1//===- llvm-link.cpp - Low-level LLVM linker ------------------------------===//
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// This utility may be invoked in the following manner:
10//  llvm-link a.bc b.bc c.bc -o x.bc
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/ADT/STLExtras.h"
15#include "llvm/Bitcode/BitcodeReader.h"
16#include "llvm/Bitcode/BitcodeWriter.h"
17#include "llvm/IR/AutoUpgrade.h"
18#include "llvm/IR/DiagnosticInfo.h"
19#include "llvm/IR/DiagnosticPrinter.h"
20#include "llvm/IR/LLVMContext.h"
21#include "llvm/IR/Module.h"
22#include "llvm/IR/ModuleSummaryIndex.h"
23#include "llvm/IR/Verifier.h"
24#include "llvm/IRReader/IRReader.h"
25#include "llvm/Linker/Linker.h"
26#include "llvm/Support/CommandLine.h"
27#include "llvm/Support/FileSystem.h"
28#include "llvm/Support/InitLLVM.h"
29#include "llvm/Support/Path.h"
30#include "llvm/Support/SourceMgr.h"
31#include "llvm/Support/SystemUtils.h"
32#include "llvm/Support/ToolOutputFile.h"
33#include "llvm/Support/WithColor.h"
34#include "llvm/Transforms/IPO/FunctionImport.h"
35#include "llvm/Transforms/IPO/Internalize.h"
36#include "llvm/Transforms/Utils/FunctionImportUtils.h"
37
38#include <memory>
39#include <utility>
40using namespace llvm;
41
42static cl::list<std::string>
43InputFilenames(cl::Positional, cl::OneOrMore,
44               cl::desc("<input bitcode files>"));
45
46static cl::list<std::string> OverridingInputs(
47    "override", cl::ZeroOrMore, cl::value_desc("filename"),
48    cl::desc(
49        "input bitcode file which can override previously defined symbol(s)"));
50
51// Option to simulate function importing for testing. This enables using
52// llvm-link to simulate ThinLTO backend processes.
53static cl::list<std::string> Imports(
54    "import", cl::ZeroOrMore, cl::value_desc("function:filename"),
55    cl::desc("Pair of function name and filename, where function should be "
56             "imported from bitcode in filename"));
57
58// Option to support testing of function importing. The module summary
59// must be specified in the case were we request imports via the -import
60// option, as well as when compiling any module with functions that may be
61// exported (imported by a different llvm-link -import invocation), to ensure
62// consistent promotion and renaming of locals.
63static cl::opt<std::string>
64    SummaryIndex("summary-index", cl::desc("Module summary index filename"),
65                 cl::init(""), cl::value_desc("filename"));
66
67static cl::opt<std::string>
68OutputFilename("o", cl::desc("Override output filename"), cl::init("-"),
69               cl::value_desc("filename"));
70
71static cl::opt<bool>
72Internalize("internalize", cl::desc("Internalize linked symbols"));
73
74static cl::opt<bool>
75    DisableDITypeMap("disable-debug-info-type-map",
76                     cl::desc("Don't use a uniquing type map for debug info"));
77
78static cl::opt<bool>
79OnlyNeeded("only-needed", cl::desc("Link only needed symbols"));
80
81static cl::opt<bool>
82Force("f", cl::desc("Enable binary output on terminals"));
83
84static cl::opt<bool>
85    DisableLazyLoad("disable-lazy-loading",
86                    cl::desc("Disable lazy module loading"));
87
88static cl::opt<bool>
89    OutputAssembly("S", cl::desc("Write output as LLVM assembly"), cl::Hidden);
90
91static cl::opt<bool>
92Verbose("v", cl::desc("Print information about actions taken"));
93
94static cl::opt<bool>
95DumpAsm("d", cl::desc("Print assembly as linked"), cl::Hidden);
96
97static cl::opt<bool>
98SuppressWarnings("suppress-warnings", cl::desc("Suppress all linking warnings"),
99                 cl::init(false));
100
101static cl::opt<bool> PreserveBitcodeUseListOrder(
102    "preserve-bc-uselistorder",
103    cl::desc("Preserve use-list order when writing LLVM bitcode."),
104    cl::init(true), cl::Hidden);
105
106static cl::opt<bool> PreserveAssemblyUseListOrder(
107    "preserve-ll-uselistorder",
108    cl::desc("Preserve use-list order when writing LLVM assembly."),
109    cl::init(false), cl::Hidden);
110
111static ExitOnError ExitOnErr;
112
113// Read the specified bitcode file in and return it. This routine searches the
114// link path for the specified file to try to find it...
115//
116static std::unique_ptr<Module> loadFile(const char *argv0,
117                                        const std::string &FN,
118                                        LLVMContext &Context,
119                                        bool MaterializeMetadata = true) {
120  SMDiagnostic Err;
121  if (Verbose)
122    errs() << "Loading '" << FN << "'\n";
123  std::unique_ptr<Module> Result;
124  if (DisableLazyLoad)
125    Result = parseIRFile(FN, Err, Context);
126  else
127    Result = getLazyIRFileModule(FN, Err, Context, !MaterializeMetadata);
128
129  if (!Result) {
130    Err.print(argv0, errs());
131    return nullptr;
132  }
133
134  if (MaterializeMetadata) {
135    ExitOnErr(Result->materializeMetadata());
136    UpgradeDebugInfo(*Result);
137  }
138
139  return Result;
140}
141
142namespace {
143
144/// Helper to load on demand a Module from file and cache it for subsequent
145/// queries during function importing.
