xref: /freebsd/contrib/llvm-project/lld/ELF/LTO.cpp (revision 2f513db72b034fd5ef7f080b11be5c711c15186a)
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