llvm/tools/gccld/Linker.cpp - toolchain/llvm-project - Gitiles

 //===- Linker.cpp - Link together LLVM objects and libraries --------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file was developed by the LLVM research group and is distributed under
 // the University of Illinois Open Source License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains routines to handle linking together LLVM bytecode files,
 // and to handle annoying things like static libraries.
 //
 //===----------------------------------------------------------------------===//

 #include "gccld.h"
 #include "llvm/Module.h"
 #include "llvm/PassManager.h"
 #include "llvm/Bytecode/Reader.h"
 #include "llvm/Bytecode/WriteBytecodePass.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Linker.h"
 #include "Support/CommandLine.h"
 #include "Support/FileUtilities.h"
 #include "Support/Signals.h"
 #include "Support/SystemUtils.h"
 #include <algorithm>
 #include <fstream>
 #include <memory>
 #include <set>
 using namespace llvm;

 /// FindLib - Try to convert Filename into the name of a file that we can open,
 /// if it does not already name a file we can open, by first trying to open
 /// Filename, then libFilename.<suffix> for each of a set of several common
 /// library suffixes, in each of the directories in Paths and the directory
 /// named by the value of the environment variable LLVM_LIB_SEARCH_PATH. Returns
 /// an empty string if no matching file can be found.
 ///
 std::string llvm::FindLib(const std::string &Filename,
                           const std::vector<std::string> &Paths,
                           bool SharedObjectOnly) {
   // Determine if the pathname can be found as it stands.
   if (FileOpenable(Filename))
     return Filename;

   // If that doesn't work, convert the name into a library name.
   std::string LibName = "lib" + Filename;

   // Iterate over the directories in Paths to see if we can find the library
   // there.
   for (unsigned Index = 0; Index != Paths.size(); ++Index) {
     std::string Directory = Paths[Index] + "/";

     if (!SharedObjectOnly && FileOpenable(Directory + LibName + ".bc"))
       return Directory + LibName + ".bc";

     if (FileOpenable(Directory + LibName + ".so"))
       return Directory + LibName + ".so";

     if (!SharedObjectOnly && FileOpenable(Directory + LibName + ".a"))
       return Directory + LibName + ".a";
   }

   // One last hope: Check LLVM_LIB_SEARCH_PATH.
   char *SearchPath = getenv("LLVM_LIB_SEARCH_PATH");
   if (SearchPath == NULL)
     return std::string();

   LibName = std::string(SearchPath) + "/" + LibName;
   if (FileOpenable(LibName))
     return LibName;

   return std::string();
 }

 /// GetAllDefinedSymbols - Modifies its parameter DefinedSymbols to contain the
 /// name of each externally-visible symbol defined in M.
 ///
 void llvm::GetAllDefinedSymbols(Module *M,
                                 std::set<std::string> &DefinedSymbols) {
   for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
     if (I->hasName() && !I->isExternal() && !I->hasInternalLinkage())
       DefinedSymbols.insert(I->getName());
   for (Module::giterator I = M->gbegin(), E = M->gend(); I != E; ++I)
     if (I->hasName() && !I->isExternal() && !I->hasInternalLinkage())
       DefinedSymbols.insert(I->getName());
 }

 /// GetAllUndefinedSymbols - calculates the set of undefined symbols that still
 /// exist in an LLVM module. This is a bit tricky because there may be two
 /// symbols with the same name but different LLVM types that will be resolved to
 /// each other but aren't currently (thus we need to treat it as resolved).
 ///
 /// Inputs:
 ///  M - The module in which to find undefined symbols.
 ///
 /// Outputs:
 ///  UndefinedSymbols - A set of C++ strings containing the name of all
 ///                     undefined symbols.
 ///
 void
 llvm::GetAllUndefinedSymbols(Module *M,
                              std::set<std::string> &UndefinedSymbols) {
   std::set<std::string> DefinedSymbols;
   UndefinedSymbols.clear();   // Start out empty

