1 //===----- ELF_i386.cpp - JIT linker implementation for ELF/i386 ----===// 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/i386 jit-link implementation. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/ExecutionEngine/JITLink/ELF_i386.h" 14 #include "DefineExternalSectionStartAndEndSymbols.h" 15 #include "ELFLinkGraphBuilder.h" 16 #include "JITLinkGeneric.h" 17 #include "llvm/BinaryFormat/ELF.h" 18 #include "llvm/ExecutionEngine/JITLink/i386.h" 19 #include "llvm/Object/ELFObjectFile.h" 20 21 #define DEBUG_TYPE "jitlink" 22 23 using namespace llvm; 24 using namespace llvm::jitlink; 25 26 namespace { 27 constexpr StringRef ELFGOTSymbolName = "_GLOBAL_OFFSET_TABLE_"; 28 29 Error buildTables_ELF_i386(LinkGraph &G) { 30 LLVM_DEBUG(dbgs() << "Visiting edges in graph:\n"); 31 32 i386::GOTTableManager GOT; 33 i386::PLTTableManager PLT(GOT); 34 visitExistingEdges(G, GOT, PLT); 35 return Error::success(); 36 } 37 } // namespace 38 39 namespace llvm::jitlink { 40 41 class ELFJITLinker_i386 : public JITLinker<ELFJITLinker_i386> { 42 friend class JITLinker<ELFJITLinker_i386>; 43 44 public: 45 ELFJITLinker_i386(std::unique_ptr<JITLinkContext> Ctx, 46 std::unique_ptr<LinkGraph> G, PassConfiguration PassConfig) 47 : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) { 48 getPassConfig().PostAllocationPasses.push_back( 49 [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); }); 50 } 51 52 private: 53 Symbol *GOTSymbol = nullptr; 54 55 Error getOrCreateGOTSymbol(LinkGraph &G) { 56 auto DefineExternalGOTSymbolIfPresent = 57 createDefineExternalSectionStartAndEndSymbolsPass( 58 [&](LinkGraph &LG, Symbol &Sym) -> SectionRangeSymbolDesc { 59 if (Sym.getName() != nullptr && 60 *Sym.getName() == ELFGOTSymbolName) 61 if (auto *GOTSection = G.findSectionByName( 62 i386::GOTTableManager::getSectionName())) { 63 GOTSymbol = &Sym; 64 return {*GOTSection, true}; 65 } 66 return {}; 67 }); 68 69 // Try to attach _GLOBAL_OFFSET_TABLE_ to the GOT if it's defined as an 70 // external. 71 if (auto Err = DefineExternalGOTSymbolIfPresent(G)) 72 return Err; 73 74 // If we succeeded then we're done. 75 if (GOTSymbol) 76 return Error::success(); 77 78 // Otherwise look for a GOT section: If it already has a start symbol we'll 79 // record it, otherwise we'll create our own. 80 // If there's a GOT section but we didn't find an external GOT symbol... 81 if (auto *GOTSection = 82 G.findSectionByName(i386::GOTTableManager::getSectionName())) { 83 84 // Check for an existing defined symbol. 85 for (auto *Sym : GOTSection->symbols()) 86 if (Sym->getName() != nullptr && *Sym->getName() == ELFGOTSymbolName) { 87 GOTSymbol = Sym; 88 return Error::success(); 89 } 90 91 // If there's no defined symbol then create one. 92 SectionRange SR(*GOTSection); 93 94 if (SR.empty()) { 95 GOTSymbol = 96 &G.addAbsoluteSymbol(ELFGOTSymbolName, orc::ExecutorAddr(), 0, 97 Linkage::Strong, Scope::Local, true); 98 } else { 99 GOTSymbol = 100 &G.addDefinedSymbol(*SR.getFirstBlock(), 0, ELFGOTSymbolName, 0, 101 Linkage::Strong, Scope::Local, false, true); 102 } 103 } 104 105 return Error::success(); 106 } 107 108 Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const { 109 return i386::applyFixup(G, B, E, GOTSymbol); 110 } 111 }; 112 113 template <typename ELFT> 114 class ELFLinkGraphBuilder_i386 : public ELFLinkGraphBuilder<ELFT> { 115 private: 116 static Expected<i386::EdgeKind_i386> getRelocationKind(const uint32_t Type) { 117 using namespace i386; 118 switch (Type) { 119 case ELF::R_386_NONE: 120 return EdgeKind_i386::None; 121 case ELF::R_386_32: 122 return EdgeKind_i386::Pointer32; 123 case ELF::R_386_PC32: 124 return EdgeKind_i386::PCRel32; 125 case ELF::R_386_16: 126 return EdgeKind_i386::Pointer16; 127 case ELF::R_386_PC16: 128 return EdgeKind_i386::PCRel16; 129 case ELF::R_386_GOT32: 130 return EdgeKind_i386::RequestGOTAndTransformToDelta32FromGOT; 131 case ELF::R_386_GOTPC: 132 return EdgeKind_i386::Delta32; 133 case ELF::R_386_GOTOFF: 134 return EdgeKind_i386::Delta32FromGOT; 135 case ELF::R_386_PLT32: 136 return EdgeKind_i386::BranchPCRel32; 137 } 138 139 return make_error<JITLinkError>("Unsupported i386 relocation:" + 140 formatv("{0:d}", Type)); 141 } 142 143 Error addRelocations() override { 144 LLVM_DEBUG(dbgs() << "Adding relocations\n"); 145 using Base = ELFLinkGraphBuilder<ELFT>; 146 using Self = ELFLinkGraphBuilder_i386; 147 148 for (const auto &RelSect : Base::Sections) { 149 // Validate the section to read relocation entries from. 150 if (RelSect.sh_type == ELF::SHT_RELA) 151 return