lib/Linker/LinkArchives.cpp

   1 //===- lib/Linker/LinkArchives.cpp - Link LLVM objects and libraries ------===//
   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 file contains routines to handle linking together LLVM bitcode files,
  11 // and to handle annoying things like static libraries.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Linker.h"
  16 #include "llvm/Module.h"
  17 #include "llvm/ModuleProvider.h"
  18 #include "llvm/ADT/SetOperations.h"
  19 #include "llvm/Bitcode/Archive.h"
  20 #include "llvm/Config/config.h"
  21 #include <memory>
  22 #include <set>
  23 using namespace llvm;
  24
  25 /// GetAllUndefinedSymbols - calculates the set of undefined symbols that still
  26 /// exist in an LLVM module. This is a bit tricky because there may be two
  27 /// symbols with the same name but different LLVM types that will be resolved to
  28 /// each other but aren't currently (thus we need to treat it as resolved).
  29 ///
  30 /// Inputs:
  31 ///  M - The module in which to find undefined symbols.
  32 ///
  33 /// Outputs:
  34 ///  UndefinedSymbols - A set of C++ strings containing the name of all
  35 ///                     undefined symbols.
  36 ///
  37 static void
  38 GetAllUndefinedSymbols(Module *M, std::set<std::string> &UndefinedSymbols) {
  39   std::set<std::string> DefinedSymbols;
  40   UndefinedSymbols.clear();
  41
  42   // If the program doesn't define a main, try pulling one in from a .a file.
  43   // This is needed for programs where the main function is defined in an
  44   // archive, such f2c'd programs.
  45   Function *Main = M->getFunction("main");
  46   if (Main == 0 || Main->isDeclaration())
  47     UndefinedSymbols.insert("main");
  48
  49   for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
  50     if (I->hasName()) {
  51       if (I->isDeclaration())
  52         UndefinedSymbols.insert(I->getName());
  53       else if (!I->hasLocalLinkage()) {
  54         assert(!I->hasDLLImportLinkage()
  55                && "Found dllimported non-external symbol!");
  56         DefinedSymbols.insert(I->getName());
  57       }
  58     }
  59
  60   for (Module::global_iterator I = M->global_begin(), E = M->global_end();
  61        I != E; ++I)
  62     if (I->hasName()) {
  63       if (I->isDeclaration())
  64         UndefinedSymbols.insert(I->getName());
  65       else if (!I->hasLocalLinkage()) {
  66         assert(!I->hasDLLImportLinkage()
  67                && "Found dllimported non-external symbol!");
  68         DefinedSymbols.insert(I->getName());
  69       }
  70     }
  71
  72   for (Module::alias_iterator I = M->alias_begin(), E = M->alias_end();
  73        I != E; ++I)
  74     if (I->hasName())
  75       DefinedSymbols.insert(I->getName());
  76
  77   // Prune out any defined symbols from the undefined symbols set...
  78   for (std::set<std::string>::iterator I = UndefinedSymbols.begin();
  79        I != UndefinedSymbols.end(); )
  80     if (DefinedSymbols.count(*I))
  81       UndefinedSymbols.erase(I++);  // This symbol really is defined!
  82     else
  83       ++I; // Keep this symbol in the undefined symbols list
  84 }
  85
  86 /// LinkInArchive - opens an archive library and link in all objects which
  87 /// provide symbols that are currently undefined.
  88 ///
  89 /// Inputs:
  90 ///  Filename - The pathname of the archive.
  91 ///
  92 /// Return Value:
  93 ///  TRUE  - An error occurred.
  94 ///  FALSE - No errors.
  95 bool
  96 Linker::LinkInArchive(const sys::Path &Filename, bool &is_native) {
  97   // Make sure this is an archive file we're dealing with
  98   if (!Filename.isArchive())
  99     return error("File '" + Filename.toString() + "' is not an archive.");
 100
 101   // Open the archive file
 102   verbose("Linking archive file '" + Filename.toString() + "'");
 103
 104   // Find all of the symbols currently undefined in the bitcode program.
 105   // If all the symbols are defined, the program is complete, and there is
 106   // no reason to link in any archive files.