146class ModuleLazyLoaderCache {
147  /// Cache of lazily loaded module for import.
148  StringMap<std::unique_ptr<Module>> ModuleMap;
149
150  /// Retrieve a Module from the cache or lazily load it on demand.
151  std::function<std::unique_ptr<Module>(const char *argv0,
152                                        const std::string &FileName)>
153      createLazyModule;
154
155public:
156  /// Create the loader, Module will be initialized in \p Context.
157  ModuleLazyLoaderCache(std::function<std::unique_ptr<Module>(
158                            const char *argv0, const std::string &FileName)>
159                            createLazyModule)
160      : createLazyModule(std::move(createLazyModule)) {}
161
162  /// Retrieve a Module from the cache or lazily load it on demand.
163  Module &operator()(const char *argv0, const std::string &FileName);
164
165  std::unique_ptr<Module> takeModule(const std::string &FileName) {
166    auto I = ModuleMap.find(FileName);
167    assert(I != ModuleMap.end());
168    std::unique_ptr<Module> Ret = std::move(I->second);
169    ModuleMap.erase(I);
170    return Ret;
171  }
172};
173
174// Get a Module for \p FileName from the cache, or load it lazily.
175Module &ModuleLazyLoaderCache::operator()(const char *argv0,
176                                          const std::string &Identifier) {
177  auto &Module = ModuleMap[Identifier];
178  if (!Module)
179    Module = createLazyModule(argv0, Identifier);
180  return *Module;
181}
182} // anonymous namespace
183
184namespace {
185struct LLVMLinkDiagnosticHandler : public DiagnosticHandler {
186  bool handleDiagnostics(const DiagnosticInfo &DI) override {
187    unsigned Severity = DI.getSeverity();
188    switch (Severity) {
189    case DS_Error:
190      WithColor::error();
191      break;
192    case DS_Warning:
193      if (SuppressWarnings)
194        return true;
195      WithColor::warning();
196      break;
197    case DS_Remark:
198    case DS_Note:
199      llvm_unreachable("Only expecting warnings and errors");
200    }
201
202    DiagnosticPrinterRawOStream DP(errs());
203    DI.print(DP);
204    errs() << '\n';
205    return true;
206  }
207};
208}
209
210/// Import any functions requested via the -import option.
211static bool importFunctions(const char *argv0, Module &DestModule) {
212  if (SummaryIndex.empty())
213    return true;
214  std::unique_ptr<ModuleSummaryIndex> Index =
215      ExitOnErr(llvm::getModuleSummaryIndexForFile(SummaryIndex));
216
217  // Map of Module -> List of globals to import from the Module
218  FunctionImporter::ImportMapTy ImportList;
219
220  auto ModuleLoader = [&DestModule](const char *argv0,
221                                    const std::string &Identifier) {
222    return loadFile(argv0, Identifier, DestModule.getContext(), false);
223  };
224
225  ModuleLazyLoaderCache ModuleLoaderCache(ModuleLoader);
226  for (const auto &Import : Imports) {
227    // Identify the requested function and its bitcode source file.
228    size_t Idx = Import.find(':');
229    if (Idx == std::string::npos) {
230      errs() << "Import parameter bad format: " << Import << "\n";
231      return false;
232    }
233    std::string FunctionName = Import.substr(0, Idx);
234    std::string FileName = Import.substr(Idx + 1, std::string::npos);
235
236    // Load the specified source module.
237    auto &SrcModule = ModuleLoaderCache(argv0, FileName);
238
239    if (verifyModule(SrcModule, &errs())) {
240      errs() << argv0 << ": " << FileName;
241      WithColor::error() << "input module is broken!\n";
242      return false;
243    }
244
245    Function *F = SrcModule.getFunction(FunctionName);
246    if (!F) {
247      errs() << "Ignoring import request for non-existent function "
248             << FunctionName << " from " << FileName << "\n";
249      continue;
250    }
251    // We cannot import weak_any functions without possibly affecting the
252    // order they are seen and selected by the linker, changing program
253    // semantics.
254    if (F->hasWeakAnyLinkage()) {
255      errs() << "Ignoring import request for weak-any function " << FunctionName
256             << " from " << FileName << "\n";
257      continue;
258    }
259
260    if (Verbose)
261      errs() << "Importing " << FunctionName << " from " << FileName << "\n";
262
263    auto &Entry = ImportList[FileName];
264    Entry.insert(F->getGUID());
265  }
266  auto CachedModuleLoader = [&](StringRef Identifier) {
267    return ModuleLoaderCache.takeModule(Identifier);
268  };
269  FunctionImporter Importer(*Index, CachedModuleLoader);
270  ExitOnErr(Importer.importFunctions(DestModule, ImportList));
271
272  return true;
273}
274
275static bool linkFiles(const char *argv0, LLVMContext &Context, Linker &L,
276                      const cl::list<std::string> &Files,
277                      unsigned Flags) {
278  // Filter out flags that don't apply to the first file we load.
