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llvm-project/lld/ELF/Thunks.cpp

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//===- Thunks.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
//
//===---------------------------------------------------------------------===//
//
// 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;
using namespace lld;
using namespace lld::elf;
namespace {
// AArch64 long range Thunks
class AArch64ABSLongThunk final : public Thunk {
public:
AArch64ABSLongThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
class AArch64ADRPThunk final : public Thunk {
public:
AArch64ADRPThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
uint32_t size() override { return 12; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) 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, int64_t addend) : Thunk(dest, addend) {}
bool getMayUseShortThunk();
uint32_t size() override { return getMayUseShortThunk() ? 4 : sizeLong(); }
void writeTo(uint8_t *buf) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) 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, int64_t addend) : Thunk(dest, addend) {
alignment = 2;
}
bool getMayUseShortThunk();
uint32_t size() override { return getMayUseShortThunk() ? 4 : sizeLong(); }
void writeTo(uint8_t *buf) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) 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, int64_t addend) : ARMThunk(dest, addend) {}
uint32_t sizeLong() override { return 12; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
class ARMV7PILongThunk final : public ARMThunk {
public:
ARMV7PILongThunk(Symbol &dest, int64_t addend) : ARMThunk(dest, addend) {}
uint32_t sizeLong() override { return 16; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
class ThumbV7ABSLongThunk final : public ThumbThunk {
public:
ThumbV7ABSLongThunk(Symbol &dest, int64_t addend)
: ThumbThunk(dest, addend) {}
uint32_t sizeLong() override { return 10; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
class ThumbV7PILongThunk final : public ThumbThunk {
public:
ThumbV7PILongThunk(Symbol &dest, int64_t addend) : ThumbThunk(dest, addend) {}
uint32_t sizeLong() override { return 12; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
// Implementations of Thunks for older Arm architectures that do not support
// the movt/movw instructions. These thunks require at least Architecture v5
// as used on processors such as the Arm926ej-s. There are no Thumb entry
// points as there is no Thumb branch instruction on these architecture that
// can result in a thunk
class ARMV5ABSLongThunk final : public ARMThunk {
public:
ARMV5ABSLongThunk(Symbol &dest, int64_t addend) : ARMThunk(dest, addend) {}
uint32_t sizeLong() override { return 8; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) const override;
};
class ARMV5PILongThunk final : public ARMThunk {
public:
ARMV5PILongThunk(Symbol &dest, int64_t addend) : ARMThunk(dest, addend) {}
uint32_t sizeLong() override { return 16; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) const override;
};
// Implementations of Thunks for Arm v6-M. Only Thumb instructions are permitted
class ThumbV6MABSLongThunk final : public ThumbThunk {
public:
ThumbV6MABSLongThunk(Symbol &dest, int64_t addend)
: ThumbThunk(dest, addend) {}
uint32_t sizeLong() override { return 12; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
class ThumbV6MPILongThunk final : public ThumbThunk {
public:
ThumbV6MPILongThunk(Symbol &dest, int64_t addend)
: ThumbThunk(dest, addend) {}
uint32_t sizeLong() override { return 16; }
void writeLong(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
// MIPS LA25 thunk
class MipsThunk final : public Thunk {
public:
MipsThunk(Symbol &dest) : Thunk(dest, 0) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
InputSection *getTargetInputSection() const override;
};
// microMIPS R2-R5 LA25 thunk
class MicroMipsThunk final : public Thunk {
public:
MicroMipsThunk(Symbol &dest) : Thunk(dest, 0) {}
uint32_t size() override { return 14; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
InputSection *getTargetInputSection() const override;
};
// microMIPS R6 LA25 thunk
class MicroMipsR6Thunk final : public Thunk {
public:
MicroMipsR6Thunk(Symbol &dest) : Thunk(dest, 0) {}
uint32_t size() override { return 12; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
InputSection *getTargetInputSection() const override;
};
class PPC32PltCallStub final : public Thunk {
public:
// For R_PPC_PLTREL24, Thunk::addend records the addend which will be used to
// decide the offsets in the call stub.
PPC32PltCallStub(const InputSection &isec, const Relocation &rel,
Symbol &dest)
: Thunk(dest, rel.addend), file(isec.file) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec, const Relocation &rel) const override;
private:
// Records the call site of the call stub.
const InputFile *file;
};
class PPC32LongThunk final : public Thunk {
public:
PPC32LongThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
uint32_t size() override { return config->isPic ? 32 : 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
// PPC64 Plt call stubs.
