Merge bitcoin/bitcoin#34779: BIP 323: reserve version bits 5-28 as extra nonce space

107d4178d9 versionbits: update VersionBitsCache doc comment to match current behaviour (Antoine Poinsot)
94e3ac0b21 doc: release notes and bips doc update for #34779 (Antoine Poinsot)
1d5240574a qa: test we don't warn for ignored unknown version bits deployments (Antoine Poinsot)
f802edf57c versionbits: Limit live activation params and activation warnings per BIP323 (Anthony Towns)

Pull request description:

  This implements https://github.com/bitcoin/bips/pull/2116, which repurposes 24 version bits as extra nonce space for miners rather than soft fork deployment coordination. 24 bits allows a miner to perform up to 72 PH before needing a fresh job from its controller. The current 16 bits in use by miners only allow up to 280 TH, which [apparently led some ASIC designers to start rolling the timestamp field](https://github.com/bitaxeorg/ESP-Miner/pull/1553#issuecomment-3937736319) on their beefier machines.

  Mailing list discussion available [here](https://gnusha.org/pi/bitcoindev/6fa0cb45-37d6-4b41-9ff8-03730fd96d6e@mattcorallo.com/). A previous shot at this is https://github.com/bitcoin/bitcoin/pull/13972 (with a smaller extranonce space).

  This change only affects the warning logic.

ACKs for top commit:
  ajtowns:
    ACK 107d4178d9
  achow101:
    ACK 107d4178d9
  sedited:
    Re-ACK 107d4178d9
  optout21:
    ACK 107d4178d9

Tree-SHA512: cfaf5d7de1e8c020a4d7f4b1096b6c3e0e3b41ea840a4652ebcdabc345c5c557161c8304f1d7d6de541a2bf1df3c855ad7b64e49dd8c8af3937876d134bb5aba

doc/bips.md

@@ -49,6 +49,7 @@ BIPs that are implemented by Bitcoin Core:
 * [`BIP 173`](https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki): Bech32 addresses for native Segregated Witness outputs are supported as of **v0.16.0** ([PR 11167](https://github.com/bitcoin/bitcoin/pull/11167)). Bech32 addresses are generated by default as of **v0.20.0** ([PR 16884](https://github.com/bitcoin/bitcoin/pull/16884)).
 * [`BIP 174`](https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki): RPCs to operate on Partially Signed Bitcoin Transactions (PSBT) are present as of **v0.17.0** ([PR 13557](https://github.com/bitcoin/bitcoin/pull/13557)).
 * [`BIP 176`](https://github.com/bitcoin/bips/blob/master/bip-0176.mediawiki): Bits Denomination [QT only] is supported as of **v0.16.0** ([PR 12035](https://github.com/bitcoin/bitcoin/pull/12035)).
+* [`BIP 323`](https://github.com/bitcoin/bips/blob/master/bip-0323.mediawiki): BIP 9 bits 5 to 28 (inclusive) are ignored for soft-fork signalling and unknown soft fork warnings as of **v32.0**.
 * [`BIP 324`](https://github.com/bitcoin/bips/blob/master/bip-0324.mediawiki): The v2 transport protocol specified by BIP324 and the associated `NODE_P2P_V2` service bit are supported as of **v26.0**, but off by default ([PR 28331](https://github.com/bitcoin/bitcoin/pull/28331)). On by default as of **v27.0** ([PR 29347](https://github.com/bitcoin/bitcoin/pull/29347)).
 * [`BIP 325`](https://github.com/bitcoin/bips/blob/master/bip-0325.mediawiki): Signet test network is supported as of **v0.21.0** ([PR 18267](https://github.com/bitcoin/bitcoin/pull/18267)).
 * [`BIP 327`](https://github.com/bitcoin/bips/blob/master/bip-0327.mediawiki): Key aggregation via `musig()` descriptors is supported as of **v30.0** ([PR 31244](https://github.com/bitcoin/bitcoin/pull/31244)). Signing is supported as of **v31.0** ([PR 29675](https://github.com/bitcoin/bitcoin/pull/29675))

doc/release-notes-34779.md

@@ -0,0 +1,5 @@
+Logging
+-------
+
+- BIP 9 bits 5 to 28 inclusive are now ignored for soft fork signaling, as per BIP 323. We won't
+  warn about unknown deployments when receiving blocks that set any of those bits in their version.

