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      1 //===-- RuntimeDyldMachOAArch64.h -- MachO/AArch64 specific code. -*- C++ -*-=//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 
      9 #ifndef LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_TARGETS_RUNTIMEDYLDMACHOAARCH64_H
     10 #define LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_TARGETS_RUNTIMEDYLDMACHOAARCH64_H
     11 
     12 #include "../RuntimeDyldMachO.h"
     13 #include "llvm/Support/Endian.h"
     14 
     15 #define DEBUG_TYPE "dyld"
     16 
     17 namespace llvm {
     18 
     19 class RuntimeDyldMachOAArch64
     20     : public RuntimeDyldMachOCRTPBase<RuntimeDyldMachOAArch64> {
     21 public:
     22 
     23   typedef uint64_t TargetPtrT;
     24 
     25   RuntimeDyldMachOAArch64(RuntimeDyld::MemoryManager &MM,
     26                           JITSymbolResolver &Resolver)
     27       : RuntimeDyldMachOCRTPBase(MM, Resolver) {}
     28 
     29   unsigned getMaxStubSize() const override { return 8; }
     30 
     31   unsigned getStubAlignment() override { return 8; }
     32 
     33   /// Extract the addend encoded in the instruction / memory location.
     34   Expected<int64_t> decodeAddend(const RelocationEntry &RE) const {
     35     const SectionEntry &Section = Sections[RE.SectionID];
     36     uint8_t *LocalAddress = Section.getAddressWithOffset(RE.Offset);
     37     unsigned NumBytes = 1 << RE.Size;
     38     int64_t Addend = 0;
     39     // Verify that the relocation has the correct size and alignment.
     40     switch (RE.RelType) {
     41     default: {
     42       std::string ErrMsg;
     43       {
     44         raw_string_ostream ErrStream(ErrMsg);
     45         ErrStream << "Unsupported relocation type: "
     46                   << getRelocName(RE.RelType);
     47       }
     48       return make_error<StringError>(std::move(ErrMsg),
     49                                      inconvertibleErrorCode());
     50     }
     51     case MachO::ARM64_RELOC_POINTER_TO_GOT:
     52     case MachO::ARM64_RELOC_UNSIGNED: {
     53       if (NumBytes != 4 && NumBytes != 8) {
     54         std::string ErrMsg;
     55         {
     56           raw_string_ostream ErrStream(ErrMsg);
     57           ErrStream << "Invalid relocation size for relocation "
     58                     << getRelocName(RE.RelType);
     59         }
     60         return make_error<StringError>(std::move(ErrMsg),
     61                                        inconvertibleErrorCode());
     62       }
     63       break;
     64     }
     65     case MachO::ARM64_RELOC_BRANCH26:
     66     case MachO::ARM64_RELOC_PAGE21:
     67     case MachO::ARM64_RELOC_PAGEOFF12:
     68     case MachO::ARM64_RELOC_GOT_LOAD_PAGE21:
     69     case MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12:
     70       assert(NumBytes == 4 && "Invalid relocation size.");
     71       assert((((uintptr_t)LocalAddress & 0x3) == 0) &&
     72              "Instruction address is not aligned to 4 bytes.");
     73       break;
     74     }
     75 
     76     switch (RE.RelType) {
     77     default:
     78       llvm_unreachable("Unsupported relocation type!");
     79     case MachO::ARM64_RELOC_POINTER_TO_GOT:
     80     case MachO::ARM64_RELOC_UNSIGNED:
     81       // This could be an unaligned memory location.
     82       if (NumBytes == 4)
     83         Addend = *reinterpret_cast<support::ulittle32_t *>(LocalAddress);
     84       else
     85         Addend = *reinterpret_cast<support::ulittle64_t *>(LocalAddress);
     86       break;
     87     case MachO::ARM64_RELOC_BRANCH26: {
     88       // Verify that the relocation points to a B/BL instruction.
