LLVM API Documentation

Linker.h

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00001 //===- llvm/Linker.h - Module Linker Interface ------------------*- C++ -*-===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by Reid Spencer and is distributed under the
00006 // University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file defines the interface to the module/file/archive linker.
00011 //
00012 //===----------------------------------------------------------------------===//
00013 
00014 #ifndef LLVM_LINKER_H
00015 #define LLVM_LINKER_H
00016 
00017 #include "llvm/System/Path.h"
00018 #include <vector>
00019 #include <memory>
00020 
00021 namespace llvm {
00022 
00023 class Module;
00024 
00025 /// This class provides the core functionality of linking in LLVM. It retains a
00026 /// Module object which is the composite of the modules and libraries linked
00027 /// into it. The composite Module can be retrieved via the getModule() method.
00028 /// In this case the Linker still retains ownership of the Module. If the
00029 /// releaseModule() method is used, the ownership of the Module is transferred
00030 /// to the caller and the Linker object is only suitable for destruction.
00031 /// The Linker can link Modules from memory, bytecode files, or bytecode
00032 /// archives.  It retains a set of search paths in which to find any libraries
00033 /// presented to it. By default, the linker will generate error and warning
00034 /// messages to std::cerr but this capability can be turned off with the
00035 /// QuietWarnings and QuietErrors flags. It can also be instructed to verbosely
00036 /// print out the linking actions it is taking with the Verbose flag.
00037 /// @brief The LLVM Linker.
00038 class Linker {
00039 
00040   /// @name Types
00041   /// @{
00042   public:
00043     /// This type is used to pass the linkage items (libraries and files) to
00044     /// the LinkItems function. It is composed of string/bool pairs. The string
00045     /// provides the name of the file or library (as with the -l option). The
00046     /// bool should be true for libraries and false for files, signifying
00047     /// "isLibrary".
00048     /// @brief A list of linkage items
00049     typedef std::vector<std::pair<std::string,bool> > ItemList;
00050 
00051     /// This enumeration is used to control various optional features of the
00052     /// linker.
00053     enum ControlFlags {
00054       Verbose       = 1, ///< Print to std::cerr what steps the linker is taking
00055       QuietWarnings = 2, ///< Don't print errors and warnings to std::cerr.
00056       QuietErrors   = 4  ///< Indicate that this link is for a native executable
00057     };
00058 
00059   /// @}
00060   /// @name Constructors
00061   /// @{
00062   public:
00063     /// Construct the Linker with an empty module which will be given the
00064     /// name \p progname. \p progname will also be used for error messages.
00065     /// @brief Construct with empty module
00066     Linker(
00067         const std::string& progname, ///< name of tool running linker
00068         const std::string& modulename, ///< name of linker's end-result module
00069         unsigned Flags = 0  ///< ControlFlags (one or more |'d together)
00070     );
00071 
00072     /// Construct the Linker with a previously defined module, \p aModule. Use
00073     /// \p progname for the name of the program in error messages.
00074     /// @brief Construct with existing module
00075     Linker(const std::string& progname, Module* aModule, unsigned Flags = 0);
00076 
00077     /// Destruct the Linker.
00078     /// @brief Destructor
00079     ~Linker();
00080 
00081   /// @}
00082   /// @name Accessors
00083   /// @{
00084   public:
00085     /// This method gets the composite module into which linking is being
00086     /// done. The Composite module starts out empty and accumulates modules
00087     /// linked into it via the various LinkIn* methods. This method does not
00088     /// release the Module to the caller. The Linker retains ownership and will
00089     /// destruct the Module when the Linker is destructed.
00090     /// @see releaseModule
00091     /// @brief Get the linked/composite module.
00092     Module* getModule() const { return Composite; }
00093 
00094     /// This method releases the composite Module into which linking is being
00095     /// done. Ownership of the composite Module is transferred to the caller who
00096     /// must arrange for its destruct. After this method is called, the Linker
00097     /// terminates the linking session for the returned Module. It will no
00098     /// longer utilize the returned Module but instead resets itself for
00099     /// subsequent linking as if the constructor had been called. The Linker's
00100     /// LibPaths and flags to be reset, and memory will be released.
00101     /// @brief Release the linked/composite module.
00102     Module* releaseModule();
00103 
00104     /// This method gets the list of libraries that form the path that the
00105     /// Linker will search when it is presented with a library name.