src/test/fuzz/versionbits.cpp

@@ -14,6 +14,7 @@
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
+#include <test/util/versionbits.h>
 
 #include <cstdint>
 #include <limits>
@@ -31,7 +32,7 @@ public:
     {
         assert(dep.period > 0);
         assert(dep.threshold <= dep.period);
-        assert(0 <= dep.bit && dep.bit < 32 && dep.bit < VERSIONBITS_NUM_BITS);
+        assert(0 <= dep.bit && dep.bit < 32 && dep.bit < VERSIONBITS_MAX_NUM_BITS);
         assert(0 <= dep.min_activation_height);
     }
 
@@ -126,7 +127,7 @@ FUZZ_TARGET(versionbits, .init = initialize)
         assert(0 < dep.threshold && dep.threshold <= dep.period); // must be able to both pass and fail threshold!
 
         // select deployment parameters: bit, start time, timeout
-        dep.bit = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, VERSIONBITS_NUM_BITS - 1);
+        dep.bit = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, VERSIONBITS_MAX_NUM_BITS - 1);
 
         if (always_active_test) {
             dep.nStartTime = Consensus::BIP9Deployment::ALWAYS_ACTIVE;

src/test/util/versionbits.h

@@ -0,0 +1,13 @@
+// Copyright (c) 2026-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_TEST_UTIL_VERSIONBITS_H
+#define BITCOIN_TEST_UTIL_VERSIONBITS_H
+
+#include <versionbits.h>
+
+/** Total possible bits available for versionbits per original BIP 9 specification */
+static constexpr int VERSIONBITS_MAX_NUM_BITS{29};
+
+#endif // BITCOIN_TEST_UTIL_VERSIONBITS_H

src/test/versionbits_tests.cpp

@@ -8,6 +8,7 @@
 #include <test/util/random.h>
 #include <test/util/common.h>
 #include <test/util/setup_common.h>
+#include <test/util/versionbits.h>
 #include <util/chaintype.h>
 #include <versionbits.h>
 #include <versionbits_impl.h>
@@ -454,9 +455,19 @@ BOOST_FIXTURE_TEST_CASE(versionbits_computeblockversion, BlockVersionTest)
             // not take precedence over STARTED/LOCKED_IN. So all softforks on
             // the same bit might overlap, even when non-overlapping start-end
             // times are picked.
-            const uint32_t dep_mask{uint32_t{1} << chainParams->GetConsensus().vDeployments[dep].bit};
+            const auto& dep_info = chainParams->GetConsensus().vDeployments[dep];
+            const uint32_t dep_mask{uint32_t{1} << dep_info.bit};
             BOOST_CHECK(!(chain_all_vbits & dep_mask));
             chain_all_vbits |= dep_mask;
+            BOOST_CHECK(0 <= dep_info.bit && dep_info.bit < VERSIONBITS_MAX_NUM_BITS);
+            if (chain_type != ChainType::REGTEST) {
+                if (dep == Consensus::DEPLOYMENT_TESTDUMMY) {
+                    BOOST_CHECK_EQUAL(dep_info.nStartTime, Consensus::BIP9Deployment::NEVER_ACTIVE);
+                    BOOST_CHECK_EQUAL(dep_info.nTimeout, Consensus::BIP9Deployment::NO_TIMEOUT);
+                } else {
+                    BOOST_CHECK(dep_info.bit < VERSIONBITS_NUM_BITS);
+                }
+            }
             check_computeblockversion(vbcache, chainParams->GetConsensus(), dep);
         }
     }

src/versionbits.h

@@ -21,8 +21,8 @@ static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
 static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
 /** What bitmask determines whether versionbits is in use */
 static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
-/** Total bits available for versionbits */
-static const int32_t VERSIONBITS_NUM_BITS = 29;
+/** Total bits available for versionbits (BIP 323) */
+static const int32_t VERSIONBITS_NUM_BITS = 5;
 
