lld/ELF/Target.cpp

   1 //===- Target.cpp ---------------------------------------------------------===//
   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 // Machine-specific things, such as applying relocations, creation of
  10 // GOT or PLT entries, etc., are handled in this file.
  11 //
  12 // Refer the ELF spec for the single letter variables, S, A or P, used
  13 // in this file.
  14 //
  15 // Some functions defined in this file has "relaxTls" as part of their names.
  16 // They do peephole optimization for TLS variables by rewriting instructions.
  17 // They are not part of the ABI but optional optimization, so you can skip
  18 // them if you are not interested in how TLS variables are optimized.
  19 // See the following paper for the details.
  20 //
  21 //   Ulrich Drepper, ELF Handling For Thread-Local Storage
  22 //   http://www.akkadia.org/drepper/tls.pdf
  23 //
  24 //===----------------------------------------------------------------------===//
  25
  26 #include "Target.h"
  27 #include "InputFiles.h"
  28 #include "OutputSections.h"
  29 #include "SymbolTable.h"
  30 #include "Symbols.h"
  31 #include "SyntheticSections.h"
  32 #include "lld/Common/ErrorHandler.h"
  33 #include "llvm/Object/ELF.h"
  34
  35 using namespace llvm;
  36 using namespace llvm::object;
  37 using namespace llvm::ELF;
  38 using namespace lld;
  39 using namespace lld::elf;
  40
  41 const TargetInfo *elf::target;
  42
  43 std::string lld::toString(RelType type) {
  44   StringRef s = getELFRelocationTypeName(elf::config->emachine, type);
  45   if (s == "Unknown")
  46     return ("Unknown (" + Twine(type) + ")").str();
  47   return std::string(s);
  48 }
  49
  50 TargetInfo *elf::getTarget() {
  51   switch (config->emachine) {
  52   case EM_386:
  53   case EM_IAMCU:
  54     return getX86TargetInfo();
  55   case EM_AARCH64:
  56     return getAArch64TargetInfo();
  57   case EM_AMDGPU:
  58     return getAMDGPUTargetInfo();
  59   case EM_ARM:
  60     return getARMTargetInfo();
  61   case EM_AVR:
  62     return getAVRTargetInfo();
  63   case EM_HEXAGON:
  64     return getHexagonTargetInfo();
  65   case EM_LOONGARCH:
  66     return getLoongArchTargetInfo();
  67   case EM_MIPS:
  68     switch (config->ekind) {
  69     case ELF32LEKind:
  70       return getMipsTargetInfo<ELF32LE>();
  71     case ELF32BEKind:
  72       return getMipsTargetInfo<ELF32BE>();
  73     case ELF64LEKind:
  74       return getMipsTargetInfo<ELF64LE>();
  75     case ELF64BEKind:
  76       return getMipsTargetInfo<ELF64BE>();
  77     default:
  78       llvm_unreachable("unsupported MIPS target");
  79     }
  80   case EM_MSP430:
  81     return getMSP430TargetInfo();
  82   case EM_PPC:
  83     return getPPCTargetInfo();
  84   case EM_PPC64:
  85     return getPPC64TargetInfo();
  86   case EM_RISCV:
  87     return getRISCVTargetInfo();
  88   case EM_SPARCV9:
  89     return getSPARCV9TargetInfo();
  90   case EM_X86_64:
  91     return getX86_64TargetInfo();
  92   }
  93   llvm_unreachable("unknown target machine");
  94 }
  95
  96 ErrorPlace elf::getErrorPlace(const uint8_t *loc) {
  97   assert(loc != nullptr);
  98   for (InputSectionBase *d : ctx.inputSections) {
  99     auto *isec = dyn_cast<InputSection>(d);
 100     if (!isec || !isec->getParent() || (isec->type & SHT_NOBITS))
 101       continue;
 102
 103     const uint8_t *isecLoc =
 104         Out::bufferStart
 105             ? (Out::bufferStart + isec->getParent()->offset + isec->outSecOff)
 106             : isec->contentMaybeDecompress().data();
 107     if (isecLoc == nullptr) {
 108       assert(isa<SyntheticSection>(isec) && "No data but not synthetic?");
 109       continue;
 110     }
 111     if (isecLoc <= loc && loc < isecLoc + isec->getSize()) {
 112       std::string objLoc = isec->getLocation(loc - isecLoc);
 113       // Return object file location and source file location.
 114       // TODO: Refactor getSrcMsg not to take a variable.
 115       Undefined dummy(nullptr, "", STB_LOCAL, 0, 0);
 116       return {isec, objLoc + ": ",
 117               isec->file ? isec->getSrcMsg(dummy, loc - isecLoc) : ""};
 118     }
 119   }
 120   return {};
 121 }
 122
 123 TargetInfo::~TargetInfo() {}
 124
 125 int64_t TargetInfo::getImplicitAddend(const uint8_t *buf, RelType type) const {
 126   internalLinkerError(getErrorLocation(buf),
 127                       "cannot read addend for relocation " + toString(type));
 128   return 0;
 129 }
 130
 131 bool TargetInfo::usesOnlyLowPageBits(RelType type) const { return false; }
 132
 133 bool TargetInfo::needsThunk(RelExpr expr, RelType type, const InputFile *file,
 134                             uint64_t branchAddr, const Symbol &s,
 135                             int64_t a) const {
 136   return false;
 137 }
 138
 139 bool TargetInfo::adjustPrologueForCrossSplitStack(uint8_t *loc, uint8_t *end,
 140                                                   uint8_t stOther) const {
 141   llvm_unreachable("Target doesn't support split stacks.");
 142 }
 143
 144 bool TargetInfo::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
 145   return true;
 146 }
 147
 148 RelExpr TargetInfo::adjustTlsExpr(RelType type, RelExpr expr) const {
 149   return expr;
 150 }
 151
 152 RelExpr TargetInfo::adjustGotPcExpr(RelType type, int64_t addend,
 153                                     const uint8_t *data) const {
 154   return R_GOT_PC;
 155 }
 156
 157 void TargetInfo::relocateAlloc(InputSectionBase &sec, uint8_t *buf) const {
 158   const unsigned bits = config->is64 ? 64 : 32;
 159   uint64_t secAddr = sec.getOutputSection()->addr;
 160   if (auto *s = dyn_cast<InputSection>(&sec))
 161     secAddr += s->outSecOff;
 162   else if (auto *ehIn = dyn_cast<EhInputSection>(&sec))
 163     secAddr += ehIn->getParent()->outSecOff;
 164   for (const Relocation &rel : sec.relocs()) {
 165     uint8_t *loc = buf + rel.offset;
 166     const uint64_t val = SignExtend64(
 167         sec.getRelocTargetVA(sec.file, rel.type, rel.addend,
 168                              secAddr + rel.offset, *rel.sym, rel.expr),
 169         bits);
 170     if (rel.expr != R_RELAX_HINT)
 171       relocate(loc, rel, val);
 172   }
 173 }
 174
 175 uint64_t TargetInfo::getImageBase() const {
 176   // Use --image-base if set. Fall back to the target default if not.
 177   if (config->imageBase)
 178     return *config->imageBase;
 179   return config->isPic ? 0 : defaultImageBase;
 180 }