279  unsigned ApplicableFlags = Flags & Linker::Flags::OverrideFromSrc;
280  // Similar to some flags, internalization doesn't apply to the first file.
281  bool InternalizeLinkedSymbols = false;
282  for (const auto &File : Files) {
283    std::unique_ptr<Module> M = loadFile(argv0, File, Context);
284    if (!M.get()) {
285      errs() << argv0 << ": ";
286      WithColor::error() << " loading file '" << File << "'\n";
287      return false;
288    }
289
290    // Note that when ODR merging types cannot verify input files in here When
291    // doing that debug metadata in the src module might already be pointing to
292    // the destination.
293    if (DisableDITypeMap && verifyModule(*M, &errs())) {
294      errs() << argv0 << ": " << File << ": ";
295      WithColor::error() << "input module is broken!\n";
296      return false;
297    }
298
299    // If a module summary index is supplied, load it so linkInModule can treat
300    // local functions/variables as exported and promote if necessary.
301    if (!SummaryIndex.empty()) {
302      std::unique_ptr<ModuleSummaryIndex> Index =
303          ExitOnErr(llvm::getModuleSummaryIndexForFile(SummaryIndex));
304
305      // Conservatively mark all internal values as promoted, since this tool
306      // does not do the ThinLink that would normally determine what values to
307      // promote.
308      for (auto &I : *Index) {
309        for (auto &S : I.second.SummaryList) {
310          if (GlobalValue::isLocalLinkage(S->linkage()))
311            S->setLinkage(GlobalValue::ExternalLinkage);
312        }
313      }
314
315      // Promotion
316      if (renameModuleForThinLTO(*M, *Index))
317        return true;
318    }
319
320    if (Verbose)
321      errs() << "Linking in '" << File << "'\n";
322
323    bool Err = false;
324    if (InternalizeLinkedSymbols) {
325      Err = L.linkInModule(
326          std::move(M), ApplicableFlags, [](Module &M, const StringSet<> &GVS) {
327            internalizeModule(M, [&GVS](const GlobalValue &GV) {
328              return !GV.hasName() || (GVS.count(GV.getName()) == 0);
329            });
330          });
331    } else {
332      Err = L.linkInModule(std::move(M), ApplicableFlags);
333    }
334
335    if (Err)
336      return false;
337
338    // Internalization applies to linking of subsequent files.
339    InternalizeLinkedSymbols = Internalize;
340
341    // All linker flags apply to linking of subsequent files.
342    ApplicableFlags = Flags;
343  }
344
345  return true;
346}
347
348int main(int argc, char **argv) {
349  InitLLVM X(argc, argv);
350  ExitOnErr.setBanner(std::string(argv[0]) + ": ");
351
352  LLVMContext Context;
353  Context.setDiagnosticHandler(
354    std::make_unique<LLVMLinkDiagnosticHandler>(), true);
355  cl::ParseCommandLineOptions(argc, argv, "llvm linker\n");
356
357  if (!DisableDITypeMap)
358    Context.enableDebugTypeODRUniquing();
359
360  auto Composite = std::make_unique<Module>("llvm-link", Context);
361  Linker L(*Composite);
362
363  unsigned Flags = Linker::Flags::None;
364  if (OnlyNeeded)
365    Flags |= Linker::Flags::LinkOnlyNeeded;
366
367  // First add all the regular input files
368  if (!linkFiles(argv[0], Context, L, InputFilenames, Flags))
369    return 1;
370
371  // Next the -override ones.
372  if (!linkFiles(argv[0], Context, L, OverridingInputs,
373                 Flags | Linker::Flags::OverrideFromSrc))
374    return 1;
375
376  // Import any functions requested via -import
377  if (!importFunctions(argv[0], *Composite))
378    return 1;
379
380  if (DumpAsm)
381    errs() << "Here's the assembly:\n" << *Composite;
382
383  std::error_code EC;
384  ToolOutputFile Out(OutputFilename, EC, sys::fs::OF_None);
385  if (EC) {
386    WithColor::error() << EC.message() << '\n';
387    return 1;
388  }
389
390  if (verifyModule(*Composite, &errs())) {
391    errs() << argv[0] << ": ";
392    WithColor::error() << "linked module is broken!\n";
393    return 1;
394  }
395
396  if (Verbose)
397    errs() << "Writing bitcode...\n";
398  if (OutputAssembly) {
399    Composite->print(Out.os(), nullptr, PreserveAssemblyUseListOrder);
400  } else if (Force || !CheckBitcodeOutputToConsole(Out.os(), true))
401    WriteBitcodeToFile(*Composite, Out.os(), PreserveBitcodeUseListOrder);
402
403  // Declare success.
404  Out.keep();
405
406  return 0;
407}
408