1 //===---- ELF_x86_64.cpp -JIT linker implementation for ELF/x86-64 ----===// 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 // ELF/x86-64 jit-link implementation. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/ExecutionEngine/JITLink/ELF_x86_64.h" 14 #include "llvm/ExecutionEngine/JITLink/DWARFRecordSectionSplitter.h" 15 #include "llvm/ExecutionEngine/JITLink/JITLink.h" 16 #include "llvm/ExecutionEngine/JITLink/TableManager.h" 17 #include "llvm/ExecutionEngine/JITLink/x86_64.h" 18 #include "llvm/Object/ELFObjectFile.h" 19 20 #include "DefineExternalSectionStartAndEndSymbols.h" 21 #include "EHFrameSupportImpl.h" 22 #include "ELFLinkGraphBuilder.h" 23 #include "JITLinkGeneric.h" 24 25 #define DEBUG_TYPE "jitlink" 26 27 using namespace llvm; 28 using namespace llvm::jitlink; 29 30 namespace { 31 32 constexpr StringRef ELFGOTSymbolName = "_GLOBAL_OFFSET_TABLE_"; 33 constexpr StringRef ELFTLSInfoSectionName = "$__TLSINFO"; 34 35 class TLSInfoTableManager_ELF_x86_64 36 : public TableManager<TLSInfoTableManager_ELF_x86_64> { 37 public: 38 static const uint8_t TLSInfoEntryContent[16]; 39 40 static StringRef getSectionName() { return ELFTLSInfoSectionName; } 41 42 bool visitEdge(LinkGraph &G, Block *B, Edge &E) { 43 if (E.getKind() == x86_64::RequestTLSDescInGOTAndTransformToDelta32) { 44 LLVM_DEBUG({ 45 dbgs() << " Fixing " << G.getEdgeKindName(E.getKind()) << " edge at " 46 << formatv("{0:x}", B->getFixupAddress(E)) << " (" 47 << formatv("{0:x}", B->getAddress()) << " + " 48 << formatv("{0:x}", E.getOffset()) << ")\n"; 49 }); 50 E.setKind(x86_64::Delta32); 51 E.setTarget(getEntryForTarget(G, E.getTarget())); 52 return true; 53 } 54 return false; 55 } 56 57 Symbol &createEntry(LinkGraph &G, Symbol &Target) { 58 // the TLS Info entry's key value will be written by the fixTLVSectionByName 59 // pass, so create mutable content. 60 auto &TLSInfoEntry = G.createMutableContentBlock( 61 getTLSInfoSection(G), G.allocateContent(getTLSInfoEntryContent()), 62 orc::ExecutorAddr(), 8, 0); 63 TLSInfoEntry.addEdge(x86_64::Pointer64, 8, Target, 0); 64 return G.addAnonymousSymbol(TLSInfoEntry, 0, 16, false, false); 65 } 66 67 private: 68 Section &getTLSInfoSection(LinkGraph &G) { 69 if (!TLSInfoTable) 70 TLSInfoTable = 71 &G.createSection(ELFTLSInfoSectionName, orc::MemProt::Read); 72 return *TLSInfoTable; 73 } 74 75 ArrayRef<char> getTLSInfoEntryContent() const { 76 return {reinterpret_cast<const char *>(TLSInfoEntryContent), 77 sizeof(TLSInfoEntryContent)}; 78 } 79 80 Section *TLSInfoTable = nullptr; 81 }; 82 83 const uint8_t TLSInfoTableManager_ELF_x86_64::TLSInfoEntryContent[16] = { 84 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /*pthread key */ 85 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 /*data address*/ 86 }; 87 88 Error buildTables_ELF_x86_64(LinkGraph &G) { 89 LLVM_DEBUG(dbgs() << "Visiting edges in graph:\n"); 90 91 x86_64::GOTTableManager GOT; 92 x86_64::PLTTableManager PLT(GOT); 93 TLSInfoTableManager_ELF_x86_64 TLSInfo; 94 visitExistingEdges(G, GOT, PLT, TLSInfo); 95 return Error::success(); 96 } 97 } // namespace 98 99 namespace