00106     /// @brief Get the Linkers library path
00107     const std::vector<sys::Path>& getLibPaths() const { return LibPaths; }
00108 
00109     /// This method returns an error string suitable for printing to the user.
00110     /// The return value will be empty unless an error occurred in one of the
00111     /// LinkIn* methods. In those cases, the LinkIn* methods will have returned
00112     /// true, indicating an error occurred. At most one error is retained so
00113     /// this function always returns the last error that occurred. Note that if
00114     /// the Quiet control flag is not set, the error string will have already
00115     /// been printed to std::cerr.
00116     /// @brief Get the text of the last error that occurred.
00117     const std::string& getLastError() const { return Error; }
00118 
00119   /// @}
00120   /// @name Mutators
00121   /// @{
00122   public:
00123     /// Add a path to the list of paths that the Linker will search. The Linker
00124     /// accumulates the set of libraries added
00125     /// library paths for the target platform. The standard libraries will
00126     /// always be searched last. The added libraries will be searched in the
00127     /// order added.
00128     /// @brief Add a path.
00129     void addPath(const sys::Path& path);
00130 
00131     /// Add a set of paths to the list of paths that the linker will search. The
00132     /// Linker accumulates the set of libraries added. The \p paths will be
00133     /// added to the end of the Linker's list. Order will be retained.
00134     /// @brief Add a set of paths.
00135     void addPaths(const std::vector<std::string>& paths);
00136 
00137     /// This method augments the Linker's list of library paths with the system
00138     /// paths of the host operating system, include LLVM_LIB_SEARCH_PATH.
00139     /// @brief Add the system paths.
00140     void addSystemPaths();
00141 
00142     /// Control optional linker behavior by setting a group of flags. The flags
00143     /// are defined in the ControlFlags enumeration.
00144     /// @see ControlFlags
00145     /// @brief Set control flags.
00146     void setFlags(unsigned flags) { Flags = flags; }
00147 
00148     /// This method is the main interface to the linker. It can be used to
00149     /// link a set of linkage items into a module. A linkage item is either a
00150     /// file name with fully qualified path, or a library for which the Linker's
00151     /// LibraryPath will be utilized to locate the library. The bool value in
00152     /// the LinkItemKind should be set to true for libraries.  This function
00153     /// allows linking to preserve the order of specification associated with
00154     /// the command line, or for other purposes. Each item will be linked in
00155     /// turn as it occurs in \p Items.
00156     /// @returns true if an error occurred, false otherwise
00157     /// @see LinkItemKind
00158     /// @see getLastError
00159     /// @throws nothing
00160     bool LinkInItems (
00161       const ItemList& Items, ///< Set of libraries/files to link in
00162       ItemList& NativeItems  ///< Output list of native files/libs
00163     );
00164 
00165     /// This function links the bytecode \p Files into the composite module.
00166     /// Note that this does not do any linking of unresolved symbols. The \p
00167     /// Files are all completely linked into \p HeadModule regardless of
00168     /// unresolved symbols. This function just loads each bytecode file and
00169     /// calls LinkInModule on them.
00170     /// @returns true if an error occurs, false otherwise
00171     /// @see getLastError
00172     /// @brief Link in multiple files.
00173     bool LinkInFiles (
00174       const std::vector<sys::Path> & Files ///< Files to link in
00175     );
00176 
00177     /// This function links a single bytecode file, \p File, into the composite
00178     /// module. Note that this does not attempt to resolve symbols. This method
00179     /// just loads the bytecode file and calls LinkInModule on it. If an error
00180     /// occurs, the Linker's error string is set.
00181     /// @returns true if an error occurs, false otherwise
00182     /// @see getLastError
00183     /// @brief Link in a single file.
00184     bool LinkInFile(
00185       const sys::Path& File ///< File to link in.
00186     );
00187 
00188     /// This function provides a way to selectively link in a set of modules,
00189     /// found in libraries, based on the unresolved symbols in the composite
00190     /// module. Each item in \p Libraries should be the base name of a library,
00191     /// as if given with the -l option of a linker tool.  The Linker's LibPaths
00192     /// are searched for the \p Libraries and any found will be linked in with
00193     /// LinkInArchive.  If an error occurs, the Linker's error string is set.