   for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
     if (I->hasName()) {
       if (I->isExternal())
         UndefinedSymbols.insert(I->getName());
       else if (!I->hasInternalLinkage())
         DefinedSymbols.insert(I->getName());
     }
   for (Module::giterator I = M->gbegin(), E = M->gend(); I != E; ++I)
     if (I->hasName()) {
       if (I->isExternal())
         UndefinedSymbols.insert(I->getName());
       else if (!I->hasInternalLinkage())
         DefinedSymbols.insert(I->getName());
     }

   // Prune out any defined symbols from the undefined symbols set...
   for (std::set<std::string>::iterator I = UndefinedSymbols.begin();
        I != UndefinedSymbols.end(); )
     if (DefinedSymbols.count(*I))
       UndefinedSymbols.erase(I++);  // This symbol really is defined!
     else
       ++I; // Keep this symbol in the undefined symbols list
 }


 /// LoadObject - Read in and parse the bytecode file named by FN and return the
 /// module it contains (wrapped in an auto_ptr), or 0 and set ErrorMessage if an
 /// error occurs.
 ///
 std::auto_ptr<Module> llvm::LoadObject(const std::string &FN,
                                        std::string &ErrorMessage) {
   std::string ParserErrorMessage;
   Module *Result = ParseBytecodeFile(FN, &ParserErrorMessage);
   if (Result) return std::auto_ptr<Module>(Result);
   ErrorMessage = "Bytecode file '" + FN + "' could not be loaded";
   if (ParserErrorMessage.size()) ErrorMessage += ": " + ParserErrorMessage;
   return std::auto_ptr<Module>();
 }

 /// LinkInArchive - opens an archive library and link in all objects which
 /// provide symbols that are currently undefined.
 ///
 /// Inputs:
 ///  M        - The module in which to link the archives.
 ///  Filename - The pathname of the archive.
 ///  Verbose  - Flags whether verbose messages should be printed.
 ///
 /// Outputs:
 ///  ErrorMessage - A C++ string detailing what error occurred, if any.
 ///
 /// Return Value:
 ///  TRUE  - An error occurred.
 ///  FALSE - No errors.
 ///
 static bool LinkInArchive(Module *M,
                           const std::string &Filename,
                           std::string &ErrorMessage,
                           bool Verbose)
 {
   // Find all of the symbols currently undefined in the bytecode program.
   // If all the symbols are defined, the program is complete, and there is
   // no reason to link in any archive files.
   std::set<std::string> UndefinedSymbols;
   GetAllUndefinedSymbols(M, UndefinedSymbols);
   if (UndefinedSymbols.empty()) {
     if (Verbose) std::cerr << "  No symbols undefined, don't link library!\n";
     return false;  // No need to link anything in!
   }

   // Load in the archive objects.
   if (Verbose) std::cerr << "  Loading archive file '" << Filename << "'\n";
   std::vector<Module*> Objects;
   if (ReadArchiveFile(Filename, Objects, &ErrorMessage))
     return true;

   // Figure out which symbols are defined by all of the modules in the archive.
   std::vector<std::set<std::string> > DefinedSymbols;
   DefinedSymbols.resize(Objects.size());
   for (unsigned i = 0; i != Objects.size(); ++i) {
     GetAllDefinedSymbols(Objects[i], DefinedSymbols[i]);
   }

   // While we are linking in object files, loop.
   bool Linked = true;
   while (Linked) {
     Linked = false;

     for (unsigned i = 0; i != Objects.size(); ++i) {
       // Consider whether we need to link in this module...  we only need to
       // link it in if it defines some symbol which is so far undefined.
       //
       const std::set<std::string> &DefSymbols = DefinedSymbols[i];

       bool ObjectRequired = false;