// Any call site that needs to call through a plt entry needs a call stub in
// the .text section. The call stub is responsible for:
// 1) Saving the toc-pointer to the stack.
// 2) Loading the target functions address from the procedure linkage table into
// r12 for use by the target functions global entry point, and into the count
// register.
// 3) Transferring control to the target function through an indirect branch.
class PPC64PltCallStub final : public Thunk {
public:
PPC64PltCallStub(Symbol &dest) : Thunk(dest, 0) {}
uint32_t size() override { return 20; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) const override;
};
// PPC64 R2 Save Stub
// When the caller requires a valid R2 TOC pointer but the callee does not
// require a TOC pointer and the callee cannot guarantee that it doesn't
// clobber R2 then we need to save R2. This stub:
// 1) Saves the TOC pointer to the stack.
// 2) Tail calls the callee.
class PPC64R2SaveStub final : public Thunk {
public:
PPC64R2SaveStub(Symbol &dest, int64_t addend) : Thunk(dest, addend) {
alignment = 16;
}
// To prevent oscillations in layout when moving from short to long thunks
// we make sure that once a thunk has been set to long it cannot go back.
bool getMayUseShortThunk() {
if (!mayUseShortThunk)
return false;
if (!isInt<26>(computeOffset())) {
mayUseShortThunk = false;
return false;
}
return true;
}
uint32_t size() override { return getMayUseShortThunk() ? 8 : 20; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
private:
// Transitioning from long to short can create layout oscillations in
// certain corner cases which would prevent the layout from converging.
// This is similar to the handling for ARMThunk.
bool mayUseShortThunk = true;
int64_t computeOffset() const {
return destination.getVA() - (getThunkTargetSym()->getVA() + 4);
}
};
// PPC64 R12 Setup Stub
// When a caller that does not maintain a toc-pointer performs a local call to
// a callee which requires a toc-pointer then we need this stub to place the
// callee's global entry point into r12 without a save of R2.
class PPC64R12SetupStub final : public Thunk {
public:
PPC64R12SetupStub(Symbol &dest) : Thunk(dest, 0) { alignment = 16; }
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
// PPC64 PC-relative PLT Stub
// When a caller that does not maintain a toc-pointer performs an extern call
// then this stub is needed for:
// 1) Loading the target functions address from the procedure linkage table into
// r12 for use by the target functions global entry point, and into the count
// register with pc-relative instructions.
// 2) Transferring control to the target function through an indirect branch.
class PPC64PCRelPLTStub final : public Thunk {
public:
PPC64PCRelPLTStub(Symbol &dest) : Thunk(dest, 0) { alignment = 16; }
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) const override;
};
// A bl instruction uses a signed 24 bit offset, with an implicit 4 byte
// alignment. This gives a possible 26 bits of 'reach'. If the call offset is
// larger than that we need to emit a long-branch thunk. The target address
// of the callee is stored in a table to be accessed TOC-relative. Since the
// call must be local (a non-local call will have a PltCallStub instead) the
// table stores the address of the callee's local entry point. For
// position-independent code a corresponding relative dynamic relocation is
// used.
class PPC64LongBranchThunk : public Thunk {
public:
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) const override;
protected:
PPC64LongBranchThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
};
class PPC64PILongBranchThunk final : public PPC64LongBranchThunk {
public:
PPC64PILongBranchThunk(Symbol &dest, int64_t addend)
: PPC64LongBranchThunk(dest, addend) {
assert(!dest.isPreemptible);
if (Optional<uint32_t> index =
in.ppc64LongBranchTarget->addEntry(&dest, addend)) {
mainPart->relaDyn->addReloc(
{target->relativeRel, in.ppc64LongBranchTarget, *index * UINT64_C(8),
true, &dest,
addend + getPPC64GlobalEntryToLocalEntryOffset(dest.stOther)});
}
}
};
class PPC64PDLongBranchThunk final : public PPC64LongBranchThunk {
public:
PPC64PDLongBranchThunk(Symbol &dest, int64_t addend)
: PPC64LongBranchThunk(dest, addend) {
in.ppc64LongBranchTarget->addEntry(&dest, addend);
}
};
// A bl instruction uses a signed 24 bit offset, with an implicit 4 byte
// alignment. This gives a possible 26 bits of 'reach'. If the caller and
// callee do not use toc and the call offset is larger than 26 bits,
// we need to emit a pc-rel based long-branch thunk. The target address of
// the callee is computed with a PC-relative offset.
