fuzz: Add and use NodeClockContext #34479

maflcko commented at 12:36 PM on February 2, 2026: member

Iterating over fuzz inputs will usually be done in the same process. As the mocktime is global, it can theoretically leak from one fuzz input run into the next run, making it less deterministic.

Fix this issue, by adding and using a context manager to handle the mocktime and reset it before the end.

This refactor should not change any behavior.

DrahtBot renamed this:
~~fuzz: Add and use NodeClockContext~~
fuzz: Add and use NodeClockContext
on Feb 2, 2026

DrahtBot added the label Fuzzing on Feb 2, 2026

DrahtBot commented at 12:36 PM on February 2, 2026: contributor

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Reviews

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Type	Reviewers
ACK	seduless, dergoegge, brunoerg

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Conflicts

Reviewers, this pull request conflicts with the following ones:

#33421 (node: add BlockTemplateCache by ismaelsadeeq)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

brunoerg commented at 11:52 PM on February 3, 2026: contributor

Wouldn't it need to change the warning (replacing SetMockTime to NodeClockContext) in CheckGlobalsImpl for when the target accesses system time?

maflcko force-pushed on Feb 9, 2026

seduless commented at 12:32 AM on March 8, 2026: contributor

Approach ACK 666643be8fcdbf587f8fd18edea064ee3c547936

grep -rn 'SetMockTime' src/test/fuzz/ src/wallet/test/fuzz/ shows several remaining calls. Of those, these two follow the same ConsumeTime pattern and could be included:

src/test/fuzz/block_index_tree.cpp:44
src/wallet/test/fuzz/fees.cpp:65

Built with libfuzzer, verified both targets pass with this diff applied:

bitcoin pr-34479 !❄ ❯ git diff -U1
diff --git a/src/test/fuzz/block_index_tree.cpp b/src/test/fuzz/block_index_tree.cpp
index a4bbe95840..bff8eafa92 100644
--- a/src/test/fuzz/block_index_tree.cpp
+++ b/src/test/fuzz/block_index_tree.cpp
@@ -14,2 +14,3 @@
 #include <test/util/setup_common.h>
+#include <test/util/time.h>
 #include <test/util/validation.h>
@@ -43,3 +44,3 @@ FUZZ_TARGET(block_index_tree, .init = initialize_block_index_tree)
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
-    SetMockTime(ConsumeTime(fuzzed_data_provider));
+    NodeClockContext clock_ctx{ConsumeTime(fuzzed_data_provider)};
     auto& chainman = static_cast<TestChainstateManager&>(*g_setup->m_node.chainman);
diff --git a/src/wallet/test/fuzz/fees.cpp b/src/wallet/test/fuzz/fees.cpp
index 6d9de0cc0f..03a5e2abc9 100644
--- a/src/wallet/test/fuzz/fees.cpp
+++ b/src/wallet/test/fuzz/fees.cpp
@@ -8,2 +8,3 @@
 #include <test/util/setup_common.h>
+#include <test/util/time.h>
 #include <test/util/txmempool.h>
@@ -64,3 +65,3 @@ FUZZ_TARGET(wallet_fees, .init = initialize_setup)
     FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
-    SetMockTime(ConsumeTime(fuzzed_data_provider));
+    NodeClockContext clock_ctx{ConsumeTime(fuzzed_data_provider)};
     auto& node{g_setup->m_node};

test: Add NodeClockContext

This makes it easier to use mock-time in tests. Also, it resets the
global mocktime, so that no state is leaked between test cases.

fa4fae6227

fuzz: Use NodeClockContext

This refactor does not change any behavior.

However, it is nice to know that no global mocktime leaks from the fuzz
init step to the first fuzz input, or from one fuzz input execution to
the next.
With the clock context, the global is re-set at the end of the context.

eeeeb2a0b9

maflcko force-pushed on Mar 10, 2026

maflcko commented at 10:06 AM on March 10, 2026: member

Thx, I pushed your diff and rebased. Should be easy to re-review via git range-diff bitcoin-core/master 666643be8f fa1f69d02d

in src/util/time.h:36 in fa1f69d02d

  31 | @@ -31,10 +32,9 @@ using SteadyMicroseconds = std::chrono::time_point<std::chrono::steady_clock, st
  32 |  
  33 |  using SystemClock = std::chrono::system_clock;
  34 |  
  35 | -/**
  36 | - * Version of SteadyClock that is mockable in the context of tests (set the
  37 | - * current value with SetMockTime), otherwise the system steady clock.
  38 | - */
  39 | +/// Version of SteadyClock that is mockable in the context of tests (via
  40 | +/// SteadyClockContext, or self.SetMockTime), otherwise the system steady

seduless commented at 6:44 PM on March 11, 2026:

nit: The LLM linter caught self.SetMockTime in the doc comment, however the suggested fix seems off since it shouldn't use the global ::SetMockTime. Not blocking, but if you need another push you can update to MockableSteadyClock::SetMockTime.

maflcko commented at 5:14 PM on March 12, 2026:

I didn't want to repeat the class name, but I see it is static, so self. makes less sense than Self::, so I switched to that for now.

seduless commented at 6:50 PM on March 11, 2026: contributor

ACK fa1f69d02d80aedabc94a4de33091deb511440a0

Verified via git range-diff bitcoin-core/master 666643be8f fa1f69d02d that the only changes from the prior version are the two additional targets (block_index_tree.cpp, fees.cpp) and rebase context
Re: #34479#pullrequestreview-3748248600, CheckGlobalsImpl is handled and the warning message now references NodeClockContext and SteadyClockContext
Built with libfuzzer, verified all impacted fuzz targets pass

test: Fixup docs for NodeClockContext and SteadyClockContext faea12ecd9

maflcko force-pushed on Mar 12, 2026

seduless commented at 11:25 PM on March 13, 2026: contributor

re-ACK faea12ecd9fe026876a3278782a9320934214905

dergoegge approved

dergoegge commented at 2:11 PM on March 18, 2026: member

utACK faea12ecd9fe026876a3278782a9320934214905

brunoerg approved

brunoerg commented at 2:16 PM on March 18, 2026: contributor

code review ACK faea12ecd9fe026876a3278782a9320934214905

sedited merged this on Mar 18, 2026

sedited closed this on Mar 18, 2026