       //
       // If the object defines main() and the program currently has main()
       // undefined, then automatically link in the module.  Otherwise, look to
       // see if it defines a symbol that is currently undefined.
       //
       if ((M->getMainFunction() == NULL) &&
           ((DefSymbols.find ("main")) != DefSymbols.end())) {
         ObjectRequired = true;
       } else {
         for (std::set<std::string>::iterator I = UndefinedSymbols.begin(),
                E = UndefinedSymbols.end(); I != E; ++I)
           if (DefSymbols.count(*I)) {
             if (Verbose)
               std::cerr << "  Found object '"
                         << Objects[i]->getModuleIdentifier ()
                         << "' providing symbol '" << *I << "'...\n";
             ObjectRequired = true;
             break;
           }
       }

       // We DO need to link this object into the program...
       if (ObjectRequired) {
         if (LinkModules(M, Objects[i], &ErrorMessage))
           return true;   // Couldn't link in the right object file...

         // Since we have linked in this object, delete it from the list of
         // objects to consider in this archive file.
         std::swap(Objects[i], Objects.back());
         std::swap(DefinedSymbols[i], DefinedSymbols.back());
         Objects.pop_back();
         DefinedSymbols.pop_back();
         --i;   // Do not skip an entry

         // The undefined symbols set should have shrunk.
         GetAllUndefinedSymbols(M, UndefinedSymbols);
         Linked = true;  // We have linked something in!
       }
     }
   }

   return false;
 }

 /// LinkInFile - opens a bytecode file and links in all objects which
 /// provide symbols that are currently undefined.
 ///
 /// Inputs:
 ///  HeadModule - The module in which to link the bytecode file.
 ///  Filename   - The pathname of the bytecode file.
 ///  Verbose    - Flags whether verbose messages should be printed.
 ///
 /// Outputs:
 ///  ErrorMessage - A C++ string detailing what error occurred, if any.
 ///
 /// Return Value:
 ///  TRUE  - An error occurred.
 ///  FALSE - No errors.
 ///
 static bool LinkInFile(Module *HeadModule,
                        const std::string &Filename,
                        std::string &ErrorMessage,
                        bool Verbose)
 {
   std::auto_ptr<Module> M(LoadObject(Filename, ErrorMessage));
   if (M.get() == 0) return true;
   bool Result = LinkModules(HeadModule, M.get(), &ErrorMessage);
   if (Verbose) std::cerr << "Linked in bytecode file '" << Filename << "'\n";
   return Result;
 }

 /// LinkFiles - takes a module and a list of files and links them all together.
 /// It locates the file either in the current directory, as its absolute
 /// or relative pathname, or as a file somewhere in LLVM_LIB_SEARCH_PATH.
 ///
 /// Inputs:
 ///  progname   - The name of the program (infamous argv[0]).
 ///  HeadModule - The module under which all files will be linked.
 ///  Files      - A vector of C++ strings indicating the LLVM bytecode filenames
 ///               to be linked.  The names can refer to a mixture of pure LLVM
 ///               bytecode files and archive (ar) formatted files.
 ///  Verbose    - Flags whether verbose output should be printed while linking.
 ///
 /// Outputs:
 ///  HeadModule - The module will have the specified LLVM bytecode files linked
 ///               in.
 ///
 /// Return value:
 ///  FALSE - No errors.
 ///  TRUE  - Some error occurred.
 ///
 bool llvm::LinkFiles(const char *progname, Module *HeadModule,
                      const std::vector<std::string> &Files, bool Verbose) {
   // String in which to receive error messages.
   std::string ErrorMessage;

   // Full pathname of the file
   std::string Pathname;

   // Get the library search path from the environment
   char *SearchPath = getenv("LLVM_LIB_SEARCH_PATH");

   for (unsigned i = 0; i < Files.size(); ++i) {
     // Determine where this file lives.
     if (FileOpenable(Files[i])) {
       Pathname = Files[i];
     } else {
       if (SearchPath == NULL) {
         std::cerr << progname << ": Cannot find linker input file '"
                   << Files[i] << "'\n";
         std::cerr << progname
                   << ": Warning: Your LLVM_LIB_SEARCH_PATH is unset.\n";
         return true;
       }