class PPC64PCRelLongBranchThunk final : public Thunk {
public:
PPC64PCRelLongBranchThunk(Symbol &dest, int64_t addend)
: Thunk(dest, addend) {
alignment = 16;
}
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
bool isCompatibleWith(const InputSection &isec,
const Relocation &rel) 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, int64_t a) {
uint64_t v = s.isInPlt() ? s.getPltVA() : s.getVA(a);
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, addend);
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf + 8, R_AARCH64_ABS64, s);
}
void AArch64ABSLongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__AArch64AbsLongThunk_" + destination.getName()),
STT_FUNC, 0, isec);
addSymbol("$x", STT_NOTYPE, 0, isec);
addSymbol("$d", STT_NOTYPE, 8, isec);
}
// 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, addend);
uint64_t p = getThunkTargetSym()->getVA();
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf, R_AARCH64_ADR_PREL_PG_HI21,
getAArch64Page(s) - getAArch64Page(p));
target->relocateNoSym(buf + 4, R_AARCH64_ADD_ABS_LO12_NC, s);
}
void AArch64ADRPThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__AArch64ADRPThunk_" + destination.getName()), STT_FUNC,
0, isec);
addSymbol("$x", STT_NOTYPE, 0, isec);
}
// 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::getMayUseShortThunk() {
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 (!getMayUseShortThunk()) {
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->relocateNoSym(buf, R_ARM_JUMP24, offset);
}
bool ARMThunk::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
// Thumb branch relocations can't use BLX
return rel.type != R_ARM_THM_JUMP19 && rel.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::getMayUseShortThunk() {
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 (!getMayUseShortThunk()) {
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->relocateNoSym(buf, R_ARM_THM_JUMP24, offset);
}
bool ThumbThunk::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
// ARM branch relocations can't use BLX
return rel.type != R_ARM_JUMP24 && rel.type != R_ARM_PC24 && rel.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->relocateNoSym(buf, R_ARM_MOVW_ABS_NC, s);
target->relocateNoSym(buf + 4, R_ARM_MOVT_ABS, s);
}
void ARMV7ABSLongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__ARMv7ABSLongThunk_" + destination.getName()),
STT_FUNC, 0, isec);
addSymbol("$a", STT_NOTYPE, 0, isec);
}
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->relocateNoSym(buf, R_ARM_THM_MOVW_ABS_NC, s);
target->relocateNoSym(buf + 4, R_ARM_THM_MOVT_ABS, s);
}
void ThumbV7ABSLongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__Thumbv7ABSLongThunk_" + destination.getName()),
STT_FUNC, 1, isec);
addSymbol("$t", STT_NOTYPE, 0, isec);
}
void ARMV7PILongThunk::writeLong(uint8_t *buf) {
const uint8_t data[] = {
0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) + 8)
0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P) + 8)
0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc
0x1c, 0xff, 0x2f, 0xe1, // bx ip
};
uint64_t s = getARMThunkDestVA(destination);
uint64_t p = getThunkTargetSym()->getVA();
int64_t offset = s - p - 16;
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf, R_ARM_MOVW_PREL_NC, offset);
target->relocateNoSym(buf + 4, R_ARM_MOVT_PREL, offset);
}
void ARMV7PILongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__ARMV7PILongThunk_" + destination.getName()), STT_FUNC,