 /** Opaque type for BIP9 state. See versionbits_impl.h for details. */
 enum class ThresholdState : uint8_t;
@@ -72,7 +72,8 @@ struct BIP9GBTStatus {
 };
 
 /** BIP 9 allows multiple softforks to be deployed in parallel. We cache
- *  per-period state for every one of them. */
+ *  per-period state for every one we implement and warning state for each
+ *  BIP 323 allowed bit. */
 class VersionBitsCache
 {
 private:

test/functional/feature_versionbits_warning.py

@@ -18,8 +18,13 @@ from test_framework.test_framework import BitcoinTestFramework
 VB_PERIOD = 144           # versionbits period length for regtest
 VB_THRESHOLD = 108        # versionbits activation threshold for regtest
 VB_TOP_BITS = 0x20000000
-VB_UNKNOWN_BIT = 27       # Choose a bit unassigned to any deployment
+
+# Choose a bit unassigned to any deployment, or start the
+# node with the deployment matching this bit disabled.
+VB_UNKNOWN_BIT = 3
 VB_UNKNOWN_VERSION = VB_TOP_BITS | (1 << VB_UNKNOWN_BIT)
+VB_IGNORED_BIT = 5
+VB_IGNORED_VERSION = VB_TOP_BITS | (1 << VB_IGNORED_BIT)
 
 WARN_UNKNOWN_RULES_ACTIVE = f"Unknown new rules activated (versionbit {VB_UNKNOWN_BIT})"
 VB_PATTERN = re.compile("Unknown new rules activated.*versionbit")
@@ -76,11 +81,24 @@ class VersionBitsWarningTest(BitcoinTestFramework):
         assert not VB_PATTERN.match(",".join(node.getmininginfo()["warnings"]))
         assert not VB_PATTERN.match(",".join(node.getnetworkinfo()["warnings"]))
 
+        self.log.info("Check that there is no warning if previous VB_BLOCKS have VB_PERIOD blocks with ignored versionbits version.")
+        # Build one period of blocks with VB_THRESHOLD blocks signaling some unknown bit
+        self.send_blocks_with_version(peer, VB_THRESHOLD, VB_IGNORED_VERSION)
+        self.generatetoaddress(node, VB_PERIOD - VB_THRESHOLD, node_deterministic_address)
+
+        # Move the ignored deployment state to ACTIVE and make sure we're out of IBD.
+        self.generatetoaddress(node, VB_PERIOD, node_deterministic_address)
+        self.wait_until(lambda: not node.getblockchaininfo()['initialblockdownload'])
+
+        # Check that we're not getting any versionbit-related warnings in get*info()
+        assert not VB_PATTERN.match(", ".join(node.getmininginfo()["warnings"]))
+        assert not VB_PATTERN.match(", ".join(node.getnetworkinfo()["warnings"]))
+
+        self.log.info("Check that there is a warning if previous VB_BLOCKS have >=VB_THRESHOLD blocks with unknown versionbits version.")
         # Build one period of blocks with VB_THRESHOLD blocks signaling some unknown bit
         self.send_blocks_with_version(peer, VB_THRESHOLD, VB_UNKNOWN_VERSION)
         self.generatetoaddress(node, VB_PERIOD - VB_THRESHOLD, node_deterministic_address)
 
-        self.log.info("Check that there is a warning if previous VB_BLOCKS have >=VB_THRESHOLD blocks with unknown versionbits version.")
         # Mine a period worth of expected blocks so the generic block-version warning
         # is cleared. This will move the versionbit state to ACTIVE.
         self.generatetoaddress(node, VB_PERIOD, node_deterministic_address)