       Pathname = std::string(SearchPath)+"/"+Files[i];
       if (!FileOpenable(Pathname)) {
         std::cerr << progname << ": Cannot find linker input file '"
                   << Files[i] << "'\n";
         return true;
       }
     }

     // A user may specify an ar archive without -l, perhaps because it
     // is not installed as a library. Detect that and link the library.
     if (IsArchive(Pathname)) {
       if (Verbose)
         std::cerr << "Trying to link archive '" << Pathname << "'\n";

       if (LinkInArchive(HeadModule, Pathname, ErrorMessage, Verbose)) {
         PrintAndReturn(progname, ErrorMessage,
                        ": Error linking in archive '" + Pathname + "'");
         return true;
       }
     } else if (IsBytecode(Pathname)) {
       if (Verbose)
         std::cerr << "Trying to link bytecode file '" << Pathname << "'\n";

       if (LinkInFile(HeadModule, Pathname, ErrorMessage, Verbose)) {
         PrintAndReturn(progname, ErrorMessage,
                        ": Error linking in bytecode file '" + Pathname + "'");
         return true;
       }
     }
   }

   return false;
 }

 /// LinkLibraries - takes the specified library files and links them into the
 /// main bytecode object file.
 ///
 /// Inputs:
 ///  progname   - The name of the program (infamous argv[0]).
 ///  HeadModule - The module into which all necessary libraries will be linked.
 ///  Libraries  - The list of libraries to link into the module.
 ///  LibPaths   - The list of library paths in which to find libraries.
 ///  Verbose    - Flags whether verbose messages should be printed.
 ///  Native     - Flags whether native code is being generated.
 ///
 /// Outputs:
 ///  HeadModule - The module will have all necessary libraries linked in.
 ///
 /// Return value:
 ///  FALSE - No error.
 ///  TRUE  - Error.
 ///
 void llvm::LinkLibraries(const char *progname, Module *HeadModule,
                          const std::vector<std::string> &Libraries,
                          const std::vector<std::string> &LibPaths,
                          bool Verbose, bool Native) {
   // String in which to receive error messages.
   std::string ErrorMessage;

   for (unsigned i = 0; i < Libraries.size(); ++i) {
     // Determine where this library lives.
     std::string Pathname = FindLib(Libraries[i], LibPaths);
     if (Pathname.empty()) {
       // If the pathname does not exist, then continue to the next one if
       // we're doing a native link and give an error if we're doing a bytecode
       // link.
       if (!Native) {
         std::cerr << progname << ": WARNING: Cannot find library -l"
                   << Libraries[i] << "\n";
         continue;
       }
     }

     // A user may specify an ar archive without -l, perhaps because it
     // is not installed as a library. Detect that and link the library.
     if (IsArchive(Pathname)) {
       if (Verbose)
         std::cerr << "Trying to link archive '" << Pathname << "' (-l"
                   << Libraries[i] << ")\n";

       if (LinkInArchive(HeadModule, Pathname, ErrorMessage, Verbose)) {
         std::cerr << progname << ": " << ErrorMessage
                   << ": Error linking in archive '" << Pathname << "' (-l"
                   << Libraries[i] << ")\n";
         exit(1);
       }
     } else if (IsBytecode(Pathname)) {
       if (Verbose)
         std::cerr << "Trying to link bytecode file '" << Pathname
                   << "' (-l" << Libraries[i] << ")\n";

       if (LinkInFile(HeadModule, Pathname, ErrorMessage, Verbose)) {
         std::cerr << progname << ": " << ErrorMessage
                   << ": error linking in bytecode file '" << Pathname << "' (-l"
                   << Libraries[i] << ")\n";
         exit(1);
       }
     }
   }
 }
	//===- Linker.cpp - Link together LLVM objects and libraries --------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file was developed by the LLVM research group and is distributed under
	// the University of Illinois Open Source License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file contains routines to handle linking together LLVM bytecode files,
	// and to handle annoying things like static libraries.
	//
	//===----------------------------------------------------------------------===//