0, isec);
addSymbol("$a", STT_NOTYPE, 0, isec);
}
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 ip, pc
0x60, 0x47, // bx ip
};
uint64_t s = getARMThunkDestVA(destination);
uint64_t p = getThunkTargetSym()->getVA() & ~0x1;
int64_t offset = s - p - 12;
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf, R_ARM_THM_MOVW_PREL_NC, offset);
target->relocateNoSym(buf + 4, R_ARM_THM_MOVT_PREL, offset);
}
void ThumbV7PILongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__ThumbV7PILongThunk_" + destination.getName()),
STT_FUNC, 1, isec);
addSymbol("$t", STT_NOTYPE, 0, isec);
}
void ARMV5ABSLongThunk::writeLong(uint8_t *buf) {
const uint8_t data[] = {
0x04, 0xf0, 0x1f, 0xe5, // ldr pc, [pc,#-4] ; L1
0x00, 0x00, 0x00, 0x00, // L1: .word S
};
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf + 4, R_ARM_ABS32, getARMThunkDestVA(destination));
}
void ARMV5ABSLongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__ARMv5ABSLongThunk_" + destination.getName()),
STT_FUNC, 0, isec);
addSymbol("$a", STT_NOTYPE, 0, isec);
addSymbol("$d", STT_NOTYPE, 4, isec);
}
bool ARMV5ABSLongThunk::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
// Thumb branch relocations can't use BLX
return rel.type != R_ARM_THM_JUMP19 && rel.type != R_ARM_THM_JUMP24;
}
void ARMV5PILongThunk::writeLong(uint8_t *buf) {
const uint8_t data[] = {
0x04, 0xc0, 0x9f, 0xe5, // P: ldr ip, [pc,#4] ; L2
0x0c, 0xc0, 0x8f, 0xe0, // L1: add ip, pc, ip
0x1c, 0xff, 0x2f, 0xe1, // bx ip
0x00, 0x00, 0x00, 0x00, // L2: .word S - (P + (L1 - P) + 8)
};
uint64_t s = getARMThunkDestVA(destination);
uint64_t p = getThunkTargetSym()->getVA() & ~0x1;
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf + 12, R_ARM_REL32, s - p - 12);
}
void ARMV5PILongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__ARMV5PILongThunk_" + destination.getName()), STT_FUNC,
0, isec);
addSymbol("$a", STT_NOTYPE, 0, isec);
addSymbol("$d", STT_NOTYPE, 12, isec);
}
bool ARMV5PILongThunk::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
// Thumb branch relocations can't use BLX
return rel.type != R_ARM_THM_JUMP19 && rel.type != R_ARM_THM_JUMP24;
}
void ThumbV6MABSLongThunk::writeLong(uint8_t *buf) {
// Most Thumb instructions cannot access the high registers r8 - r15. As the
// only register we can corrupt is r12 we must instead spill a low register
// to the stack to use as a scratch register. We push r1 even though we
// don't need to get some space to use for the return address.
const uint8_t data[] = {
0x03, 0xb4, // push {r0, r1} ; Obtain scratch registers
0x01, 0x48, // ldr r0, [pc, #4] ; L1
0x01, 0x90, // str r0, [sp, #4] ; SP + 4 = S
0x01, 0xbd, // pop {r0, pc} ; restore r0 and branch to dest
0x00, 0x00, 0x00, 0x00 // L1: .word S
};
uint64_t s = getARMThunkDestVA(destination);
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf + 8, R_ARM_ABS32, s);
}
void ThumbV6MABSLongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__Thumbv6MABSLongThunk_" + destination.getName()),
STT_FUNC, 1, isec);
addSymbol("$t", STT_NOTYPE, 0, isec);
addSymbol("$d", STT_NOTYPE, 8, isec);
}
void ThumbV6MPILongThunk::writeLong(uint8_t *buf) {
// Most Thumb instructions cannot access the high registers r8 - r15. As the
// only register we can corrupt is ip (r12) we must instead spill a low
// register to the stack to use as a scratch register.
