1 //===- llvm-link.cpp - Low-level LLVM linker ------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This utility may be invoked in the following manner:
11 //  llvm-link a.bc b.bc c.bc -o x.bc
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/Linker/Linker.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/Bitcode/ReaderWriter.h"
18 #include "llvm/IR/AutoUpgrade.h"
19 #include "llvm/IR/DiagnosticInfo.h"
20 #include "llvm/IR/DiagnosticPrinter.h"
21 #include "llvm/IR/FunctionInfo.h"
22 #include "llvm/IR/LLVMContext.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/IR/Verifier.h"
25 #include "llvm/IRReader/IRReader.h"
26 #include "llvm/Object/FunctionIndexObjectFile.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/FileSystem.h"
29 #include "llvm/Support/ManagedStatic.h"
30 #include "llvm/Support/Path.h"
31 #include "llvm/Support/PrettyStackTrace.h"
32 #include "llvm/Support/Signals.h"
33 #include "llvm/Support/SourceMgr.h"
34 #include "llvm/Support/SystemUtils.h"
35 #include "llvm/Support/ToolOutputFile.h"
36 #include <memory>
37 using namespace llvm;
38 
39 static cl::list<std::string>
40 InputFilenames(cl::Positional, cl::OneOrMore,
41                cl::desc("<input bitcode files>"));
42 
43 static cl::list<std::string> OverridingInputs(
44     "override", cl::ZeroOrMore, cl::value_desc("filename"),
45     cl::desc(
46         "input bitcode file which can override previously defined symbol(s)"));
47 
48 // Option to simulate function importing for testing. This enables using
49 // llvm-link to simulate ThinLTO backend processes.
50 static cl::list<std::string> Imports(
51     "import", cl::ZeroOrMore, cl::value_desc("function:filename"),
52     cl::desc("Pair of function name and filename, where function should be "
53              "imported from bitcode in filename"));
54 
55 // Option to support testing of function importing. The function index
56 // must be specified in the case were we request imports via the -import
57 // option, as well as when compiling any module with functions that may be
58 // exported (imported by a different llvm-link -import invocation), to ensure
59 // consistent promotion and renaming of locals.
60 static cl::opt<std::string> FunctionIndex("functionindex",
61                                           cl::desc("Function index filename"),
62                                           cl::init(""),
63                                           cl::value_desc("filename"));
64 
65 static cl::opt<std::string>
66 OutputFilename("o", cl::desc("Override output filename"), cl::init("-"),
67                cl::value_desc("filename"));
68 
69 static cl::opt<bool>
70 Internalize("internalize", cl::desc("Internalize linked symbols"));
71 
72 static cl::opt<bool>
73 OnlyNeeded("only-needed", cl::desc("Link only needed symbols"));
74 
75 static cl::opt<bool>
76 Force("f", cl::desc("Enable binary output on terminals"));
77 
78 static cl::opt<bool>
79 OutputAssembly("S",
80          cl::desc("Write output as LLVM assembly"), cl::Hidden);
81 
82 static cl::opt<bool>
83 Verbose("v", cl::desc("Print information about actions taken"));
84 
85 static cl::opt<bool>
86 DumpAsm("d", cl::desc("Print assembly as linked"), cl::Hidden);
87 
88 static cl::opt<bool>
89 SuppressWarnings("suppress-warnings", cl::desc("Suppress all linking warnings"),
90                  cl::init(false));
91 
92 static cl::opt<bool>
93     PreserveModules("preserve-modules",
94                     cl::desc("Preserve linked modules for testing"));
95 
96 static cl::opt<bool> PreserveBitcodeUseListOrder(
97     "preserve-bc-uselistorder",
98     cl::desc("Preserve use-list order when writing LLVM bitcode."),
99     cl::init(true), cl::Hidden);
100 
101 static cl::opt<bool> PreserveAssemblyUseListOrder(
102     "preserve-ll-uselistorder",
103     cl::desc("Preserve use-list order when writing LLVM assembly."),
104     cl::init(false), cl::Hidden);
105 
106 // Read the specified bitcode file in and return it. This routine searches the
107 // link path for the specified file to try to find it...