00194     /// @see LinkInArchive
00195     /// @see getLastError
00196     /// @returns true if an error occurs, false otherwise
00197     /// @brief Link libraries into the module
00198     bool LinkInLibraries (
00199       const std::vector<std::string> & Libraries ///< Libraries to link in
00200     );
00201 
00202     /// This function provides a way to selectively link in a set of modules,
00203     /// found in one library, based on the unresolved symbols in the composite
00204     /// module.The \p Library should be the base name of a library, as if given
00205     /// with the -l option of a linker tool. The Linker's LibPaths are searched
00206     /// for the \P Library and if found, it will be linked in with via the
00207     /// LinkInArchive method. If an error occurs, the Linker's error string is
00208     /// set.
00209     /// @see LinkInArchive
00210     /// @see getLastError
00211     /// @returns true if an error occurs, false otherwise
00212     /// @brief Link one library into the module
00213     bool LinkInLibrary (
00214       const std::string& Library, ///< The library to link in
00215       bool& is_file               ///< Indicates if lib is really a bc file
00216     );
00217 
00218     /// This function links one bytecode archive, \p Filename, into the module.
00219     /// The archive is searched to resolve outstanding symbols. Any modules in
00220     /// the archive that resolve outstanding symbols will be linked in. The
00221     /// library is searched repeatedly until no more modules that resolve
00222     /// symbols can be found. If an error occurs, the error string is  set.
00223     /// To speed up this function, ensure the the archive has been processed
00224     /// llvm-ranlib or the S option was given to llvm-ar when the archive was
00225     /// created. These tools add a symbol table to the archive which makes the
00226     /// search for undefined symbols much faster.
00227     /// @see getLastError
00228     /// @returns true if an error occurs, otherwise false.
00229     /// @brief Link in one archive.
00230     bool LinkInArchive(
00231       const sys::Path& Filename ///< Filename of the archive to link
00232     );
00233 
00234     /// This method links the \p Src module into the Linker's Composite module
00235     /// by calling LinkModules.  All the other LinkIn* methods eventually
00236     /// result in calling this method to link a Module into the Linker's
00237     /// composite.
00238     /// @see LinkModules
00239     /// @returns True if an error occurs, false otherwise.
00240     /// @brief Link in a module.
00241     bool LinkInModule(
00242       Module* Src     ///< Module linked into \p Dest
00243     ) { return LinkModules(Composite, Src, &Error); }
00244 
00245     /// This is the heart of the linker. This method will take unconditional
00246     /// control of the \p Src module and link it into the \p Dest module. The
00247     /// \p Src module will be destructed or subsumed by this method. In either
00248     /// case it is not usable by the caller after this method is invoked. Only
00249     /// the \p Dest module will remain. The \p Src module is linked into the
00250     /// Linker's composite module such that types, global variables, functions,
00251     /// and etc. are matched and resolved.  If an error occurs, this function
00252     /// returns true and ErrorMsg is set to a descriptive message about the
00253     /// error.
00254     /// @returns True if an error occurs, false otherwise.
00255     /// @brief Generically link two modules together.
00256     static bool LinkModules(Module* Dest, Module* Src, std::string* ErrorMsg);
00257 
00258     /// This function looks through the Linker's LibPaths to find a library with
00259     /// the name \p Filename. If the library cannot be found, the returned path
00260     /// will be empty (i.e. sys::Path::isEmpty() will return true).
00261     /// @returns A sys::Path to the found library
00262     /// @brief Find a library from its short name.
00263     sys::Path FindLib(const std::string &Filename);
00264 
00265   /// @}
00266   /// @name Implementation
00267   /// @{
00268   private:
00269     /// Read in and parse the bytecode file named by FN and return the
00270     /// Module it contains (wrapped in an auto_ptr), or 0 if an error occurs.
00271     std::auto_ptr<Module> LoadObject(const sys::Path& FN);
00272 
00273     bool warning(const std::string& message);
00274     bool error(const std::string& message);
00275     void verbose(const std::string& message);
00276 
00277   /// @}
00278   /// @name Data
00279   /// @{
00280   private:
00281     Module* Composite; ///< The composite module linked together
00282     std::vector<sys::Path> LibPaths; ///< The library search paths
00283     unsigned Flags;    ///< Flags to control optional behavior.
00284     std::string Error; ///< Text of error that occurred.
00285     std::string ProgramName; ///< Name of the program being linked
00286   /// @}
00287 
00288 };
00289 
00290 } // End llvm namespace
00291 
00292 #endif