const uint8_t data[] = {
0x01, 0xb4, // P: push {r0} ; Obtain scratch register
0x02, 0x48, // ldr r0, [pc, #8] ; L2
0x84, 0x46, // mov ip, r0 ; high to low register
0x01, 0xbc, // pop {r0} ; restore scratch register
0xe7, 0x44, // L1: add pc, ip ; transfer control
0xc0, 0x46, // nop ; pad to 4-byte boundary
0x00, 0x00, 0x00, 0x00, // L2: .word S - (P + (L1 - P) + 4)
};
uint64_t s = getARMThunkDestVA(destination);
uint64_t p = getThunkTargetSym()->getVA() & ~0x1;
memcpy(buf, data, sizeof(data));
target->relocateNoSym(buf + 12, R_ARM_REL32, s - p - 12);
}
void ThumbV6MPILongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__Thumbv6MPILongThunk_" + destination.getName()),
STT_FUNC, 1, isec);
addSymbol("$t", STT_NOTYPE, 0, isec);
addSymbol("$d", STT_NOTYPE, 12, isec);
}
// 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->relocateNoSym(buf, R_MIPS_HI16, s);
target->relocateNoSym(buf + 8, R_MIPS_LO16, s);
}
void MipsThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__LA25Thunk_" + destination.getName()), STT_FUNC, 0,
isec);
}
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();
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->relocateNoSym(buf, R_MICROMIPS_HI16, s);
target->relocateNoSym(buf + 4, R_MICROMIPS_26_S1, s);
target->relocateNoSym(buf + 8, R_MICROMIPS_LO16, s);
}
void MicroMipsThunk::addSymbols(ThunkSection &isec) {
Defined *d = addSymbol(
saver.save("__microLA25Thunk_" + destination.getName()), STT_FUNC, 0, isec);
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();
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->relocateNoSym(buf, R_MICROMIPS_HI16, s);
target->relocateNoSym(buf + 4, R_MICROMIPS_LO16, s);
target->relocateNoSym(buf + 8, R_MICROMIPS_PC26_S1, s - p - 12);
}
void MicroMipsR6Thunk::addSymbols(ThunkSection &isec) {
Defined *d = addSymbol(
saver.save("__microLA25Thunk_" + destination.getName()), STT_FUNC, 0, isec);
d->stOther |= STO_MIPS_MICROMIPS;
}
InputSection *MicroMipsR6Thunk::getTargetInputSection() const {
auto &dr = cast<Defined>(destination);
return dyn_cast<InputSection>(dr.section);
}
void elf::writePPC32PltCallStub(uint8_t *buf, uint64_t gotPltVA,
const InputFile *file, int64_t addend) {
if (!config->isPic) {
write32(buf + 0, 0x3d600000 | (gotPltVA + 0x8000) >> 16); // lis r11,ha
write32(buf + 4, 0x816b0000 | (uint16_t)gotPltVA); // lwz r11,l(r11)
write32(buf + 8, 0x7d6903a6); // mtctr r11
write32(buf + 12, 0x4e800420); // bctr
return;
}
uint32_t offset;
if (addend >= 0x8000) {
// The stub loads an address relative to r30 (.got2+Addend). Addend is
// almost always 0x8000. The address of .got2 is different in another object
// file, so a stub cannot be shared.
offset = gotPltVA - (in.ppc32Got2->getParent()->getVA() +
file->ppc32Got2OutSecOff + addend);
} else {
// The stub loads an address relative to _GLOBAL_OFFSET_TABLE_ (which is
// currently the address of .got).
offset = gotPltVA - in.got->getVA();
}
uint16_t ha = (offset + 0x8000) >> 16, l = (uint16_t)offset;
if (ha == 0) {
write32(buf + 0, 0x817e0000 | l); // lwz r11,l(r30)
write32(buf + 4, 0x7d6903a6); // mtctr r11
write32(buf + 8, 0x4e800420); // bctr
write32(buf + 12, 0x60000000); // nop
} else {
write32(buf + 0, 0x3d7e0000 | ha); // addis r11,r30,ha
write32(buf + 4, 0x816b0000 | l); // lwz r11,l(r11)
write32(buf + 8, 0x7d6903a6); // mtctr r11
write32(buf + 12, 0x4e800420); // bctr
}
}
void PPC32PltCallStub::writeTo(uint8_t *buf) {
writePPC32PltCallStub(buf, destination.getGotPltVA(), file, addend);
}
void PPC32PltCallStub::addSymbols(ThunkSection &isec) {
std::string buf;