     89       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
     90       assert(((*p & 0xFC000000) == 0x14000000 ||
     91               (*p & 0xFC000000) == 0x94000000) &&
     92              "Expected branch instruction.");
     93 
     94       // Get the 26 bit addend encoded in the branch instruction and sign-extend
     95       // to 64 bit. The lower 2 bits are always zeros and are therefore implicit
     96       // (<< 2).
     97       Addend = (*p & 0x03FFFFFF) << 2;
     98       Addend = SignExtend64(Addend, 28);
     99       break;
    100     }
    101     case MachO::ARM64_RELOC_GOT_LOAD_PAGE21:
    102     case MachO::ARM64_RELOC_PAGE21: {
    103       // Verify that the relocation points to the expected adrp instruction.
    104       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    105       assert((*p & 0x9F000000) == 0x90000000 && "Expected adrp instruction.");
    106 
    107       // Get the 21 bit addend encoded in the adrp instruction and sign-extend
    108       // to 64 bit. The lower 12 bits (4096 byte page) are always zeros and are
    109       // therefore implicit (<< 12).
    110       Addend = ((*p & 0x60000000) >> 29) | ((*p & 0x01FFFFE0) >> 3) << 12;
    111       Addend = SignExtend64(Addend, 33);
    112       break;
    113     }
    114     case MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12: {
    115       // Verify that the relocation points to one of the expected load / store
    116       // instructions.
    117       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    118       (void)p;
    119       assert((*p & 0x3B000000) == 0x39000000 &&
    120              "Only expected load / store instructions.");
    121       LLVM_FALLTHROUGH;
    122     }
    123     case MachO::ARM64_RELOC_PAGEOFF12: {
    124       // Verify that the relocation points to one of the expected load / store
    125       // or add / sub instructions.
    126       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    127       assert((((*p & 0x3B000000) == 0x39000000) ||
    128               ((*p & 0x11C00000) == 0x11000000)   ) &&
    129              "Expected load / store  or add/sub instruction.");
    130 
    131       // Get the 12 bit addend encoded in the instruction.
    132       Addend = (*p & 0x003FFC00) >> 10;
    133 
    134       // Check which instruction we are decoding to obtain the implicit shift
    135       // factor of the instruction.
    136       int ImplicitShift = 0;
    137       if ((*p & 0x3B000000) == 0x39000000) { // << load / store
    138         // For load / store instructions the size is encoded in bits 31:30.
    139         ImplicitShift = ((*p >> 30) & 0x3);
    140         if (ImplicitShift == 0) {
    141           // Check if this a vector op to get the correct shift value.
    142           if ((*p & 0x04800000) == 0x04800000)
    143             ImplicitShift = 4;
    144         }
    145       }
    146       // Compensate for implicit shift.
    147       Addend <<= ImplicitShift;
    148       break;
    149     }
    150     }
    151     return Addend;
    152   }
    153 
    154   /// Extract the addend encoded in the instruction.
    155   void encodeAddend(uint8_t *LocalAddress, unsigned NumBytes,
    156                     MachO::RelocationInfoType RelType, int64_t Addend) const {
    157     // Verify that the relocation has the correct alignment.
    158     switch (RelType) {
    159     default:
    160       llvm_unreachable("Unsupported relocation type!");
    161     case MachO::ARM64_RELOC_POINTER_TO_GOT:
    162     case MachO::ARM64_RELOC_UNSIGNED:
    163       assert((NumBytes == 4 || NumBytes == 8) && "Invalid relocation size.");
    164       break;
    165     case MachO::ARM64_RELOC_BRANCH26:
    166     case MachO::ARM64_RELOC_PAGE21:
    167     case MachO::ARM64_RELOC_PAGEOFF12:
    168     case MachO::ARM64_RELOC_GOT_LOAD_PAGE21:
    169     case MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12:
    170       assert(NumBytes == 4 && "Invalid relocation size.");
    171       assert((((uintptr_t)LocalAddress & 0x3) == 0) &&
    172              "Instruction address is not aligned to 4 bytes.");
    173       break;
    174     }
    175 
    176     switch (RelType) {
    177     default:
    178       llvm_unreachable("Unsupported relocation type!");
    179     case MachO::ARM64_RELOC_POINTER_TO_GOT:
    180     case MachO::ARM64_RELOC_UNSIGNED:
    181       // This could be an unaligned memory location.
