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llvm-project/lld/ELF/Thunks.cpp

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//===- Thunks.cpp --------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//
//
// This file contains Thunk subclasses.
//
// A thunk is a small piece of code written after an input section
// which is used to jump between "incompatible" functions
// such as MIPS PIC and non-PIC or ARM non-Thumb and Thumb functions.
//
// If a jump target is too far and its address doesn't fit to a
// short jump instruction, we need to create a thunk too, but we
// haven't supported it yet.
//
// i386 and x86-64 don't need thunks.
//
//===---------------------------------------------------------------------===//
#include "Thunks.h"
#include "Config.h"
#include "InputSection.h"
#include "OutputSections.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include <cstdint>
#include <cstring>
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
namespace lld {
namespace elf {
namespace {
// AArch64 long range Thunks
class AArch64ABSLongThunk final : public Thunk {
public:
AArch64ABSLongThunk(Symbol &Dest) : Thunk(Dest) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
};
class AArch64ADRPThunk final : public Thunk {
public:
AArch64ADRPThunk(Symbol &Dest) : Thunk(Dest) {}
uint32_t size() override { return 12; }
void writeTo(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
};
// Base class for ARM thunks.
//
// An ARM thunk may be either short or long. A short thunk is simply a branch
// (B) instruction, and it may be used to call ARM functions when the distance
// from the thunk to the target is less than 32MB. Long thunks can branch to any
// virtual address and can switch between ARM and Thumb, and they are
// implemented in the derived classes. This class tries to create a short thunk
// if the target is in range, otherwise it creates a long thunk.
class ARMThunk : public Thunk {
public:
ARMThunk(Symbol &Dest) : Thunk(Dest) {}
bool mayUseShortThunk();
uint32_t size() override { return mayUseShortThunk() ? 4 : sizeLong(); }
void writeTo(uint8_t *Buf) override;
bool isCompatibleWith(RelType Type) const override;
// Returns the size of a long thunk.
virtual uint32_t sizeLong() = 0;
// Writes a long thunk to Buf.
virtual void writeLong(uint8_t *Buf) = 0;
private:
// This field tracks whether all previously considered layouts would allow
// this thunk to be short. If we have ever needed a long thunk, we always
// create a long thunk, even if the thunk may be short given the current
// distance to the target. We do this because transitioning from long to short
// can create layout oscillations in certain corner cases which would prevent
// the layout from converging.
bool MayUseShortThunk = true;
};
// Base class for Thumb-2 thunks.
//
// This class is similar to ARMThunk, but it uses the Thumb-2 B.W instruction
// which has a range of 16MB.
class ThumbThunk : public Thunk {
public:
ThumbThunk(Symbol &Dest) : Thunk(Dest) { Alignment = 2; }
bool mayUseShortThunk();
uint32_t size() override { return mayUseShortThunk() ? 4 : sizeLong(); }
void writeTo(uint8_t *Buf) override;
bool isCompatibleWith(RelType Type) const override;
// Returns the size of a long thunk.
virtual uint32_t sizeLong() = 0;
// Writes a long thunk to Buf.
virtual void writeLong(uint8_t *Buf) = 0;
private:
// See comment in ARMThunk above.