	#include "gccld.h"
	#include "llvm/Module.h"
	#include "llvm/PassManager.h"
	#include "llvm/Bytecode/Reader.h"
	#include "llvm/Bytecode/WriteBytecodePass.h"
	#include "llvm/Target/TargetData.h"
	#include "llvm/Transforms/IPO.h"
	#include "llvm/Transforms/Scalar.h"
	#include "llvm/Transforms/Utils/Linker.h"
	#include "Support/CommandLine.h"
	#include "Support/FileUtilities.h"
	#include "Support/Signals.h"
	#include "Support/SystemUtils.h"
	#include <algorithm>
	#include <fstream>
	#include <memory>
	#include <set>
	using namespace llvm;

	/// FindLib - Try to convert Filename into the name of a file that we can open,
	/// if it does not already name a file we can open, by first trying to open
	/// Filename, then libFilename.<suffix> for each of a set of several common
	/// library suffixes, in each of the directories in Paths and the directory
	/// named by the value of the environment variable LLVM_LIB_SEARCH_PATH. Returns
	/// an empty string if no matching file can be found.
	///
	std::string llvm::FindLib(const std::string &Filename,
	const std::vector<std::string> &Paths,
	bool SharedObjectOnly) {
	// Determine if the pathname can be found as it stands.
	if (FileOpenable(Filename))
	return Filename;

	// If that doesn't work, convert the name into a library name.
	std::string LibName = "lib" + Filename;

	// Iterate over the directories in Paths to see if we can find the library
	// there.
	for (unsigned Index = 0; Index != Paths.size(); ++Index) {
	std::string Directory = Paths[Index] + "/";

	if (!SharedObjectOnly && FileOpenable(Directory + LibName + ".bc"))
	return Directory + LibName + ".bc";

	if (FileOpenable(Directory + LibName + ".so"))
	return Directory + LibName + ".so";

	if (!SharedObjectOnly && FileOpenable(Directory + LibName + ".a"))
	return Directory + LibName + ".a";
	}

	// One last hope: Check LLVM_LIB_SEARCH_PATH.
	char *SearchPath = getenv("LLVM_LIB_SEARCH_PATH");
	if (SearchPath == NULL)
	return std::string();

	LibName = std::string(SearchPath) + "/" + LibName;
	if (FileOpenable(LibName))
	return LibName;

	return std::string();
	}

	/// GetAllDefinedSymbols - Modifies its parameter DefinedSymbols to contain the
	/// name of each externally-visible symbol defined in M.
	///
	void llvm::GetAllDefinedSymbols(Module *M,
	std::set<std::string> &DefinedSymbols) {
	for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
	if (I->hasName() && !I->isExternal() && !I->hasInternalLinkage())
	DefinedSymbols.insert(I->getName());
	for (Module::giterator I = M->gbegin(), E = M->gend(); I != E; ++I)
	if (I->hasName() && !I->isExternal() && !I->hasInternalLinkage())
	DefinedSymbols.insert(I->getName());
	}

