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 "FuzzerDefs.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