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(G); 92 x86_64::PLTTableManager PLT(G, 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_PC16: 160 Kind = x86_64::Delta16; 161 break; 162 case ELF::R_X86_64_PC32: 163 case ELF::R_X86_64_GOTPC32: 164 Kind = x86_64::Delta32; 165 break; 166 case ELF::R_X86_64_PC64: 167 case ELF::R_X86_64_GOTPC64: 168 Kind = x86_64::Delta64; 169 break; 170 case ELF::R_X86_64_32: 171 Kind = x86_64::Pointer32; 172 break; 173 case ELF::R_X86_64_16: 174 Kind = x86_64::Pointer16; 175 break; 176 case ELF::R_X86_64_8: 177 Kind = x86_64::Pointer8; 178 break; 179 case ELF::R_X86_64_32S: 180 Kind = x86_64::Pointer32Signed; 181 break; 182 case ELF::R_X86_64_64: 183 Kind = x86_64::Pointer64; 184 break; 185 case ELF::R_X86_64_SIZE32: 186 Kind = x86_64::Size32; 187 break; 188 case ELF::R_X86_64_SIZE64: 189 Kind = x86_64::Size64; 190 break; 191 case ELF::R_X86_64_GOTPCREL: 192 Kind = x86_64::RequestGOTAndTransformToDelta32; 193 break; 194 case ELF::R_X86_64_REX_GOTPCRELX: 195 Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable; 196 Addend = 0; 197 break; 198 case ELF::R_X86_64_TLSGD: 199 Kind = x86_64::RequestTLSDescInGOTAndTransformToDelta32; 200 break; 201 case ELF::R_X86_64_GOTPCRELX: 202 Kind = x86_64::RequestGOTAndTransformToPCRel32GOTLoadRelaxable; 203 Addend = 0; 204 break; 205 case ELF::R_X86_64_GOTPCREL64: 206 Kind = x86_64::RequestGOTAndTransformToDelta64; 207 break; 208 case ELF::R_X86_64_GOT64: 209 Kind = x86_64::RequestGOTAndTransformToDelta64FromGOT; 210 break; 211 case ELF::R_X86_64_GOTOFF64: 212 Kind = x86_64::Delta64FromGOT; 213 break; 214 case ELF::R_X86_64_PLT32: 215 Kind = x86_64::BranchPCRel32; 216 // BranchPCRel32 implicitly handles the '-4' PC adjustment, so we have to 217 // adjust the addend by '+4' to compensate. 218 Addend += 4; 219 break; 220 default: 221 return make_error<JITLinkError>( 222 "In " + G->getName() + ": Unsupported x86-64 relocation type " + 223 object::getELFRelocationTypeName(ELF::EM_X86_64, ELFReloc)); 224 } 225 226 auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset; 227 Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress(); 228 Edge GE(Kind, Offset, *GraphSymbol, Addend); 229 LLVM_DEBUG({ 230 dbgs() << " "; 231 printEdge(dbgs(), BlockToFix, GE, x86_64::getEdgeKindName(Kind)); 232 dbgs() << "\n"; 233 }); 234 235 BlockToFix.addEdge(std::move(GE)); 236 return Error::success(); 237 } 238 239 public: 240 ELFLinkGraphBuilder_x86_64(StringRef FileName, 241 std::shared_ptr<orc::SymbolStringPool> SSP, 242 const object::ELFFile<object::ELF64LE> &Obj, 243 SubtargetFeatures Features) 244 : ELFLinkGraphBuilder(Obj, std::move(SSP), Triple("x86_64-unknown-linux"), 245 std::move(Features), FileName, 246 x86_64::getEdgeKindName) {} 247 }; 248 249 class ELFJITLinker_x86_64 : public JITLinker<ELFJITLinker_x86_64> { 250 friend class JITLinker<ELFJITLinker_x86_64>; 251 252 public: 253 ELFJITLinker_x86_64(std::unique_ptr<JITLinkContext> Ctx, 254 std::unique_ptr<LinkGraph> G, 255 PassConfiguration PassConfig) 256 : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) { 257 258 if (shouldAddDefaultTargetPasses(getGraph().getTargetTriple())) 259 getPassConfig().PostAllocationPasses.push_back( 260 [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); }); 261 } 262 263 private: 264 Symbol *GOTSymbol = nullptr; 265 Error getOrCreateGOTSymbol(LinkGraph &G) { 266 auto DefineExternalGOTSymbolIfPresent = 267 createDefineExternalSectionStartAndEndSymbolsPass( 268 [&](LinkGraph &LG, Symbol &Sym) -> SectionRangeSymbolDesc { 269 if (Sym.getName() != nullptr && 270 *Sym.getName() == ELFGOTSymbolName) 271 if (auto *GOTSection = G.findSectionByName( 272 x86_64::GOTTableManager::getSectionName())) { 273 GOTSymbol = &Sym; 274 return {*GOTSection, true}; 275 } 276 return {}; 277 }); 278 279 // Try to attach _GLOBAL_OFFSET_TABLE_ to the GOT if it's defined as an 280 // external. 