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