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 53namespace 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. 73struct IncludeFile { 74 explicit IncludeFile(const void *); 75}; 76 77} 78 79#endif 80