // When frequencies match, secondarily sort on encoding
+                 // to maintain parity with validate-unwind-info.py
+                 return a.first > b.first;
+               return a.second > b.second;
+             });
+
+  // Truncate the vector to 127 elements.
+  // Common encoding indexes are limited to 0..126, while encoding
+  // indexes 127..255 are local to each second-level page
+  if (commonEncodings.size() > COMMON_ENCODINGS_MAX)
+    commonEncodings.resize(COMMON_ENCODINGS_MAX);
+
+  // Create a map from encoding to common-encoding-table index
+  for (size_t i = 0; i < commonEncodings.size(); i++)
+    commonEncodingIndexes[commonEncodings[i].first] = i;
+
+  // Split folded encodings into pages, where each page is limited by ...
+  // (a) 4 KiB capacity
+  // (b) 24-bit difference between first & final function address
+  // (c) 8-bit compact-encoding-table index,
+  //     for which 0..126 references the global common-encodings table,
+  //     and 127..255 references a local per-second-level-page table.
+  // First we try the compact format and determine how many entries fit.
+  // If more entries fit in the regular format, we use that.
+  for (size_t i = 0; i < cuPtrVector.size();) {
+    secondLevelPages.emplace_back();
+    SecondLevelPage &page = secondLevelPages.back();
+    page.entryIndex = i;
+    uintptr_t functionAddressMax =
+        cuPtrVector[i]->functionAddress + COMPRESSED_ENTRY_FUNC_OFFSET_MASK;
+    size_t n = commonEncodings.size();
+    size_t wordsRemaining =
+        SECOND_LEVEL_PAGE_WORDS -
+        sizeof(unwind_info_compressed_second_level_page_header) /
+            sizeof(uint32_t);
+    while (wordsRemaining >= 1 && i < cuPtrVector.size()) {
+      const CompactUnwindEntry<Ptr> *cuPtr = cuPtrVector[i];
+      if (cuPtr->functionAddress >= functionAddressMax) {
+        break;
+      } else if (commonEncodingIndexes.count(cuPtr->encoding) ||
+                 page.localEncodingIndexes.count(cuPtr->encoding)) {
+        i++;
+        wordsRemaining--;
+      } else if (wordsRemaining >= 2 && n < COMPACT_ENCODINGS_MAX) {
+        page.localEncodings.emplace_back(cuPtr->encoding);
+        page.localEncodingIndexes[cuPtr->encoding] = n++;
+        i++;
+        wordsRemaining -= 2;
+      } else {
+        break;
+      }
+    }
+    page.entryCount = i - page.entryIndex;
+
+    // If this is not the final page, see if it's possible to fit more
+    // entries by using the regular format. This can happen when there
+    // are many unique encodings, and we we saturated the local
+    // encoding table early.
+    if (i < cuPtrVector.size() &&
+        page.entryCount < REGULAR_SECOND_LEVEL_ENTRIES_MAX) {
+      page.kind = UNWIND_SECOND_LEVEL_REGULAR;
+      page.entryCount = std::min(REGULAR_SECOND_LEVEL_ENTRIES_MAX,
+                                 cuPtrVector.size() - page.entryIndex);
+      i = page.entryIndex + page.entryCount;
+    } else {
+      page.kind = UNWIND_SECOND_LEVEL_COMPRESSED;
+    }
+  }
+
+  for (const CompactUnwindEntry<Ptr> *cu : cuPtrVector) {
+    uint32_t functionOffset = cu->functionAddress - in.header->addr;
+    functionToLsdaIndex[functionOffset] = lsdaEntries.size();
+    if (cu->lsda != 0)
+      lsdaEntries.push_back(
+          {functionOffset, static_cast<uint32_t>(cu->lsda - in.header->addr)});
+  }
+
+  // compute size of __TEXT,__unwind_info section
+  level2PagesOffset =
+      sizeof(unwind_info_section_header) +
+      commonEncodings.size() * sizeof(uint32_t) +
+      personalities.size() * sizeof(uint32_t) +
+      // The extra second-level-page entry is for the sentinel
+      (secondLevelPages.size() + 1) *
+          sizeof(unwind_info_section_header_index_entry) +
+      lsdaEntries.size() * sizeof(unwind_info_section_header_lsda_index_entry);
+  unwindInfoSize =
+      level2PagesOffset + secondLevelPages.size() * SECOND_LEVEL_PAGE_BYTES;
+}
+
+// All inputs are relocated and output addresses are known, so write!