	/// GetAllUndefinedSymbols - calculates the set of undefined symbols that still
	/// exist in an LLVM module. This is a bit tricky because there may be two
	/// symbols with the same name but different LLVM types that will be resolved to
	/// each other but aren't currently (thus we need to treat it as resolved).
	///
	/// Inputs:
	/// M - The module in which to find undefined symbols.
	///
	/// Outputs:
	/// UndefinedSymbols - A set of C++ strings containing the name of all
	/// undefined symbols.
	///
	void
	llvm::GetAllUndefinedSymbols(Module *M,
	std::set<std::string> &UndefinedSymbols) {
	std::set<std::string> DefinedSymbols;
	UndefinedSymbols.clear(); // Start out empty

	for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
	if (I->hasName()) {
	if (I->isExternal())
	UndefinedSymbols.insert(I->getName());
	else if (!I->hasInternalLinkage())
	DefinedSymbols.insert(I->getName());
	}
	for (Module::giterator I = M->gbegin(), E = M->gend(); I != E; ++I)
	if (I->hasName()) {
	if (I->isExternal())
	UndefinedSymbols.insert(I->getName());
	else if (!I->hasInternalLinkage())
	DefinedSymbols.insert(I->getName());
	}

	// Prune out any defined symbols from the undefined symbols set...
	for (std::set<std::string>::iterator I = UndefinedSymbols.begin();
	I != UndefinedSymbols.end(); )
	if (DefinedSymbols.count(*I))
	UndefinedSymbols.erase(I++); // This symbol really is defined!
	else
	++I; // Keep this symbol in the undefined symbols list
	}


	/// LoadObject - Read in and parse the bytecode file named by FN and return the
	/// module it contains (wrapped in an auto_ptr), or 0 and set ErrorMessage if an
	/// error occurs.
	///
	std::auto_ptr<Module> llvm::LoadObject(const std::string &FN,
	std::string &ErrorMessage) {
	std::string ParserErrorMessage;
	Module *Result = ParseBytecodeFile(FN, &ParserErrorMessage);
	if (Result) return std::auto_ptr<Module>(Result);
	ErrorMessage = "Bytecode file '" + FN + "' could not be loaded";
	if (ParserErrorMessage.size()) ErrorMessage += ": " + ParserErrorMessage;
	return std::auto_ptr<Module>();
	}

	/// LinkInArchive - opens an archive library and link in all objects which
	/// provide symbols that are currently undefined.
	///
	/// Inputs:
	/// M - The module in which to link the archives.
	/// Filename - The pathname of the archive.
	/// Verbose - Flags whether verbose messages should be printed.
	///
	/// Outputs:
	/// ErrorMessage - A C++ string detailing what error occurred, if any.
	///
	/// Return Value:
	/// TRUE - An error occurred.
	/// FALSE - No errors.
	///
	static bool LinkInArchive(Module *M,
	const std::string &Filename,
	std::string &ErrorMessage,
	bool Verbose)
	{
	// Find all of the symbols currently undefined in the bytecode program.
	// If all the symbols are defined, the program is complete, and there is
	// no reason to link in any archive files.
	std::set<std::string> UndefinedSymbols;
	GetAllUndefinedSymbols(M, UndefinedSymbols);
	if (UndefinedSymbols.empty()) {
	if (Verbose) std::cerr << " No symbols undefined, don't link library!\n";
	return false; // No need to link anything in!
	}

	// Load in the archive objects.
	if (Verbose) std::cerr << " Loading archive file '" << Filename << "'\n";
	std::vector<Module*> Objects;
	if (ReadArchiveFile(Filename, Objects, &ErrorMessage))
	return true;

	// Figure out which symbols are defined by all of the modules in the archive.
	std::vector<std::set<std::string> > DefinedSymbols;
	DefinedSymbols.resize(Objects.size());
	for (unsigned i = 0; i != Objects.size(); ++i) {
	GetAllDefinedSymbols(Objects[i], DefinedSymbols[i]);
	}

	// While we are linking in object files, loop.
	bool Linked = true;
	while (Linked) {
	Linked = false;

	for (unsigned i = 0; i != Objects.size(); ++i) {
	// Consider whether we need to link in this module... we only need to
	// link it in if it defines some symbol which is so far undefined.
	//
	const std::set<std::string> &DefSymbols = DefinedSymbols[i];

	bool ObjectRequired = false;

