tests: Provide main(...) function in fuzzer

Author: practicalswift

src/test/fuzz/fuzz.cpp

@@ -12,7 +12,16 @@
 
 const std::function<void(const std::string&)> G_TEST_LOG_FUN{};
 
-#if defined(__AFL_COMPILER)
+// Decide if main(...) should be provided:
+// * AFL needs main(...) regardless of platform.
+// * macOS handles __attribute__((weak)) main(...) poorly when linking
+//   against libFuzzer. See https://github.com/bitcoin/bitcoin/pull/18008
+//   for details.
+#if defined(__AFL_COMPILER) || !defined(MAC_OSX)
+#define PROVIDE_MAIN_FUNCTION
+#endif
+
+#if defined(PROVIDE_MAIN_FUNCTION)
 static bool read_stdin(std::vector<uint8_t>& data)
 {
     uint8_t buffer[1024];
@@ -44,9 +53,8 @@ extern "C" int LLVMFuzzerInitialize(int* argc, char*** argv)
     return 0;
 }
 
-// Generally, the fuzzer will provide main(), except for AFL
-#if defined(__AFL_COMPILER)
-int main(int argc, char** argv)
+#if defined(PROVIDE_MAIN_FUNCTION)
+__attribute__((weak)) int main(int argc, char** argv)
 {
     initialize();
 #ifdef __AFL_INIT