raw_string_ostream os(buf);
os << format_hex_no_prefix(addend, 8);
if (!config->isPic)
os << ".plt_call32.";
else if (addend >= 0x8000)
os << ".got2.plt_pic32.";
else
os << ".plt_pic32.";
os << destination.getName();
addSymbol(saver.save(os.str()), STT_FUNC, 0, isec);
}
bool PPC32PltCallStub::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
return !config->isPic || (isec.file == file && rel.addend == addend);
}
void PPC32LongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__LongThunk_" + destination.getName()), STT_FUNC, 0,
isec);
}
void PPC32LongThunk::writeTo(uint8_t *buf) {
auto ha = [](uint32_t v) -> uint16_t { return (v + 0x8000) >> 16; };
auto lo = [](uint32_t v) -> uint16_t { return v; };
uint32_t d = destination.getVA(addend);
if (config->isPic) {
uint32_t off = d - (getThunkTargetSym()->getVA() + 8);
write32(buf + 0, 0x7c0802a6); // mflr r12,0
write32(buf + 4, 0x429f0005); // bcl r20,r31,.+4
write32(buf + 8, 0x7d8802a6); // mtctr r12
write32(buf + 12, 0x3d8c0000 | ha(off)); // addis r12,r12,off@ha
write32(buf + 16, 0x398c0000 | lo(off)); // addi r12,r12,off@l
write32(buf + 20, 0x7c0803a6); // mtlr r0
buf += 24;
} else {
write32(buf + 0, 0x3d800000 | ha(d)); // lis r12,d@ha
write32(buf + 4, 0x398c0000 | lo(d)); // addi r12,r12,d@l
buf += 8;
}
write32(buf + 0, 0x7d8903a6); // mtctr r12
write32(buf + 4, 0x4e800420); // bctr
}
void elf::writePPC64LoadAndBranch(uint8_t *buf, int64_t offset) {
uint16_t offHa = (offset + 0x8000) >> 16;
uint16_t offLo = offset & 0xffff;
write32(buf + 0, 0x3d820000 | offHa); // addis r12, r2, OffHa
write32(buf + 4, 0xe98c0000 | offLo); // ld r12, OffLo(r12)
write32(buf + 8, 0x7d8903a6); // mtctr r12
write32(buf + 12, 0x4e800420); // bctr
}
void PPC64PltCallStub::writeTo(uint8_t *buf) {
int64_t offset = destination.getGotPltVA() - getPPC64TocBase();
// Save the TOC pointer to the save-slot reserved in the call frame.
write32(buf + 0, 0xf8410018); // std r2,24(r1)
writePPC64LoadAndBranch(buf + 4, offset);
}
void PPC64PltCallStub::addSymbols(ThunkSection &isec) {
Defined *s = addSymbol(saver.save("__plt_" + destination.getName()), STT_FUNC,
0, isec);
s->needsTocRestore = true;
s->file = destination.file;
}
bool PPC64PltCallStub::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
return rel.type == R_PPC64_REL24 || rel.type == R_PPC64_REL14;
}
void PPC64R2SaveStub::writeTo(uint8_t *buf) {
const int64_t offset = computeOffset();
write32(buf + 0, 0xf8410018); // std r2,24(r1)
// The branch offset needs to fit in 26 bits.
if (getMayUseShortThunk()) {
write32(buf + 4, 0x48000000 | (offset & 0x03fffffc)); // b <offset>
} else if (isInt<34>(offset)) {
const uint64_t paddi = PADDI_R12_NO_DISP |
(((offset >> 16) & 0x3ffff) << 32) |
(offset & 0xffff);
writePrefixedInstruction(buf + 4, paddi); // paddi r12, 0, func@pcrel, 1
write32(buf + 12, MTCTR_R12); // mtctr r12
write32(buf + 16, BCTR); // bctr
} else {
in.ppc64LongBranchTarget->addEntry(&destination, addend);
const int64_t offsetFromTOC =
in.ppc64LongBranchTarget->getEntryVA(&destination, addend) -
getPPC64TocBase();
writePPC64LoadAndBranch(buf + 4, offsetFromTOC);
}
}
void PPC64R2SaveStub::addSymbols(ThunkSection &isec) {
Defined *s = addSymbol(saver.save("__toc_save_" + destination.getName()),
STT_FUNC, 0, isec);
s->needsTocRestore = true;
}
void PPC64R12SetupStub::writeTo(uint8_t *buf) {
int64_t offset = destination.getVA() - getThunkTargetSym()->getVA();
if (!isInt<34>(offset))
reportRangeError(buf, offset, 34, destination, "R12 setup stub offset");
uint64_t paddi = PADDI_R12_NO_DISP | (((offset >> 16) & 0x3ffff) << 32) |