    182       if (NumBytes == 4)
    183         *reinterpret_cast<support::ulittle32_t *>(LocalAddress) = Addend;
    184       else
    185         *reinterpret_cast<support::ulittle64_t *>(LocalAddress) = Addend;
    186       break;
    187     case MachO::ARM64_RELOC_BRANCH26: {
    188       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    189       // Verify that the relocation points to the expected branch instruction.
    190       assert(((*p & 0xFC000000) == 0x14000000 ||
    191               (*p & 0xFC000000) == 0x94000000) &&
    192              "Expected branch instruction.");
    193 
    194       // Verify addend value.
    195       assert((Addend & 0x3) == 0 && "Branch target is not aligned");
    196       assert(isInt<28>(Addend) && "Branch target is out of range.");
    197 
    198       // Encode the addend as 26 bit immediate in the branch instruction.
    199       *p = (*p & 0xFC000000) | ((uint32_t)(Addend >> 2) & 0x03FFFFFF);
    200       break;
    201     }
    202     case MachO::ARM64_RELOC_GOT_LOAD_PAGE21:
    203     case MachO::ARM64_RELOC_PAGE21: {
    204       // Verify that the relocation points to the expected adrp instruction.
    205       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    206       assert((*p & 0x9F000000) == 0x90000000 && "Expected adrp instruction.");
    207 
    208       // Check that the addend fits into 21 bits (+ 12 lower bits).
    209       assert((Addend & 0xFFF) == 0 && "ADRP target is not page aligned.");
    210       assert(isInt<33>(Addend) && "Invalid page reloc value.");
    211 
    212       // Encode the addend into the instruction.
    213       uint32_t ImmLoValue = ((uint64_t)Addend << 17) & 0x60000000;
    214       uint32_t ImmHiValue = ((uint64_t)Addend >> 9) & 0x00FFFFE0;
    215       *p = (*p & 0x9F00001F) | ImmHiValue | ImmLoValue;
    216       break;
    217     }
    218     case MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12: {
    219       // Verify that the relocation points to one of the expected load / store
    220       // instructions.
    221       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    222       assert((*p & 0x3B000000) == 0x39000000 &&
    223              "Only expected load / store instructions.");
    224       (void)p;
    225       LLVM_FALLTHROUGH;
    226     }
    227     case MachO::ARM64_RELOC_PAGEOFF12: {
    228       // Verify that the relocation points to one of the expected load / store
    229       // or add / sub instructions.
    230       auto *p = reinterpret_cast<support::aligned_ulittle32_t *>(LocalAddress);
    231       assert((((*p & 0x3B000000) == 0x39000000) ||
    232               ((*p & 0x11C00000) == 0x11000000)   ) &&
    233              "Expected load / store  or add/sub instruction.");
    234 
    235       // Check which instruction we are decoding to obtain the implicit shift
    236       // factor of the instruction and verify alignment.
    237       int ImplicitShift = 0;
    238       if ((*p & 0x3B000000) == 0x39000000) { // << load / store
    239         // For load / store instructions the size is encoded in bits 31:30.
    240         ImplicitShift = ((*p >> 30) & 0x3);
    241         switch (ImplicitShift) {
    242         case 0:
    243           // Check if this a vector op to get the correct shift value.
    244           if ((*p & 0x04800000) == 0x04800000) {
    245             ImplicitShift = 4;
    246             assert(((Addend & 0xF) == 0) &&
    247                    "128-bit LDR/STR not 16-byte aligned.");
    248           }
    249           break;
    250         case 1:
    251           assert(((Addend & 0x1) == 0) && "16-bit LDR/STR not 2-byte aligned.");
    252           break;
    253         case 2:
    254           assert(((Addend & 0x3) == 0) && "32-bit LDR/STR not 4-byte aligned.");
    255           break;
    256         case 3:
    257           assert(((Addend & 0x7) == 0) && "64-bit LDR/STR not 8-byte aligned.");
    258           break;
    259         }
    260       }
    261       // Compensate for implicit shift.
