1 //===- LTO.cpp ------------------------------------------------------------===// 2 // 3 // The LLVM Linker 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "LTO.h" 11 #include "Config.h" 12 #include "InputFiles.h" 13 #include "LinkerScript.h" 14 #include "SymbolTable.h" 15 #include "Symbols.h" 16 #include "lld/Common/ErrorHandler.h" 17 #include "lld/Common/TargetOptionsCommandFlags.h" 18 #include "llvm/ADT/STLExtras.h" 19 #include "llvm/ADT/SmallString.h" 20 #include "llvm/ADT/StringRef.h" 21 #include "llvm/ADT/Twine.h" 22 #include "llvm/BinaryFormat/ELF.h" 23 #include "llvm/IR/DiagnosticPrinter.h" 24 #include "llvm/LTO/Caching.h" 25 #include "llvm/LTO/Config.h" 26 #include "llvm/LTO/LTO.h" 27 #include "llvm/Object/SymbolicFile.h" 28 #include "llvm/Support/CodeGen.h" 29 #include "llvm/Support/Error.h" 30 #include "llvm/Support/FileSystem.h" 31 #include "llvm/Support/MemoryBuffer.h" 32 #include "llvm/Support/raw_ostream.h" 33 #include <algorithm> 34 #include <cstddef> 35 #include <memory> 36 #include <string> 37 #include <system_error> 38 #include <vector> 39 40 using namespace llvm; 41 using namespace llvm::object; 42 using namespace llvm::ELF; 43 44 using namespace lld; 45 using namespace lld::elf; 46 47 // This is for use when debugging LTO. 48 static void saveBuffer(StringRef Buffer, const Twine &Path) { 49 std::error_code EC; 50 raw_fd_ostream OS(Path.str(), EC, sys::fs::OpenFlags::F_None); 51 if (EC) 52 error("cannot create " + Path + ": " + EC.message()); 53 OS << Buffer; 54 } 55 56 static void diagnosticHandler(const DiagnosticInfo &DI) { 57 SmallString<128> ErrStorage; 58 raw_svector_ostream OS(ErrStorage); 59 DiagnosticPrinterRawOStream DP(OS); 60 DI.print(DP); 61 warn(ErrStorage); 62 } 63 64 static void checkError(Error E) { 65 handleAllErrors(std::move(E), 66 [&](ErrorInfoBase &EIB) { error(EIB.message()); }); 67 } 68 69 static std::unique_ptr<lto::LTO> createLTO() { 70 lto::Config Conf; 71 72 // LLD supports the new relocations. 73 Conf.Options = InitTargetOptionsFromCodeGenFlags(); 74 Conf.Options.RelaxELFRelocations = true; 75 76 // Always emit a section per function/datum with LTO. 77 Conf.Options.FunctionSections = true; 78 Conf.Options.DataSections = true; 79 80 if (Config->Relocatable) 81 Conf.RelocModel = None; 82 else if (Config->Pic) 83 Conf.RelocModel = Reloc::PIC_; 84 else 85 Conf.RelocModel = Reloc::Static; 86 Conf.CodeModel = GetCodeModelFromCMModel(); 87 Conf.DisableVerify = Config->DisableVerify; 88 Conf.DiagHandler = diagnosticHandler; 89 Conf.OptLevel = Config->LTOO; 90 Conf.CPU = GetCPUStr(); 91 92 // Set up a custom pipeline if we've been asked to. 93 Conf.OptPipeline = Config->LTONewPmPasses; 94 Conf.AAPipeline = Config->LTOAAPipeline; 95 96 // Set up optimization remarks if we've been asked to. 97 Conf.RemarksFilename = Config->OptRemarksFilename; 98 Conf.RemarksWithHotness = Config->OptRemarksWithHotness; 99 100 if (Config->SaveTemps) 101 checkError(Conf.addSaveTemps(std::string(Config->OutputFile) + ".", 102 /*UseInputModulePath*/ true)); 103 104 lto::ThinBackend Backend; 105 if (Config->ThinLTOJobs != -1u) 106 Backend = lto::createInProcessThinBackend(Config->ThinLTOJobs); 107 return llvm::make_unique<lto::LTO>(std::move(Conf), Backend, 108 Config->LTOPartitions); 109 } 110 111 BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) { 112 for (Symbol *Sym : Symtab->getSymbols()) { 113 StringRef Name = Sym->getName(); 114 for (StringRef Prefix : {"__start_", "__stop_"}) 115 if (Name.startswith(Prefix)) 116 UsedStartStop.insert(Name.substr(Prefix.size())); 117 } 118 } 119 120 BitcodeCompiler::~BitcodeCompiler() = default; 121 122 static void undefine(Symbol *S) { 123 replaceSymbol<Undefined>(S, nullptr, S->getName(), STB_GLOBAL, STV_DEFAULT, 124 S->Type); 125 } 126 127 void BitcodeCompiler::add(BitcodeFile &F) { 128 lto::InputFile &Obj = *F.Obj; 129 unsigned SymNum = 0; 130 std::vector<Symbol *> Syms = F.getSymbols(); 131 std::vector<lto::SymbolResolution> Resols(Syms.size()); 132 133 bool IsExecutable = !Config->Shared && !Config->Relocatable; 134 135 // Provide a resolution to the LTO API for each symbol. 