1 //===---- llvm-jitlink-elf.cpp -- ELF parsing support for llvm-jitlink ----===// 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 parsing support for llvm-jitlink. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm-jitlink.h" 14 15 #include "llvm/Support/Error.h" 16 #include "llvm/Support/Path.h" 17 18 #define DEBUG_TYPE "llvm_jitlink" 19 20 using namespace llvm; 21 using namespace llvm::jitlink; 22 23 static bool isELFGOTSection(Section &S) { return S.getName() == "$__GOT"; } 24 25 static bool isELFStubsSection(Section &S) { return S.getName() == "$__STUBS"; } 26 27 static bool isELFAArch32StubsSection(Section &S) { 28 return S.getName().starts_with("__llvm_jitlink_aarch32_STUBS_"); 29 } 30 31 static Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) { 32 auto EItr = 33 llvm::find_if(B.edges(), [](Edge &E) { return E.isRelocation(); }); 34 if (EItr == B.edges().end()) 35 return make_error<StringError>("GOT entry in " + G.getName() + ", \"" + 36 B.getSection().getName() + 37 "\" has no relocations", 38 inconvertibleErrorCode()); 39 return *EItr; 40 } 41 42 static Expected<Symbol &> getELFGOTTarget(LinkGraph &G, Block &B) { 43 auto E = getFirstRelocationEdge(G, B); 44 if (!E) 45 return E.takeError(); 46 auto &TargetSym = E->getTarget(); 47 if (!TargetSym.hasName()) 48 return make_error<StringError>( 49 "GOT entry in " + G.getName() + ", \"" + 50 TargetSym.getBlock().getSection().getName() + 51 "\" points to anonymous " 52 "symbol", 53 inconvertibleErrorCode()); 54 return TargetSym; 55 } 56 57 static Expected<Symbol &> getELFStubTarget(LinkGraph &G, Block &B) { 58 auto E = getFirstRelocationEdge(G, B); 59 if (!E) 60 return E.takeError(); 61 auto &GOTSym = E->getTarget(); 62 if (!GOTSym.isDefined()) 63 return make_error<StringError>("Stubs entry in " + G.getName() + 64 " does not point to GOT entry", 65 inconvertibleErrorCode()); 66 if (!isELFGOTSection(GOTSym.getBlock().getSection())) 67 return make_error<StringError>( 68 "Stubs entry in " + G.getName() + ", \"" + 69 GOTSym.getBlock().getSection().getName() + 70 "\" does not point to GOT entry", 71 inconvertibleErrorCode()); 72 return getELFGOTTarget(G, GOTSym.getBlock()); 73 } 74 75 static Expected<Symbol &> getELFAArch32StubTarget(LinkGraph &G, Block &B) { 76 auto E = getFirstRelocationEdge(G, B); 77 if (!E) 78 return E.takeError(); 79 return E->getTarget(); 80 } 81 82 enum SectionType { GOT, Stubs, AArch32Stubs, Other }; 83 84 static Error registerSymbol(LinkGraph &G, Symbol &Sym, Session::FileInfo &FI, 85 SectionType SecType) { 86 switch (SecType) { 87 case GOT: 88 if (Sym.getSize() == 0) 89 return Error::success(); // Skip the GOT start symbol 90 return FI.registerGOTEntry(G, Sym, getELFGOTTarget); 91 case Stubs: 92 return FI.registerStubEntry(G, Sym, getELFStubTarget); 93 case AArch32Stubs: 94 return FI.registerMultiStubEntry(G, Sym, getELFAArch32StubTarget); 95 case Other: 96 return Error::success(); 97 } 98 llvm_unreachable("Unhandled SectionType enum"); 99 } 100 101 namespace llvm { 102 103 Error registerELFGraphInfo(Session &S, LinkGraph &G) { 104 std::lock_guard<std::mutex> Lock(S.M); 105 106 auto FileName = sys::path::filename(G.getName()); 107 if (S.FileInfos.count(FileName)) { 108 return make_error<StringError>("When -check is passed, file names must be " 109 "distinct (duplicate: \"" + 110 FileName + "\")", 111 inconvertibleErrorCode()); 112 } 113 114 auto &FileInfo = S.FileInfos[FileName]; 115 LLVM_DEBUG({ 116 dbgs() << "Registering ELF file info for \"" << FileName << "\"\n"; 117 }); 118 for (auto &Sec : G.sections()) { 119 LLVM_DEBUG({ 120 dbgs() << " Section \"" << Sec.getName() << "\": " 121 << (Sec.symbols().empty() ? "empty. skipping." : "processing...") 122 << "\n"; 123 }); 124 125 // Skip empty sections. 126 if (Sec.symbols().empty()) 127 continue; 128 129 if (FileInfo.SectionInfos.count(Sec.getName())) 130 return make_error<StringError>("Encountered duplicate section name \"" + 131 Sec.getName() + "\" in \"" + FileName + 132 "\"", 133 inconvertibleErrorCode()); 134 135 SectionType SecType; 136 if (isELFGOTSection(Sec)) { 137 SecType = GOT; 138 } else if (isELFStubsSection(Sec)) { 139 SecType = Stubs; 140 } else if (isELFAArch32StubsSection(Sec)) { 141 SecType = AArch32Stubs; 142 } else { 143 SecType = Other; 144 } 145 146 bool SectionContainsContent = false; 147 bool SectionContainsZeroFill = false; 148 149 auto *FirstSym = *Sec.symbols().begin(); 150 auto *LastSym = FirstSym; 151 for (auto *Sym : Sec.symbols()) { 152 if (Sym->getAddress() < FirstSym->getAddress()) 153 FirstSym = Sym; 154 if (Sym->getAddress() > LastSym->getAddress()) 155 LastSym = Sym; 156 157 if (SecType != Other) { 158 if (Error Err = registerSymbol(G, *Sym, FileInfo, SecType)) 159 return Err; 160 SectionContainsContent = true; 161 } 162 163 if (Sym->hasName()) { 164 if (Sym->isSymbolZeroFill()) { 165 S.SymbolInfos[Sym->getName()] = {Sym->getSize(), 166 Sym->getAddress().getValue()}; 167 SectionContainsZeroFill = true; 168 } else { 169 S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(), 170 Sym->getAddress().getValue(), 171 Sym->getTargetFlags()}; 172 SectionContainsContent = true; 173 } 174 } 175 } 176 177 // Add symbol info for absolute symbols. 178 for (auto *Sym : G.absolute_symbols()) 179 S.SymbolInfos[Sym->getName()] = {Sym->getSize(), 180 Sym->getAddress().getValue()}; 181 182 auto SecAddr = FirstSym->getAddress(); 183 auto SecSize = 184 (LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) - 185 SecAddr; 186 187 if (SectionContainsZeroFill && SectionContainsContent) 188 return make_error<StringError>("Mixed zero-fill and content sections not " 189 "supported yet", 190 inconvertibleErrorCode()); 191 if (SectionContainsZeroFill) 192 FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr.getValue()}; 193 else 194 FileInfo.SectionInfos[Sec.getName()] = { 195 ArrayRef<char>(FirstSym->getBlock().getContent().data(), SecSize), 196 SecAddr.getValue(), FirstSym->getTargetFlags()}; 197 } 198 199 return Error::success(); 200 } 201 202 } // end namespace llvm 203