ELF: Make required Thunk methods pure virtual and remove an unused argument. NFC.

[pcc]

• Also make certain Thunk methods non-const as this will be required for an upcoming change

[ruiu]

LGTM

lld/ELF/SyntheticSections.cpp

void ThunkSection::addThunk(Thunk *T) {
   T->Offset = Off;
   Thunks.push_back(T);
   T->addSymbols(*this);
   Size = Off + T->size();
 }
 
 void ThunkSection::writeTo(uint8_t *Buf) {
   for (const Thunk *T : Thunks)
-    T->writeTo(Buf + T->Offset, *this);
+    T->writeTo(Buf + T->Offset);
 }
 
 InputSection *ThunkSection::getTargetInputSection() const {
   if (Thunks.empty())
     return nullptr;
   const Thunk *T = Thunks.front();
   return T->getTargetInputSection();
 }

lld/ELF/Thunks.h

 // Thunks can be created for Defined, Shared and Undefined Symbols.
 // Thunks are assigned to synthetic ThunkSections
 class Thunk {
 public:
   Thunk(Symbol &Destination);
   virtual ~Thunk();
 
   virtual uint32_t size() const { return 0; }
-  virtual void writeTo(uint8_t *Buf, ThunkSection &IS) const {}
+  virtual void writeTo(uint8_t *Buf) const = 0;
 
   // All Thunks must define at least one symbol ThunkSym so that we can
   // redirect relocations to it.
-  virtual void addSymbols(ThunkSection &IS) {}
+  virtual void addSymbols(ThunkSection &IS) = 0;
 
   // Some Thunks must be placed immediately before their Target as they elide
   // a branch and fall through to the first Symbol in the Target.
   virtual InputSection *getTargetInputSection() const { return nullptr; }
 
   // To reuse a Thunk the caller as identified by the Type must be
   // compatible with it.
   virtual bool isCompatibleWith(RelType Type) const { return true; }

lld/ELF/Thunks.cpp

 
 namespace {
 
 // AArch64 long range Thunks
 class AArch64ABSLongThunk final : public Thunk {
 public:
   AArch64ABSLongThunk(Symbol &Dest) : Thunk(Dest) {}
   uint32_t size() const override { return 16; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
 };
 
 class AArch64ADRPThunk final : public Thunk {
 public:
   AArch64ADRPThunk(Symbol &Dest) : Thunk(Dest) {}
   uint32_t size() const override { return 12; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
 };
 
 // Specific ARM Thunk implementations. The naming convention is:
 // Source State, TargetState, Target Requirement, ABS or PI, Range
 class ARMV7ABSLongThunk final : public Thunk {
 public:
   ARMV7ABSLongThunk(Symbol &Dest) : Thunk(Dest) {}
 
   uint32_t size() const override { return 12; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   bool isCompatibleWith(RelType Type) const override;
 };
 
 class ARMV7PILongThunk final : public Thunk {
 public:
   ARMV7PILongThunk(Symbol &Dest) : Thunk(Dest) {}
 
   uint32_t size() const override { return 16; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   bool isCompatibleWith(RelType Type) const override;
 };
 
 class ThumbV7ABSLongThunk final : public Thunk {
 public:
   ThumbV7ABSLongThunk(Symbol &Dest) : Thunk(Dest) { Alignment = 2; }
 
   uint32_t size() const override { return 10; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   bool isCompatibleWith(RelType Type) const override;
 };
 
 class ThumbV7PILongThunk final : public Thunk {
 public:
   ThumbV7PILongThunk(Symbol &Dest) : Thunk(Dest) { Alignment = 2; }
 
   uint32_t size() const override { return 12; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   bool isCompatibleWith(RelType Type) const override;
 };
 
 // MIPS LA25 thunk
 class MipsThunk final : public Thunk {
 public:
   MipsThunk(Symbol &Dest) : Thunk(Dest) {}
 
   uint32_t size() const override { return 16; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   InputSection *getTargetInputSection() const override;
 };
 
 // microMIPS R2-R5 LA25 thunk
 class MicroMipsThunk final : public Thunk {
 public:
   MicroMipsThunk(Symbol &Dest) : Thunk(Dest) {}
 
   uint32_t size() const override { return 14; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   InputSection *getTargetInputSection() const override;
 };
 
 // microMIPS R6 LA25 thunk
 class MicroMipsR6Thunk final : public Thunk {
 public:
   MicroMipsR6Thunk(Symbol &Dest) : Thunk(Dest) {}
 
   uint32_t size() const override { return 12; }
-  void writeTo(uint8_t *Buf, ThunkSection &IS) const override;
+  void writeTo(uint8_t *Buf) const override;
   void addSymbols(ThunkSection &IS) override;
   InputSection *getTargetInputSection() const override;
 };
 
 } // end anonymous namespace
 
 // AArch64 long range Thunks
 
 static uint64_t getAArch64ThunkDestVA(const Symbol &S) {
   uint64_t V = S.isInPlt() ? S.getPltVA() : S.getVA();
   return V;
 }
 
