1 //===- LTO.cpp ------------------------------------------------------------===// 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 #include "LTO.h" 10 #include "Config.h" 11 #include "InputFiles.h" 12 #include "LinkerScript.h" 13 #include "SymbolTable.h" 14 #include "Symbols.h" 15 #include "lld/Common/Args.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/Bitcode/BitcodeReader.h" 24 #include "llvm/Bitcode/BitcodeWriter.h" 25 #include "llvm/IR/DiagnosticPrinter.h" 26 #include "llvm/LTO/Caching.h" 27 #include "llvm/LTO/Config.h" 28 #include "llvm/LTO/LTO.h" 29 #include "llvm/Object/SymbolicFile.h" 30 #include "llvm/Support/CodeGen.h" 31 #include "llvm/Support/Error.h" 32 #include "llvm/Support/FileSystem.h" 33 #include "llvm/Support/MemoryBuffer.h" 34 #include <algorithm> 35 #include <cstddef> 36 #include <memory> 37 #include <string> 38 #include <system_error> 39 #include <vector> 40 41 using namespace llvm; 42 using namespace llvm::object; 43 using namespace llvm::ELF; 44 45 using namespace lld; 46 using namespace lld::elf; 47 48 // Creates an empty file to store a list of object files for final 49 // linking of distributed ThinLTO. 50 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) { 51 std::error_code ec; 52 auto ret = 53 llvm::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::F_None); 54 if (ec) { 55 error("cannot open " + file + ": " + ec.message()); 56 return nullptr; 57 } 58 return ret; 59 } 60 61 static std::string getThinLTOOutputFile(StringRef modulePath) { 62 return lto::getThinLTOOutputFile(modulePath, 63 config->thinLTOPrefixReplace.first, 64 config->thinLTOPrefixReplace.second); 65 } 66 67 static lto::Config createConfig() { 68 lto::Config c; 69 70 // LLD supports the new relocations and address-significance tables. 71 c.Options = initTargetOptionsFromCodeGenFlags(); 72 c.Options.RelaxELFRelocations = true; 73 c.Options.EmitAddrsig = true; 74 75 // Always emit a section per function/datum with LTO. 76 c.Options.FunctionSections = true; 77 c.Options.DataSections = true; 78 79 if (config->relocatable) 80 c.RelocModel = None; 81 else if (config->isPic) 82 c.RelocModel = Reloc::PIC_; 83 else 84 c.RelocModel = Reloc::Static; 85 86 c.CodeModel = getCodeModelFromCMModel(); 87 c.DisableVerify = config->disableVerify; 88 c.DiagHandler = diagnosticHandler; 89 c.OptLevel = config->ltoo; 90 c.CPU = getCPUStr(); 91 c.MAttrs = getMAttrs(); 92 c.CGOptLevel = args::getCGOptLevel(config->ltoo); 93 94 // Set up a custom pipeline if we've been asked to. 95 c.OptPipeline = config->ltoNewPmPasses; 96 c.AAPipeline = config->ltoAAPipeline; 97 98 // Set up optimization remarks if we've been asked to. 99 c.RemarksFilename = config->optRemarksFilename; 100 c.RemarksPasses = config->optRemarksPasses; 101 c.RemarksWithHotness = config->optRemarksWithHotness; 102 c.RemarksFormat = config->optRemarksFormat; 103 104 c.SampleProfile = config->ltoSampleProfile; 105 c.UseNewPM = config->ltoNewPassManager; 106 c.DebugPassManager = config->ltoDebugPassManager; 107 c.DwoDir = config->dwoDir; 108 109 c.CSIRProfile = config->ltoCSProfileFile; 110 c.RunCSIRInstr = config->ltoCSProfileGenerate; 111 112 if (config->emitLLVM) { 113 c.PostInternalizeModuleHook = [](size_t task, const Module &m) { 114 if (std::unique_ptr<raw_fd_ostream> os = openFile(config->outputFile)) 115 WriteBitcodeToFile(m, *os, false); 116 return false; 117 }; 118 } 119 120 if (config->saveTemps) 121 checkError(c.addSaveTemps(config->outputFile.str() + ".", 122 /*UseInputModulePath*/ true)); 123 return c; 124 } 125 126 BitcodeCompiler::BitcodeCompiler() { 127 // Initialize indexFile. 