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 Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) { 28 auto EItr = std::find_if(B.edges().begin(), B.edges().end(), 29 [](Edge &E) { return E.isRelocation(); }); 30 if (EItr == B.edges().end()) 31 return make_error<StringError>("GOT entry in " + G.getName() + ", \"" + 32 B.getSection().getName() + 33 "\" has no relocations", 34 inconvertibleErrorCode()); 35 return *EItr; 36 } 37 38 static Expected<Symbol &> getELFGOTTarget(LinkGraph &G, Block &B) { 39 auto E = getFirstRelocationEdge(G, B); 40 if (!E) 41 return E.takeError(); 42 auto &TargetSym = E->getTarget(); 43 if (!TargetSym.hasName()) 44 return make_error<StringError>( 45 "GOT entry in " + G.getName() + ", \"" + 46 TargetSym.getBlock().getSection().getName() + 47 "\" points to anonymous " 48 "symbol", 49 inconvertibleErrorCode()); 50 return TargetSym; 51 } 52 53 static Expected<Symbol &> getELFStubTarget(LinkGraph &G, Block &B) { 54 auto E = getFirstRelocationEdge(G, B); 55 if (!E) 56 return E.takeError(); 57 auto &GOTSym = E->getTarget(); 58 if (!GOTSym.isDefined() || !isELFGOTSection(GOTSym.getBlock().getSection())) 59 return make_error<StringError>( 60 "Stubs entry in " + G.getName() + ", \"" + 61 GOTSym.getBlock().getSection().getName() + 62 "\" does not point to GOT entry", 63 inconvertibleErrorCode()); 64 return getELFGOTTarget(G, GOTSym.getBlock()); 65 } 66 67 namespace llvm { 68 69 Error registerELFGraphInfo(Session &S, LinkGraph &G) { 70 auto FileName = sys::path::filename(G.getName()); 71 if (S.FileInfos.count(FileName)) { 72 return make_error<StringError>("When -check is passed, file names must be " 73 "distinct (duplicate: \"" + 74 FileName + "\")", 75 inconvertibleErrorCode()); 76 } 77 78 auto &FileInfo = S.FileInfos[FileName]; 79 LLVM_DEBUG({ 80 dbgs() << "Registering ELF file info for \"" << FileName << "\"\n"; 81 }); 82 for (auto &Sec : G.sections()) { 83 LLVM_DEBUG({ 84 dbgs() << " Section \"" << Sec.getName() << "\": " 85 << (llvm::empty(Sec.symbols()) ? "empty. skipping." 86 : "processing...") 87 << "\n"; 88 }); 89 90 // Skip empty sections. 91 if (llvm::empty(Sec.symbols())) 92 continue; 93 94 if (FileInfo.SectionInfos.count(Sec.getName())) 95 return make_error<StringError>("Encountered duplicate section name \"" + 96 Sec.getName() + "\" in \"" + FileName + 97 "\"", 98 inconvertibleErrorCode()); 99 100 bool isGOTSection = isELFGOTSection(Sec); 101 bool isStubsSection = isELFStubsSection(Sec); 102 103 bool SectionContainsContent = false; 104 bool SectionContainsZeroFill = false; 105 106 auto *FirstSym = *Sec.symbols().begin(); 107 auto *LastSym = FirstSym; 108 for (auto *Sym : Sec.symbols()) { 109 if (Sym->getAddress() < FirstSym->getAddress()) 110 FirstSym = Sym; 111 if (Sym->getAddress() > LastSym->getAddress()) 112 LastSym = Sym; 113 114 if (isGOTSection) { 115 if (Sym->isSymbolZeroFill()) 116 return make_error<StringError>("zero-fill atom in GOT section", 117 inconvertibleErrorCode()); 118 119 if (auto TS = getELFGOTTarget(G, Sym->getBlock())) 120 FileInfo.GOTEntryInfos[TS->getName()] = {Sym->getSymbolContent(), 121 Sym->getAddress()}; 122 else 123 return TS.takeError(); 124 SectionContainsContent = true; 125 } else if (isStubsSection) { 126 if (Sym->isSymbolZeroFill()) 127 return make_error<StringError>("zero-fill atom in Stub section", 128 inconvertibleErrorCode()); 129 130 if (auto TS = getELFStubTarget(G, Sym->getBlock())) 131 FileInfo.StubInfos[TS->getName()] = {Sym->getSymbolContent(), 132 Sym->getAddress()}; 133 else 134 return TS.takeError(); 135 SectionContainsContent = true; 136 } 137 138 if (Sym->hasName()) { 139 if (Sym->isSymbolZeroFill()) { 140 S.SymbolInfos[Sym->getName()] = {Sym->getSize(), Sym->getAddress()}; 141 SectionContainsZeroFill = true; 142 } else { 143 S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(), 144 Sym->getAddress()}; 145 SectionContainsContent = true; 146 } 147 } 148 } 149 150 JITTargetAddress SecAddr = FirstSym->getAddress(); 151 uint64_t SecSize = 152 (LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) - 153 SecAddr; 154 155 if (SectionContainsZeroFill && SectionContainsContent) 156 return make_error<StringError>("Mixed zero-fill and content sections not " 157 "supported yet", 158 inconvertibleErrorCode()); 159 if (SectionContainsZeroFill) 160 FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr}; 161 else 162 FileInfo.SectionInfos[Sec.getName()] = { 163 StringRef(FirstSym->getBlock().getContent().data(), SecSize), 164 SecAddr}; 165 } 166 167 return Error::success(); 168 } 169 170 } // end namespace llvm 171