108 //
109 static std::unique_ptr<Module>
110 loadFile(const char *argv0, const std::string &FN, LLVMContext &Context) {
111   SMDiagnostic Err;
112   if (Verbose) errs() << "Loading '" << FN << "'\n";
113   std::unique_ptr<Module> Result = getLazyIRFileModule(FN, Err, Context);
114   if (!Result)
115     Err.print(argv0, errs());
116 
117   Result->materializeMetadata();
118   UpgradeDebugInfo(*Result);
119 
120   return Result;
121 }
122 
123 static void diagnosticHandler(const DiagnosticInfo &DI) {
124   unsigned Severity = DI.getSeverity();
125   switch (Severity) {
126   case DS_Error:
127     errs() << "ERROR: ";
128     break;
129   case DS_Warning:
130     if (SuppressWarnings)
131       return;
132     errs() << "WARNING: ";
133     break;
134   case DS_Remark:
135   case DS_Note:
136     llvm_unreachable("Only expecting warnings and errors");
137   }
138 
139   DiagnosticPrinterRawOStream DP(errs());
140   DI.print(DP);
141   errs() << '\n';
142 }
143 
144 /// Import any functions requested via the -import option.
145 static bool importFunctions(const char *argv0, LLVMContext &Context,
146                             Linker &L) {
147   for (const auto &Import : Imports) {
148     // Identify the requested function and its bitcode source file.
149     size_t Idx = Import.find(':');
150     if (Idx == std::string::npos) {
151       errs() << "Import parameter bad format: " << Import << "\n";
152       return false;
153     }
154     std::string FunctionName = Import.substr(0, Idx);
155     std::string FileName = Import.substr(Idx + 1, std::string::npos);
156 
157     // Load the specified source module.
158     std::unique_ptr<Module> M = loadFile(argv0, FileName, Context);
159     if (!M.get()) {
160       errs() << argv0 << ": error loading file '" << FileName << "'\n";
161       return false;
162     }
163 
164     if (verifyModule(*M, &errs())) {
165       errs() << argv0 << ": " << FileName
166              << ": error: input module is broken!\n";
167       return false;
168     }
169 
170     Function *F = M->getFunction(FunctionName);
171     if (!F) {
172       errs() << "Ignoring import request for non-existent function "
173              << FunctionName << " from " << FileName << "\n";
174       continue;
175     }
176     // We cannot import weak_any functions without possibly affecting the
177     // order they are seen and selected by the linker, changing program
178     // semantics.
179     if (F->hasWeakAnyLinkage()) {
180       errs() << "Ignoring import request for weak-any function " << FunctionName
181              << " from " << FileName << "\n";
182       continue;
183     }
184 
185     if (Verbose)
186       errs() << "Importing " << FunctionName << " from " << FileName << "\n";
187 
188     std::unique_ptr<FunctionInfoIndex> Index;
189     if (!FunctionIndex.empty()) {
190       ErrorOr<std::unique_ptr<FunctionInfoIndex>> IndexOrErr =
191           llvm::getFunctionIndexForFile(FunctionIndex, diagnosticHandler);
192       std::error_code EC = IndexOrErr.getError();
193       if (EC) {
194         errs() << EC.message() << '\n';
195         return false;
196       }
197       Index = std::move(IndexOrErr.get());
198     }
199 
200     // Link in the specified function.
201     DenseSet<const GlobalValue *> FunctionsToImport;
202     FunctionsToImport.insert(F);
203     if (L.linkInModule(*M, Linker::Flags::None, Index.get(),
204                        &FunctionsToImport))
205       return false;
206   }
207   return true;
208 }
209 
210 static bool linkFiles(const char *argv0, LLVMContext &Context, Linker &L,
211                       const cl::list<std::string> &Files,
212                       unsigned Flags) {
213   // Filter out flags that don't apply to the first file we load.
