Make G_FUZZING constexpr, require -DBUILD_FOR_FUZZING=ON to execute a fuzz target

CMakeLists.txt

@@ -234,6 +234,10 @@ if(BUILD_FOR_FUZZING)
   set(BUILD_GUI_TESTS OFF)
   set(BUILD_BENCH OFF)
   set(BUILD_FUZZ_BINARY ON)
+
+  target_compile_definitions(core_interface INTERFACE
+    FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+  )
 endif()
 
 include(ProcessConfigurations)

src/pow.cpp

@@ -139,7 +139,7 @@ bool PermittedDifficultyTransition(const Consensus::Params& params, int64_t heig
 // the most signficant bit of the last byte of the hash is set.
 bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params& params)
 {
-    if (g_fuzzing) return (hash.data()[31] & 0x80) == 0;
+    if constexpr (G_FUZZING) return (hash.data()[31] & 0x80) == 0;
     return CheckProofOfWorkImpl(hash, nBits, params);
 }
 

src/test/fuzz/fuzz.cpp

@@ -102,8 +102,6 @@ void ResetCoverageCounters() {}
 
 void initialize()
 {
-    g_fuzzing = true;
-
     // By default, make the RNG deterministic with a fixed seed. This will affect all
     // randomness during the fuzz test, except:
     // - GetStrongRandBytes(), which is used for the creation of private key material.
@@ -156,6 +154,10 @@ void initialize()
         std::cerr << "No fuzz target compiled for " << g_fuzz_target << "." << std::endl;
         std::exit(EXIT_FAILURE);
     }
+    if constexpr (!G_FUZZING) {
+        std::cerr << "Must compile with -DBUILD_FOR_FUZZING=ON to execute a fuzz target." << std::endl;
+        std::exit(EXIT_FAILURE);
+    }
     Assert(!g_test_one_input);
     g_test_one_input = &it->second.test_one_input;
     it->second.opts.init();

src/util/check.cpp

@@ -14,8 +14,6 @@
 #include <string>
 #include <string_view>
 
-bool g_fuzzing = false;
-
 std::string StrFormatInternalBug(std::string_view msg, std::string_view file, int line, std::string_view func)
 {
     return strprintf("Internal bug detected: %s\n%s:%d (%s)\n"

src/util/check.h

@@ -13,7 +13,13 @@
 #include <string_view>
 #include <utility>
 
-extern bool g_fuzzing;
+constexpr bool G_FUZZING{
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    true
+#else
+    false
+#endif
+};
 
 std::string StrFormatInternalBug(std::string_view msg, std::string_view file, int line, std::string_view func);
 
@@ -44,7 +50,7 @@ void assertion_fail(std::string_view file, int line, std::string_view func, std:
 template <bool IS_ASSERT, typename T>
 constexpr T&& inline_assertion_check(LIFETIMEBOUND T&& val, [[maybe_unused]] const char* file, [[maybe_unused]] int line, [[maybe_unused]] const char* func, [[maybe_unused]] const char* assertion)
 {
-    if (IS_ASSERT || std::is_constant_evaluated() || g_fuzzing
+    if (IS_ASSERT || std::is_constant_evaluated() || G_FUZZING
 #ifdef ABORT_ON_FAILED_ASSUME
         || true
 #endif