    262       Addend >>= ImplicitShift;
    263       assert(isUInt<12>(Addend) && "Addend cannot be encoded.");
    264 
    265       // Encode the addend into the instruction.
    266       *p = (*p & 0xFFC003FF) | ((uint32_t)(Addend << 10) & 0x003FFC00);
    267       break;
    268     }
    269     }
    270   }
    271 
    272   Expected<relocation_iterator>
    273   processRelocationRef(unsigned SectionID, relocation_iterator RelI,
    274                        const ObjectFile &BaseObjT,
    275                        ObjSectionToIDMap &ObjSectionToID,
    276                        StubMap &Stubs) override {
    277     const MachOObjectFile &Obj =
    278       static_cast<const MachOObjectFile &>(BaseObjT);
    279     MachO::any_relocation_info RelInfo =
    280         Obj.getRelocation(RelI->getRawDataRefImpl());
    281 
    282     if (Obj.isRelocationScattered(RelInfo))
    283       return make_error<RuntimeDyldError>("Scattered relocations not supported "
    284                                           "for MachO AArch64");
    285 
    286     // ARM64 has an ARM64_RELOC_ADDEND relocation type that carries an explicit
    287     // addend for the following relocation. If found: (1) store the associated
    288     // addend, (2) consume the next relocation, and (3) use the stored addend to
    289     // override the addend.
    290     int64_t ExplicitAddend = 0;
    291     if (Obj.getAnyRelocationType(RelInfo) == MachO::ARM64_RELOC_ADDEND) {
    292       assert(!Obj.getPlainRelocationExternal(RelInfo));
    293       assert(!Obj.getAnyRelocationPCRel(RelInfo));
    294       assert(Obj.getAnyRelocationLength(RelInfo) == 2);
    295       int64_t RawAddend = Obj.getPlainRelocationSymbolNum(RelInfo);
    296       // Sign-extend the 24-bit to 64-bit.
    297       ExplicitAddend = SignExtend64(RawAddend, 24);
    298       ++RelI;
    299       RelInfo = Obj.getRelocation(RelI->getRawDataRefImpl());
    300     }
    301 
    302     if (Obj.getAnyRelocationType(RelInfo) == MachO::ARM64_RELOC_SUBTRACTOR)
    303       return processSubtractRelocation(SectionID, RelI, Obj, ObjSectionToID);
    304 
    305     RelocationEntry RE(getRelocationEntry(SectionID, Obj, RelI));
    306 
    307     if (RE.RelType == MachO::ARM64_RELOC_POINTER_TO_GOT) {
    308       bool Valid =
    309           (RE.Size == 2 && RE.IsPCRel) || (RE.Size == 3 && !RE.IsPCRel);
    310       if (!Valid)
    311         return make_error<StringError>("ARM64_RELOC_POINTER_TO_GOT supports "
    312                                        "32-bit pc-rel or 64-bit absolute only",
    313                                        inconvertibleErrorCode());
    314     }
    315 
    316     if (auto Addend = decodeAddend(RE))
    317       RE.Addend = *Addend;
    318     else
    319       return Addend.takeError();
    320 
    321     assert((ExplicitAddend == 0 || RE.Addend == 0) && "Relocation has "\
    322       "ARM64_RELOC_ADDEND and embedded addend in the instruction.");
    323     if (ExplicitAddend)
    324       RE.Addend = ExplicitAddend;
    325 
    326     RelocationValueRef Value;
    327     if (auto ValueOrErr = getRelocationValueRef(Obj, RelI, RE, ObjSectionToID))
    328       Value = *ValueOrErr;
    329     else
    330       return ValueOrErr.takeError();
    331 
    332     bool IsExtern = Obj.getPlainRelocationExternal(RelInfo);
    333     if (RE.RelType == MachO::ARM64_RELOC_POINTER_TO_GOT) {
    334       // We'll take care of the offset in processGOTRelocation.
