1 /* A C macro for emitting warnings if a function is used. 2 Copyright (C) 2010-2022 Free Software Foundation, Inc. 3 4 This program is free software: you can redistribute it and/or modify it 5 under the terms of the GNU Lesser General Public License as published 6 by the Free Software Foundation; either version 2 of the License, or 7 (at your option) any later version. 8 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 12 Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public License 15 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 16 17 /* _GL_WARN_ON_USE (function, "literal string") issues a declaration 18 for FUNCTION which will then trigger a compiler warning containing 19 the text of "literal string" anywhere that function is called, if 20 supported by the compiler. If the compiler does not support this 21 feature, the macro expands to an unused extern declaration. 22 23 _GL_WARN_ON_USE_ATTRIBUTE ("literal string") expands to the 24 attribute used in _GL_WARN_ON_USE. If the compiler does not support 25 this feature, it expands to empty. 26 27 These macros are useful for marking a function as a potential 28 portability trap, with the intent that "literal string" include 29 instructions on the replacement function that should be used 30 instead. 31 _GL_WARN_ON_USE is for functions with 'extern' linkage. 32 _GL_WARN_ON_USE_ATTRIBUTE is for functions with 'static' or 'inline' 33 linkage. 34 35 However, one of the reasons that a function is a portability trap is 36 if it has the wrong signature. Declaring FUNCTION with a different 37 signature in C is a compilation error, so this macro must use the 38 same type as any existing declaration so that programs that avoid 39 the problematic FUNCTION do not fail to compile merely because they 40 included a header that poisoned the function. But this implies that 41 _GL_WARN_ON_USE is only safe to use if FUNCTION is known to already 42 have a declaration. Use of this macro implies that there must not 43 be any other macro hiding the declaration of FUNCTION; but 44 undefining FUNCTION first is part of the poisoning process anyway 45 (although for symbols that are provided only via a macro, the result 46 is a compilation error rather than a warning containing 47 "literal string"). Also note that in C++, it is only safe to use if 48 FUNCTION has no overloads. 49 50 For an example, it is possible to poison 'getline' by: 51 - adding a call to gl_WARN_ON_USE_PREPARE([[#include <stdio.h>]], 52 [getline]) in configure.ac, which potentially defines 53 HAVE_RAW_DECL_GETLINE 54 - adding this code to a header that wraps the system <stdio.h>: 55 #undef getline 56 #if HAVE_RAW_DECL_GETLINE 57 _GL_WARN_ON_USE (getline, "getline is required by POSIX 2008, but" 58 "not universally present; use the gnulib module getline"); 59 #endif 60 61 It is not possible to directly poison global variables. But it is 62 possible to write a wrapper accessor function, and poison that 63 (less common usage, like &environ, will cause a compilation error 64 rather than issue the nice warning, but the end result of informing 65 the developer about their portability problem is still achieved): 66 #if HAVE_RAW_DECL_ENVIRON 67 static char *** 68 rpl_environ (void) { return &environ; } 69 _GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared"); 70 # undef environ 71 # define environ (*rpl_environ ()) 72 #endif 73 or better (avoiding contradictory use of 'static' and 'extern'): 74 #if HAVE_RAW_DECL_ENVIRON 75 static char *** 76 _GL_WARN_ON_USE_ATTRIBUTE ("environ is not always properly declared") 77 rpl_environ (void) { return &environ; } 78 # undef environ 79 # define environ (*rpl_environ ()) 80 #endif 81 */ 82 #ifndef _GL_WARN_ON_USE 83 84 # if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__) 85 /* A compiler attribute is available in gcc versions 4.3.0 and later. */ 86 # define _GL_WARN_ON_USE(function, message) \ 87 _GL_WARN_EXTERN_C __typeof__ (function) function __attribute__ ((__warning__ (message))) 88 # define _GL_WARN_ON_USE_ATTRIBUTE(message) \ 89 __attribute__ ((__warning__ (message))) 90 # elif __clang_major__ >= 4 91 /* Another compiler attribute is available in clang. */ 92 # define _GL_WARN_ON_USE(function, message) \ 93 _GL_WARN_EXTERN_C __typeof__ (function) function \ 94 __attribute__ ((__diagnose_if__ (1, message, "warning"))) 95 # define _GL_WARN_ON_USE_ATTRIBUTE(message) \ 96 __attribute__ ((__diagnose_if__ (1, message, "warning"))) 97 # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING 98 /* Verify the existence of the function. */ 99 # define _GL_WARN_ON_USE(function, message) \ 100 _GL_WARN_EXTERN_C __typeof__ (function) function 101 # define _GL_WARN_ON_USE_ATTRIBUTE(message) 102 # else /* Unsupported. */ 103 # define _GL_WARN_ON_USE(function, message) \ 104 _GL_WARN_EXTERN_C int _gl_warn_on_use 105 # define _GL_WARN_ON_USE_ATTRIBUTE(message) 106 # endif 107 #endif 108 109 /* _GL_WARN_ON_USE_CXX (function, rettype_gcc, rettype_clang, parameters_and_attributes, "message") 110 is like _GL_WARN_ON_USE (function, "message"), except that in C++ mode the 111 function is declared with the given prototype, consisting of return type, 112 parameters, and attributes. 113 This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does 114 not work in this case. */ 115 #ifndef _GL_WARN_ON_USE_CXX 116 # if !defined __cplusplus 117 # define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ 118 _GL_WARN_ON_USE (function, msg) 119 # else 120 # if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__) 121 /* A compiler attribute is available in gcc versions 4.3.0 and later. */ 122 # define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ 123 extern rettype_gcc function parameters_and_attributes \ 124 __attribute__ ((__warning__ (msg))) 125 # elif __clang_major__ >= 4 126 /* Another compiler attribute is available in clang. */ 127 # define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ 128 extern rettype_clang function parameters_and_attributes \ 129 __attribute__ ((__diagnose_if__ (1, msg, "warning"))) 130 # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING 131 /* Verify the existence of the function. */ 132 # define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ 133 extern rettype_gcc function parameters_and_attributes 134 # else /* Unsupported. */ 135 # define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ 136 _GL_WARN_EXTERN_C int _gl_warn_on_use 137 # endif 138 # endif 139 #endif 140 141 /* _GL_WARN_EXTERN_C declaration; 142 performs the declaration with C linkage. */ 143 #ifndef _GL_WARN_EXTERN_C 144 # if defined __cplusplus 145 # define _GL_WARN_EXTERN_C extern "C" 146 # else 147 # define _GL_WARN_EXTERN_C extern 148 # endif 149 #endif 150
Indexes created Sat Feb 28 05:31:39 UTC 2026