Add support for chained fixup load commands to MachOObjectFile

[aprantl]

Summary

This is part of a series of patches to upstream support for Mach-O chained fixups.

This patch adds support for parsing the chained fixup load command and parsing the chained fixups header. It also puts into place the abstract interface that will be used to iterate over the fixups.

[rastogishubham]

llvm/include/llvm/BinaryFormat/MachO.h

1009

Minor issue, but you have a typo in your comment here

[aprantl]

Rebased & fixed typo

[JDevlieghere]

llvm/lib/Object/MachOObjectFile.cpp

3257–3270

Could this be a static factory method that returns an Expected<MachOChainedFixupEntry>?

4306–4310

If Start fails but Finish succeeds, won't this trigger the unchecked Error assert?

[aprantl]

Rebased.

llvm/lib/Object/MachOObjectFile.cpp

3257–3270

Definitely, but I'm trying hard to minimize differences with the downstream code as much as possible. I'm more than happy to refactor the code at the end of patch series though!

4306–4310

Good question! No. Finish is initialized with Parse=false and thus will not overwrite Err. This pattern is used all over the file.

[kstoimenov]

llvm/include/llvm/Object/MachO.h

378

It looks like this change in breaking the sanitizer Android build: https://lab.llvm.org/buildbot/#/builders/77/builds/14698. Could you please fix that?

[abrachet]

We're also seeing build failures https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-linux-x64/b8821495090978835697/overview

llvm/lib/Object/MachOObjectFile.cpp

3258

Error here

error: member initializer 'Kind' does not name a non-static data member or base class
    : MachOAbstractFixupEntry(E, O), Kind(Kind)

llvm/include/llvm/BinaryFormat/MachO.h

enum BindType {
   BIND_TYPE_POINTER = 1u,
   BIND_TYPE_TEXT_ABSOLUTE32 = 2u,
   BIND_TYPE_TEXT_PCREL32 = 3u
 };
 
 enum BindSpecialDylib {
   BIND_SPECIAL_DYLIB_SELF = 0,
   BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE = -1,
-  BIND_SPECIAL_DYLIB_FLAT_LOOKUP = -2
+  BIND_SPECIAL_DYLIB_FLAT_LOOKUP = -2,
+  BIND_SPECIAL_DYLIB_WEAK_LOOKUP = -3
 };
 
 enum {
   BIND_SYMBOL_FLAGS_WEAK_IMPORT = 0x1u,
   BIND_SYMBOL_FLAGS_NON_WEAK_DEFINITION = 0x8u,
 
   BIND_OPCODE_MASK = 0xF0u,
   BIND_IMMEDIATE_MASK = 0x0Fu

 struct nlist_64 {
   uint32_t n_strx;
   uint8_t n_type;
   uint8_t n_sect;
   uint16_t n_desc;
   uint64_t n_value;
 };
 
+/// Structs for dyld chained fixups.
+/// dyld_chained_fixups_header is the data pointed to by LC_DYLD_CHAINED_FIXUPS
+/// load command.
+struct dyld_chained_fixups_header {
+  uint32_t fixups_version; ///< 0
+  uint32_t starts_offset;  ///< Ooffset of dyld_chained_starts_in_image.
+  uint32_t imports_offset; ///< Offset of imports table in chain_data.
+  uint32_t symbols_offset; ///< Offset of symbol strings in chain_data.
+  uint32_t imports_count;  ///< Number of imported symbol names.
+  uint32_t imports_format; ///< DYLD_CHAINED_IMPORT*
+  uint32_t symbols_format; ///< 0 => uncompressed, 1 => zlib compressed
+};
+
 // Byte order swapping functions for MachO structs
 
 inline void swapStruct(fat_header &mh) {
   sys::swapByteOrder(mh.magic);
   sys::swapByteOrder(mh.nfat_arch);
 }
 
 inline void swapStruct(fat_arch &mh) {

 #define LOAD_COMMAND_STRUCT(LCStruct) LCStruct LCStruct##_data;
 
 LLVM_PACKED_START
 union alignas(4) macho_load_command {
 #include "llvm/BinaryFormat/MachO.def"
 };
 LLVM_PACKED_END
 
