LLVM API Documentation
00001 //===- llvm/System/IncludeFile.h - Ensure Linking Of Library ---*- 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 FORCE_DEFINING_FILE_TO_BE_LINKED and DEFINE_FILE_FOR 00011 // macros. 00012 // 00013 //===----------------------------------------------------------------------===// 00014 00015 #ifndef LLVM_SYSTEM_INCLUDEFILE_H 00016 #define LLVM_SYSTEM_INCLUDEFILE_H 00017 00018 /// This macro is the public interface that IncludeFile.h exports. This gives 00019 /// us the option to implement the "link the definition" capability in any 00020 /// manner that we choose. All header files that depend on a specific .cpp 00021 /// file being linked at run time should use this macro instead of the 00022 /// IncludeFile class directly. 00023 /// 00024 /// For example, foo.h would use:<br/> 00025 /// <tt>FORCE_DEFINING_FILE_TO_BE_LINKED(foo)</tt><br/> 00026 /// 00027 /// And, foo.cp would use:<br/> 00028 /// <tt>DEFINING_FILE_FOR(foo)</tt><br/> 00029 #define FORCE_DEFINING_FILE_TO_BE_LINKED(name) \ 00030 namespace llvm { \ 00031 extern char name ## LinkVar; \ 00032 static IncludeFile name ## LinkObj ( &name ## LinkVar ); \ 00033 } 00034 00035 /// This macro is the counterpart to FORCE_DEFINING_FILE_TO_BE_LINKED. It should 00036 /// be used in a .cpp file to define the name referenced in a header file that 00037 /// will cause linkage of the .cpp file. It should only be used at extern level. 00038 #define DEFINING_FILE_FOR(name) namespace llvm { char name ## LinkVar; } 00039 00040 namespace llvm { 00041 00042 /// This class is used in the implementation of FORCE_DEFINING_FILE_TO_BE_LINKED 00043 /// macro to make sure that the implementation of a header file is included 00044 /// into a tool that uses the header. This is solely 00045 /// to overcome problems linking .a files and not getting the implementation 00046 /// of compilation units we need. This is commonly an issue with the various 00047 /// Passes but also occurs elsewhere in LLVM. We like to use .a files because 00048 /// they link faster and provide the smallest executables. However, sometimes 00049 /// those executables are too small, if the program doesn't reference something 00050 /// that might be needed, especially by a loaded share object. This little class 00051 /// helps to resolve that problem. The basic strategy is to use this class in 00052 /// a header file and pass the address of a variable to the constructor. If the 00053 /// variable is defined in the header file's corresponding .cpp file then all 00054 /// tools/libraries that #include the header file will require the .cpp as well. 00055 /// For example:<br/> 00056 /// <tt>extern int LinkMyCodeStub;</tt><br/> 00057 /// <tt>static IncludeFile LinkMyModule(&LinkMyCodeStub);</tt><br/> 00058 /// @brief Class to ensure linking of corresponding object file. 00059 struct IncludeFile { 00060 IncludeFile(void *); 00061 }; 00062 00063 } 00064 00065 #endif