make_error<StringError>( 152 "No SHT_RELA in valid i386 ELF object files", 153 inconvertibleErrorCode()); 154 155 if (Error Err = Base::forEachRelRelocation(RelSect, this, 156 &Self::addSingleRelocation)) 157 return Err; 158 } 159 160 return Error::success(); 161 } 162 163 Error addSingleRelocation(const typename ELFT::Rel &Rel, 164 const typename ELFT::Shdr &FixupSection, 165 Block &BlockToFix) { 166 using Base = ELFLinkGraphBuilder<ELFT>; 167 168 uint32_t SymbolIndex = Rel.getSymbol(false); 169 auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec); 170 if (!ObjSymbol) 171 return ObjSymbol.takeError(); 172 173 Symbol *GraphSymbol = Base::getGraphSymbol(SymbolIndex); 174 if (!GraphSymbol) 175 return make_error<StringError>( 176 formatv("Could not find symbol at given index, did you add it to " 177 "JITSymbolTable? index: {0}, shndx: {1} Size of table: {2}", 178 SymbolIndex, (*ObjSymbol)->st_shndx, 179 Base::GraphSymbols.size()), 180 inconvertibleErrorCode()); 181 182 Expected<i386::EdgeKind_i386> Kind = getRelocationKind(Rel.getType(false)); 183 if (!Kind) 184 return Kind.takeError(); 185 186 auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset; 187 int64_t Addend = 0; 188 189 switch (*Kind) { 190 case i386::EdgeKind_i386::None: 191 break; 192 case i386::EdgeKind_i386::Pointer32: 193 case i386::EdgeKind_i386::PCRel32: 194 case i386::EdgeKind_i386::RequestGOTAndTransformToDelta32FromGOT: 195 case i386::EdgeKind_i386::Delta32: 196 case i386::EdgeKind_i386::Delta32FromGOT: 197 case i386::EdgeKind_i386::BranchPCRel32: 198 case i386::EdgeKind_i386::BranchPCRel32ToPtrJumpStub: 199 case i386::EdgeKind_i386::BranchPCRel32ToPtrJumpStubBypassable: { 200 const char *FixupContent = BlockToFix.getContent().data() + 201 (FixupAddress - BlockToFix.getAddress()); 202 Addend = *(const support::little32_t *)FixupContent; 203 break; 204 } 205 case i386::EdgeKind_i386::Pointer16: 206 case i386::EdgeKind_i386::PCRel16: { 207 const char *FixupContent = BlockToFix.getContent().data() + 208 (FixupAddress - BlockToFix.getAddress()); 209 Addend = *(const support::little16_t *)FixupContent; 210 break; 211 } 212 } 213 214 Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress(); 215 Edge GE(*Kind, Offset, *GraphSymbol, Addend); 216 LLVM_DEBUG({ 217 dbgs() << " "; 218 printEdge(dbgs(), BlockToFix, GE, i386::getEdgeKindName(*Kind)); 219 dbgs() << "\n"; 220 }); 221 222 BlockToFix.addEdge(std::move(GE)); 223 return Error::success(); 224 } 225 226 public: 227 ELFLinkGraphBuilder_i386(StringRef FileName, const object::ELFFile<ELFT> &Obj, 228 std::shared_ptr<orc::SymbolStringPool> SSP, 229 Triple TT, SubtargetFeatures Features) 230 : ELFLinkGraphBuilder<ELFT>(Obj, std::move(SSP), std::move(TT), 231 std::move(Features), FileName, 232 i386::getEdgeKindName) {} 233 }; 234 235 Expected<std::unique_ptr<LinkGraph>> 236 createLinkGraphFromELFObject_i386(MemoryBufferRef ObjectBuffer, 237 std::shared_ptr<orc::SymbolStringPool> SSP) { 238 LLVM_DEBUG({ 239 dbgs() << "Building jitlink graph for new input " 240 << ObjectBuffer.getBufferIdentifier() << "...\n"; 241 }); 242 243 auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer); 244 if (!ELFObj) 245 return ELFObj.takeError(); 246 247 auto Features = (*ELFObj)->getFeatures(); 248 if (!Features) 249 return Features.takeError(); 250 251 assert((*ELFObj)->getArch() == Triple::x86 && 252 "Only i386 (little endian) is supported for now"); 253 254 auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF32LE>>(**ELFObj); 255 256 return ELFLinkGraphBuilder_i386<object::ELF32LE>( 257 (*ELFObj)->getFileName(), ELFObjFile.getELFFile(), std::move(SSP), 258 (*ELFObj)->makeTriple(), std::move(*Features)) 259 .buildGraph(); 260 } 261 262 void link_ELF_i386(std::unique_ptr<LinkGraph> G, 263 std::unique_ptr<JITLinkContext> Ctx) { 264 PassConfiguration Config; 265 const Triple &TT = G->getTargetTriple(); 266 if (Ctx->shouldAddDefaultTargetPasses(TT)) { 267 if (auto MarkLive = Ctx->getMarkLivePass(TT)) 268 Config.PrePrunePasses.push_back(std::move(MarkLive)); 269 else 270 Config.PrePrunePasses.push_back(markAllSymbolsLive); 271 272 // Add an in-place GOT and PLT build pass. 273 Config.PostPrunePasses.push_back(buildTables_ELF_i386); 274 275 // Add GOT/Stubs optimizer pass. 276 Config.PreFixupPasses.push_back(i386::optimizeGOTAndStubAccesses); 277 } 278 if (auto Err = Ctx->modifyPassConfig(*G, Config)) 279 return Ctx->notifyFailed(std::move(Err)); 280 281 ELFJITLinker_i386::link(std::move(Ctx), std::move(G), std::move(Config)); 282 } 283 284 } // namespace llvm::jitlink 285