+inline void swapStruct(dyld_chained_fixups_header &C) {
+  sys::swapByteOrder(C.fixups_version);
+  sys::swapByteOrder(C.starts_offset);
+  sys::swapByteOrder(C.imports_offset);
+  sys::swapByteOrder(C.symbols_offset);
+  sys::swapByteOrder(C.imports_count);
+  sys::swapByteOrder(C.imports_format);
+  sys::swapByteOrder(C.symbols_format);
+}
+
 /* code signing attributes of a process */
 
 enum CodeSignAttrs {
   CS_VALID = 0x00000001,          /* dynamically valid */
   CS_ADHOC = 0x00000002,          /* ad hoc signed */
   CS_GET_TASK_ALLOW = 0x00000004, /* has get-task-allow entitlement */
   CS_INSTALLER = 0x00000008,      /* has installer entitlement */
 

llvm/include/llvm/Object/MachO.h

private:
   uint64_t AdvanceAmount = 0;
   uint8_t  BindType = 0;
   uint8_t  PointerSize;
   Kind     TableKind;
   bool     Done = false;
 };
 using bind_iterator = content_iterator<MachOBindEntry>;
 
+/// ChainedFixupTarget holds all the information about an external symbol
+/// necessary to bind this binary to that symbol. These values are referenced
+/// indirectly by chained fixup binds. This structure captures values from all
+/// import and symbol formats.
+///
+/// Be aware there are two notions of weak here:
+///   WeakImport == true
+///     The associated bind may be set to 0 if this symbol is missing from its
+///     parent library. This is called a "weak import."
+///   LibOrdinal == BIND_SPECIAL_DYLIB_WEAK_LOOKUP
+///     This symbol may be coalesced with other libraries vending the same
+///     symbol. E.g., C++'s "operator new". This is called a "weak bind."
+struct ChainedFixupTarget {
+public:
+  ChainedFixupTarget(int LibOrdinal, StringRef Symbol, uint64_t Addend,
+                     bool WeakImport)
+      : LibOrdinal(LibOrdinal), SymbolName(Symbol), Addend(Addend),
+        WeakImport(WeakImport) {}
+
+  int libOrdinal() { return LibOrdinal; }
+  StringRef symbolName() { return SymbolName; }
+  uint64_t addend() { return Addend; }
+  bool weakImport() { return WeakImport; }
+  bool weakBind() {
+    return LibOrdinal == MachO::BIND_SPECIAL_DYLIB_WEAK_LOOKUP;
+  }
+
+private:
+  int LibOrdinal;
+  StringRef SymbolName;
+  uint64_t Addend;
+  bool WeakImport;
+};
+
+/// MachOAbstractFixupEntry is an abstract class representing a fixup in a
+/// MH_DYLDLINK file. Fixups generally represent rebases and binds. Binds also
+/// subdivide into additional subtypes (weak, lazy, reexport).
+///
+/// The two concrete subclasses of MachOAbstractFixupEntry are:
+///
+///   MachORebaseBindEntry   - for dyld opcode-based tables, including threaded-
+///                            rebase, where rebases are mixed in with other
+///                            bind opcodes.
+///   MachOChainedFixupEntry - for pointer chains embedded in data pages.
+class MachOAbstractFixupEntry {
+public:
+  MachOAbstractFixupEntry(Error *Err, const MachOObjectFile *O);
+
+  int32_t segmentIndex() const;
+  uint64_t segmentOffset() const;
+  uint64_t segmentAddress() const;
+  StringRef segmentName() const;
+  StringRef sectionName() const;
+  StringRef typeName() const;
+  StringRef symbolName() const;
+  uint32_t flags() const;
+  int64_t addend() const;
+  int ordinal() const;
+
+  /// \return the location of this fixup as a VM Address. For the VM
+  /// Address this fixup is pointing to, use pointerValue().
+  uint64_t address() const;
+
+  /// \return the VM Address pointed to by this fixup. Use
+  /// pointerValue() to compare against other VM Addresses, such as
+  /// section addresses or segment vmaddrs.
+  uint64_t pointerValue() const { return PointerValue; }
+
+  /// \return the raw "on-disk" representation of the fixup. For
+  /// Threaded rebases and Chained pointers these values are generally
+  /// encoded into various different pointer formats. This value is
+  /// exposed in API for tools that want to display and annotate the
+  /// raw bits.
+  uint64_t rawValue() const { return RawValue; }
+
+  void moveNext();
+
+protected:
+  Error *E;
+  const MachOObjectFile *O;
+  uint64_t SegmentOffset = 0;
+  int32_t SegmentIndex = -1;
+  StringRef SymbolName;
+  int32_t Ordinal = 0;
+  uint32_t Flags = 0;
+  int64_t Addend = 0;
+  uint64_t PointerValue = 0;
+  uint64_t RawValue = 0;
+  bool Done = false;
+
+  void moveToFirst();
+  void moveToEnd();
+
+  /// \return the vm address of the start of __TEXT segment.
+  uint64_t textAddress() const { return TextAddress; }
+
+private:
+  uint64_t TextAddress;
+};
+
+class MachOChainedFixupEntry : public MachOAbstractFixupEntry {
+public:
+  enum class FixupKind { All, Bind, WeakBind, Rebase };
+
+  MachOChainedFixupEntry(Error *Err, const MachOObjectFile *O, FixupKind Kind,
+                         bool Parse);
+
+  bool operator==(const MachOChainedFixupEntry &) const;
+
+  void moveNext();
+  void moveToFirst();
+  void moveToEnd();
+
+private:
+  std::vector<ChainedFixupTarget> FixupTargets;
+  uint32_t FixupIndex = 0;
+  FixupKind Kind;
+};
+using fixup_iterator = content_iterator<MachOChainedFixupEntry>;
+
 class MachOObjectFile : public ObjectFile {
 public:
   struct LoadCommandInfo {
     const char *Ptr;      // Where in memory the load command is.
     MachO::load_command C; // The command itself.
   };
   using LoadCommandList = SmallVector<LoadCommandInfo, 4>;
   using load_command_iterator = LoadCommandList::const_iterator;
public:
   static iterator_range<rebase_iterator> rebaseTable(Error &Err,
                                                      MachOObjectFile *O,
                                                      ArrayRef<uint8_t> Opcodes,
                                                      bool is64);
 