llvm { 100 namespace jitlink { 101 102 class ELFLinkGraphBuilder_x86_64 : public ELFLinkGraphBuilder<object::ELF64LE> { 103 private: 104 using ELFT = object::ELF64LE; 105 106 Error addRelocations() override { 107 LLVM_DEBUG(dbgs() << "Processing relocations:\n"); 108 109 using Base = ELFLinkGraphBuilder<ELFT>; 110 using Self = ELFLinkGraphBuilder_x86_64; 111 for (const auto &RelSect : Base::Sections) { 112 // Validate the section to read relocation entries from. 113 if (RelSect.sh_type == ELF::SHT_REL) 114 return make_error<StringError>( 115 "No SHT_REL in valid x64 ELF object files", 116 inconvertibleErrorCode()); 117 118 if (Error Err = Base::forEachRelaRelocation(RelSect, this, 119 &Self::addSingleRelocation)) 120 return Err; 121 } 122 123 return Error::success(); 124 } 125 126 Error addSingleRelocation(const typename ELFT::Rela &Rel, 127 const typename ELFT::Shdr &FixupSection, 128 Block &BlockToFix) { 129 using Base = ELFLinkGraphBuilder<ELFT>; 130 131 auto ELFReloc = Rel.getType(false); 132 133 // R_X86_64_NONE is a no-op. 134 if (LLVM_UNLIKELY(ELFReloc == ELF::R_X86_64_NONE)) 135 return Error::success(); 136 137 uint32_t SymbolIndex = Rel.getSymbol(false); 138 auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec); 139 if (!ObjSymbol) 140 return ObjSymbol.takeError(); 141 142 Symbol *GraphSymbol = Base::getGraphSymbol(SymbolIndex); 143 if (!GraphSymbol) 144 return make_error<StringError>( 145 formatv("Could not find symbol at given index, did you add it to " 146 "JITSymbolTable? index: {0}, shndx: {1} Size of table: {2}", 147 SymbolIndex, (*ObjSymbol)->st_shndx, 148 Base::GraphSymbols.size()), 149 inconvertibleErrorCode()); 150 151 // Validate the relocation kind. 152 int64_t Addend = Rel.r_addend; 153 Edge::Kind Kind = Edge::Invalid; 154 155 switch (ELFReloc) { 156 case ELF::R_X86_64_PC8: 157 Kind = x86_64::Delta8; 158 break; 159 case ELF::R_X86_64_PC32: 160 case ELF::R_X86_64_GOTPC32: 161 Kind = x86_64::Delta32; 162 break; 163 case ELF::R_X86_64_PC64: 164 case ELF::R_X86_64_GOTPC64: 165 Kind = x86_64::Delta64; 166 break; 167 case ELF::R_X86_64_32: 168 Kind = x86_64::Pointer32; 169 break; 170 case ELF::R_X86_64_16: 171 Kind = x86_64::Pointer16; 172 break; 173 case ELF::R_X86_64_8: 174 Kind = x86_64::Pointer8; 175 break; 176 case ELF::R_X86_64_32S: 177 Kind = x86_64::Pointer32Signed; 178 break; 179 case ELF::R_X86_64_64: 180 Kind = x86_64::Pointer64; 181 break; 182 case ELF::R_X86_64_GOTPCREL: 183 Kind = x86_64::RequestGOTAndTransformToDelta32; 184 break; 185 case ELF::R_X86_64_REX_GOTPCRELX: 186 Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable; 187 Addend = 0; 188 break; 189 case ELF::R_X86_64_TLSGD: 190 Kind = x86_64::RequestTLSDescInGOTAndTransformToDelta32; 191 break; 192 case ELF::R_X86_64_GOTPCRELX: 193 Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadRelaxable; 194 Addend = 0; 195 break; 196 case ELF::R_X86_64_GOTPCREL64: 197 Kind = x86_64::RequestGOTAndTransformToDelta64; 198 break; 199 case ELF::R_X86_64_GOT64: 200 Kind = x86_64::RequestGOTAndTransformToDelta64FromGOT; 201 break; 202 case ELF::R_X86_64_GOTOFF64: 203 Kind = x86_64::Delta64FromGOT; 204 break; 205 case ELF::R_X86_64_PLT32: 206 Kind = x86_64::BranchPCRel32; 207 // BranchPCRel32 implicitly handles the '-4' PC adjustment, so we have to 208 // adjust the addend by '+4' to compensate. 