	//
	// If the object defines main() and the program currently has main()
	// undefined, then automatically link in the module. Otherwise, look to
	// see if it defines a symbol that is currently undefined.
	//
	if ((M->getMainFunction() == NULL) &&
	((DefSymbols.find ("main")) != DefSymbols.end())) {
	ObjectRequired = true;
	} else {
	for (std::set<std::string>::iterator I = UndefinedSymbols.begin(),
	E = UndefinedSymbols.end(); I != E; ++I)
	if (DefSymbols.count(*I)) {
	if (Verbose)
	std::cerr << " Found object '"
	<< Objects[i]->getModuleIdentifier ()
	<< "' providing symbol '" << *I << "'...\n";
	ObjectRequired = true;
	break;
	}
	}

	// We DO need to link this object into the program...
	if (ObjectRequired) {
	if (LinkModules(M, Objects[i], &ErrorMessage))
	return true; // Couldn't link in the right object file...

	// Since we have linked in this object, delete it from the list of
	// objects to consider in this archive file.
	std::swap(Objects[i], Objects.back());
	std::swap(DefinedSymbols[i], DefinedSymbols.back());
	Objects.pop_back();
	DefinedSymbols.pop_back();
	--i; // Do not skip an entry

	// The undefined symbols set should have shrunk.
	GetAllUndefinedSymbols(M, UndefinedSymbols);
	Linked = true; // We have linked something in!
	}
	}
	}

	return false;
	}

	/// LinkInFile - opens a bytecode file and links in all objects which
	/// provide symbols that are currently undefined.
	///
	/// Inputs:
	/// HeadModule - The module in which to link the bytecode file.
	/// Filename - The pathname of the bytecode file.
	/// Verbose - Flags whether verbose messages should be printed.
	///
	/// Outputs:
	/// ErrorMessage - A C++ string detailing what error occurred, if any.
	///
	/// Return Value:
	/// TRUE - An error occurred.
	/// FALSE - No errors.
	///
	static bool LinkInFile(Module *HeadModule,
	const std::string &Filename,
	std::string &ErrorMessage,
	bool Verbose)
	{
	std::auto_ptr<Module> M(LoadObject(Filename, ErrorMessage));
	if (M.get() == 0) return true;
	bool Result = LinkModules(HeadModule, M.get(), &ErrorMessage);
	if (Verbose) std::cerr << "Linked in bytecode file '" << Filename << "'\n";
	return Result;
	}

	/// LinkFiles - takes a module and a list of files and links them all together.
	/// It locates the file either in the current directory, as its absolute
	/// or relative pathname, or as a file somewhere in LLVM_LIB_SEARCH_PATH.
	///
	/// Inputs:
	/// progname - The name of the program (infamous argv[0]).
	/// HeadModule - The module under which all files will be linked.
	/// Files - A vector of C++ strings indicating the LLVM bytecode filenames
	/// to be linked. The names can refer to a mixture of pure LLVM
	/// bytecode files and archive (ar) formatted files.
	/// Verbose - Flags whether verbose output should be printed while linking.
	///
	/// Outputs:
	/// HeadModule - The module will have the specified LLVM bytecode files linked
	/// in.
	///
	/// Return value:
	/// FALSE - No errors.
	/// TRUE - Some error occurred.
	///
	bool llvm::LinkFiles(const char progname, Module HeadModule,
	const std::vector<std::string> &Files, bool Verbose) {
	// String in which to receive error messages.
	std::string ErrorMessage;

	// Full pathname of the file
	std::string Pathname;

	// Get the library search path from the environment
	char *SearchPath = getenv("LLVM_LIB_SEARCH_PATH");

	for (unsigned i = 0; i < Files.size(); ++i) {
	// Determine where this file lives.
	if (FileOpenable(Files[i])) {
	Pathname = Files[i];
	} else {
	if (SearchPath == NULL) {
	std::cerr << progname << ": Cannot find linker input file '"
	<< Files[i] << "'\n";
	std::cerr << progname
	<< ": Warning: Your LLVM_LIB_SEARCH_PATH is unset.\n";
	return true;
	}