   /// For use iterating over all bind table entries.
   iterator_range<bind_iterator> bindTable(Error &Err);
 
+  /// For iterating over all chained fixups.
+  iterator_range<fixup_iterator>
+  fixupTable(Error &Err, MachOChainedFixupEntry::FixupKind Kind);
+
   /// For use iterating over all lazy bind table entries.
   iterator_range<bind_iterator> lazyBindTable(Error &Err);
 
   /// For use iterating over all weak bind table entries.
   iterator_range<bind_iterator> weakBindTable(Error &Err);
 
   /// For use examining bind opcodes in a MachOObjectFile.
   static iterator_range<bind_iterator> bindTable(Error &Err,
public:
   MachO::symtab_command getSymtabLoadCommand() const;
   MachO::dysymtab_command getDysymtabLoadCommand() const;
   MachO::linkedit_data_command getDataInCodeLoadCommand() const;
   MachO::linkedit_data_command getLinkOptHintsLoadCommand() const;
   ArrayRef<uint8_t> getDyldInfoRebaseOpcodes() const;
   ArrayRef<uint8_t> getDyldInfoBindOpcodes() const;
   ArrayRef<uint8_t> getDyldInfoWeakBindOpcodes() const;
   ArrayRef<uint8_t> getDyldInfoLazyBindOpcodes() const;
+  Expected<std::vector<ChainedFixupTarget>> getDyldChainedFixupTargets() const;
   ArrayRef<uint8_t> getDyldInfoExportsTrie() const;
   ArrayRef<uint8_t> getUuid() const;
 
   StringRef getStringTableData() const;
   bool is64Bit() const;
   void ReadULEB128s(uint64_t Index, SmallVectorImpl<uint64_t> &Out) const;
 
   static StringRef guessLibraryShortName(StringRef Name, bool &isFramework,
private:
   BuildToolList BuildTools;
   mutable LibraryShortName LibrariesShortNames;
   std::unique_ptr<BindRebaseSegInfo> BindRebaseSectionTable;
   const char *SymtabLoadCmd = nullptr;
   const char *DysymtabLoadCmd = nullptr;
   const char *DataInCodeLoadCmd = nullptr;
   const char *LinkOptHintsLoadCmd = nullptr;
   const char *DyldInfoLoadCmd = nullptr;
+  const char *DyldChainedFixupsLoadCmd = nullptr;
   const char *UuidLoadCmd = nullptr;
   bool HasPageZeroSegment = false;
 };
 
