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/Object/Archive.h"
15#include "llvm/ADT/STLExtras.h"
16#include "llvm/Bitcode/BitcodeReader.h"
17#include "llvm/Bitcode/BitcodeWriter.h"
18#include "llvm/IR/AutoUpgrade.h"
19#include "llvm/IR/DiagnosticInfo.h"
20#include "llvm/IR/DiagnosticPrinter.h"
21#include "llvm/IR/LLVMContext.h"
22#include "llvm/IR/Module.h"
23#include "llvm/IR/ModuleSummaryIndex.h"
24#include "llvm/IR/Verifier.h"
25#include "llvm/IRReader/IRReader.h"
26#include "llvm/Linker/Linker.h"
27#include "llvm/Support/CommandLine.h"
28#include "llvm/Support/FileSystem.h"
29#include "llvm/Support/InitLLVM.h"
30#include "llvm/Support/Path.h"
31#include "llvm/Support/SourceMgr.h"
32#include "llvm/Support/SystemUtils.h"
33#include "llvm/Support/ToolOutputFile.h"
34#include "llvm/Support/WithColor.h"
35#include "llvm/Transforms/IPO/FunctionImport.h"
36#include "llvm/Transforms/IPO/Internalize.h"
37#include "llvm/Transforms/Utils/FunctionImportUtils.h"
38
39#include <memory>
40#include <utility>
41using namespace llvm;
42
43static cl::list<std::string>
44InputFilenames(cl::Positional, cl::OneOrMore,
45               cl::desc("<input bitcode files>"));
46
47static cl::list<std::string> OverridingInputs(
48    "override", cl::ZeroOrMore, cl::value_desc("filename"),
49    cl::desc(
50        "input bitcode file which can override previously defined symbol(s)"));
51
52// Option to simulate function importing for testing. This enables using
53// llvm-link to simulate ThinLTO backend processes.
54static cl::list<std::string> Imports(
55    "import", cl::ZeroOrMore, cl::value_desc("function:filename"),
56    cl::desc("Pair of function name and filename, where function should be "
57             "imported from bitcode in filename"));
58
59// Option to support testing of function importing. The module summary
60// must be specified in the case were we request imports via the -import
61// option, as well as when compiling any module with functions that may be
62// exported (imported by a different llvm-link -import invocation), to ensure
63// consistent promotion and renaming of locals.
64static cl::opt<std::string>
65    SummaryIndex("summary-index", cl::desc("Module summary index filename"),
66                 cl::init(""), cl::value_desc("filename"));
67
68static cl::opt<std::string>
69OutputFilename("o", cl::desc("Override output filename"), cl::init("-"),
70               cl::value_desc("filename"));
71
72static cl::opt<bool>
73Internalize("internalize", cl::desc("Internalize linked symbols"));
74
75static cl::opt<bool>
76    DisableDITypeMap("disable-debug-info-type-map",
77                     cl::desc("Don't use a uniquing type map for debug info"));
78
79static cl::opt<bool>
80OnlyNeeded("only-needed", cl::desc("Link only needed symbols"));
81
82static cl::opt<bool>
83Force("f", cl::desc("Enable binary output on terminals"));
84
85static cl::opt<bool>
86    DisableLazyLoad("disable-lazy-loading",
87                    cl::desc("Disable lazy module loading"));
88
89static cl::opt<bool>
90    OutputAssembly("S", cl::desc("Write output as LLVM assembly"), cl::Hidden);
91
92static cl::opt<bool>
93Verbose("v", cl::desc("Print information about actions taken"));
94
95static cl::opt<bool>
96DumpAsm("d", cl::desc("Print assembly as linked"), cl::Hidden);
97
98static cl::opt<bool>
99SuppressWarnings("suppress-warnings", cl::desc("Suppress all linking warnings"),
100                 cl::init(false));
101
102static cl::opt<bool> PreserveBitcodeUseListOrder(
103    "preserve-bc-uselistorder",
104    cl::desc("Preserve use-list order when writing LLVM bitcode."),
105    cl::init(true), cl::Hidden);
106
107static cl::opt<bool> PreserveAssemblyUseListOrder(
108    "preserve-ll-uselistorder",
109    cl::desc("Preserve use-list order when writing LLVM assembly."),
110    cl::init(false), cl::Hidden);
111
112static ExitOnError ExitOnErr;
113
114// Read the specified bitcode file in and return it. This routine searches the
115// link path for the specified file to try to find it...