    335       Value.Offset = 0;
    336     } else if (!IsExtern && RE.IsPCRel)
    337       makeValueAddendPCRel(Value, RelI, 1 << RE.Size);
    338 
    339     RE.Addend = Value.Offset;
    340 
    341     if (RE.RelType == MachO::ARM64_RELOC_GOT_LOAD_PAGE21 ||
    342         RE.RelType == MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12 ||
    343         RE.RelType == MachO::ARM64_RELOC_POINTER_TO_GOT)
    344       processGOTRelocation(RE, Value, Stubs);
    345     else {
    346       if (Value.SymbolName)
    347         addRelocationForSymbol(RE, Value.SymbolName);
    348       else
    349         addRelocationForSection(RE, Value.SectionID);
    350     }
    351 
    352     return ++RelI;
    353   }
    354 
    355   void resolveRelocation(const RelocationEntry &RE, uint64_t Value) override {
    356     LLVM_DEBUG(dumpRelocationToResolve(RE, Value));
    357 
    358     const SectionEntry &Section = Sections[RE.SectionID];
    359     uint8_t *LocalAddress = Section.getAddressWithOffset(RE.Offset);
    360     MachO::RelocationInfoType RelType =
    361       static_cast<MachO::RelocationInfoType>(RE.RelType);
    362 
    363     switch (RelType) {
    364     default:
    365       llvm_unreachable("Invalid relocation type!");
    366     case MachO::ARM64_RELOC_UNSIGNED: {
    367       assert(!RE.IsPCRel && "PCRel and ARM64_RELOC_UNSIGNED not supported");
    368       // Mask in the target value a byte at a time (we don't have an alignment
    369       // guarantee for the target address, so this is safest).
    370       if (RE.Size < 2)
    371         llvm_unreachable("Invalid size for ARM64_RELOC_UNSIGNED");
    372 
    373       encodeAddend(LocalAddress, 1 << RE.Size, RelType, Value + RE.Addend);
    374       break;
    375     }
    376 
    377     case MachO::ARM64_RELOC_POINTER_TO_GOT: {
    378       assert(((RE.Size == 2 && RE.IsPCRel) || (RE.Size == 3 && !RE.IsPCRel)) &&
    379              "ARM64_RELOC_POINTER_TO_GOT only supports 32-bit pc-rel or 64-bit "
    380              "absolute");
    381       // Addend is the GOT entry address and RE.Offset the target of the
    382       // relocation.
    383       uint64_t Result =
    384           RE.IsPCRel ? (RE.Addend - RE.Offset) : (Value + RE.Addend);
    385       encodeAddend(LocalAddress, 1 << RE.Size, RelType, Result);
    386       break;
    387     }
    388 
    389     case MachO::ARM64_RELOC_BRANCH26: {
    390       assert(RE.IsPCRel && "not PCRel and ARM64_RELOC_BRANCH26 not supported");
    391       // Check if branch is in range.
    392       uint64_t FinalAddress = Section.getLoadAddressWithOffset(RE.Offset);
    393       int64_t PCRelVal = Value - FinalAddress + RE.Addend;
    394       encodeAddend(LocalAddress, /*Size=*/4, RelType, PCRelVal);
    395       break;
    396     }
    397     case MachO::ARM64_RELOC_GOT_LOAD_PAGE21:
    398     case MachO::ARM64_RELOC_PAGE21: {
    399       assert(RE.IsPCRel && "not PCRel and ARM64_RELOC_PAGE21 not supported");
    400       // Adjust for PC-relative relocation and offset.