 /// DiceRef
 inline DiceRef::DiceRef(DataRefImpl DiceP, const ObjectFile *Owner)
   : DicePimpl(DiceP) , OwningObject(Owner) {}
 

llvm/lib/Object/MachOObjectFile.cpp

for (unsigned I = 0; I < LoadCommandCount; ++I) {
     } else if (Load.C.cmd == MachO::LC_DYLD_INFO) {
       if ((Err = checkDyldInfoCommand(*this, Load, I, &DyldInfoLoadCmd,
                                       "LC_DYLD_INFO", Elements)))
         return;
     } else if (Load.C.cmd == MachO::LC_DYLD_INFO_ONLY) {
       if ((Err = checkDyldInfoCommand(*this, Load, I, &DyldInfoLoadCmd,
                                       "LC_DYLD_INFO_ONLY", Elements)))
         return;
+    } else if (Load.C.cmd == MachO::LC_DYLD_CHAINED_FIXUPS) {
+      if ((Err = checkLinkeditDataCommand(*this, Load, I,
+                                          &DyldChainedFixupsLoadCmd,
+                                          "LC_DYLD_CHAINED_FIXUPS", Elements,
+                                          "chained fixups")))
+        return;
     } else if (Load.C.cmd == MachO::LC_UUID) {
       if (Load.C.cmdsize != sizeof(MachO::uuid_command)) {
         Err = malformedError("LC_UUID command " + Twine(I) + " has incorrect "
                              "cmdsize");
         return;
       }
       if (UuidLoadCmd) {
         Err = malformedError("more than one LC_UUID command");
MachOObjectFile::exports(Error &E, ArrayRef<uint8_t> Trie,
 
   return make_range(export_iterator(Start), export_iterator(Finish));
 }
 
 iterator_range<export_iterator> MachOObjectFile::exports(Error &Err) const {
   return exports(Err, getDyldInfoExportsTrie(), this);
 }
 
+MachOAbstractFixupEntry::MachOAbstractFixupEntry(Error *E,
+                                                 const MachOObjectFile *O)
+  : E(E), O(O) {
+    // Cache the vmaddress of __TEXT
+    for (const auto &Command : O->load_commands()) {
+      if (Command.C.cmd == MachO::LC_SEGMENT) {
+        MachO::segment_command SLC = O->getSegmentLoadCommand(Command);
+        if (StringRef(SLC.segname) == StringRef("__TEXT")) {
+          TextAddress = SLC.vmaddr;
+          break;
+        }
+      } else if (Command.C.cmd == MachO::LC_SEGMENT_64) {
+        MachO::segment_command_64 SLC_64 = O->getSegment64LoadCommand(Command);
+        if (StringRef(SLC_64.segname) == StringRef("__TEXT")) {
+          TextAddress = SLC_64.vmaddr;
+          break;
+        }
+      }
+    }
+  }
+
+int32_t MachOAbstractFixupEntry::segmentIndex() const { return SegmentIndex; }
+
+uint64_t MachOAbstractFixupEntry::segmentOffset() const { return SegmentOffset; }
+
+uint64_t MachOAbstractFixupEntry::segmentAddress() const {
+  return O->BindRebaseAddress(SegmentIndex, 0);
+}
+
+StringRef MachOAbstractFixupEntry::segmentName() const {
+  return O->BindRebaseSegmentName(SegmentIndex);
+}
+
+StringRef MachOAbstractFixupEntry::sectionName() const {
+  return O->BindRebaseSectionName(SegmentIndex, SegmentOffset);
+}
+
+uint64_t MachOAbstractFixupEntry::address() const {
+  return O->BindRebaseAddress(SegmentIndex, SegmentOffset);
+}
+
+StringRef MachOAbstractFixupEntry::symbolName() const { return SymbolName; }
+
+int64_t MachOAbstractFixupEntry::addend() const { return Addend; }
+
+uint32_t MachOAbstractFixupEntry::flags() const { return Flags; }
+
+int MachOAbstractFixupEntry::ordinal() const { return Ordinal; }
+
+StringRef MachOAbstractFixupEntry::typeName() const {
+  return "unknown";
+}
+
+void MachOAbstractFixupEntry::moveToFirst() {
+  SegmentOffset = 0;
+  SegmentIndex = -1;
+  Ordinal = 0;
+  Flags = 0;
+  Addend = 0;
+  Done = false;
+}
+
+void MachOAbstractFixupEntry::moveToEnd() {
+  Done = true;
+}
+
+MachOChainedFixupEntry::MachOChainedFixupEntry(Error *E,
+                                               const MachOObjectFile *O,
+                                               FixupKind Kind, bool Parse)
+    : MachOAbstractFixupEntry(E, O), Kind(Kind) {
+  ErrorAsOutParameter e(E);
+  if (Parse) {
+    if (auto FixupTargetsOrErr = O->getDyldChainedFixupTargets())
+      FixupTargets = *FixupTargetsOrErr;
+    else {
+      *E = FixupTargetsOrErr.takeError();
+      return;
+    }
+  }
+}
+
+void MachOChainedFixupEntry::moveToFirst() {
+  MachOAbstractFixupEntry::moveToFirst();
+  FixupIndex = 0;
+  moveNext();
+}
+
+void MachOChainedFixupEntry::moveToEnd() {
+  MachOAbstractFixupEntry::moveToEnd();
+}
+
+void MachOChainedFixupEntry::moveNext() {
+  Done = true;
+}
+
+bool MachOChainedFixupEntry::operator==(const MachOChainedFixupEntry &Other)
+const {
+  if (Done == Other.Done)
+    return true;
+  if ((FixupIndex == Other.FixupIndex))
+    return true;
+  return false;
+}
+
 MachORebaseEntry::MachORebaseEntry(Error *E, const MachOObjectFile *O,
                                    ArrayRef<uint8_t> Bytes, bool is64Bit)
     : E(E), O(O), Opcodes(Bytes), Ptr(Bytes.begin()),
       PointerSize(is64Bit ? 8 : 4) {}
 