128 if (!config->thinLTOIndexOnlyArg.empty()) 129 indexFile = openFile(config->thinLTOIndexOnlyArg); 130 131 // Initialize ltoObj. 132 lto::ThinBackend backend; 133 if (config->thinLTOIndexOnly) { 134 auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); }; 135 backend = lto::createWriteIndexesThinBackend( 136 config->thinLTOPrefixReplace.first, config->thinLTOPrefixReplace.second, 137 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite); 138 } else if (config->thinLTOJobs != -1U) { 139 backend = lto::createInProcessThinBackend(config->thinLTOJobs); 140 } 141 142 ltoObj = llvm::make_unique<lto::LTO>(createConfig(), backend, 143 config->ltoPartitions); 144 145 // Initialize usedStartStop. 146 symtab->forEachSymbol([&](Symbol *sym) { 147 StringRef s = sym->getName(); 148 for (StringRef prefix : {"__start_", "__stop_"}) 149 if (s.startswith(prefix)) 150 usedStartStop.insert(s.substr(prefix.size())); 151 }); 152 } 153 154 BitcodeCompiler::~BitcodeCompiler() = default; 155 156 void BitcodeCompiler::add(BitcodeFile &f) { 157 lto::InputFile &obj = *f.obj; 158 bool isExec = !config->shared && !config->relocatable; 159 160 if (config->thinLTOIndexOnly) 161 thinIndices.insert(obj.getName()); 162 163 ArrayRef<Symbol *> syms = f.getSymbols(); 164 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols(); 165 std::vector<lto::SymbolResolution> resols(syms.size()); 166 167 // Provide a resolution to the LTO API for each symbol. 168 for (size_t i = 0, e = syms.size(); i != e; ++i) { 169 Symbol *sym = syms[i]; 170 const lto::InputFile::Symbol &objSym = objSyms[i]; 171 lto::SymbolResolution &r = resols[i]; 172 173 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 174 // reports two symbols for module ASM defined. Without this check, lld 175 // flags an undefined in IR with a definition in ASM as prevailing. 176 // Once IRObjectFile is fixed to report only one symbol this hack can 177 // be removed. 178 r.Prevailing = !objSym.isUndefined() && sym->file == &f; 179 180 // We ask LTO to preserve following global symbols: 181 // 1) All symbols when doing relocatable link, so that them can be used 182 // for doing final link. 183 // 2) Symbols that are used in regular objects. 184 // 3) C named sections if we have corresponding __start_/__stop_ symbol. 185 // 4) Symbols that are defined in bitcode files and used for dynamic linking. 186 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj || 187 (r.Prevailing && sym->includeInDynsym()) || 188 usedStartStop.count(objSym.getSectionName()); 189 const auto *dr = dyn_cast<Defined>(sym); 190 r.FinalDefinitionInLinkageUnit = 191 (isExec || sym->visibility != STV_DEFAULT) && dr && 192 // Skip absolute symbols from ELF objects, otherwise PC-rel relocations 193 // will be generated by for them, triggering linker errors. 194 // Symbol section is always null for bitcode symbols, hence the check 195 // for isElf(). Skip linker script defined symbols as well: they have 196 // no File defined. 197 !(dr->section == nullptr && (!sym->file || sym->file->isElf())); 198 199 if (r.Prevailing) 200 sym->replace(Undefined{nullptr, sym->getName(), STB_GLOBAL, STV_DEFAULT, 201 sym->type}); 202 203 // We tell LTO to not apply interprocedural optimization for wrapped 204 // (with --wrap) symbols because otherwise LTO would inline them while 205 // their values are still not final. 