    401       uint64_t FinalAddress = Section.getLoadAddressWithOffset(RE.Offset);
    402       int64_t PCRelVal =
    403         ((Value + RE.Addend) & (-4096)) - (FinalAddress & (-4096));
    404       encodeAddend(LocalAddress, /*Size=*/4, RelType, PCRelVal);
    405       break;
    406     }
    407     case MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12:
    408     case MachO::ARM64_RELOC_PAGEOFF12: {
    409       assert(!RE.IsPCRel && "PCRel and ARM64_RELOC_PAGEOFF21 not supported");
    410       // Add the offset from the symbol.
    411       Value += RE.Addend;
    412       // Mask out the page address and only use the lower 12 bits.
    413       Value &= 0xFFF;
    414       encodeAddend(LocalAddress, /*Size=*/4, RelType, Value);
    415       break;
    416     }
    417     case MachO::ARM64_RELOC_SUBTRACTOR: {
    418       uint64_t SectionABase = Sections[RE.Sections.SectionA].getLoadAddress();
    419       uint64_t SectionBBase = Sections[RE.Sections.SectionB].getLoadAddress();
    420       assert((Value == SectionABase || Value == SectionBBase) &&
    421              "Unexpected SUBTRACTOR relocation value.");
    422       Value = SectionABase - SectionBBase + RE.Addend;
    423       writeBytesUnaligned(Value, LocalAddress, 1 << RE.Size);
    424       break;
    425     }
    426 
    427     case MachO::ARM64_RELOC_TLVP_LOAD_PAGE21:
    428     case MachO::ARM64_RELOC_TLVP_LOAD_PAGEOFF12:
    429       llvm_unreachable("Relocation type not yet implemented!");
    430     case MachO::ARM64_RELOC_ADDEND:
    431       llvm_unreachable("ARM64_RELOC_ADDEND should have been handeled by "
    432                        "processRelocationRef!");
    433     }
    434   }
    435 
    436   Error finalizeSection(const ObjectFile &Obj, unsigned SectionID,
    437                        const SectionRef &Section) {
    438     return Error::success();
    439   }
    440 
    441 private:
    442   void processGOTRelocation(const RelocationEntry &RE,
    443                             RelocationValueRef &Value, StubMap &Stubs) {
    444     assert((RE.RelType == MachO::ARM64_RELOC_POINTER_TO_GOT &&
    445             (RE.Size == 2 || RE.Size == 3)) ||
    446            RE.Size == 2);
    447     SectionEntry &Section = Sections[RE.SectionID];
    448     StubMap::const_iterator i = Stubs.find(Value);
    449     int64_t Offset;
    450     if (i != Stubs.end())
    451       Offset = static_cast<int64_t>(i->second);
    452     else {
    453       // FIXME: There must be a better way to do this then to check and fix the
    454       // alignment every time!!!
    455       uintptr_t BaseAddress = uintptr_t(Section.getAddress());
    456       uintptr_t StubAlignment = getStubAlignment();
    457       uintptr_t StubAddress =
    458           (BaseAddress + Section.getStubOffset() + StubAlignment - 1) &
    459           -StubAlignment;
    460       unsigned StubOffset = StubAddress - BaseAddress;
    461       Stubs[Value] = StubOffset;
    462       assert(((StubAddress % getStubAlignment()) == 0) &&
    463              "GOT entry not aligned");
    464       RelocationEntry GOTRE(RE.SectionID, StubOffset,
    465                             MachO::ARM64_RELOC_UNSIGNED, Value.Offset,
    466                             /*IsPCRel=*/false, /*Size=*/3);
    467       if (Value.SymbolName)
    468         addRelocationForSymbol(GOTRE, Value.SymbolName);
    469       else
    470         addRelocationForSection(GOTRE, Value.SectionID);