 void MachORebaseEntry::moveToFirst() {
   Ptr = Opcodes.begin();
   moveNext();
return bindTable(Err, this, getDyldInfoLazyBindOpcodes(), is64Bit(),
                    MachOBindEntry::Kind::Lazy);
 }
 
 iterator_range<bind_iterator> MachOObjectFile::weakBindTable(Error &Err) {
   return bindTable(Err, this, getDyldInfoWeakBindOpcodes(), is64Bit(),
                    MachOBindEntry::Kind::Weak);
 }
 
+iterator_range<fixup_iterator>
+MachOObjectFile::fixupTable(Error &Err,
+                            MachOChainedFixupEntry::FixupKind Kind) {
+  MachOChainedFixupEntry Start(&Err, this, Kind, true);
+  Start.moveToFirst();
+
+  MachOChainedFixupEntry Finish(&Err, this, Kind, false);
+  Finish.moveToEnd();
+
+  return make_range(fixup_iterator(Start), fixup_iterator(Finish));
+}
+
 MachOObjectFile::load_command_iterator
 MachOObjectFile::begin_load_commands() const {
   return LoadCommands.begin();
 }
 
 MachOObjectFile::load_command_iterator
 MachOObjectFile::end_load_commands() const {
   return LoadCommands.end();
ArrayRef<uint8_t> MachOObjectFile::getDyldInfoLazyBindOpcodes() const {
   if (!DyldInfoOrErr)
     return None;
   MachO::dyld_info_command DyldInfo = DyldInfoOrErr.get();
   const uint8_t *Ptr =
       reinterpret_cast<const uint8_t *>(getPtr(*this, DyldInfo.lazy_bind_off));
   return makeArrayRef(Ptr, DyldInfo.lazy_bind_size);
 }
 
+Expected<std::vector<ChainedFixupTarget>>
+MachOObjectFile::getDyldChainedFixupTargets() const {
+  // Load the dyld chained fixups load command.
+  if (!DyldChainedFixupsLoadCmd)
+    return std::vector<ChainedFixupTarget>();
+  auto DyldChainedFixupsOrErr =
+    getStructOrErr<MachO::linkedit_data_command>(*this,
+                                                 DyldChainedFixupsLoadCmd);
+  if (!DyldChainedFixupsOrErr)
+    return DyldChainedFixupsOrErr.takeError();
+  MachO::linkedit_data_command DyldChainedFixups = DyldChainedFixupsOrErr.get();
+
+  // If the load command is present but the data offset has been zeroed out,
+  // as is the case for dylib stubs, return an empty list of targets.
+  uint64_t CFHeaderOffset = DyldChainedFixups.dataoff;
+  std::vector<ChainedFixupTarget> Targets;
+  if (CFHeaderOffset == 0)
+    return Targets;
+
+  // Load the dyld chained fixups header.
+  const char* CFHeaderPtr = getPtr(*this, CFHeaderOffset);
+  auto CFHeaderOrErr =
+    getStructOrErr<MachO::dyld_chained_fixups_header>(*this, CFHeaderPtr);
+  if (!CFHeaderOrErr)
+    return CFHeaderOrErr.takeError();
+  MachO::dyld_chained_fixups_header CFHeader = CFHeaderOrErr.get();
+
+  // Reject unknown chained fixup formats.
+  if (CFHeader.fixups_version != 0)
+    return malformedError(Twine("bad chained fixups: unknown version: ") +
+                          Twine(CFHeader.fixups_version));
+  if (CFHeader.imports_format < 1 || CFHeader.imports_format > 3)
+    return malformedError(
+        Twine("bad chained fixups: unknown imports format: ") +
+        Twine(CFHeader.imports_format));
+
+  return Targets;
+}
+
 ArrayRef<uint8_t> MachOObjectFile::getDyldInfoExportsTrie() const {
   if (!DyldInfoLoadCmd)
     return None;
 