+
+template <class Ptr>
+void UnwindInfoSectionImpl<Ptr>::writeTo(uint8_t *buf) const {
+  // section header
+  auto *uip = reinterpret_cast<unwind_info_section_header *>(buf);
+  uip->version = 1;
+  uip->commonEncodingsArraySectionOffset = sizeof(unwind_info_section_header);
+  uip->commonEncodingsArrayCount = commonEncodings.size();
+  uip->personalityArraySectionOffset =
+      uip->commonEncodingsArraySectionOffset +
+      (uip->commonEncodingsArrayCount * sizeof(uint32_t));
+  uip->personalityArrayCount = personalities.size();
+  uip->indexSectionOffset = uip->personalityArraySectionOffset +
+                            (uip->personalityArrayCount * sizeof(uint32_t));
+  uip->indexCount = secondLevelPages.size() + 1;
+
+  // Common encodings
+  auto *i32p = reinterpret_cast<uint32_t *>(&uip[1]);
+  for (const auto &encoding : commonEncodings)
+    *i32p++ = encoding.first;
+
+  // Personalities
+  for (const uint32_t &personality : personalities)
+    *i32p++ =
+        in.got->addr + (personality - 1) * target->wordSize - in.header->addr;
+
+  // Level-1 index
+  uint32_t lsdaOffset =
+      uip->indexSectionOffset +
+      uip->indexCount * sizeof(unwind_info_section_header_index_entry);
+  uint64_t l2PagesOffset = level2PagesOffset;
+  auto *iep = reinterpret_cast<unwind_info_section_header_index_entry *>(i32p);
+  for (const SecondLevelPage &page : secondLevelPages) {
+    iep->functionOffset =
+        cuPtrVector[page.entryIndex]->functionAddress - in.header->addr;
+    iep->secondLevelPagesSectionOffset = l2PagesOffset;
+    iep->lsdaIndexArraySectionOffset =
+        lsdaOffset + functionToLsdaIndex.lookup(iep->functionOffset) *
+                         sizeof(unwind_info_section_header_lsda_index_entry);
+    iep++;
+    l2PagesOffset += SECOND_LEVEL_PAGE_BYTES;
+  }
+  // Level-1 sentinel
+  const CompactUnwindEntry<Ptr> &cuEnd = cuVector.back();
+  iep->functionOffset = cuEnd.functionAddress + cuEnd.functionLength;
+  iep->secondLevelPagesSectionOffset = 0;
+  iep->lsdaIndexArraySectionOffset =
+      lsdaOffset +
+      lsdaEntries.size() * sizeof(unwind_info_section_header_lsda_index_entry);
+  iep++;
+
+  // LSDAs
+  size_t lsdaBytes =
+      lsdaEntries.size() * sizeof(unwind_info_section_header_lsda_index_entry);
+  if (lsdaBytes > 0)
+    memcpy(iep, lsdaEntries.data(), lsdaBytes);
+
+  // Level-2 pages
+  auto *pp = reinterpret_cast<uint32_t *>(reinterpret_cast<uint8_t *>(iep) +
+                                          lsdaBytes);
+  for (const SecondLevelPage &page : secondLevelPages) {
+    if (page.kind == UNWIND_SECOND_LEVEL_COMPRESSED) {
+      uintptr_t functionAddressBase =
+          cuPtrVector[page.entryIndex]->functionAddress;
+      auto *p2p =
+          reinterpret_cast<unwind_info_compressed_second_level_page_header *>(
+              pp);
+      p2p->kind = page.kind;
+      p2p->entryPageOffset =
+          sizeof(unwind_info_compressed_second_level_page_header);
+      p2p->entryCount = page.entryCount;
+      p2p->encodingsPageOffset =
+          p2p->entryPageOffset + p2p->entryCount * sizeof(uint32_t);
+      p2p->encodingsCount = page.localEncodings.size();
+      auto *ep = reinterpret_cast<uint32_t *>(&p2p[1]);
+      for (size_t i = 0; i < page.entryCount; i++) {
+        const CompactUnwindEntry<Ptr> *cuep = cuPtrVector[page.entryIndex + i];
+        auto it = commonEncodingIndexes.find(cuep->encoding);
+        if (it == commonEncodingIndexes.end())
+          it = page.localEncodingIndexes.find(cuep->encoding);
+        *ep++ = (it->second << COMPRESSED_ENTRY_FUNC_OFFSET_BITS) |
+                (cuep->functionAddress - functionAddressBase);
+      }
+      if (page.localEncodings.size() != 0)
+        memcpy(ep, page.localEncodings.data(),
+               page.localEncodings.size() * sizeof(uint32_t));
+    } else {
+      auto *p2p =
+          reinterpret_cast<unwind_info_regular_second_level_page_header *>(pp);
+      p2p->kind = page.kind;
+      p2p->entryPageOffset =
+          sizeof(unwind_info_regular_second_level_page_header);
+      p2p->entryCount = page.entryCount;
+      auto *ep = reinterpret_cast<uint32_t *>(&p2p[1]);
+      for (size_t i = 0; i < page.entryCount; i++) {
+        const CompactUnwindEntry<Ptr> *cuep = cuPtrVector[page.entryIndex + i];
+        *ep++ = cuep->functionAddress;
+        *ep++ = cuep->encoding;
+      }
+    }
+    pp += SECOND_LEVEL_PAGE_WORDS;
+  }
+}
+
+UnwindInfoSection *macho::makeUnwindInfoSection() {
+  if (target->wordSize == 8)
+    return make<UnwindInfoSectionImpl<uint64_t>>();
+  else
+    return make<UnwindInfoSectionImpl<uint32_t>>();
+}