1//===-- sanitizer_win_defs.h ------------------------------------*- C++ -*-===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// Common definitions for Windows-specific code. 10// 11//===----------------------------------------------------------------------===// 12#ifndef SANITIZER_WIN_DEFS_H 13#define SANITIZER_WIN_DEFS_H 14 15#include "sanitizer_platform.h" 16#if SANITIZER_WINDOWS 17 18#ifndef WINAPI 19#if defined(_M_IX86) || defined(__i386__) 20#define WINAPI __stdcall 21#else 22#define WINAPI 23#endif 24#endif 25 26#if defined(_M_IX86) || defined(__i386__) 27#define WIN_SYM_PREFIX "_" 28#else 29#define WIN_SYM_PREFIX 30#endif 31 32// For MinGW, the /export: directives contain undecorated symbols, contrary to 33// link/lld-link. The GNU linker doesn't support /alternatename and /include 34// though, thus lld-link in MinGW mode interprets them in the same way as 35// in the default mode. 36#ifdef __MINGW32__ 37#define WIN_EXPORT_PREFIX 38#else 39#define WIN_EXPORT_PREFIX WIN_SYM_PREFIX 40#endif 41 42// Intermediate macro to ensure the parameter is expanded before stringified. 43#define STRINGIFY_(A) #A 44#define STRINGIFY(A) STRINGIFY_(A) 45 46#if !SANITIZER_GO 47 48// ----------------- A workaround for the absence of weak symbols -------------- 49// We don't have a direct equivalent of weak symbols when using MSVC, but we can 50// use the /alternatename directive to tell the linker to default a specific 51// symbol to a specific value. 52// Take into account that this is a pragma directive for the linker, so it will 53// be ignored by the compiler and the function will be marked as UNDEF in the 54// symbol table of the resulting object file. The linker won't find the default 55// implementation until it links with that object file. 56// So, suppose we provide a default implementation "fundef" for "fun", and this 57// is compiled into the object file "test.obj" including the pragma directive. 58// If we have some code with references to "fun" and we link that code with 59// "test.obj", it will work because the linker always link object files. 60// But, if "test.obj" is included in a static library, like "test.lib", then the 61// liker will only link to "test.obj" if necessary. If we only included the 62// definition of "fun", it won't link to "test.obj" (from test.lib) because 63// "fun" appears as UNDEF, so it doesn't resolve the symbol "fun", and will 64// result in a link error (the linker doesn't find the pragma directive). 65// So, a workaround is to force linkage with the modules that include weak 66// definitions, with the following macro: WIN_FORCE_LINK() 67 68#define WIN_WEAK_ALIAS(Name, Default) \ 69 __pragma(comment(linker, "/alternatename:" WIN_SYM_PREFIX STRINGIFY(Name) "="\ 70 WIN_SYM_PREFIX STRINGIFY(Default))) 71 72#define WIN_FORCE_LINK(Name) \ 73 __pragma(comment(linker, "/include:" WIN_SYM_PREFIX STRINGIFY(Name))) 74 75#define WIN_EXPORT(ExportedName, Name) \ 76 __pragma(comment(linker, "/export:" WIN_EXPORT_PREFIX STRINGIFY(ExportedName)\ 77 "=" WIN_EXPORT_PREFIX STRINGIFY(Name))) 78 79// We cannot define weak functions on Windows, but we can use WIN_WEAK_ALIAS() 80// which defines an alias to a default implementation, and only works when 81// linking statically. 82// So, to define a weak function "fun", we define a default implementation with 83// a different name "fun__def" and we create a "weak alias" fun = fun__def. 84// Then, users can override it just defining "fun". 85// We impose "extern "C"" because otherwise WIN_WEAK_ALIAS() will fail because 86// of name mangling. 87 88// Dummy name for default implementation of weak function. 89# define WEAK_DEFAULT_NAME(Name) Name##__def 90// Name for exported implementation of weak function. 91# define WEAK_EXPORT_NAME(Name) Name##__dll 92 93// Use this macro when you need to define and export a weak function from a 94// library. For example: 95// WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; } 96# define WIN_WEAK_EXPORT_DEF(ReturnType, Name, ...) \ 97 WIN_WEAK_ALIAS(Name, WEAK_DEFAULT_NAME(Name)) \ 98 WIN_EXPORT(WEAK_EXPORT_NAME(Name), Name) \ 99 extern "C" ReturnType Name(__VA_ARGS__); \ 100 extern "C" ReturnType WEAK_DEFAULT_NAME(Name)(__VA_ARGS__) 101 102// Use this macro when you need to import a weak function from a library. It 103// defines a weak alias to the imported function from the dll. For example: 104// WIN_WEAK_IMPORT_DEF(compare) 105# define WIN_WEAK_IMPORT_DEF(Name) \ 106 WIN_WEAK_ALIAS(Name, WEAK_EXPORT_NAME(Name)) 107 108// So, for Windows we provide something similar to weak symbols in Linux, with 109// some differences: 110// + A default implementation must always be provided. 111// 112// + When linking statically it works quite similarly. For example: 113// 114// // libExample.cc 115// WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; } 116// 117// // client.cc 118// // We can use the default implementation from the library: 119// compare(1, 2); 120// // Or we can override it: 121// extern "C" bool compare (int a, int b) { return a >= b; } 122// 123// And it will work fine. If we don't override the function, we need to ensure 124// that the linker includes the object file with the default implementation. 125// We can do so with the linker option "-wholearchive:". 126// 127// + When linking dynamically with a library (dll), weak functions are exported 128// with "__dll" suffix. Clients can use the macro WIN_WEAK_IMPORT_DEF(fun) 129// which defines a "weak alias" fun = fun__dll. 130// 131// // libExample.cc 132// WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; } 133// 134// // client.cc 135// WIN_WEAK_IMPORT_DEF(compare) 136// // We can use the default implementation from the library: 137// compare(1, 2); 138// // Or we can override it: 139// extern "C" bool compare (int a, int b) { return a >= b; } 140// 141// But if we override the function, the dlls don't have access to it (which 142// is different in linux). If that is desired, the strong definition must be 143// exported and interception can be used from the rest of the dlls. 144// 145// // libExample.cc 146// WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; } 147// // When initialized, check if the main executable defined "compare". 148// int libExample_init() { 149// uptr fnptr = __interception::InternalGetProcAddress( 150// (void *)GetModuleHandleA(0), "compare"); 151// if (fnptr && !__interception::OverrideFunction((uptr)compare, fnptr, 0)) 152// abort(); 153// return 0; 154// } 155// 156// // client.cc 157// WIN_WEAK_IMPORT_DEF(compare) 158// // We override and export compare: 159// extern "C" __declspec(dllexport) bool compare (int a, int b) { 160// return a >= b; 161// } 162// 163 164#else // SANITIZER_GO 165 166// Go neither needs nor wants weak references. 167// The shenanigans above don't work for gcc. 168# define WIN_WEAK_EXPORT_DEF(ReturnType, Name, ...) \ 169 extern "C" ReturnType Name(__VA_ARGS__) 170 171#endif // SANITIZER_GO 172 173#endif // SANITIZER_WINDOWS 174#endif // SANITIZER_WIN_DEFS_H 175