1 //===-- sanitizer_win_defs.h ------------------------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Common definitions for Windows-specific code.
12 //===----------------------------------------------------------------------===//
13 #ifndef SANITIZER_WIN_DEFS_H
14 #define SANITIZER_WIN_DEFS_H
16 #include "sanitizer_platform.h"
20 #if defined(_M_IX86) || defined(__i386__)
21 #define WINAPI __stdcall
27 #if defined(_M_IX86) || defined(__i386__)
28 #define WIN_SYM_PREFIX "_"
30 #define WIN_SYM_PREFIX
33 // For MinGW, the /export: directives contain undecorated symbols, contrary to
34 // link/lld-link. The GNU linker doesn't support /alternatename and /include
35 // though, thus lld-link in MinGW mode interprets them in the same way as
36 // in the default mode.
38 #define WIN_EXPORT_PREFIX
40 #define WIN_EXPORT_PREFIX WIN_SYM_PREFIX
43 // Intermediate macro to ensure the parameter is expanded before stringified.
44 #define STRINGIFY_(A) #A
45 #define STRINGIFY(A) STRINGIFY_(A)
47 // ----------------- A workaround for the absence of weak symbols --------------
48 // We don't have a direct equivalent of weak symbols when using MSVC, but we can
49 // use the /alternatename directive to tell the linker to default a specific
50 // symbol to a specific value.
51 // Take into account that this is a pragma directive for the linker, so it will
52 // be ignored by the compiler and the function will be marked as UNDEF in the
53 // symbol table of the resulting object file. The linker won't find the default
54 // implementation until it links with that object file.
55 // So, suppose we provide a default implementation "fundef" for "fun", and this
56 // is compiled into the object file "test.obj" including the pragma directive.
57 // If we have some code with references to "fun" and we link that code with
58 // "test.obj", it will work because the linker always link object files.
59 // But, if "test.obj" is included in a static library, like "test.lib", then the
60 // liker will only link to "test.obj" if necessary. If we only included the
61 // definition of "fun", it won't link to "test.obj" (from test.lib) because
62 // "fun" appears as UNDEF, so it doesn't resolve the symbol "fun", and will
63 // result in a link error (the linker doesn't find the pragma directive).
64 // So, a workaround is to force linkage with the modules that include weak
65 // definitions, with the following macro: WIN_FORCE_LINK()
67 #define WIN_WEAK_ALIAS(Name, Default) \
68 __pragma(comment(linker, "/alternatename:" WIN_SYM_PREFIX STRINGIFY(Name) "="\
69 WIN_SYM_PREFIX STRINGIFY(Default)))
71 #define WIN_FORCE_LINK(Name) \
72 __pragma(comment(linker, "/include:" WIN_SYM_PREFIX STRINGIFY(Name)))
74 #define WIN_EXPORT(ExportedName, Name) \
75 __pragma(comment(linker, "/export:" WIN_EXPORT_PREFIX STRINGIFY(ExportedName)\
76 "=" WIN_EXPORT_PREFIX STRINGIFY(Name)))
78 // We cannot define weak functions on Windows, but we can use WIN_WEAK_ALIAS()
79 // which defines an alias to a default implementation, and only works when
80 // linking statically.
81 // So, to define a weak function "fun", we define a default implementation with
82 // a different name "fun__def" and we create a "weak alias" fun = fun__def.
83 // Then, users can override it just defining "fun".
84 // We impose "extern "C"" because otherwise WIN_WEAK_ALIAS() will fail because
87 // Dummy name for default implementation of weak function.
88 # define WEAK_DEFAULT_NAME(Name) Name##__def
89 // Name for exported implementation of weak function.
90 # define WEAK_EXPORT_NAME(Name) Name##__dll
92 // Use this macro when you need to define and export a weak function from a
93 // library. For example:
94 // WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; }
95 # define WIN_WEAK_EXPORT_DEF(ReturnType, Name, ...) \
96 WIN_WEAK_ALIAS(Name, WEAK_DEFAULT_NAME(Name)) \
97 WIN_EXPORT(WEAK_EXPORT_NAME(Name), Name) \
98 extern "C" ReturnType Name(__VA_ARGS__); \
99 extern "C" ReturnType WEAK_DEFAULT_NAME(Name)(__VA_ARGS__)
101 // Use this macro when you need to import a weak function from a library. It
102 // defines a weak alias to the imported function from the dll. For example:
103 // WIN_WEAK_IMPORT_DEF(compare)
104 # define WIN_WEAK_IMPORT_DEF(Name) \
105 WIN_WEAK_ALIAS(Name, WEAK_EXPORT_NAME(Name))
107 // So, for Windows we provide something similar to weak symbols in Linux, with
109 // + A default implementation must always be provided.
111 // + When linking statically it works quite similarly. For example:
114 // WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; }
117 // // We can use the default implementation from the library:
119 // // Or we can override it:
120 // extern "C" bool compare (int a, int b) { return a >= b; }
122 // And it will work fine. If we don't override the function, we need to ensure
123 // that the linker includes the object file with the default implementation.
124 // We can do so with the linker option "-wholearchive:".
126 // + When linking dynamically with a library (dll), weak functions are exported
127 // with "__dll" suffix. Clients can use the macro WIN_WEAK_IMPORT_DEF(fun)
128 // which defines a "weak alias" fun = fun__dll.
131 // WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; }
134 // WIN_WEAK_IMPORT_DEF(compare)
135 // // We can use the default implementation from the library:
137 // // Or we can override it:
138 // extern "C" bool compare (int a, int b) { return a >= b; }
140 // But if we override the function, the dlls don't have access to it (which
141 // is different in linux). If that is desired, the strong definition must be
142 // exported and interception can be used from the rest of the dlls.
145 // WIN_WEAK_EXPORT_DEF(bool, compare, int a, int b) { return a > b; }
146 // // When initialized, check if the main executable defined "compare".
147 // int libExample_init() {
148 // uptr fnptr = __interception::InternalGetProcAddress(
149 // (void *)GetModuleHandleA(0), "compare");
150 // if (fnptr && !__interception::OverrideFunction((uptr)compare, fnptr, 0))
156 // WIN_WEAK_IMPORT_DEF(compare)
157 // // We override and export compare:
158 // extern "C" __declspec(dllexport) bool compare (int a, int b) {
162 #endif // SANITIZER_WINDOWS
163 #endif // SANITIZER_WIN_DEFS_H