	Pathname = std::string(SearchPath)+"/"+Files[i];
	if (!FileOpenable(Pathname)) {
	std::cerr << progname << ": Cannot find linker input file '"
	<< Files[i] << "'\n";
	return true;
	}
	}

	// A user may specify an ar archive without -l, perhaps because it
	// is not installed as a library. Detect that and link the library.
	if (IsArchive(Pathname)) {
	if (Verbose)
	std::cerr << "Trying to link archive '" << Pathname << "'\n";

	if (LinkInArchive(HeadModule, Pathname, ErrorMessage, Verbose)) {
	PrintAndReturn(progname, ErrorMessage,
	": Error linking in archive '" + Pathname + "'");
	return true;
	}
	} else if (IsBytecode(Pathname)) {
	if (Verbose)
	std::cerr << "Trying to link bytecode file '" << Pathname << "'\n";

	if (LinkInFile(HeadModule, Pathname, ErrorMessage, Verbose)) {
	PrintAndReturn(progname, ErrorMessage,
	": Error linking in bytecode file '" + Pathname + "'");
	return true;
	}
	}
	}

	return false;
	}

	/// LinkLibraries - takes the specified library files and links them into the
	/// main bytecode object file.
	///
	/// Inputs:
	/// progname - The name of the program (infamous argv[0]).
	/// HeadModule - The module into which all necessary libraries will be linked.
	/// Libraries - The list of libraries to link into the module.
	/// LibPaths - The list of library paths in which to find libraries.
	/// Verbose - Flags whether verbose messages should be printed.
	/// Native - Flags whether native code is being generated.
	///
	/// Outputs:
	/// HeadModule - The module will have all necessary libraries linked in.
	///
	/// Return value:
	/// FALSE - No error.
	/// TRUE - Error.
	///
	void llvm::LinkLibraries(const char progname, Module HeadModule,
	const std::vector<std::string> &Libraries,
	const std::vector<std::string> &LibPaths,
	bool Verbose, bool Native) {
	// String in which to receive error messages.
	std::string ErrorMessage;

	for (unsigned i = 0; i < Libraries.size(); ++i) {
	// Determine where this library lives.
	std::string Pathname = FindLib(Libraries[i], LibPaths);
	if (Pathname.empty()) {
	// If the pathname does not exist, then continue to the next one if
	// we're doing a native link and give an error if we're doing a bytecode
	// link.
	if (!Native) {
	std::cerr << progname << ": WARNING: Cannot find library -l"
	<< Libraries[i] << "\n";
	continue;
	}
	}

	// A user may specify an ar archive without -l, perhaps because it
	// is not installed as a library. Detect that and link the library.
	if (IsArchive(Pathname)) {
	if (Verbose)
	std::cerr << "Trying to link archive '" << Pathname << "' (-l"
	<< Libraries[i] << ")\n";

	if (LinkInArchive(HeadModule, Pathname, ErrorMessage, Verbose)) {
	std::cerr << progname << ": " << ErrorMessage
	<< ": Error linking in archive '" << Pathname << "' (-l"
	<< Libraries[i] << ")\n";
	exit(1);
	}
	} else if (IsBytecode(Pathname)) {
	if (Verbose)
	std::cerr << "Trying to link bytecode file '" << Pathname
	<< "' (-l" << Libraries[i] << ")\n";

	if (LinkInFile(HeadModule, Pathname, ErrorMessage, Verbose)) {
	std::cerr << progname << ": " << ErrorMessage
	<< ": error linking in bytecode file '" << Pathname << "' (-l"
	<< Libraries[i] << ")\n";
	exit(1);
	}
	}
	}
	}