116//
117static std::unique_ptr<Module> loadFile(const char *argv0,
118                                        const std::string &FN,
119                                        LLVMContext &Context,
120                                        bool MaterializeMetadata = true) {
121  SMDiagnostic Err;
122  if (Verbose)
123    errs() << "Loading '" << FN << "'\n";
124  std::unique_ptr<Module> Result;
125  if (DisableLazyLoad)
126    Result = parseIRFile(FN, Err, Context);
127  else
128    Result = getLazyIRFileModule(FN, Err, Context, !MaterializeMetadata);
129
130  if (!Result) {
131    Err.print(argv0, errs());
132    return nullptr;
133  }
134
135  if (MaterializeMetadata) {
136    ExitOnErr(Result->materializeMetadata());
137    UpgradeDebugInfo(*Result);
138  }
139
140  return Result;
141}
142
143static std::unique_ptr<Module> loadArFile(const char *Argv0,
144                                          const std::string &ArchiveName,
145                                          LLVMContext &Context, Linker &L,
146                                          unsigned OrigFlags,
147                                          unsigned ApplicableFlags) {
148  std::unique_ptr<Module> Result(new Module("ArchiveModule", Context));
149  if (Verbose)
150    errs() << "Reading library archive file '" << ArchiveName
151           << "' to memory\n";
152  ErrorOr<std::unique_ptr<MemoryBuffer>> Buf =
153    MemoryBuffer::getFile(ArchiveName, -1, false);
154  ExitOnErr(errorCodeToError(Buf.getError()));
155  Error Err = Error::success();
156  object::Archive Archive(Buf.get()->getMemBufferRef(), Err);
157  ExitOnErr(std::move(Err));
158  for (const object::Archive::Child &C : Archive.children(Err)) {
159    Expected<StringRef> Ename = C.getName();
160    if (Error E = Ename.takeError()) {
161      errs() << Argv0 << ": ";
162      WithColor::error()
163          << " failed to read name of archive member"
164          << ArchiveName << "'\n";
165      return nullptr;
166    };
167    std::string ChildName = Ename.get().str();
168    if (Verbose)
169      errs() << "Parsing member '" << ChildName
170             << "' of archive library to module.\n";
171    SMDiagnostic ParseErr;
172    Expected<MemoryBufferRef> MemBuf = C.getMemoryBufferRef();
173    if (Error E = MemBuf.takeError()) {
174      errs() << Argv0 << ": ";
175      WithColor::error() << " loading memory for member '" << ChildName
176                         << "' of archive library failed'" << ArchiveName
177                         << "'\n";
178      return nullptr;
179    };
180
181    if (!isBitcode(reinterpret_cast<const unsigned char *>
182                   (MemBuf.get().getBufferStart()),
183                   reinterpret_cast<const unsigned char *>
184                   (MemBuf.get().getBufferEnd()))) {
185      errs() << Argv0 << ": ";
186      WithColor::error() << "  member of archive is not a bitcode file: '"
187                         << ChildName << "'\n";
188      return nullptr;
189    }
190
191    std::unique_ptr<Module> M = parseIR(MemBuf.get(), ParseErr, Context);
192
193    if (!M.get()) {
194      errs() << Argv0 << ": ";
195      WithColor::error() << " parsing member '" << ChildName
196                         << "' of archive library failed'" << ArchiveName
197                         << "'\n";
198      return nullptr;
199    }
200    if (Verbose)
201      errs() << "Linking member '" << ChildName << "' of archive library.\n";
202    if (L.linkModules(*Result, std::move(M), ApplicableFlags))
203      return nullptr;
204    ApplicableFlags = OrigFlags;
205  } // end for each child
206  ExitOnErr(std::move(Err));
207  return Result;
208}
209
210namespace {
211
212/// Helper to load on demand a Module from file and cache it for subsequent
213/// queries during function importing.
214class ModuleLazyLoaderCache {
215  /// Cache of lazily loaded module for import.
216  StringMap<std::unique_ptr<Module>> ModuleMap;
217
218  /// Retrieve a Module from the cache or lazily load it on demand.
219  std::function<std::unique_ptr<Module>(const char *argv0,
220                                        const std::string &FileName)>
221      createLazyModule;
222
223public:
224  /// Create the loader, Module will be initialized in \p Context.
225  ModuleLazyLoaderCache(std::function<std::unique_ptr<Module>(
226                            const char *argv0, const std::string &FileName)>
227                            createLazyModule)
228      : createLazyModule(std::move(createLazyModule)) {}
229
230  /// Retrieve a Module from the cache or lazily load it on demand.
