fuzz: share a single FakeNodeClock in the chainman-resetting fuzz targets

cmpctblock, process_message, process_messages, and utxo_snapshot rebuild
the chainman from a helper called out of the target body, while the
body itself holds or mutates mocktime through a FakeNodeClock. Since
FakeNodeClock is a LimitOne type, the helper cannot hold one of its
own and reaches for the SetMockTime() global mutator instead, so it is
unclear which of the two owns mocktime.

Add a GetFakeNodeClock() that returns a single process-wide
FakeNodeClock and route these targets through it, replacing their
local FakeNodeClock and genesis-time SetMockTime() calls.

It is initialized with 0s rather than a default-constructed
FakeNodeClock{}, which would read mocktime at whatever point the
static happens to be constructed. Every user sets the time before use
anyway.

src/test/fuzz/cmpctblock.cpp

@@ -109,7 +109,7 @@ public:
 
 void ResetChainmanAndMempool(TestingSetup& setup)
 {
-    SetMockTime(Params().GenesisBlock().Time());
+    GetFakeNodeClock().set(Params().GenesisBlock().Time());
 
     bilingual_str error{};
     setup.m_node.mempool.reset();
@@ -163,7 +163,7 @@ FUZZ_TARGET(cmpctblock, .init = initialize_cmpctblock)
     SeedRandomStateForTest(SeedRand::ZEROS);
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
 
-    FakeNodeClock clock{1610000000s};
+    GetFakeNodeClock().set(1610000000s);
     FakeSteadyClock steady_clock;
 
     auto setup = g_setup;
@@ -453,10 +453,10 @@ FUZZ_TARGET(cmpctblock, .init = initialize_cmpctblock)
             [&]() {
                 // Set mock time randomly or to tip's time.
                 if (fuzzed_data_provider.ConsumeBool()) {
-                    clock.set(ConsumeTime(fuzzed_data_provider));
+                    GetFakeNodeClock().set(ConsumeTime(fuzzed_data_provider));
                 } else {
                     const NodeSeconds tip_time = WITH_LOCK(::cs_main, return chainman.ActiveChain().Tip()->Time());
-                    clock.set(tip_time);
+                    GetFakeNodeClock().set(tip_time);
                 }
 
                 sent_net_msg = false;

src/test/fuzz/process_message.cpp

@@ -46,7 +46,7 @@ std::string_view LIMIT_TO_MESSAGE_TYPE{};
 
 void ResetChainman(TestingSetup& setup)
 {
-    SetMockTime(setup.m_node.chainman->GetParams().GenesisBlock().Time());
+    GetFakeNodeClock().set(setup.m_node.chainman->GetParams().GenesisBlock().Time());
     setup.m_node.chainman.reset();
     setup.m_make_chainman();
     setup.LoadVerifyActivateChainstate();
@@ -83,7 +83,7 @@ FUZZ_TARGET(process_message, .init = initialize_process_message)
     connman.Reset();
     auto& chainman{static_cast<TestChainstateManager&>(*node.chainman)};
     const auto block_index_size{WITH_LOCK(chainman.GetMutex(), return chainman.BlockIndex().size())};
-    FakeNodeClock clock{1610000000s}; // any time to successfully reset ibd
+    GetFakeNodeClock().set(1610000000s); // any time to successfully reset ibd
     FakeSteadyClock steady_clock;
     chainman.ResetIbd();
     chainman.DisableNextWrite();
@@ -117,7 +117,7 @@ FUZZ_TARGET(process_message, .init = initialize_process_message)
     connman.AddTestNode(p2p_node);
     FillNode(fuzzed_data_provider, connman, p2p_node);
 
-    clock.set(ConsumeTime(fuzzed_data_provider));
+    GetFakeNodeClock().set(ConsumeTime(fuzzed_data_provider));
 
     CSerializedNetMsg net_msg;
     net_msg.m_type = random_message_type;

src/test/fuzz/process_messages.cpp

@@ -40,7 +40,7 @@ TestingSetup* g_setup;
 
 void ResetChainman(TestingSetup& setup)
 {
-    SetMockTime(setup.m_node.chainman->GetParams().GenesisBlock().Time());
+    GetFakeNodeClock().set(setup.m_node.chainman->GetParams().GenesisBlock().Time());
     setup.m_node.chainman.reset();
     setup.m_make_chainman();
     setup.LoadVerifyActivateChainstate();
@@ -72,7 +72,7 @@ FUZZ_TARGET(process_messages, .init = initialize_process_messages)
     connman.Reset();
     auto& chainman{static_cast<TestChainstateManager&>(*node.chainman)};
     const auto block_index_size{WITH_LOCK(chainman.GetMutex(), return chainman.BlockIndex().size())};
-    FakeNodeClock clock{1610000000s}; // any time to successfully reset ibd
+    GetFakeNodeClock().set(1610000000s); // any time to successfully reset ibd
     FakeSteadyClock steady_clock;
     chainman.ResetIbd();
     chainman.DisableNextWrite();
@@ -110,7 +110,7 @@ FUZZ_TARGET(process_messages, .init = initialize_process_messages)
     LIMITED_WHILE (fuzzed_data_provider.ConsumeBool(), 30) {
         const std::string random_message_type{fuzzed_data_provider.ConsumeBytesAsString(CMessageHeader::MESSAGE_TYPE_SIZE).c_str()};
 
-        clock.set(ConsumeTime(fuzzed_data_provider));
+        GetFakeNodeClock().set(ConsumeTime(fuzzed_data_provider));
 
         CSerializedNetMsg net_msg;
         net_msg.m_type = random_message_type;

src/test/fuzz/utxo_snapshot.cpp

@@ -73,7 +73,7 @@ void initialize_chain()
     const auto params{CreateChainParams(ArgsManager{}, ChainType::REGTEST)};
     static const auto chain{CreateBlockChain(2 * COINBASE_MATURITY, *params)};
     g_chain = &chain;
-    SetMockTime(chain.back()->Time());
+    GetFakeNodeClock().set(chain.back()->Time());
 
     // Make sure we can generate a valid snapshot.
     sanity_check_snapshot();
@@ -104,7 +104,7 @@ void utxo_snapshot_fuzz(FuzzBufferType buffer)
 {
     SeedRandomStateForTest(SeedRand::ZEROS);
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
-    FakeNodeClock clock{ConsumeTime(fuzzed_data_provider, /*min=*/1296688602)}; // regtest genesis block timestamp
+    GetFakeNodeClock().set(ConsumeTime(fuzzed_data_provider, /*min=*/1296688602)); // regtest genesis block timestamp
     auto& setup{*g_setup};
     bool dirty_chainman{false}; // Reuse the global chainman, but reset it when it is dirty
     auto& chainman{*setup.m_node.chainman};

src/test/util/time.h

@@ -76,4 +76,10 @@ public:
     void operator-=(std::chrono::seconds d) { set(m_t -= d); }
 };
 
+inline FakeNodeClock& GetFakeNodeClock()
+{
+    static FakeNodeClock g_fake_node_clock{0s};
+    return g_fake_node_clock;
+}
+
 #endif // BITCOIN_TEST_UTIL_TIME_H