209 Addend += 4; 210 break; 211 default: 212 return make_error<JITLinkError>( 213 "In " + G->getName() + ": Unsupported x86-64 relocation type " + 214 object::getELFRelocationTypeName(ELF::EM_X86_64, ELFReloc)); 215 } 216 217 auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset; 218 Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress(); 219 Edge GE(Kind, Offset, *GraphSymbol, Addend); 220 LLVM_DEBUG({ 221 dbgs() << " "; 222 printEdge(dbgs(), BlockToFix, GE, x86_64::getEdgeKindName(Kind)); 223 dbgs() << "\n"; 224 }); 225 226 BlockToFix.addEdge(std::move(GE)); 227 return Error::success(); 228 } 229 230 public: 231 ELFLinkGraphBuilder_x86_64(StringRef FileName, 232 const object::ELFFile<object::ELF64LE> &Obj, 233 SubtargetFeatures Features) 234 : ELFLinkGraphBuilder(Obj, Triple("x86_64-unknown-linux"), 235 std::move(Features), FileName, 236 x86_64::getEdgeKindName) {} 237 }; 238 239 class ELFJITLinker_x86_64 : public JITLinker<ELFJITLinker_x86_64> { 240 friend class JITLinker<ELFJITLinker_x86_64>; 241 242 public: 243 ELFJITLinker_x86_64(std::unique_ptr<JITLinkContext> Ctx, 244 std::unique_ptr<LinkGraph> G, 245 PassConfiguration PassConfig) 246 : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) { 247 248 if (shouldAddDefaultTargetPasses(getGraph().getTargetTriple())) 249 getPassConfig().PostAllocationPasses.push_back( 250 [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); }); 251 } 252 253 private: 254 Symbol *GOTSymbol = nullptr; 255 256 Error getOrCreateGOTSymbol(LinkGraph &G) { 257 auto DefineExternalGOTSymbolIfPresent = 258 createDefineExternalSectionStartAndEndSymbolsPass( 259 [&](LinkGraph &LG, Symbol &Sym) -> SectionRangeSymbolDesc { 260 if (Sym.getName() == ELFGOTSymbolName) 261 if (auto *GOTSection = G.findSectionByName( 262 x86_64::GOTTableManager::getSectionName())) { 263 GOTSymbol = &Sym; 264 return {*GOTSection, true}; 265 } 266 return {}; 267 }); 268 269 // Try to attach _GLOBAL_OFFSET_TABLE_ to the GOT if it's defined as an 270 // external. 271 if (auto Err = DefineExternalGOTSymbolIfPresent(G)) 272 return Err; 273 274 // If we succeeded then we're done. 275 if (GOTSymbol) 276 return Error::success(); 277 278 // Otherwise look for a GOT section: If it already has a start symbol we'll 279 // record it, otherwise we'll create our own. 280 // If there's a GOT section but we didn't find an external GOT symbol... 281 if (auto *GOTSection = 282 G.findSectionByName(x86_64::GOTTableManager::getSectionName())) { 283 284 // Check for an existing defined symbol. 285 for (auto *Sym : GOTSection->symbols()) 286 if (Sym->getName() == ELFGOTSymbolName) { 287 GOTSymbol = Sym; 288 return Error::success(); 289 } 290 291 // If there's no defined symbol then create one. 292 SectionRange SR(*GOTSection); 293 if (SR.empty()) 294 GOTSymbol = 295 &G.addAbsoluteSymbol(ELFGOTSymbolName, orc::ExecutorAddr(), 0, 296 Linkage::Strong, Scope::Local, true); 297 else 298 GOTSymbol = 299 &G.addDefinedSymbol(*SR.getFirstBlock(), 0, ELFGOTSymbolName, 0, 300 Linkage::Strong, Scope::Local, false, true); 301 } 302 303 // If we still haven't found a GOT symbol then double check the externals. 