bool MayUseShortThunk = true;
};
// Specific ARM Thunk implementations. The naming convention is:
// Source State, TargetState, Target Requirement, ABS or PI, Range
class ARMV7ABSLongThunk final : public ARMThunk {
public:
ARMV7ABSLongThunk(Symbol &Dest) : ARMThunk(Dest) {}
uint32_t sizeLong() override { return 12; }
void writeLong(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
};
class ARMV7PILongThunk final : public ARMThunk {
public:
ARMV7PILongThunk(Symbol &Dest) : ARMThunk(Dest) {}
uint32_t sizeLong() override { return 16; }
void writeLong(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
};
class ThumbV7ABSLongThunk final : public ThumbThunk {
public:
ThumbV7ABSLongThunk(Symbol &Dest) : ThumbThunk(Dest) {}
uint32_t sizeLong() override { return 10; }
void writeLong(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
};
class ThumbV7PILongThunk final : public ThumbThunk {
public:
ThumbV7PILongThunk(Symbol &Dest) : ThumbThunk(Dest) {}
uint32_t sizeLong() override { return 12; }
void writeLong(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
};
// MIPS LA25 thunk
class MipsThunk final : public Thunk {
public:
MipsThunk(Symbol &Dest) : Thunk(Dest) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *Buf) 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() override { return 14; }
void writeTo(uint8_t *Buf) 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() override { return 12; }
void writeTo(uint8_t *Buf) override;
void addSymbols(ThunkSection &IS) override;
InputSection *getTargetInputSection() const override;
};
} // end anonymous namespace
Defined *Thunk::addSymbol(StringRef Name, uint8_t Type, uint64_t Value,
InputSectionBase &Section) {
Defined *D = addSyntheticLocal(Name, Type, Value, /*Size=*/0, Section);
Syms.push_back(D);
return D;
}
void Thunk::setOffset(uint64_t NewOffset) {
for (Defined *D : Syms)
D->Value = D->Value - Offset + NewOffset;
Offset = NewOffset;
}
// 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) {
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) {
addSymbol(Saver.save("__AArch64AbsLongThunk_" + Destination.getName()),
STT_FUNC, 0, IS);
addSymbol("$x", STT_NOTYPE, 0, IS);
addSymbol("$d", STT_NOTYPE, 8, 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) {
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 = getThunkTargetSym()->getVA();
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_AARCH64_ADR_PREL_PG_HI21,
getAArch64Page(S) - getAArch64Page(P));
Target->relocateOne(Buf + 4, R_AARCH64_ADD_ABS_LO12_NC, S);
}
void AArch64ADRPThunk::addSymbols(ThunkSection &IS) {
addSymbol(Saver.save("__AArch64ADRPThunk_" + Destination.getName()), STT_FUNC,
0, IS);
addSymbol("$x", STT_NOTYPE, 0, IS);
}
// ARM Target Thunks
static uint64_t getARMThunkDestVA(const Symbol &S) {
uint64_t V = S.isInPlt() ? S.getPltVA() : S.getVA();
return SignExtend64<32>(V);
}
// This function returns true if the target is not Thumb and is within 2^26, and
// it has not previously returned false (see comment for MayUseShortThunk).
bool ARMThunk::mayUseShortThunk() {
if (!MayUseShortThunk)
return false;
uint64_t S = getARMThunkDestVA(Destination);
if (S & 1) {
MayUseShortThunk = false;
return false;
}
uint64_t P = getThunkTargetSym()->getVA();
int64_t Offset = S - P - 8;
MayUseShortThunk = llvm::isInt<26>(Offset);
return MayUseShortThunk;
}
void ARMThunk::writeTo(uint8_t *Buf) {
if (!mayUseShortThunk()) {
writeLong(Buf);
return;
}
uint64_t S = getARMThunkDestVA(Destination);
uint64_t P = getThunkTargetSym()->getVA();
int64_t Offset = S - P - 8;
const uint8_t Data[] = {
0x00, 0x00, 0x00, 0xea, // b S
};
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_ARM_JUMP24, Offset);
}
bool ARMThunk::isCompatibleWith(RelType Type) const {
// Thumb branch relocations can't use BLX
return Type != R_ARM_THM_JUMP19 && Type != R_ARM_THM_JUMP24;
}
// This function returns true if the target is Thumb and is within 2^25, and
// it has not previously returned false (see comment for MayUseShortThunk).
bool ThumbThunk::mayUseShortThunk() {
if (!MayUseShortThunk)
return false;
uint64_t S = getARMThunkDestVA(Destination);
if ((S & 1) == 0) {
MayUseShortThunk = false;
return false;
}
uint64_t P = getThunkTargetSym()->getVA() & ~1;
int64_t Offset = S - P - 4;
MayUseShortThunk = llvm::isInt<25>(Offset);
return MayUseShortThunk;
}
void ThumbThunk::writeTo(uint8_t *Buf) {
if (!mayUseShortThunk()) {
writeLong(Buf);
return;
}
uint64_t S = getARMThunkDestVA(Destination);
uint64_t P = getThunkTargetSym()->getVA();
int64_t Offset = S - P - 4;
