[libFuzzer] Use dynamic loading for External Functions on Windows.

Replace weak aliases with dynamic loading.
Weak aliases were generating some problems when linking for MT on Windows. For
MT, compiler-rt's libraries are statically linked to the main executable the
same than libFuzzer, so if we use weak aliases, we are providing two different
default implementations for the same weak function and the linker fails.

In this diff I re implement ExternalFunctions() using dynamic loading, so it
works in both cases (MD and MT). Also, dynamic loading is simpler, since we are
not defining any auxiliary external function, and we don't need to deal with
weak aliases.
This is equivalent to the implementation using dlsym(RTLD_DEFAULT, FnName) for
Posix.

Differential revision: https://reviews.llvm.org/D29751

llvm-svn: 294687

2 files changed, 61 insertions, 1 deletions

diff --git a/llvm/lib/Fuzzer/CMakeLists.txt b/llvm/lib/Fuzzer/CMakeLists.txt
index 4b947d87e6d..5ba126e69cc 100644
--- a/llvm/lib/Fuzzer/CMakeLists.txt
+++ b/llvm/lib/Fuzzer/CMakeLists.txt
@@ -12,8 +12,8 @@ if( LLVM_USE_SANITIZE_COVERAGE )
     FuzzerCrossOver.cpp
     FuzzerDriver.cpp
     FuzzerExtFunctionsDlsym.cpp
+    FuzzerExtFunctionsDlsymWin.cpp
     FuzzerExtFunctionsWeak.cpp
-    FuzzerExtFunctionsWeakAlias.cpp
     FuzzerIO.cpp
     FuzzerIOPosix.cpp
     FuzzerIOWindows.cpp
diff --git a/llvm/lib/Fuzzer/FuzzerExtFunctionsDlsymWin.cpp b/llvm/lib/Fuzzer/FuzzerExtFunctionsDlsymWin.cpp
new file mode 100644
index 00000000000..77521698c80
--- /dev/null
+++ b/llvm/lib/Fuzzer/FuzzerExtFunctionsDlsymWin.cpp
@@ -0,0 +1,60 @@
+//===- FuzzerExtFunctionsDlsymWin.cpp - Interface to external functions ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Implementation using dynamic loading for Windows.
+//===----------------------------------------------------------------------===//
+#include "FuzzerDefs.h"
+#if LIBFUZZER_WINDOWS
+
+#include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
+#include "Windows.h"
+#include "Psapi.h"
+
+namespace fuzzer {
+
+ExternalFunctions::ExternalFunctions() {
+  HMODULE Modules[1024];
+  DWORD BytesNeeded;
+  HANDLE CurrentProcess = GetCurrentProcess();
+
+  if (!EnumProcessModules(CurrentProcess, Modules, sizeof(Modules),
+                          &BytesNeeded)) {
+    Printf("EnumProcessModules failed (error: %d).\n", GetLastError());
+    exit(1);
+  }
+
+  if (sizeof(Modules) < BytesNeeded) {
+    Printf("Error: the array is not big enough to hold all loaded modules.\n");
+    exit(1);
+  }
+
+  for (size_t i = 0; i < (BytesNeeded / sizeof(HMODULE)); i++)
+  {
+    FARPROC Fn;
+#define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN)                            \
+    if (this->NAME == nullptr) {                                               \
+      Fn = GetProcAddress(Modules[i], #NAME);                                  \
+      if (Fn == nullptr)                                                       \
+         Fn = GetProcAddress(Modules[i], #NAME "__dll");                       \
+      this->NAME = (decltype(ExternalFunctions::NAME)) Fn;                     \
+    }
+#include "FuzzerExtFunctions.def"
+#undef EXT_FUNC
+  }
+
+#define EXT_FUNC(NAME, RETURN_TYPE, FUNC_SIG, WARN)                            \
+  if (this->NAME == nullptr && WARN)                                           \
+    Printf("WARNING: Failed to find function \"%s\".\n", #NAME);
+#include "FuzzerExtFunctions.def"
+#undef EXT_FUNC
+}
+
+} // namespace fuzzer
+
+#endif // LIBFUZZER_WINDOWS