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