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 auto FileName = sys::path::filename(G.getName()); 105 if (S.FileInfos.count(FileName)) { 106 return make_error<StringError>("When -check is passed, file names must be " 107 "distinct (duplicate: \"" + 108 FileName + "\")", 109 inconvertibleErrorCode()); 110 } 111 112 auto &FileInfo = S.FileInfos[FileName]; 113 LLVM_DEBUG({ 114 dbgs() << "Registering ELF file info for \"" << FileName << "\"\n"; 115 }); 116 for (auto &Sec : G.sections()) { 117 LLVM_DEBUG({ 118 dbgs() << " Section \"" << Sec.getName() << "\": " 119 << (Sec.symbols().empty() ? "empty. skipping." : "processing...") 120 << "\n"; 121 }); 122 123 // Skip empty sections. 124 if (Sec.symbols().empty()) 125 continue; 126 127 if (FileInfo.SectionInfos.count(Sec.getName())) 128 return make_error<StringError>("Encountered duplicate section name \"" + 129 Sec.getName() + "\" in \"" + FileName + 130 "\"", 131 inconvertibleErrorCode()); 132 133 SectionType SecType; 134 if (isELFGOTSection(Sec)) { 135 SecType = GOT; 136 } else if (isELFStubsSection(Sec)) { 137 SecType = Stubs; 138 } else if (isELFAArch32StubsSection(Sec)) { 139 SecType = AArch32Stubs; 140 } else { 141 SecType = Other; 142 } 143 144 bool SectionContainsContent = false; 145 bool SectionContainsZeroFill = false; 146 147 auto *FirstSym = *Sec.symbols().begin(); 148 auto *LastSym = FirstSym; 149 for (auto *Sym : Sec.symbols()) { 150 if (Sym->getAddress() < FirstSym->getAddress()) 151 FirstSym = Sym; 152 if (Sym->getAddress() > LastSym->getAddress()) 153 LastSym = Sym; 154 155 if (SecType != Other) { 156 if (Error Err = registerSymbol(G, *Sym, FileInfo, SecType)) 157 return Err; 158 SectionContainsContent = true; 159 } 160 161 if (Sym->hasName()) { 162 if (Sym->isSymbolZeroFill()) { 163 S.SymbolInfos[Sym->getName()] = {Sym->getSize(), 164 Sym->getAddress().getValue()}; 165 SectionContainsZeroFill = true; 166 } else { 167 S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(), 168 Sym->getAddress().getValue(), 169 Sym->getTargetFlags()}; 170 SectionContainsContent = true; 171 } 172 } 173 } 174 175 // Add symbol info for absolute symbols. 176 for (auto *Sym : G.absolute_symbols()) 177 S.SymbolInfos[Sym->getName()] = {Sym->getSize(), 178 Sym->getAddress().getValue()}; 179 180 auto SecAddr = FirstSym->getAddress(); 181 auto SecSize = 182 (LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) - 183 SecAddr; 184 185 if (SectionContainsZeroFill && SectionContainsContent) 186 return make_error<StringError>("Mixed zero-fill and content sections not " 187 "supported yet", 188 inconvertibleErrorCode()); 189 if (SectionContainsZeroFill) 190 FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr.getValue()}; 191 else 192 FileInfo.SectionInfos[Sec.getName()] = { 193 ArrayRef<char>(FirstSym->getBlock().getContent().data(), SecSize), 194 SecAddr.getValue(), FirstSym->getTargetFlags()}; 195 } 196 197 return Error::success(); 198 } 199 200 } // end namespace llvm 201