llvm-project/lld/ELF/Target.cpp

//===- Target.cpp ---------------------------------------------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "Target.h"
#include "Error.h"
#include "OutputSections.h"
#include "Symbols.h"

#include "llvm/ADT/ArrayRef.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ELF.h"

using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::ELF;

namespace lld {
namespace elf2 {

std::unique_ptr<TargetInfo> Target;

TargetInfo::~TargetInfo() {}

bool TargetInfo::relocPointsToGot(uint32_t Type) const { return false; }

bool TargetInfo::isRelRelative(uint32_t Type) const { return true; }

X86TargetInfo::X86TargetInfo() {
  PCRelReloc = R_386_PC32;
  GotReloc = R_386_GLOB_DAT;
  GotRefReloc = R_386_GOT32;
  VAStart = 0x10000;
}

void X86TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                  uint64_t PltEntryAddr) const {
  // jmpl *val; nop; nop
  const uint8_t Inst[] = {0xff, 0x25, 0, 0, 0, 0, 0x90, 0x90};
  memcpy(Buf, Inst, sizeof(Inst));
  assert(isUInt<32>(GotEntryAddr));
  write32le(Buf + 2, GotEntryAddr);
}

bool X86TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
  return Type == R_386_GOT32 || relocNeedsPlt(Type, S);
}

bool X86TargetInfo::relocPointsToGot(uint32_t Type) const {
  return Type == R_386_GOTPC;
}

bool X86TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  return Type == R_386_PLT32 || (Type == R_386_PC32 && S.isShared());
}

static void add32le(uint8_t *L, int32_t V) { write32le(L, read32le(L) + V); }
static void or32le(uint8_t *L, int32_t V) { write32le(L, read32le(L) | V); }

void X86TargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                uint64_t BaseAddr, uint64_t SymVA) const {
  typedef ELFFile<ELF32LE>::Elf_Rel Elf_Rel;
  auto &Rel = *reinterpret_cast<const Elf_Rel *>(RelP);

  uint32_t Offset = Rel.r_offset;
  uint8_t *Loc = Buf + Offset;
  switch (Type) {
  case R_386_GOT32:
    add32le(Loc, SymVA - Out<ELF32LE>::Got->getVA());
    break;
  case R_386_PC32:
    add32le(Loc, SymVA - (BaseAddr + Offset));
    break;
  case R_386_32:
    add32le(Loc, SymVA);
    break;
  default:
    error(Twine("unrecognized reloc ") + Twine(Type));
    break;
  }
}

X86_64TargetInfo::X86_64TargetInfo() {
  PCRelReloc = R_X86_64_PC32;
  GotReloc = R_X86_64_GLOB_DAT;
  GotRefReloc = R_X86_64_PC32;
  RelativeReloc = R_X86_64_RELATIVE;

  // On freebsd x86_64 the first page cannot be mmaped.
  // On linux that is controled by vm.mmap_min_addr. At least on some x86_64
  // installs that is 65536, so the first 15 pages cannot be used.
  // Given that, the smallest value that can be used in here is 0x10000.
  // If using 2MB pages, the smallest page aligned address that works is
  // 0x200000, but it looks like every OS uses 4k pages for executables.
  VAStart = 0x10000;
}

void X86_64TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                     uint64_t PltEntryAddr) const {
  // jmpq *val(%rip); nop; nop
  const uint8_t Inst[] = {0xff, 0x25, 0, 0, 0, 0, 0x90, 0x90};
  memcpy(Buf, Inst, sizeof(Inst));

  uint64_t NextPC = PltEntryAddr + 6;
  int64_t Delta = GotEntryAddr - NextPC;
  assert(isInt<32>(Delta));
  write32le(Buf + 2, Delta);
}

bool X86_64TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
  return Type == R_X86_64_GOTPCREL || relocNeedsPlt(Type, S);
}

