1 //===- llvm/Support/IncludeFile.h - Ensure Linking Of Library ---*- C++ -*-===// 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 defines the FORCE_DEFINING_FILE_TO_BE_LINKED and DEFINE_FILE_FOR 11 // macros. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_SYSTEM_INCLUDEFILE_H 16 #define LLVM_SYSTEM_INCLUDEFILE_H 17 18 /// This macro is the public interface that IncludeFile.h exports. This gives 19 /// us the option to implement the "link the definition" capability in any 20 /// manner that we choose. All header files that depend on a specific .cpp 21 /// file being linked at run time should use this macro instead of the 22 /// IncludeFile class directly. 23 /// 24 /// For example, foo.h would use:<br/> 25 /// <tt>FORCE_DEFINING_FILE_TO_BE_LINKED(foo)</tt><br/> 26 /// 27 /// And, foo.cp would use:<br/> 28 /// <tt>DEFINING_FILE_FOR(foo)</tt><br/> 29 #ifdef __GNUC__ 30 // If the `used' attribute is available, use it to create a variable 31 // with an initializer that will force the linking of the defining file. 32 #define FORCE_DEFINING_FILE_TO_BE_LINKED(name) \ 33 namespace llvm { \ 34 extern const char name ## LinkVar; \ 35 __attribute__((used)) static const char *const name ## LinkObj = \ 36 &name ## LinkVar; \ 37 } 38 #else 39 // Otherwise use a constructor call. 40 #define FORCE_DEFINING_FILE_TO_BE_LINKED(name) \ 41 namespace llvm { \ 42 extern const char name ## LinkVar; \ 43 static const IncludeFile name ## LinkObj ( &name ## LinkVar ); \ 44 } 45 #endif 46 47 /// This macro is the counterpart to FORCE_DEFINING_FILE_TO_BE_LINKED. It should 48 /// be used in a .cpp file to define the name referenced in a header file that 49 /// will cause linkage of the .cpp file. It should only be used at extern level. 50 #define DEFINING_FILE_FOR(name) \ 51 namespace llvm { const char name ## LinkVar = 0; } 52 53 namespace llvm { 54 55 /// This class is used in the implementation of FORCE_DEFINING_FILE_TO_BE_LINKED 56 /// macro to make sure that the implementation of a header file is included 57 /// into a tool that uses the header. This is solely 58 /// to overcome problems linking .a files and not getting the implementation 59 /// of compilation units we need. This is commonly an issue with the various 60 /// Passes but also occurs elsewhere in LLVM. We like to use .a files because 61 /// they link faster and provide the smallest executables. However, sometimes 62 /// those executables are too small, if the program doesn't reference something 63 /// that might be needed, especially by a loaded share object. This little class 64 /// helps to resolve that problem. The basic strategy is to use this class in 65 /// a header file and pass the address of a variable to the constructor. If the 66 /// variable is defined in the header file's corresponding .cpp file then all 67 /// tools/libraries that \#include the header file will require the .cpp as 68 /// well. 69 /// For example:<br/> 70 /// <tt>extern int LinkMyCodeStub;</tt><br/> 71 /// <tt>static IncludeFile LinkMyModule(&LinkMyCodeStub);</tt><br/> 72 /// @brief Class to ensure linking of corresponding object file. 73 struct IncludeFile { 74 explicit IncludeFile(const void *); 75 }; 76 77 } 78 79 #endif 80