206 r.LinkerRedefined = !sym->canInline; 207 } 208 checkError(ltoObj->add(std::move(f.obj), resols)); 209 } 210 211 // If LazyObjFile has not been added to link, emit empty index files. 212 // This is needed because this is what GNU gold plugin does and we have a 213 // distributed build system that depends on that behavior. 214 static void thinLTOCreateEmptyIndexFiles() { 215 for (LazyObjFile *f : lazyObjFiles) { 216 if (!isBitcode(f->mb)) 217 continue; 218 std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName())); 219 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc"); 220 if (!os) 221 continue; 222 223 ModuleSummaryIndex m(/*HaveGVs*/ false); 224 m.setSkipModuleByDistributedBackend(); 225 WriteIndexToFile(m, *os); 226 if (config->thinLTOEmitImportsFiles) 227 openFile(path + ".imports"); 228 } 229 } 230 231 // Merge all the bitcode files we have seen, codegen the result 232 // and return the resulting ObjectFile(s). 233 std::vector<InputFile *> BitcodeCompiler::compile() { 234 unsigned maxTasks = ltoObj->getMaxTasks(); 235 buf.resize(maxTasks); 236 files.resize(maxTasks); 237 238 // The --thinlto-cache-dir option specifies the path to a directory in which 239 // to cache native object files for ThinLTO incremental builds. If a path was 240 // specified, configure LTO to use it as the cache directory. 241 lto::NativeObjectCache cache; 242 if (!config->thinLTOCacheDir.empty()) 243 cache = check( 244 lto::localCache(config->thinLTOCacheDir, 245 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) { 246 files[task] = std::move(mb); 247 })); 248 249 if (!bitcodeFiles.empty()) 250 checkError(ltoObj->run( 251 [&](size_t task) { 252 return llvm::make_unique<lto::NativeObjectStream>( 253 llvm::make_unique<raw_svector_ostream>(buf[task])); 254 }, 255 cache)); 256 257 // Emit empty index files for non-indexed files 258 for (StringRef s : thinIndices) { 259 std::string path = getThinLTOOutputFile(s); 260 openFile(path + ".thinlto.bc"); 261 if (config->thinLTOEmitImportsFiles) 262 openFile(path + ".imports"); 263 } 264 265 if (config->thinLTOIndexOnly) { 266 thinLTOCreateEmptyIndexFiles(); 267 268 if (!config->ltoObjPath.empty()) 269 saveBuffer(buf[0], config->ltoObjPath); 270 271 // ThinLTO with index only option is required to generate only the index 272 // files. After that, we exit from linker and ThinLTO backend runs in a 273 // distributed environment. 274 if (indexFile) 275 indexFile->close(); 276 return {}; 277 } 278 279 if (!config->thinLTOCacheDir.empty()) 280 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy); 281 282 if (!config->ltoObjPath.empty()) { 283 saveBuffer(buf[0], config->ltoObjPath); 284 for (unsigned i = 1; i != maxTasks; ++i) 285 saveBuffer(buf[i], config->ltoObjPath + Twine(i)); 286 } 287 288 if (config->saveTemps) { 289 saveBuffer(buf[0], config->outputFile + ".lto.o"); 290 for (unsigned i = 1; i != maxTasks; ++i) 291 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o"); 292 } 293 294 std::vector<InputFile *> ret; 295 for (unsigned i = 0; i != maxTasks; ++i) 296 if (!buf[i].empty()) 297 ret.push_back(createObjectFile(MemoryBufferRef(buf[i], "lto.tmp"))); 298 299 for (std::unique_ptr<MemoryBuffer> &file : files) 300 if (file) 301 ret.push_back(createObjectFile(*file)); 302 return ret; 303 } 304