bool X86_64TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  switch (Type) {
  default:
    return false;
  case R_X86_64_PC32:
    // This relocation is defined to have a value of (S + A - P).
    // The problems start when a non PIC program calls a function in a shared
    // library.
    // In an ideal world, we could just report an error saying the relocation
    // can overflow at runtime.
    // In the real world with glibc, crt1.o has a R_X86_64_PC32 pointing to
    // libc.so.
    //
    // The general idea on how to handle such cases is to create a PLT entry
    // and use that as the function value.
    //
    // For the static linking part, we just return true and everything else
    // will use the the PLT entry as the address.
    //
    // The remaining (unimplemented) problem is making sure pointer equality
    // still works. We need the help of the dynamic linker for that. We
    // let it know that we have a direct reference to a so symbol by creating
    // an undefined symbol with a non zero st_value. Seeing that, the
    // dynamic linker resolves the symbol to the value of the symbol we created.
    // This is true even for got entries, so pointer equality is maintained.
    // To avoid an infinite loop, the only entry that points to the
    // real function is a dedicated got entry used by the plt. That is
    // identified by special relocation types (R_X86_64_JUMP_SLOT,
    // R_386_JMP_SLOT, etc).
    return S.isShared();
  case R_X86_64_PLT32:
    return true;
  }
}

bool X86_64TargetInfo::isRelRelative(uint32_t Type) const {
  switch (Type) {
  default:
    return false;
  case R_X86_64_PC64:
  case R_X86_64_PC32:
  case R_X86_64_PC16:
  case R_X86_64_PC8:
    return true;
  }
}

void X86_64TargetInfo::relocateOne(uint8_t *Buf, const void *RelP,
                                   uint32_t Type, uint64_t BaseAddr,
                                   uint64_t SymVA) const {
  typedef ELFFile<ELF64LE>::Elf_Rela Elf_Rela;
  auto &Rel = *reinterpret_cast<const Elf_Rela *>(RelP);

  uint64_t Offset = Rel.r_offset;
  uint8_t *Loc = Buf + Offset;
  switch (Type) {
  case R_X86_64_PC32:
  case R_X86_64_GOTPCREL:
    write32le(Loc, SymVA + Rel.r_addend - (BaseAddr + Offset));
    break;
  case R_X86_64_64:
    write64le(Loc, SymVA + Rel.r_addend);
    break;
  case R_X86_64_32: {
  case R_X86_64_32S:
    uint64_t VA = SymVA + Rel.r_addend;
    if (Type == R_X86_64_32 && !isUInt<32>(VA))
      error("R_X86_64_32 out of range");
    else if (!isInt<32>(VA))
      error("R_X86_64_32S out of range");

    write32le(Loc, VA);
    break;
  }
  default:
    error(Twine("unrecognized reloc ") + Twine(Type));
    break;
  }
}

PPC64TargetInfo::PPC64TargetInfo() {
  // PCRelReloc = FIXME
  // GotReloc = FIXME
  PltEntrySize = 32;
  PageSize = 65536;
  VAStart = 0x10000000;
}
void PPC64TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                    uint64_t PltEntryAddr) const {}
bool PPC64TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
  return false;
}
bool PPC64TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  return false;
}
void PPC64TargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                  uint64_t BaseAddr, uint64_t SymVA) const {
  typedef ELFFile<ELF64BE>::Elf_Rela Elf_Rela;
  auto &Rel = *reinterpret_cast<const Elf_Rela *>(RelP);

  uint64_t Offset = Rel.r_offset;
  uint8_t *Loc = Buf + Offset;
  switch (Type) {
  case R_PPC64_ADDR64:
    write64be(Loc, SymVA + Rel.r_addend);
    break;
  case R_PPC64_TOC:
    // We don't create a TOC yet.
    break;
  default:
    error(Twine("unrecognized reloc ") + Twine(Type));
    break;
  }
}

PPCTargetInfo::PPCTargetInfo() {
  // PCRelReloc = FIXME
  // GotReloc = FIXME
  PageSize = 65536;
  VAStart = 0x10000000;
}
void PPCTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                  uint64_t PltEntryAddr) const {}
bool PPCTargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
  return false;
}
bool PPCTargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  return false;
}
void PPCTargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                uint64_t BaseAddr, uint64_t SymVA) const {}