214   unsigned ApplicableFlags = Flags & Linker::Flags::OverrideFromSrc;
215   for (const auto &File : Files) {
216     std::unique_ptr<Module> M = loadFile(argv0, File, Context);
217     if (!M.get()) {
218       errs() << argv0 << ": error loading file '" << File << "'\n";
219       return false;
220     }
221 
222     if (verifyModule(*M, &errs())) {
223       errs() << argv0 << ": " << File << ": error: input module is broken!\n";
224       return false;
225     }
226 
227     // If a function index is supplied, load it so linkInModule can treat
228     // local functions/variables as exported and promote if necessary.
229     std::unique_ptr<FunctionInfoIndex> Index;
230     if (!FunctionIndex.empty()) {
231       ErrorOr<std::unique_ptr<FunctionInfoIndex>> IndexOrErr =
232           llvm::getFunctionIndexForFile(FunctionIndex, diagnosticHandler);
233       std::error_code EC = IndexOrErr.getError();
234       if (EC) {
235         errs() << EC.message() << '\n';
236         return false;
237       }
238       Index = std::move(IndexOrErr.get());
239     }
240 
241     if (Verbose)
242       errs() << "Linking in '" << File << "'\n";
243 
244     if (L.linkInModule(*M, ApplicableFlags, Index.get()))
245       return false;
246     // All linker flags apply to linking of subsequent files.
247     ApplicableFlags = Flags;
248 
249     // If requested for testing, preserve modules by releasing them from
250     // the unique_ptr before the are freed. This can help catch any
251     // cross-module references from e.g. unneeded metadata references
252     // that aren't properly set to null but instead mapped to the source
253     // module version. The bitcode writer will assert if it finds any such
254     // cross-module references.
255     if (PreserveModules)
256       M.release();
257   }
258 
259   return true;
260 }
261 
262 int main(int argc, char **argv) {
263   // Print a stack trace if we signal out.
264   sys::PrintStackTraceOnErrorSignal();
265   PrettyStackTraceProgram X(argc, argv);
266 
267   LLVMContext &Context = getGlobalContext();
268   llvm_shutdown_obj Y;  // Call llvm_shutdown() on exit.
269   cl::ParseCommandLineOptions(argc, argv, "llvm linker\n");
270 
271   auto Composite = make_unique<Module>("llvm-link", Context);
272   Linker L(*Composite, diagnosticHandler);
273 
274   unsigned Flags = Linker::Flags::None;
275   if (Internalize)
276     Flags |= Linker::Flags::InternalizeLinkedSymbols;
277   if (OnlyNeeded)
278     Flags |= Linker::Flags::LinkOnlyNeeded;
279 
280   // First add all the regular input files
281   if (!linkFiles(argv[0], Context, L, InputFilenames, Flags))
282     return 1;
283 
284   // Next the -override ones.
285   if (!linkFiles(argv[0], Context, L, OverridingInputs,
286                  Flags | Linker::Flags::OverrideFromSrc))
287     return 1;
288 
289   // Import any functions requested via -import
290   if (!importFunctions(argv[0], Context, L))
291     return 1;
292 
293   if (DumpAsm) errs() << "Here's the assembly:\n" << *Composite;
294 
295   std::error_code EC;
296   tool_output_file Out(OutputFilename, EC, sys::fs::F_None);
297   if (EC) {
298     errs() << EC.message() << '\n';
299     return 1;
300   }
301 
302   if (verifyModule(*Composite, &errs())) {
303     errs() << argv[0] << ": error: linked module is broken!\n";
304     return 1;
305   }
306 
307   if (Verbose) errs() << "Writing bitcode...\n";
308   if (OutputAssembly) {
309     Composite->print(Out.os(), nullptr, PreserveAssemblyUseListOrder);
310   } else if (Force || !CheckBitcodeOutputToConsole(Out.os(), true))
311     WriteBitcodeToFile(Composite.get(), Out.os(), PreserveBitcodeUseListOrder);
312 
313   // Declare success.
314   Out.keep();
315 
316   return 0;
317 }
318