const uint8_t Data[] = {
0x00, 0xf0, 0x00, 0xb0, // b.w S
};
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_ARM_THM_JUMP24, Offset);
}
bool ThumbThunk::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 ARMV7ABSLongThunk::writeLong(uint8_t *Buf) {
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) {
addSymbol(Saver.save("__ARMv7ABSLongThunk_" + Destination.getName()),
STT_FUNC, 0, IS);
addSymbol("$a", STT_NOTYPE, 0, IS);
}
void ThumbV7ABSLongThunk::writeLong(uint8_t *Buf) {
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) {
addSymbol(Saver.save("__Thumbv7ABSLongThunk_" + Destination.getName()),
STT_FUNC, 1, IS);
addSymbol("$t", STT_NOTYPE, 0, IS);
}
void ARMV7PILongThunk::writeLong(uint8_t *Buf) {
const uint8_t Data[] = {
0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) + 8)
0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P) + 8)
0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc
0x1c, 0xff, 0x2f, 0xe1, // bx r12
};
uint64_t S = getARMThunkDestVA(Destination);
uint64_t P = getThunkTargetSym()->getVA();
uint64_t Offset = S - P - 16;
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, Offset);
Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, Offset);
}
void ARMV7PILongThunk::addSymbols(ThunkSection &IS) {
addSymbol(Saver.save("__ARMV7PILongThunk_" + Destination.getName()), STT_FUNC,
0, IS);
addSymbol("$a", STT_NOTYPE, 0, IS);
}
void ThumbV7PILongThunk::writeLong(uint8_t *Buf) {
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 = getThunkTargetSym()->getVA() & ~0x1;
uint64_t Offset = S - P - 12;
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, Offset);
Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, Offset);
}
void ThumbV7PILongThunk::addSymbols(ThunkSection &IS) {
addSymbol(Saver.save("__ThumbV7PILongThunk_" + Destination.getName()),
STT_FUNC, 1, IS);
addSymbol("$t", STT_NOTYPE, 0, IS);
}
// Write MIPS LA25 thunk code to call PIC function from the non-PIC one.
void MipsThunk::writeTo(uint8_t *Buf) {
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) {
addSymbol(Saver.save("__LA25Thunk_" + Destination.getName()), STT_FUNC, 0,
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) {
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) {
Defined *D = addSymbol(
Saver.save("__microLA25Thunk_" + Destination.getName()), STT_FUNC, 0, IS);
D->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) {
uint64_t S = Destination.getVA() | 1;
uint64_t P = getThunkTargetSym()->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);
}
void MicroMipsR6Thunk::addSymbols(ThunkSection &IS) {
Defined *D = addSymbol(
Saver.save("__microLA25Thunk_" + Destination.getName()), STT_FUNC, 0, IS);
D->StOther |= STO_MIPS_MICROMIPS;
}
InputSection *MicroMipsR6Thunk::getTargetInputSection() const {
auto &DR = cast<Defined>(Destination);
return dyn_cast<InputSection>(DR.Section);
}
Thunk::Thunk(Symbol &D) : Destination(D), Offset(0) {}
Thunk::~Thunk() = default;
static Thunk *addThunkAArch64(RelType Type, Symbol &S) {
if (Type != R_AARCH64_CALL26 && Type != R_AARCH64_JUMP26)
fatal("unrecognized relocation type");
if (Config->Pic)
return make<AArch64ADRPThunk>(S);
return make<AArch64ABSLongThunk>(S);
}
// Creates a thunk for Thumb-ARM interworking.
static Thunk *addThunkArm(RelType Reloc, Symbol &S) {
// ARM relocations need ARM to Thumb interworking Thunks.
// Thumb relocations need Thumb to ARM relocations.
// Use position independent Thunks if we require position independent code.
switch (Reloc) {
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_JUMP24:
case R_ARM_CALL:
if (Config->Pic)
return make<ARMV7PILongThunk>(S);
return make<ARMV7ABSLongThunk>(S);
case R_ARM_THM_JUMP19:
case R_ARM_THM_JUMP24:
case R_ARM_THM_CALL:
if (Config->Pic)
return make<ThumbV7PILongThunk>(S);
return make<ThumbV7ABSLongThunk>(S);
}
fatal("unrecognized relocation type");
}
static Thunk *addThunkMips(RelType Type, Symbol &S) {
if ((S.StOther & STO_MIPS_MICROMIPS) && isMipsR6())
return make<MicroMipsR6Thunk>(S);
if (S.StOther & STO_MIPS_MICROMIPS)
return make<MicroMipsThunk>(S);
return make<MipsThunk>(S);
}
Thunk *addThunk(RelType Type, Symbol &S) {
if (Config->EMachine == EM_AARCH64)
return addThunkAArch64(Type, S);
else if (Config->EMachine == EM_ARM)
return addThunkArm(Type, S);
else if (Config->EMachine == EM_MIPS)
return addThunkMips(Type, S);
llvm_unreachable("add Thunk only supported for ARM and Mips");
return nullptr;
}
} // end namespace elf
} // end namespace lld
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