   auto DyldInfoOrErr =
     getStructOrErr<MachO::dyld_info_command>(*this, DyldInfoLoadCmd);
   if (!DyldInfoOrErr)
     return None;

llvm/test/Object/AArch64/chained-fixups-header.test

+RUN: cat %p/../Inputs/MachO/chained-fixups.yaml \
+RUN:   | sed 's/__LINKEDIT:      00000000/__LINKEDIT:      AB000000/' \
+RUN:   | yaml2obj | not llvm-objdump --macho --dyld_info - 2>&1 \
+RUN:   | FileCheck %s --check-prefix=HEADER1
+HEADER1: truncated or malformed object (bad chained fixups: unknown version: 171)
+
+RUN: cat %p/../Inputs/MachO/chained-fixups.yaml \
+RUN:   | sed 's/1000000010000000/1000000AB0000000/' \
+RUN:   | yaml2obj | not llvm-objdump --macho --dyld_info - 2>&1 \
+RUN:   | FileCheck %s --check-prefix=HEADER2
+HEADER2: truncated or malformed object (bad chained fixups: unknown imports format: 171)

llvm/test/Object/Inputs/MachO/chained-fixups.yaml

+# This file was produced using:
+#   echo "int ext;" > a.c
+#   xcrun --sdk iphoneos clang -target arm64-apple-ios15.1 -o a.o a.c -c
+#   xcrun --sdk iphoneos clang -target arm64-apple-ios15.1 -dynamiclib a.o -o liba.dylib -install_name @executable_path/liba.dylib
+#   echo "extern int ext;" > b.c
+#   echo "int padding;" >> b.c
+#   echo "int *p = &ext + 4;" >> b.c
+#   xcrun --sdk iphoneos clang -target arm64-apple-ios15.1 -o b.o b.c -c
+#   xcrun --sdk iphoneos clang -target arm64-apple-ios15.1 -dynamiclib b.o -o libfixups.dylib -install_name @executable_path/libfixups.dylib -L. -la
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x100000C
+  cpusubtype:      0x0
+  filetype:        0x6
+  ncmds:           16
+  sizeofcmds:      816
+  flags:           0x100085
+  reserved:        0x0
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         152
+    segname:         __TEXT
+    vmaddr:          0
+    vmsize:          16384
+    fileoff:         0
+    filesize:        16384
+    maxprot:         5
+    initprot:        5
+    nsects:          1
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x4000
+        size:            0
+        offset:          0x4000
+        align:           0
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         ''
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         152
+    segname:         __DATA
+    vmaddr:          16384
+    vmsize:          16384
+    fileoff:         16384
+    filesize:        16384
+    maxprot:         3
+    initprot:        3
+    nsects:          1
+    flags:           0
+    Sections:
+      - sectname:        __data
+        segname:         __DATA
+        addr:            0x4000
+        size:            8
+        offset:          0x4000
+        align:           3
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x0
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         '0000001000000080'
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         72
+    segname:         __LINKEDIT
+    vmaddr:          32768
+    vmsize:          16384
+    fileoff:         32768
+    filesize:        160
+    maxprot:         1
+    initprot:        1
+    nsects:          0
+    flags:           0
+  - cmd:             LC_ID_DYLIB
+    cmdsize:         64
+    dylib:
+      name:            24
+      timestamp:       1
+      current_version: 0
+      compatibility_version: 0
+    Content:         '@executable_path/libfixups.dylib'
+    ZeroPadBytes:    8
+  - cmd:             LC_DYLD_CHAINED_FIXUPS
+    cmdsize:         16
+    dataoff:         32768
+    datasize:        88
+  - cmd:             LC_DYLD_EXPORTS_TRIE
+    cmdsize:         16