    471       Section.advanceStubOffset(getMaxStubSize());
    472       Offset = static_cast<int64_t>(StubOffset);
    473     }
    474     RelocationEntry TargetRE(RE.SectionID, RE.Offset, RE.RelType, Offset,
    475                              RE.IsPCRel, RE.Size);
    476     addRelocationForSection(TargetRE, RE.SectionID);
    477   }
    478 
    479   Expected<relocation_iterator>
    480   processSubtractRelocation(unsigned SectionID, relocation_iterator RelI,
    481                             const ObjectFile &BaseObjT,
    482                             ObjSectionToIDMap &ObjSectionToID) {
    483     const MachOObjectFile &Obj =
    484         static_cast<const MachOObjectFile&>(BaseObjT);
    485     MachO::any_relocation_info RE =
    486         Obj.getRelocation(RelI->getRawDataRefImpl());
    487 
    488     unsigned Size = Obj.getAnyRelocationLength(RE);
    489     uint64_t Offset = RelI->getOffset();
    490     uint8_t *LocalAddress = Sections[SectionID].getAddressWithOffset(Offset);
    491     unsigned NumBytes = 1 << Size;
    492 
    493     Expected<StringRef> SubtrahendNameOrErr = RelI->getSymbol()->getName();
    494     if (!SubtrahendNameOrErr)
    495       return SubtrahendNameOrErr.takeError();
    496     auto SubtrahendI = GlobalSymbolTable.find(*SubtrahendNameOrErr);
    497     unsigned SectionBID = SubtrahendI->second.getSectionID();
    498     uint64_t SectionBOffset = SubtrahendI->second.getOffset();
    499     int64_t Addend =
    500       SignExtend64(readBytesUnaligned(LocalAddress, NumBytes), NumBytes * 8);
    501 
    502     ++RelI;
    503     Expected<StringRef> MinuendNameOrErr = RelI->getSymbol()->getName();
    504     if (!MinuendNameOrErr)
    505       return MinuendNameOrErr.takeError();
    506     auto MinuendI = GlobalSymbolTable.find(*MinuendNameOrErr);
    507     unsigned SectionAID = MinuendI->second.getSectionID();
    508     uint64_t SectionAOffset = MinuendI->second.getOffset();
    509 
    510     RelocationEntry R(SectionID, Offset, MachO::ARM64_RELOC_SUBTRACTOR, (uint64_t)Addend,
    511                       SectionAID, SectionAOffset, SectionBID, SectionBOffset,
    512                       false, Size);
    513 
    514     addRelocationForSection(R, SectionAID);
    515 
    516     return ++RelI;
    517   }
    518 
    519   static const char *getRelocName(uint32_t RelocType) {
    520     switch (RelocType) {
    521       case MachO::ARM64_RELOC_UNSIGNED: return "ARM64_RELOC_UNSIGNED";
    522       case MachO::ARM64_RELOC_SUBTRACTOR: return "ARM64_RELOC_SUBTRACTOR";
    523       case MachO::ARM64_RELOC_BRANCH26: return "ARM64_RELOC_BRANCH26";
    524       case MachO::ARM64_RELOC_PAGE21: return "ARM64_RELOC_PAGE21";
    525       case MachO::ARM64_RELOC_PAGEOFF12: return "ARM64_RELOC_PAGEOFF12";
    526       case MachO::ARM64_RELOC_GOT_LOAD_PAGE21: return "ARM64_RELOC_GOT_LOAD_PAGE21";
    527       case MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12: return "ARM64_RELOC_GOT_LOAD_PAGEOFF12";
    528       case MachO::ARM64_RELOC_POINTER_TO_GOT: return "ARM64_RELOC_POINTER_TO_GOT";
    529       case MachO::ARM64_RELOC_TLVP_LOAD_PAGE21: return "ARM64_RELOC_TLVP_LOAD_PAGE21";
    530       case MachO::ARM64_RELOC_TLVP_LOAD_PAGEOFF12: return "ARM64_RELOC_TLVP_LOAD_PAGEOFF12";
    531       case MachO::ARM64_RELOC_ADDEND: return "ARM64_RELOC_ADDEND";
    532     }
    533     return "Unrecognized arm64 addend";
    534   }
    535 
    536 };
    537 }
    538 
    539 #undef DEBUG_TYPE
    540 
    541 #endif
    542