1 //=== FuzzerExtWindows.cpp - Interface to external functions --------------===//
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 // Implementation of FuzzerExtFunctions for Windows. Uses alternatename when
10 // compiled with MSVC. Uses weak aliases when compiled with clang. Unfortunately
11 // the method each compiler supports is not supported by the other.
12 //===----------------------------------------------------------------------===//
13 #include "FuzzerDefs.h"
14 #if LIBFUZZER_WINDOWS
15 
16 #include "FuzzerExtFunctions.h"
17 #include "FuzzerIO.h"
18 
19 using namespace fuzzer;
20 
21 // Intermediate macro to ensure the parameter is expanded before stringified.
22 #define STRINGIFY_(A) #A
23 #define STRINGIFY(A) STRINGIFY_(A)
24 
25 #if LIBFUZZER_MSVC
26 // Copied from compiler-rt/lib/sanitizer_common/sanitizer_win_defs.h
27 #if defined(_M_IX86) || defined(__i386__)
28 #define WIN_SYM_PREFIX "_"
29 #else
30 #define WIN_SYM_PREFIX
31 #endif
32 
33 // Declare external functions as having alternativenames, so that we can
34 // determine if they are not defined.
35 #define EXTERNAL_FUNC(Name, Default)                                   \
36   __pragma(comment(linker, "/alternatename:" WIN_SYM_PREFIX STRINGIFY( \
37                                Name) "=" WIN_SYM_PREFIX STRINGIFY(Default)))
38 #else
39 // Declare external functions as weak to allow them to default to a specified
40 // function if not defined explicitly. We must use weak symbols because clang's
41 // support for alternatename is not 100%, see
42 // https://bugs.llvm.org/show_bug.cgi?id=40218 for more details.
43 #define EXTERNAL_FUNC(Name, Default) \
44   __attribute__((weak, alias(STRINGIFY(Default))))
45 #endif  // LIBFUZZER_MSVC
46 
47 extern "C" {
48 #define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN)         \
49   RETURN_TYPE NAME##Def FUNC_SIG {                          \
50     Printf("ERROR: Function \"%s\" not defined.\n", #NAME); \
51     exit(1);                                                \
52   }                                                         \
53   EXTERNAL_FUNC(NAME, NAME##Def) RETURN_TYPE NAME FUNC_SIG;
54 
55 #include "FuzzerExtFunctions.def"
56 
57 #undef EXT_FUNC
58 }
59 
60 template <typename T>
61 static T *GetFnPtr(T *Fun, T *FunDef, const char *FnName, bool WarnIfMissing) {
62   if (Fun == FunDef) {
63     if (WarnIfMissing)
64       Printf("WARNING: Failed to find function \"%s\".\n", FnName);
65     return nullptr;
66   }
67   return Fun;
68 }
69 
70 namespace fuzzer {
71 
72 ExternalFunctions::ExternalFunctions() {
73 #define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN) \
74   this->NAME = GetFnPtr<decltype(::NAME)>(::NAME, ::NAME##Def, #NAME, WARN);
75 
76 #include "FuzzerExtFunctions.def"
77 
78 #undef EXT_FUNC
79 }
80 
81 }  // namespace fuzzer
82 
83 #endif // LIBFUZZER_WINDOWS
84