+    dataoff:         32856
+    datasize:        16
+  - cmd:             LC_SYMTAB
+    cmdsize:         24
+    symoff:          32880
+    nsyms:           2
+    stroff:          32912
+    strsize:         16
+  - cmd:             LC_DYSYMTAB
+    cmdsize:         80
+    ilocalsym:       0
+    nlocalsym:       0
+    iextdefsym:      0
+    nextdefsym:      1
+    iundefsym:       1
+    nundefsym:       1
+    tocoff:          0
+    ntoc:            0
+    modtaboff:       0
+    nmodtab:         0
+    extrefsymoff:    0
+    nextrefsyms:     0
+    indirectsymoff:  0
+    nindirectsyms:   0
+    extreloff:       0
+    nextrel:         0
+    locreloff:       0
+    nlocrel:         0
+  - cmd:             LC_UUID
+    cmdsize:         24
+    uuid:            56F7BCE0-C1A7-38E3-A90D-742D8E3D5FA9
+  - cmd:             LC_BUILD_VERSION
+    cmdsize:         32
+    platform:        2
+    minos:           983296
+    sdk:             983552
+    ntools:          1
+    Tools:
+      - tool:            3
+        version:         46596096
+  - cmd:             LC_SOURCE_VERSION
+    cmdsize:         16
+    version:         0
+  - cmd:             LC_ENCRYPTION_INFO_64
+    cmdsize:         24
+    cryptoff:        16384
+    cryptsize:       0
+    cryptid:         0
+    pad:             0
+  - cmd:             LC_LOAD_DYLIB
+    cmdsize:         56
+    dylib:
+      name:            24
+      timestamp:       2
+      current_version: 0
+      compatibility_version: 0
+    Content:         '@executable_path/liba.dylib'
+    ZeroPadBytes:    5
+  - cmd:             LC_LOAD_DYLIB
+    cmdsize:         56
+    dylib:
+      name:            24
+      timestamp:       2
+      current_version: 85917696
+      compatibility_version: 65536
+    Content:         '/usr/lib/libSystem.B.dylib'
+    ZeroPadBytes:    6
+  - cmd:             LC_FUNCTION_STARTS
+    cmdsize:         16
+    dataoff:         32872
+    datasize:        8
+  - cmd:             LC_DATA_IN_CODE
+    cmdsize:         16
+    dataoff:         32880
+    datasize:        0
+__LINKEDIT:      0000000020000000480000004C000000010000000100000000000000000000000300000000000000100000000000000018000000004006000040000000000000000000000100000001020000005F6578740000000000000000015F700006040080800100000000000000000000000000020000000F02000000400000000000000500000001000001000000000000000020005F70005F65787400000000000000
+...

llvm/tools/llvm-objdump/MachODump.cpp

for (uint32_t i = 0; i < nloh;) {
     }
   }
 }
 
 //===----------------------------------------------------------------------===//
 // chained fixup table dumping
 //===----------------------------------------------------------------------===//
 
+static void printMachOChainedFixups(object::MachOObjectFile *Obj,
+  MachOChainedFixupEntry::FixupKind Type) {
+  Error Err = Error::success();
+  for (const object::MachOChainedFixupEntry &Entry :
+       Obj->fixupTable(Err, Type)) {
+    (void)Entry;
+  }
+  if (Err)
+    reportError(std::move(Err), Obj->getFileName());
+}
+
+
 static void PrintDyldInfo(MachOObjectFile *O) {
   outs() << "dyld information:" << '\n';
-  outs() << "[not yet implemented].\n";
+  printMachOChainedFixups(O, MachOChainedFixupEntry::FixupKind::Bind);
 }
 
 static void PrintDylibs(MachOObjectFile *O, bool JustId) {
   unsigned Index = 0;
   for (const auto &Load : O->load_commands()) {
     if ((JustId && Load.C.cmd == MachO::LC_ID_DYLIB) ||
         (!JustId && (Load.C.cmd == MachO::LC_ID_DYLIB ||
                      Load.C.cmd == MachO::LC_LOAD_DYLIB ||