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 "Error.h" 13 #include "LinkerScript.h" 14 #include "InputFiles.h" 15 #include "SymbolTable.h" 16 #include "Symbols.h" 17 #include "lld/Core/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 91 // Set up a custom pipeline if we've been asked to. 92 Conf.OptPipeline = Config->LTONewPmPasses; 93 Conf.AAPipeline = Config->LTOAAPipeline; 94 95 // Set up optimization remarks if we've been asked to. 96 Conf.RemarksFilename = Config->OptRemarksFilename; 97 Conf.RemarksWithHotness = Config->OptRemarksWithHotness; 98 99 if (Config->SaveTemps) 100 checkError(Conf.addSaveTemps(std::string(Config->OutputFile) + ".", 101 /*UseInputModulePath*/ true)); 102 103 lto::ThinBackend Backend; 104 if (Config->ThinLTOJobs != -1u) 105 Backend = lto::createInProcessThinBackend(Config->ThinLTOJobs); 106 return llvm::make_unique<lto::LTO>(std::move(Conf), Backend, 107 Config->LTOPartitions); 108 } 109 110 BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) { 111 for (Symbol *Sym : Symtab->getSymbols()) { 112 StringRef Name = Sym->body()->getName(); 113 for (StringRef Prefix : {"__start_", "__stop_"}) 114 if (Name.startswith(Prefix)) 115 UsedStartStop.insert(Name.substr(Prefix.size())); 116 } 117 } 118 119 BitcodeCompiler::~BitcodeCompiler() = default; 120 121 static void undefine(Symbol *S) { 122 replaceBody<Undefined>(S, nullptr, S->body()->getName(), /*IsLocal=*/false, 123 STV_DEFAULT, S->body()->Type); 124 } 125 126 void BitcodeCompiler::add(BitcodeFile &F) { 127 lto::InputFile &Obj = *F.Obj; 128 unsigned SymNum = 0; 129 std::vector<SymbolBody *> Syms = F.getSymbols(); 130 std::vector<lto::SymbolResolution> Resols(Syms.size()); 131 132 DenseSet<StringRef> ScriptSymbols; 133 for (BaseCommand *Base : Script->Opt.Commands) 134 if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) 135 ScriptSymbols.insert(Cmd->Name); 136 137 // Provide a resolution to the LTO API for each symbol. 138 for (const lto::InputFile::Symbol &ObjSym : Obj.symbols()) { 139 SymbolBody *B = Syms[SymNum]; 140 Symbol *Sym = B->symbol(); 141 lto::SymbolResolution &R = Resols[SymNum]; 142 ++SymNum; 143 144 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 145 // reports two symbols for module ASM defined. Without this check, lld 146 // flags an undefined in IR with a definition in ASM as prevailing. 147 // Once IRObjectFile is fixed to report only one symbol this hack can 148 // be removed. 149 R.Prevailing = !ObjSym.isUndefined() && B->getFile() == &F; 150 151 // We ask LTO to preserve following global symbols: 152 // 1) All symbols when doing relocatable link, so that them can be used 153 // for doing final link. 154 // 2) Symbols that are used in regular objects. 155 // 3) C named sections if we have corresponding __start_/__stop_ symbol. 156 // 4) Symbols that are defined in bitcode files and used for dynamic linking. 157 R.VisibleToRegularObj = Config->Relocatable || Sym->IsUsedInRegularObj || 158 (R.Prevailing && Sym->includeInDynsym()) || 159 UsedStartStop.count(ObjSym.getSectionName()); 160 if (R.Prevailing) 161 undefine(Sym); 162 163 // We tell LTO to not apply interprocedural optimization for following 164 // symbols because otherwise LTO would inline them while their values are 165 // still not final: 166 // 1) Aliased (with --defsym) or wrapped (with --wrap) symbols. 167 // 2) Symbols redefined in linker script. 168 R.LinkerRedefined = !Sym->CanInline || ScriptSymbols.count(B->getName()); 169 } 170 checkError(LTOObj->add(std::move(F.Obj), Resols)); 171 } 172 173 // Merge all the bitcode files we have seen, codegen the result 174 // and return the resulting ObjectFile(s). 175 std::vector<InputFile *> BitcodeCompiler::compile() { 176 std::vector<InputFile *> Ret; 177 unsigned MaxTasks = LTOObj->getMaxTasks(); 178 Buff.resize(MaxTasks); 179 Files.resize(MaxTasks); 180 181 // The --thinlto-cache-dir option specifies the path to a directory in which 182 // to cache native object files for ThinLTO incremental builds. If a path was 183 // specified, configure LTO to use it as the cache directory. 184 lto::NativeObjectCache Cache; 185 if (!Config->ThinLTOCacheDir.empty()) 186 Cache = check( 187 lto::localCache(Config->ThinLTOCacheDir, 188 [&](size_t Task, std::unique_ptr<MemoryBuffer> MB, 189 StringRef Path) { Files[Task] = std::move(MB); })); 190 191 checkError(LTOObj->run( 192 [&](size_t Task) { 193 return llvm::make_unique<lto::NativeObjectStream>( 194 llvm::make_unique<raw_svector_ostream>(Buff[Task])); 195 }, 196 Cache)); 197 198 if (!Config->ThinLTOCacheDir.empty()) 199 pruneCache(Config->ThinLTOCacheDir, Config->ThinLTOCachePolicy); 200 201 for (unsigned I = 0; I != MaxTasks; ++I) { 202 if (Buff[I].empty()) 203 continue; 204 if (Config->SaveTemps) { 205 if (I == 0) 206 saveBuffer(Buff[I], Config->OutputFile + ".lto.o"); 207 else 208 saveBuffer(Buff[I], Config->OutputFile + Twine(I) + ".lto.o"); 209 } 210 InputFile *Obj = createObjectFile(MemoryBufferRef(Buff[I], "lto.tmp")); 211 Ret.push_back(Obj); 212 } 213 214 for (std::unique_ptr<MemoryBuffer> &File : Files) 215 if (File) 216 Ret.push_back(createObjectFile(*File)); 217 218 return Ret; 219 } 220