136 for (const lto::InputFile::Symbol &ObjSym : Obj.symbols()) { 137 Symbol *Sym = Syms[SymNum]; 138 lto::SymbolResolution &R = Resols[SymNum]; 139 ++SymNum; 140 141 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 142 // reports two symbols for module ASM defined. Without this check, lld 143 // flags an undefined in IR with a definition in ASM as prevailing. 144 // Once IRObjectFile is fixed to report only one symbol this hack can 145 // be removed. 146 R.Prevailing = !ObjSym.isUndefined() && Sym->File == &F; 147 148 // We ask LTO to preserve following global symbols: 149 // 1) All symbols when doing relocatable link, so that them can be used 150 // for doing final link. 151 // 2) Symbols that are used in regular objects. 152 // 3) C named sections if we have corresponding __start_/__stop_ symbol. 153 // 4) Symbols that are defined in bitcode files and used for dynamic linking. 154 R.VisibleToRegularObj = Config->Relocatable || Sym->IsUsedInRegularObj || 155 (R.Prevailing && Sym->includeInDynsym()) || 156 UsedStartStop.count(ObjSym.getSectionName()); 157 const auto *DR = dyn_cast<Defined>(Sym); 158 R.FinalDefinitionInLinkageUnit = 159 (IsExecutable || Sym->Visibility != STV_DEFAULT) && DR && 160 // Skip absolute symbols from ELF objects, otherwise PC-rel relocations 161 // will be generated by for them, triggering linker errors. 162 // Symbol section is always null for bitcode symbols, hence the check 163 // for isElf(). Skip linker script defined symbols as well: they have 164 // no File defined. 165 !(DR->Section == nullptr && (!Sym->File || Sym->File->isElf())); 166 167 if (R.Prevailing) 168 undefine(Sym); 169 170 // We tell LTO to not apply interprocedural optimization for wrapped 171 // (with --wrap) symbols because otherwise LTO would inline them while 172 // their values are still not final. 173 R.LinkerRedefined = !Sym->CanInline; 174 } 175 checkError(LTOObj->add(std::move(F.Obj), Resols)); 176 } 177 178 // Merge all the bitcode files we have seen, codegen the result 179 // and return the resulting ObjectFile(s). 180 std::vector<InputFile *> BitcodeCompiler::compile() { 181 std::vector<InputFile *> Ret; 182 unsigned MaxTasks = LTOObj->getMaxTasks(); 183 Buff.resize(MaxTasks); 184 Files.resize(MaxTasks); 185 186 // The --thinlto-cache-dir option specifies the path to a directory in which 187 // to cache native object files for ThinLTO incremental builds. If a path was 188 // specified, configure LTO to use it as the cache directory. 189 lto::NativeObjectCache Cache; 190 if (!Config->ThinLTOCacheDir.empty()) 191 Cache = check( 192 lto::localCache(Config->ThinLTOCacheDir, 193 [&](size_t Task, std::unique_ptr<MemoryBuffer> MB) { 194 Files[Task] = std::move(MB); 195 })); 196 197 checkError(LTOObj->run( 198 [&](size_t Task) { 199 return llvm::make_unique<lto::NativeObjectStream>( 200 llvm::make_unique<raw_svector_ostream>(Buff[Task])); 201 }, 202 Cache)); 203 204 if (!Config->ThinLTOCacheDir.empty()) 205 pruneCache(Config->ThinLTOCacheDir, Config->ThinLTOCachePolicy); 206 207 for (unsigned I = 0; I != MaxTasks; ++I) { 208 if (Buff[I].empty()) 209 continue; 210 if (Config->SaveTemps) { 211 if (I == 0) 212 saveBuffer(Buff[I], Config->OutputFile + ".lto.o"); 213 else 214 saveBuffer(Buff[I], Config->OutputFile + Twine(I) + ".lto.o"); 215 } 216 InputFile *Obj = createObjectFile(MemoryBufferRef(Buff[I], "lto.tmp")); 217 Ret.push_back(Obj); 218 } 219 220 for (std::unique_ptr<MemoryBuffer> &File : Files) 221 if (File) 222 Ret.push_back(createObjectFile(*File)); 223 224 return Ret; 225 } 226