ARMTargetInfo::ARMTargetInfo() {
  // PCRelReloc = FIXME
  // GotReloc = FIXME
  VAStart = 0x8000;
}
void ARMTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                  uint64_t PltEntryAddr) const {}
bool ARMTargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
  return false;
}
bool ARMTargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  return false;
}
void ARMTargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                uint64_t BaseAddr, uint64_t SymVA) const {}

AArch64TargetInfo::AArch64TargetInfo() {
  // PCRelReloc = FIXME
  // GotReloc = FIXME
  VAStart = 0x400000;
}
void AArch64TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                      uint64_t PltEntryAddr) const {}
bool AArch64TargetInfo::relocNeedsGot(uint32_t Type,
                                      const SymbolBody &S) const {
  return false;
}
bool AArch64TargetInfo::relocNeedsPlt(uint32_t Type,
                                      const SymbolBody &S) const {
  return false;
}

static void updateAArch64Adr(uint8_t *L, uint64_t Imm) {
  uint32_t ImmLo = (Imm & 0x3) << 29;
  uint32_t ImmHi = ((Imm & 0x1FFFFC) >> 2) << 5;
  uint64_t Mask = (0x3 << 29) | (0x7FFFF << 5);
  write32le(L, (read32le(L) & ~Mask) | ImmLo | ImmHi);
}

// Page(Expr) is the page address of the expression Expr, defined
// as (Expr & ~0xFFF). (This applies even if the machine page size
// supported by the platform has a different value.)
static uint64_t getAArch64Page(uint64_t Expr) {
  return Expr & (~static_cast<uint64_t>(0xFFF));
}

void AArch64TargetInfo::relocateOne(uint8_t *Buf, const void *RelP,
                                    uint32_t Type, uint64_t BaseAddr,
                                    uint64_t SymVA) const {
  typedef ELFFile<ELF64LE>::Elf_Rela Elf_Rela;
  auto &Rel = *reinterpret_cast<const Elf_Rela *>(RelP);

  uint8_t *L = Buf + Rel.r_offset;
  uint64_t S = SymVA;
  int64_t A = Rel.r_addend;
  uint64_t P = BaseAddr + Rel.r_offset;
  switch (Type) {
  case R_AARCH64_ABS16:
    if (!isInt<16>(S + A))
      error("Relocation R_AARCH64_ABS16 out of range");
    write16le(L, S + A);
    break;
  case R_AARCH64_ABS32:
    if (!isInt<32>(S + A))
      error("Relocation R_AARCH64_ABS32 out of range");
    write32le(L, S + A);
    break;
  case R_AARCH64_ABS64:
    // No overflow check needed.
    write64le(L, S + A);
    break;
  case R_AARCH64_ADD_ABS_LO12_NC:
    // No overflow check needed.
    or32le(L, ((S + A) & 0xFFF) << 10);
    break;
  case R_AARCH64_ADR_PREL_LO21: {
    uint64_t X = S + A - P;
    if (!isInt<21>(X))
      error("Relocation R_AARCH64_ADR_PREL_LO21 out of range");
    updateAArch64Adr(L, X & 0x1FFFFF);
    break;
  }
  case R_AARCH64_ADR_PREL_PG_HI21: {
    uint64_t X = getAArch64Page(S + A) - getAArch64Page(P);
    if (!isInt<33>(X))
      error("Relocation R_AARCH64_ADR_PREL_PG_HI21 out of range");
    updateAArch64Adr(L, (X >> 12) & 0x1FFFFF); // X[32:12]
    break;
  }
  default:
    error(Twine("unrecognized reloc ") + Twine(Type));
    break;
  }
}

MipsTargetInfo::MipsTargetInfo() {
  // PCRelReloc = FIXME
  // GotReloc = FIXME
  DefaultEntry = "__start";
  PageSize = 65536;
  VAStart = 0x400000;
}

void MipsTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                   uint64_t PltEntryAddr) const {}

bool MipsTargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
  return false;
}

bool MipsTargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
  return false;
}

void MipsTargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                 uint64_t BaseAddr, uint64_t SymVA) const {}
}
}