231  Module &operator()(const char *argv0, const std::string &FileName);
232
233  std::unique_ptr<Module> takeModule(const std::string &FileName) {
234    auto I = ModuleMap.find(FileName);
235    assert(I != ModuleMap.end());
236    std::unique_ptr<Module> Ret = std::move(I->second);
237    ModuleMap.erase(I);
238    return Ret;
239  }
240};
241
242// Get a Module for \p FileName from the cache, or load it lazily.
243Module &ModuleLazyLoaderCache::operator()(const char *argv0,
244                                          const std::string &Identifier) {
245  auto &Module = ModuleMap[Identifier];
246  if (!Module)
247    Module = createLazyModule(argv0, Identifier);
248  return *Module;
249}
250} // anonymous namespace
251
252namespace {
253struct LLVMLinkDiagnosticHandler : public DiagnosticHandler {
254  bool handleDiagnostics(const DiagnosticInfo &DI) override {
255    unsigned Severity = DI.getSeverity();
256    switch (Severity) {
257    case DS_Error:
258      WithColor::error();
259      break;
260    case DS_Warning:
261      if (SuppressWarnings)
262        return true;
263      WithColor::warning();
264      break;
265    case DS_Remark:
266    case DS_Note:
267      llvm_unreachable("Only expecting warnings and errors");
268    }
269
270    DiagnosticPrinterRawOStream DP(errs());
271    DI.print(DP);
272    errs() << '\n';
273    return true;
274  }
275};
276}
277
278/// Import any functions requested via the -import option.
279static bool importFunctions(const char *argv0, Module &DestModule) {
280  if (SummaryIndex.empty())
281    return true;
282  std::unique_ptr<ModuleSummaryIndex> Index =
283      ExitOnErr(llvm::getModuleSummaryIndexForFile(SummaryIndex));
284
285  // Map of Module -> List of globals to import from the Module
286  FunctionImporter::ImportMapTy ImportList;
287
288  auto ModuleLoader = [&DestModule](const char *argv0,
289                                    const std::string &Identifier) {
290    return loadFile(argv0, Identifier, DestModule.getContext(), false);
291  };
292
293  ModuleLazyLoaderCache ModuleLoaderCache(ModuleLoader);
294  for (const auto &Import : Imports) {
295    // Identify the requested function and its bitcode source file.
296    size_t Idx = Import.find(':');
297    if (Idx == std::string::npos) {
298      errs() << "Import parameter bad format: " << Import << "\n";
299      return false;
300    }
301    std::string FunctionName = Import.substr(0, Idx);
302    std::string FileName = Import.substr(Idx + 1, std::string::npos);
303
304    // Load the specified source module.
305    auto &SrcModule = ModuleLoaderCache(argv0, FileName);
306
307    if (verifyModule(SrcModule, &errs())) {
308      errs() << argv0 << ": " << FileName;
309      WithColor::error() << "input module is broken!\n";
310      return false;
311    }
312
313    Function *F = SrcModule.getFunction(FunctionName);
314    if (!F) {
315      errs() << "Ignoring import request for non-existent function "
316             << FunctionName << " from " << FileName << "\n";
317      continue;
318    }
319    // We cannot import weak_any functions without possibly affecting the
320    // order they are seen and selected by the linker, changing program
321    // semantics.
322    if (F->hasWeakAnyLinkage()) {
323      errs() << "Ignoring import request for weak-any function " << FunctionName
324             << " from " << FileName << "\n";
325      continue;
326    }
327
328    if (Verbose)
329      errs() << "Importing " << FunctionName << " from " << FileName << "\n";
330
331    auto &Entry = ImportList[FileName];
332    Entry.insert(F->getGUID());
333  }
334  auto CachedModuleLoader = [&](StringRef Identifier) {
335    return ModuleLoaderCache.takeModule(std::string(Identifier));
336  };
337  FunctionImporter Importer(*Index, CachedModuleLoader,
338                            /*ClearDSOLocalOnDeclarations=*/false);
339  ExitOnErr(Importer.importFunctions(DestModule, ImportList));
340
341  return true;
342}
343
344static bool linkFiles(const char *argv0, LLVMContext &Context, Linker &L,
345                      const cl::list<std::string> &Files,
346                      unsigned Flags) {
347  // Filter out flags that don't apply to the first file we load.
348  unsigned ApplicableFlags = Flags & Linker::Flags::OverrideFromSrc;
349  // Similar to some flags, internalization doesn't apply to the first file.