304 // We may have a GOT-relative reference but no GOT section, in which case 305 // we just need to point the GOT symbol at some address in this graph. 306 if (!GOTSymbol) { 307 for (auto *Sym : G.external_symbols()) { 308 if (Sym->getName() == ELFGOTSymbolName) { 309 auto Blocks = G.blocks(); 310 if (!Blocks.empty()) { 311 G.makeAbsolute(*Sym, (*Blocks.begin())->getAddress()); 312 GOTSymbol = Sym; 313 break; 314 } 315 } 316 } 317 } 318 319 return Error::success(); 320 } 321 322 Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const { 323 return x86_64::applyFixup(G, B, E, GOTSymbol); 324 } 325 }; 326 327 Expected<std::unique_ptr<LinkGraph>> 328 createLinkGraphFromELFObject_x86_64(MemoryBufferRef ObjectBuffer) { 329 LLVM_DEBUG({ 330 dbgs() << "Building jitlink graph for new input " 331 << ObjectBuffer.getBufferIdentifier() << "...\n"; 332 }); 333 334 auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer); 335 if (!ELFObj) 336 return ELFObj.takeError(); 337 338 auto Features = (*ELFObj)->getFeatures(); 339 if (!Features) 340 return Features.takeError(); 341 342 auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF64LE>>(**ELFObj); 343 return ELFLinkGraphBuilder_x86_64((*ELFObj)->getFileName(), 344 ELFObjFile.getELFFile(), 345 std::move(*Features)) 346 .buildGraph(); 347 } 348 349 void link_ELF_x86_64(std::unique_ptr<LinkGraph> G, 350 std::unique_ptr<JITLinkContext> Ctx) { 351 PassConfiguration Config; 352 353 if (Ctx->shouldAddDefaultTargetPasses(G->getTargetTriple())) { 354 355 Config.PrePrunePasses.push_back(DWARFRecordSectionSplitter(".eh_frame")); 356 Config.PrePrunePasses.push_back(EHFrameEdgeFixer( 357 ".eh_frame", x86_64::PointerSize, x86_64::Pointer32, x86_64::Pointer64, 358 x86_64::Delta32, x86_64::Delta64, x86_64::NegDelta32)); 359 Config.PrePrunePasses.push_back(EHFrameNullTerminator(".eh_frame")); 360 361 // Construct a JITLinker and run the link function. 362 // Add a mark-live pass. 363 if (auto MarkLive = Ctx->getMarkLivePass(G->getTargetTriple())) 364 Config.PrePrunePasses.push_back(std::move(MarkLive)); 365 else 366 Config.PrePrunePasses.push_back(markAllSymbolsLive); 367 368 // Add an in-place GOT/Stubs/TLSInfoEntry build pass. 369 Config.PostPrunePasses.push_back(buildTables_ELF_x86_64); 370 371 // Resolve any external section start / end symbols. 372 Config.PostAllocationPasses.push_back( 373 createDefineExternalSectionStartAndEndSymbolsPass( 374 identifyELFSectionStartAndEndSymbols)); 375 376 // Add GOT/Stubs optimizer pass. 377 Config.PreFixupPasses.push_back(x86_64::optimizeGOTAndStubAccesses); 378 } 379 380 if (auto Err = Ctx->modifyPassConfig(*G, Config)) 381 return Ctx->notifyFailed(std::move(Err)); 382 383 ELFJITLinker_x86_64::link(std::move(Ctx), std::move(G), std::move(Config)); 384 } 385 } // end namespace jitlink 386 } // end namespace llvm 387