-void AArch64ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
+void AArch64ABSLongThunk::writeTo(uint8_t *Buf) const {
   const uint8_t Data[] = {
     0x50, 0x00, 0x00, 0x58, //     ldr x16, L0
     0x00, 0x02, 0x1f, 0xd6, //     br  x16
     0x00, 0x00, 0x00, 0x00, // L0: .xword S
     0x00, 0x00, 0x00, 0x00,
   };
   uint64_t S = getAArch64ThunkDestVA(Destination);
   memcpy(Buf, Data, sizeof(Data));
   Target->relocateOne(Buf + 8, R_AARCH64_ABS64, S);
 }
 
 void AArch64ABSLongThunk::addSymbols(ThunkSection &IS) {
   ThunkSym = addSyntheticLocal(
       Saver.save("__AArch64AbsLongThunk_" + Destination.getName()), STT_FUNC,
       Offset, size(), IS);
   addSyntheticLocal("$x", STT_NOTYPE, Offset, 0, IS);
   addSyntheticLocal("$d", STT_NOTYPE, Offset + 8, 0, IS);
 }
 
 // This Thunk has a maximum range of 4Gb, this is sufficient for all programs
 // using the small code model, including pc-relative ones. At time of writing
 // clang and gcc do not support the large code model for position independent
 // code so it is safe to use this for position independent thunks without
 // worrying about the destination being more than 4Gb away.
-void AArch64ADRPThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
+void AArch64ADRPThunk::writeTo(uint8_t *Buf) const {
   const uint8_t Data[] = {
       0x10, 0x00, 0x00, 0x90, // adrp x16, Dest R_AARCH64_ADR_PREL_PG_HI21(Dest)
       0x10, 0x02, 0x00, 0x91, // add  x16, x16, R_AARCH64_ADD_ABS_LO12_NC(Dest)
       0x00, 0x02, 0x1f, 0xd6, // br   x16
   };
   uint64_t S = getAArch64ThunkDestVA(Destination);
   uint64_t P = ThunkSym->getVA();
   memcpy(Buf, Data, sizeof(Data));

 }
 
 // ARM Target Thunks
 static uint64_t getARMThunkDestVA(const Symbol &S) {
   uint64_t V = S.isInPlt() ? S.getPltVA() : S.getVA();
   return SignExtend64<32>(V);
 }
 
-void ARMV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
+void ARMV7ABSLongThunk::writeTo(uint8_t *Buf) const {
   const uint8_t Data[] = {
       0x00, 0xc0, 0x00, 0xe3, // movw         ip,:lower16:S
       0x00, 0xc0, 0x40, 0xe3, // movt         ip,:upper16:S
       0x1c, 0xff, 0x2f, 0xe1, // bx   ip
   };
   uint64_t S = getARMThunkDestVA(Destination);
   memcpy(Buf, Data, sizeof(Data));
   Target->relocateOne(Buf, R_ARM_MOVW_ABS_NC, S);
   Target->relocateOne(Buf + 4, R_ARM_MOVT_ABS, S);
 }
 
 void ARMV7ABSLongThunk::addSymbols(ThunkSection &IS) {
   ThunkSym = addSyntheticLocal(
       Saver.save("__ARMv7ABSLongThunk_" + Destination.getName()), STT_FUNC,
       Offset, size(), IS);
   addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, IS);
 }
 
 bool ARMV7ABSLongThunk::isCompatibleWith(RelType Type) const {
   // Thumb branch relocations can't use BLX
   return Type != R_ARM_THM_JUMP19 && Type != R_ARM_THM_JUMP24;
 }
 
-void ThumbV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
+void ThumbV7ABSLongThunk::writeTo(uint8_t *Buf) const {
   const uint8_t Data[] = {
       0x40, 0xf2, 0x00, 0x0c, // movw         ip, :lower16:S
       0xc0, 0xf2, 0x00, 0x0c, // movt         ip, :upper16:S
       0x60, 0x47,             // bx   ip
   };
   uint64_t S = getARMThunkDestVA(Destination);
   memcpy(Buf, Data, sizeof(Data));
   Target->relocateOne(Buf, R_ARM_THM_MOVW_ABS_NC, S);
   Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_ABS, S);
 }
 
 void ThumbV7ABSLongThunk::addSymbols(ThunkSection &IS) {
   ThunkSym = addSyntheticLocal(
       Saver.save("__Thumbv7ABSLongThunk_" + Destination.getName()), STT_FUNC,
       Offset | 0x1, size(), IS);
   addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, IS);
 }
 
 bool ThumbV7ABSLongThunk::isCompatibleWith(RelType Type) const {
   // ARM branch relocations can't use BLX
   return Type != R_ARM_JUMP24 && Type != R_ARM_PC24 && Type != R_ARM_PLT32;
 }
 