350  bool InternalizeLinkedSymbols = false;
351  for (const auto &File : Files) {
352    std::unique_ptr<Module> M =
353      (llvm::sys::path::extension(File) == ".a")
354          ? loadArFile(argv0, File, Context, L, Flags, ApplicableFlags)
355          : loadFile(argv0, File, Context);
356    if (!M.get()) {
357      errs() << argv0 << ": ";
358      WithColor::error() << " loading file '" << File << "'\n";
359      return false;
360    }
361
362    // Note that when ODR merging types cannot verify input files in here When
363    // doing that debug metadata in the src module might already be pointing to
364    // the destination.
365    if (DisableDITypeMap && verifyModule(*M, &errs())) {
366      errs() << argv0 << ": " << File << ": ";
367      WithColor::error() << "input module is broken!\n";
368      return false;
369    }
370
371    // If a module summary index is supplied, load it so linkInModule can treat
372    // local functions/variables as exported and promote if necessary.
373    if (!SummaryIndex.empty()) {
374      std::unique_ptr<ModuleSummaryIndex> Index =
375          ExitOnErr(llvm::getModuleSummaryIndexForFile(SummaryIndex));
376
377      // Conservatively mark all internal values as promoted, since this tool
378      // does not do the ThinLink that would normally determine what values to
379      // promote.
380      for (auto &I : *Index) {
381        for (auto &S : I.second.SummaryList) {
382          if (GlobalValue::isLocalLinkage(S->linkage()))
383            S->setLinkage(GlobalValue::ExternalLinkage);
384        }
385      }
386
387      // Promotion
388      if (renameModuleForThinLTO(*M, *Index,
389                                 /*ClearDSOLocalOnDeclarations=*/false))
390        return true;
391    }
392
393    if (Verbose)
394      errs() << "Linking in '" << File << "'\n";
395
396    bool Err = false;
397    if (InternalizeLinkedSymbols) {
398      Err = L.linkInModule(
399          std::move(M), ApplicableFlags, [](Module &M, const StringSet<> &GVS) {
400            internalizeModule(M, [&GVS](const GlobalValue &GV) {
401              return !GV.hasName() || (GVS.count(GV.getName()) == 0);
402            });
403          });
404    } else {
405      Err = L.linkInModule(std::move(M), ApplicableFlags);
406    }
407
408    if (Err)
409      return false;
410
411    // Internalization applies to linking of subsequent files.
412    InternalizeLinkedSymbols = Internalize;
413
414    // All linker flags apply to linking of subsequent files.
415    ApplicableFlags = Flags;
416  }
417
418  return true;
419}
420
421int main(int argc, char **argv) {
422  InitLLVM X(argc, argv);
423  ExitOnErr.setBanner(std::string(argv[0]) + ": ");
424
425  LLVMContext Context;
426  Context.setDiagnosticHandler(
427    std::make_unique<LLVMLinkDiagnosticHandler>(), true);
428  cl::ParseCommandLineOptions(argc, argv, "llvm linker\n");
429
430  if (!DisableDITypeMap)
431    Context.enableDebugTypeODRUniquing();
432
433  auto Composite = std::make_unique<Module>("llvm-link", Context);
434  Linker L(*Composite);
435
436  unsigned Flags = Linker::Flags::None;
437  if (OnlyNeeded)
438    Flags |= Linker::Flags::LinkOnlyNeeded;
439
440  // First add all the regular input files
441  if (!linkFiles(argv[0], Context, L, InputFilenames, Flags))
442    return 1;
443
444  // Next the -override ones.
445  if (!linkFiles(argv[0], Context, L, OverridingInputs,
446                 Flags | Linker::Flags::OverrideFromSrc))
447    return 1;
448
449  // Import any functions requested via -import
450  if (!importFunctions(argv[0], *Composite))
451    return 1;
452
453  if (DumpAsm)
454    errs() << "Here's the assembly:\n" << *Composite;
455
456  std::error_code EC;
457  ToolOutputFile Out(OutputFilename, EC, sys::fs::OF_None);
458  if (EC) {
459    WithColor::error() << EC.message() << '\n';
460    return 1;
461  }
462
463  if (verifyModule(*Composite, &errs())) {
464    errs() << argv[0] << ": ";
465    WithColor::error() << "linked module is broken!\n";
466    return 1;
467  }
468
469  if (Verbose)
470    errs() << "Writing bitcode...\n";
471  if (OutputAssembly) {
472    Composite->print(Out.os(), nullptr, PreserveAssemblyUseListOrder);
473  } else if (Force || !CheckBitcodeOutputToConsole(Out.os()))
474    WriteBitcodeToFile(*Composite, Out.os(), PreserveBitcodeUseListOrder);
475
476  // Declare success.
477  Out.keep();
478
479  return 0;
480}
481