(offset & 0xffff);
writePrefixedInstruction(buf + 0, paddi); // paddi r12, 0, func@pcrel, 1
write32(buf + 8, MTCTR_R12); // mtctr r12
write32(buf + 12, BCTR); // bctr
}
void PPC64R12SetupStub::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__gep_setup_" + destination.getName()), STT_FUNC, 0,
isec);
}
void PPC64PCRelPLTStub::writeTo(uint8_t *buf) {
int64_t offset = destination.getGotPltVA() - getThunkTargetSym()->getVA();
if (!isInt<34>(offset))
reportRangeError(buf, offset, 34, destination,
"PC-relative PLT stub offset");
uint64_t pld =
PLD_R12_NO_DISP | (((offset >> 16) & 0x3ffff) << 32) | (offset & 0xffff);
writePrefixedInstruction(buf + 0, pld); // pld r12, func@plt@pcrel
write32(buf + 8, MTCTR_R12); // mtctr r12
write32(buf + 12, BCTR); // bctr
}
void PPC64PCRelPLTStub::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__plt_pcrel_" + destination.getName()), STT_FUNC, 0,
isec);
}
bool PPC64PCRelPLTStub::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
return rel.type == R_PPC64_REL24_NOTOC;
}
void PPC64LongBranchThunk::writeTo(uint8_t *buf) {
int64_t offset = in.ppc64LongBranchTarget->getEntryVA(&destination, addend) -
getPPC64TocBase();
writePPC64LoadAndBranch(buf, offset);
}
void PPC64LongBranchThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__long_branch_" + destination.getName()), STT_FUNC, 0,
isec);
}
bool PPC64LongBranchThunk::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
return rel.type == R_PPC64_REL24 || rel.type == R_PPC64_REL14;
}
void PPC64PCRelLongBranchThunk::writeTo(uint8_t *buf) {
int64_t offset = destination.getVA() - getThunkTargetSym()->getVA();
if (!isInt<34>(offset))
reportRangeError(buf, offset, 34, destination,
"PC-relative long branch stub offset");
uint64_t paddi = PADDI_R12_NO_DISP | (((offset >> 16) & 0x3ffff) << 32) |
(offset & 0xffff);
writePrefixedInstruction(buf + 0, paddi); // paddi r12, 0, func@pcrel, 1
write32(buf + 8, MTCTR_R12); // mtctr r12
write32(buf + 12, BCTR); // bctr
}
void PPC64PCRelLongBranchThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__long_branch_pcrel_" + destination.getName()),
STT_FUNC, 0, isec);
}
bool PPC64PCRelLongBranchThunk::isCompatibleWith(const InputSection &isec,
const Relocation &rel) const {
return rel.type == R_PPC64_REL24_NOTOC;
}
Thunk::Thunk(Symbol &d, int64_t a) : destination(d), addend(a), offset(0) {}
Thunk::~Thunk() = default;
static Thunk *addThunkAArch64(RelType type, Symbol &s, int64_t a) {
if (type != R_AARCH64_CALL26 && type != R_AARCH64_JUMP26 &&
type != R_AARCH64_PLT32)
fatal("unrecognized relocation type");
if (config->picThunk)
return make<AArch64ADRPThunk>(s, a);
return make<AArch64ABSLongThunk>(s, a);
}
// Creates a thunk for Thumb-ARM interworking.
// Arm Architectures v5 and v6 do not support Thumb2 technology. This means
// - MOVT and MOVW instructions cannot be used
// - Only Thumb relocation that can generate a Thunk is a BL, this can always
// be transformed into a BLX
static Thunk *addThunkPreArmv7(RelType reloc, Symbol &s, int64_t a) {
switch (reloc) {
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_JUMP24:
case R_ARM_CALL:
case R_ARM_THM_CALL:
if (config->picThunk)
return make<ARMV5PILongThunk>(s, a);
return make<ARMV5ABSLongThunk>(s, a);
}
fatal("relocation " + toString(reloc) + " to " + toString(s) +
" not supported for Armv5 or Armv6 targets");
}
// Create a thunk for Thumb long branch on V6-M.
// Arm Architecture v6-M only supports Thumb instructions. This means
// - MOVT and MOVW instructions cannot be used.