-void ARMV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
+void ARMV7PILongThunk::writeTo(uint8_t *Buf) const {
   const uint8_t Data[] = {
       0xf0, 0xcf, 0x0f, 0xe3, // P:  movw ip,:lower16:S - (P + (L1-P) + 8)
       0x00, 0xc0, 0x40, 0xe3, //     movt ip,:upper16:S - (P + (L1-P) + 8)
       0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc
       0x1c, 0xff, 0x2f, 0xe1, //     bx r12
   };
   uint64_t S = getARMThunkDestVA(Destination);
   uint64_t P = ThunkSym->getVA();
void ARMV7PILongThunk::addSymbols(ThunkSection &IS) {
   addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, IS);
 }
 
 bool ARMV7PILongThunk::isCompatibleWith(RelType Type) const {
   // Thumb branch relocations can't use BLX
   return Type != R_ARM_THM_JUMP19 && Type != R_ARM_THM_JUMP24;
 }
 
-void ThumbV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
+void ThumbV7PILongThunk::writeTo(uint8_t *Buf) const {
   const uint8_t Data[] = {
       0x4f, 0xf6, 0xf4, 0x7c, // P:  movw ip,:lower16:S - (P + (L1-P) + 4)
       0xc0, 0xf2, 0x00, 0x0c, //     movt ip,:upper16:S - (P + (L1-P) + 4)
       0xfc, 0x44,             // L1: add  r12, pc
       0x60, 0x47,             //     bx   r12
   };
   uint64_t S = getARMThunkDestVA(Destination);
   uint64_t P = ThunkSym->getVA() & ~0x1;

 }
 
 bool ThumbV7PILongThunk::isCompatibleWith(RelType Type) const {
   // ARM branch relocations can't use BLX
   return Type != R_ARM_JUMP24 && Type != R_ARM_PC24 && Type != R_ARM_PLT32;
 }
 
 // Write MIPS LA25 thunk code to call PIC function from the non-PIC one.
-void MipsThunk::writeTo(uint8_t *Buf, ThunkSection &) const {
+void MipsThunk::writeTo(uint8_t *Buf) const {
   uint64_t S = Destination.getVA();
   write32(Buf, 0x3c190000); // lui   $25, %hi(func)
   write32(Buf + 4, 0x08000000 | (S >> 2)); // j     func
   write32(Buf + 8, 0x27390000); // addiu $25, $25, %lo(func)
   write32(Buf + 12, 0x00000000); // nop
   Target->relocateOne(Buf, R_MIPS_HI16, S);
   Target->relocateOne(Buf + 8, R_MIPS_LO16, S);
 }
 
 void MipsThunk::addSymbols(ThunkSection &IS) {
   ThunkSym =
       addSyntheticLocal(Saver.save("__LA25Thunk_" + Destination.getName()),
                         STT_FUNC, Offset, size(), IS);
 }
 
 InputSection *MipsThunk::getTargetInputSection() const {
   auto &DR = cast<Defined>(Destination);
   return dyn_cast<InputSection>(DR.Section);
 }
 
 // Write microMIPS R2-R5 LA25 thunk code
 // to call PIC function from the non-PIC one.
-void MicroMipsThunk::writeTo(uint8_t *Buf, ThunkSection &) const {
+void MicroMipsThunk::writeTo(uint8_t *Buf) const {
   uint64_t S = Destination.getVA() | 1;
   write16(Buf, 0x41b9);       // lui   $25, %hi(func)
   write16(Buf + 4, 0xd400);   // j     func
   write16(Buf + 8, 0x3339);   // addiu $25, $25, %lo(func)
   write16(Buf + 12, 0x0c00);  // nop
   Target->relocateOne(Buf, R_MICROMIPS_HI16, S);
   Target->relocateOne(Buf + 4, R_MICROMIPS_26_S1, S);
   Target->relocateOne(Buf + 8, R_MICROMIPS_LO16, S);
 }
 
 void MicroMipsThunk::addSymbols(ThunkSection &IS) {
   ThunkSym =
       addSyntheticLocal(Saver.save("__microLA25Thunk_" + Destination.getName()),
                         STT_FUNC, Offset, size(), IS);
   ThunkSym->StOther |= STO_MIPS_MICROMIPS;
 }
 
 InputSection *MicroMipsThunk::getTargetInputSection() const {
   auto &DR = cast<Defined>(Destination);
   return dyn_cast<InputSection>(DR.Section);
 }
 
 // Write microMIPS R6 LA25 thunk code
 // to call PIC function from the non-PIC one.
-void MicroMipsR6Thunk::writeTo(uint8_t *Buf, ThunkSection &) const {
+void MicroMipsR6Thunk::writeTo(uint8_t *Buf) const {
   uint64_t S = Destination.getVA() | 1;
   uint64_t P = ThunkSym->getVA();
   write16(Buf, 0x1320);       // lui   $25, %hi(func)
   write16(Buf + 4, 0x3339);   // addiu $25, $25, %lo(func)
   write16(Buf + 8, 0x9400);   // bc    func
   Target->relocateOne(Buf, R_MICROMIPS_HI16, S);
   Target->relocateOne(Buf + 4, R_MICROMIPS_LO16, S);
   Target->relocateOne(Buf + 8, R_MICROMIPS_PC26_S1, S - P - 12);