 107   std::set<std::string> UndefinedSymbols;
 108   GetAllUndefinedSymbols(Composite, UndefinedSymbols);
 109
 110   if (UndefinedSymbols.empty()) {
 111     verbose("No symbols undefined, skipping library '" +
 112             Filename.toString() + "'");
 113     return false;  // No need to link anything in!
 114   }
 115
 116   std::string ErrMsg;
 117   std::auto_ptr<Archive> AutoArch (
 118     Archive::OpenAndLoadSymbols(Filename,&ErrMsg));
 119
 120   Archive* arch = AutoArch.get();
 121
 122   if (!arch)
 123     return error("Cannot read archive '" + Filename.toString() +
 124                  "': " + ErrMsg);
 125   if (!arch->isBitcodeArchive()) {
 126     is_native = true;
 127     return false;
 128   }
 129   is_native = false;
 130
 131   // Save a set of symbols that are not defined by the archive. Since we're
 132   // entering a loop, there's no point searching for these multiple times. This
 133   // variable is used to "set_subtract" from the set of undefined symbols.
 134   std::set<std::string> NotDefinedByArchive;
 135
 136   // Save the current set of undefined symbols, because we may have to make
 137   // multiple passes over the archive:
 138   std::set<std::string> CurrentlyUndefinedSymbols;
 139
 140   do {
 141     CurrentlyUndefinedSymbols = UndefinedSymbols;
 142
 143     // Find the modules we need to link into the target module
 144     std::set<ModuleProvider*> Modules;
 145     if (!arch->findModulesDefiningSymbols(UndefinedSymbols, Modules, &ErrMsg))
 146       return error("Cannot find symbols in '" + Filename.toString() +
 147                    "': " + ErrMsg);
 148
 149     // If we didn't find any more modules to link this time, we are done
 150     // searching this archive.
 151     if (Modules.empty())
 152       break;
 153
 154     // Any symbols remaining in UndefinedSymbols after
 155     // findModulesDefiningSymbols are ones that the archive does not define. So
 156     // we add them to the NotDefinedByArchive variable now.
 157     NotDefinedByArchive.insert(UndefinedSymbols.begin(),
 158         UndefinedSymbols.end());
 159
 160     // Loop over all the ModuleProviders that we got back from the archive
 161     for (std::set<ModuleProvider*>::iterator I=Modules.begin(), E=Modules.end();
 162          I != E; ++I) {
 163
 164       // Get the module we must link in.
 165       std::string moduleErrorMsg;
 166       std::auto_ptr<Module> AutoModule((*I)->releaseModule( &moduleErrorMsg ));
 167       if (!moduleErrorMsg.empty())
 168         return error("Could not load a module: " + moduleErrorMsg);
 169
 170       Module* aModule = AutoModule.get();
 171
 172       if (aModule != NULL) {
 173         verbose("  Linking in module: " + aModule->getModuleIdentifier());
 174
 175         // Link it in
 176         if (LinkInModule(aModule, &moduleErrorMsg)) {
 177           return error("Cannot link in module '" +
 178                        aModule->getModuleIdentifier() + "': " + moduleErrorMsg);
 179         }
 180       }
 181     }
 182
 183     // Get the undefined symbols from the aggregate module. This recomputes the
 184     // symbols we still need after the new modules have been linked in.
 185     GetAllUndefinedSymbols(Composite, UndefinedSymbols);
 186
 187     // At this point we have two sets of undefined symbols: UndefinedSymbols
 188     // which holds the undefined symbols from all the modules, and
 189     // NotDefinedByArchive which holds symbols we know the archive doesn't
 190     // define. There's no point searching for symbols that we won't find in the
 191     // archive so we subtract these sets.
 192     set_subtract(UndefinedSymbols, NotDefinedByArchive);
 193
 194     // If there's no symbols left, no point in continuing to search the
 195     // archive.
 196     if (UndefinedSymbols.empty())
 197       break;
 198   } while (CurrentlyUndefinedSymbols != UndefinedSymbols);
 199
 200   return false;
 201 }