// - Only a limited number of instructions can access registers r8 and above
// - No interworking support is needed (all Thumb).
static Thunk *addThunkV6M(RelType reloc, Symbol &s, int64_t a) {
switch (reloc) {
case R_ARM_THM_JUMP19:
case R_ARM_THM_JUMP24:
case R_ARM_THM_CALL:
if (config->isPic)
return make<ThumbV6MPILongThunk>(s, a);
return make<ThumbV6MABSLongThunk>(s, a);
}
fatal("relocation " + toString(reloc) + " to " + toString(s) +
" not supported for Armv6-M targets");
}
// Creates a thunk for Thumb-ARM interworking or branch range extension.
static Thunk *addThunkArm(RelType reloc, Symbol &s, int64_t a) {
// Decide which Thunk is needed based on:
// Available instruction set
// - An Arm Thunk can only be used if Arm state is available.
// - A Thumb Thunk can only be used if Thumb state is available.
// - Can only use a Thunk if it uses instructions that the Target supports.
// Relocation is branch or branch and link
// - Branch instructions cannot change state, can only select Thunk that
// starts in the same state as the caller.
// - Branch and link relocations can change state, can select Thunks from
// either Arm or Thumb.
// Position independent Thunks if we require position independent code.
// Handle architectures that have restrictions on the instructions that they
// can use in Thunks. The flags below are set by reading the BuildAttributes
// of the input objects. InputFiles.cpp contains the mapping from ARM
// architecture to flag.
if (!config->armHasMovtMovw) {
if (!config->armJ1J2BranchEncoding)
return addThunkPreArmv7(reloc, s, a);
return addThunkV6M(reloc, s, a);
}
switch (reloc) {
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_JUMP24:
case R_ARM_CALL:
if (config->picThunk)
return make<ARMV7PILongThunk>(s, a);
return make<ARMV7ABSLongThunk>(s, a);
case R_ARM_THM_JUMP19:
case R_ARM_THM_JUMP24:
case R_ARM_THM_CALL:
if (config->picThunk)
return make<ThumbV7PILongThunk>(s, a);
return make<ThumbV7ABSLongThunk>(s, a);
}
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);
}
static Thunk *addThunkPPC32(const InputSection &isec, const Relocation &rel,
Symbol &s) {
assert((rel.type == R_PPC_LOCAL24PC || rel.type == R_PPC_REL24 ||
rel.type == R_PPC_PLTREL24) &&
"unexpected relocation type for thunk");
if (s.isInPlt())
return make<PPC32PltCallStub>(isec, rel, s);
return make<PPC32LongThunk>(s, rel.addend);
}
static Thunk *addThunkPPC64(RelType type, Symbol &s, int64_t a) {
assert((type == R_PPC64_REL14 || type == R_PPC64_REL24 ||
type == R_PPC64_REL24_NOTOC) &&
"unexpected relocation type for thunk");
if (s.isInPlt())
return type == R_PPC64_REL24_NOTOC ? (Thunk *)make<PPC64PCRelPLTStub>(s)
: (Thunk *)make<PPC64PltCallStub>(s);
// This check looks at the st_other bits of the callee. If the value is 1
// then the callee clobbers the TOC and we need an R2 save stub when RelType
// is R_PPC64_REL14 or R_PPC64_REL24.
if ((type == R_PPC64_REL14 || type == R_PPC64_REL24) && (s.stOther >> 5) == 1)
return make<PPC64R2SaveStub>(s, a);
if (type == R_PPC64_REL24_NOTOC)
return (s.stOther >> 5) > 1
? (Thunk *)make<PPC64R12SetupStub>(s)
: (Thunk *)make<PPC64PCRelLongBranchThunk>(s, a);
if (config->picThunk)
return make<PPC64PILongBranchThunk>(s, a);
return make<PPC64PDLongBranchThunk>(s, a);
}
Thunk *elf::addThunk(const InputSection &isec, Relocation &rel) {
Symbol &s = *rel.sym;
int64_t a = rel.addend;
if (config->emachine == EM_AARCH64)
return addThunkAArch64(rel.type, s, a);
if (config->emachine == EM_ARM)
return addThunkArm(rel.type, s, a);
if (config->emachine == EM_MIPS)
return addThunkMips(rel.type, s);
if (config->emachine == EM_PPC)
return addThunkPPC32(isec, rel, s);
if (config->emachine == EM_PPC64)
return addThunkPPC64(rel.type, s, a);
llvm_unreachable("add Thunk only supported for ARM, Mips and PowerPC");
}
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