281 if (auto Err = DefineExternalGOTSymbolIfPresent(G)) 282 return Err; 283 284 // If we succeeded then we're done. 285 if (GOTSymbol) 286 return Error::success(); 287 288 // Otherwise look for a GOT section: If it already has a start symbol we'll 289 // record it, otherwise we'll create our own. 290 // If there's a GOT section but we didn't find an external GOT symbol... 291 if (auto *GOTSection = 292 G.findSectionByName(x86_64::GOTTableManager::getSectionName())) { 293 294 // Check for an existing defined symbol. 295 for (auto *Sym : GOTSection->symbols()) 296 if (Sym->getName() != nullptr && *Sym->getName() == ELFGOTSymbolName) { 297 GOTSymbol = Sym; 298 return Error::success(); 299 } 300 301 // If there's no defined symbol then create one. 302 SectionRange SR(*GOTSection); 303 if (SR.empty()) 304 GOTSymbol = 305 &G.addAbsoluteSymbol(ELFGOTSymbolName, orc::ExecutorAddr(), 0, 306 Linkage::Strong, Scope::Local, true); 307 else 308 GOTSymbol = 309 &G.addDefinedSymbol(*SR.getFirstBlock(), 0, ELFGOTSymbolName, 0, 310 Linkage::Strong, Scope::Local, false, true); 311 } 312 313 // If we still haven't found a GOT symbol then double check the externals. 314 // We may have a GOT-relative reference but no GOT section, in which case 315 // we just need to point the GOT symbol at some address in this graph. 316 if (!GOTSymbol) { 317 for (auto *Sym : G.external_symbols()) { 318 if (*Sym->getName() == ELFGOTSymbolName) { 319 auto Blocks = G.blocks(); 320 if (!Blocks.empty()) { 321 G.makeAbsolute(*Sym, (*Blocks.begin())->getAddress()); 322 GOTSymbol = Sym; 323 break; 324 } 325 } 326 } 327 } 328 329 return Error::success(); 330 } 331 332 Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const { 333 return x86_64::applyFixup(G, B, E, GOTSymbol); 334 } 335 }; 336 337 Expected<std::unique_ptr<LinkGraph>> createLinkGraphFromELFObject_x86_64( 338 MemoryBufferRef ObjectBuffer, std::shared_ptr<orc::SymbolStringPool> SSP) { 339 LLVM_DEBUG({ 340 dbgs() << "Building jitlink graph for new input " 341 << ObjectBuffer.getBufferIdentifier() << "...\n"; 342 }); 343 344 auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer); 345 if (!ELFObj) 346 return ELFObj.takeError(); 347 348 auto Features = (*ELFObj)->getFeatures(); 349 if (!Features) 350 return Features.takeError(); 351 352 auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF64LE>>(**ELFObj); 353 return ELFLinkGraphBuilder_x86_64((*ELFObj)->getFileName(), std::move(SSP), 354 ELFObjFile.getELFFile(), 355 std::move(*Features)) 356 .buildGraph(); 357 } 358 359 void link_ELF_x86_64(std::unique_ptr<LinkGraph> G, 360 std::unique_ptr<JITLinkContext> Ctx) { 361 PassConfiguration Config; 362 363 if (Ctx->shouldAddDefaultTargetPasses(G->getTargetTriple())) { 364 365 Config.PrePrunePasses.push_back(DWARFRecordSectionSplitter(".eh_frame")); 366 Config.PrePrunePasses.push_back(EHFrameEdgeFixer( 367 ".eh_frame", x86_64::PointerSize, x86_64::Pointer32, x86_64::Pointer64, 368 x86_64::Delta32, x86_64::Delta64, x86_64::NegDelta32)); 369 Config.PrePrunePasses.push_back(EHFrameNullTerminator(".eh_frame")); 370 371 // Construct a JITLinker and run the link function. 372 // Add a mark-live pass. 373 if (auto MarkLive = Ctx->getMarkLivePass(G->getTargetTriple())) 374 Config.PrePrunePasses.push_back(std::move(MarkLive)); 375 else 376 Config.PrePrunePasses.push_back(markAllSymbolsLive); 377 378 // Add an in-place GOT/Stubs/TLSInfoEntry build pass. 379 Config.PostPrunePasses.push_back(buildTables_ELF_x86_64); 380 381 // Resolve any external section start / end symbols. 382 Config.PostAllocationPasses.push_back( 383 createDefineExternalSectionStartAndEndSymbolsPass( 384 identifyELFSectionStartAndEndSymbols)); 385 386 // Add GOT/Stubs optimizer pass. 387 Config.PreFixupPasses.push_back(x86_64::optimizeGOTAndStubAccesses); 388 } 389 390 if (auto Err = Ctx->modifyPassConfig(*G, Config)) 391 return Ctx->notifyFailed(std::move(Err)); 392 393 ELFJITLinker_x86_64::link(std::move(Ctx), std::move(G), std::move(Config)); 394 } 395 } // end namespace jitlink 396 } // end namespace llvm 397