Replace uses of dlsym and weak symbols

Neither is directly supported on Windows, but also not required: We can
simply not add these symbols if we are linking against a sanitizer.

driver/BUILD.bazel

@@ -84,6 +84,12 @@ cc_17_library(
 
 cc_binary(
     name = "jazzer_driver",
+    srcs = [
+        # Defines symbols otherwise defined by sanitizers to prevent linker
+        # errors and print JVM stack traces.
+        # Windows-compatible replacement for __attribute__((weak)).
+        "sanitizer_symbols.cpp",
+    ],
     data = [
         "//agent:jazzer_agent_deploy.jar",
     ],

driver/libfuzzer_driver.cpp

@@ -14,8 +14,6 @@
 
 #include "libfuzzer_driver.h"
 
-#include <dlfcn.h>
-
 #include <algorithm>
 #include <filesystem>
 #include <fstream>
@@ -44,26 +42,16 @@ DECLARE_string(id_sync_file);
 // Defined in fuzz_target_runner.cpp
 DECLARE_string(coverage_report);
 
+// This symbol is defined by sanitizers if linked into Jazzer or in
+// sanitizer_symbols.cpp if no sanitizer is used.
+extern "C" void __sanitizer_set_death_callback(void (*)());
+
 // We apply a patch to libFuzzer to make it call this function instead of
 // __sanitizer_set_death_callback to pass us the death callback.
 extern "C" [[maybe_unused]] void __jazzer_set_death_callback(
     void (*callback)()) {
   jazzer::AbstractLibfuzzerDriver::libfuzzer_print_crashing_input_ = callback;
-  void *sanitizer_set_death_callback =
-      dlsym(RTLD_DEFAULT, "__sanitizer_set_death_callback");
-  if (sanitizer_set_death_callback != nullptr)
-    reinterpret_cast<void (*)(void (*)())>(sanitizer_set_death_callback)(
-        callback);
-}
-
-// Suppress libFuzzer warnings about missing sanitizer methods in non-ASan
-// builds.
-extern "C" __attribute__((weak)) int __sanitizer_acquire_crash_state() {
-  return true;
-}
-
-extern "C" __attribute__((weak)) void __sanitizer_print_stack_trace() {
-  jazzer::DumpJvmStackTraces();
+  __sanitizer_set_death_callback(callback);
 }
 
 namespace {

driver/sanitizer_symbols.cpp

@@ -0,0 +1,29 @@
+// Copyright 2021 Code Intelligence GmbH
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Called in libfuzzer_driver.cpp.
+extern "C" void __sanitizer_set_death_callback(void (*)()) {}
+
+// Suppress libFuzzer warnings about missing sanitizer methods in non-sanitizer
+// builds.
+extern "C" int __sanitizer_acquire_crash_state() { return 1; }
+
+namespace jazzer {
+void DumpJvmStackTraces();
+}
+
+// Dump a JVM stack trace on timeouts.
+extern "C" void __sanitizer_print_stack_trace() {
+  jazzer::DumpJvmStackTraces();
+}