Merge #20065: fuzz: Configure check for main function

fae7a1c188 fuzz: Configure check for main function (MarcoFalke)

Pull request description:

  Instead of the PP jungle, use a proper configure check

  Fixes https://github.com/google/honggfuzz/issues/336#issuecomment-702972138

ACKs for top commit:
  practicalswift:
    ACK fae7a1c188

Tree-SHA512: 2e55457d01f9ac598bb1e119d8b49dca55a28f88ec164cee6b5f071c29e9791f5a46cc8ee2b801b3a3faf906348da964ce32e7254da981c1104b9210a3508100

configure.ac

@@ -1165,6 +1165,20 @@ if test "x$enable_fuzz" = "xyes"; then
   use_bench=no
   use_upnp=no
   use_zmq=no
+
+  AC_MSG_CHECKING([whether main function is needed])
+  AX_CHECK_LINK_FLAG(
+    [[-fsanitize=$use_sanitizers]],
+    [AC_MSG_RESULT([no])],
+    [AC_MSG_RESULT([yes])
+     CPPFLAGS="$CPPFLAGS -DPROVIDE_MAIN_FUNCTION"],
+    [],
+    [AC_LANG_PROGRAM([[
+      #include <cstdint>
+      #include <cstddef>
+      extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { return 0; }
+      /* unterminated comment to remove the main function ...
+    ]],[[]])])
 else
   BITCOIN_QT_INIT
 

src/test/fuzz/fuzz.cpp

@@ -12,15 +12,6 @@
 
 const std::function<void(const std::string&)> G_TEST_LOG_FUN{};
 
-// 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)
 {