Implement EIP-4788: Beacon block root in the EVM (#709)

Implement the system call from the "Block processing" of the EIP-4788.
https://eips.ethereum.org/EIPS/eip-4788#block-processing

At the beginning of each block a gas-free call is invoked from
the _system_ account (`0xff..fe`) to the specific _system_ contract.

test/blockchaintest/blockchaintest.hpp

@@ -35,6 +35,7 @@ struct BlockHeader
     hash256 hash;
     hash256 transactions_root;
     hash256 withdrawal_root;
+    hash256 parent_beacon_block_root;
 };
 
 struct TestBlock

test/blockchaintest/blockchaintest_loader.cpp

@@ -40,6 +40,7 @@ BlockHeader from_json<BlockHeader>(const json::json& j)
         .hash = from_json<hash256>(j.at("hash")),
         .transactions_root = from_json<hash256>(j.at("transactionsTrie")),
         .withdrawal_root = load_if_exists<hash256>(j, "withdrawalsRoot"),
+        .parent_beacon_block_root = load_if_exists<hash256>(j, "parentBeaconBlockRoot"),
     };
 }
 
@@ -58,6 +59,7 @@ static TestBlock load_test_block(const json::json& j, evmc_revision rev)
         tb.block_info.difficulty = tb.expected_block_header.difficulty;
         tb.block_info.prev_randao = tb.expected_block_header.prev_randao;
         tb.block_info.base_fee = tb.expected_block_header.base_fee_per_gas;
+        tb.block_info.parent_beacon_block_root = tb.expected_block_header.parent_beacon_block_root;
 
         // Override prev_randao with difficulty pre-Merge
         if (rev < EVMC_PARIS)

test/blockchaintest/blockchaintest_runner.cpp

@@ -33,6 +33,8 @@ TransitionResult apply_block(state::State& state, evmc::VM& vm, const state::Blo
     const std::vector<state::Transaction>& txs, evmc_revision rev,
     std::optional<int64_t> block_reward)
 {
+    state::system_call(state, block, rev, vm);
+
     std::vector<state::Log> txs_logs;
     int64_t block_gas_left = block.gas_limit;
 

test/state/host.cpp

@@ -319,7 +319,8 @@ evmc::Result Host::call(const evmc_message& orig_msg) noexcept
 evmc_tx_context Host::get_tx_context() const noexcept
 {
     // TODO: The effective gas price is already computed in transaction validation.
-    assert(m_tx.max_gas_price >= m_block.base_fee);
+    // TODO: The effective gas price calculation is broken for system calls (gas price 0).
+    assert(m_tx.max_gas_price >= m_block.base_fee || m_tx.max_gas_price == 0);
     const auto priority_gas_price =
         std::min(m_tx.max_priority_gas_price, m_tx.max_gas_price - m_block.base_fee);
     const auto effective_gas_price = m_block.base_fee + priority_gas_price;

test/state/state.cpp

@@ -147,6 +147,41 @@ void delete_empty_accounts(State& state)
 }
 }  // namespace
 
+void system_call(State& state, const BlockInfo& block, evmc_revision rev, evmc::VM& vm)
+{
+    static constexpr auto SystemAddress = 0xfffffffffffffffffffffffffffffffffffffffe_address;
+    static constexpr auto BeaconRootsAddress = 0x000F3df6D732807Ef1319fB7B8bB8522d0Beac02_address;
+
+    if (rev >= EVMC_CANCUN)
+    {
+        if (const auto acc = state.find(BeaconRootsAddress); acc != nullptr)
+        {
+            const evmc_message msg{
+                .kind = EVMC_CALL,
+                .gas = 30'000'000,
+                .recipient = BeaconRootsAddress,
+                .sender = SystemAddress,
+                .input_data = block.parent_beacon_block_root.bytes,
+                .input_size = sizeof(block.parent_beacon_block_root),
+            };
+
+            const Transaction empty_tx{};
+            Host host{rev, vm, state, block, empty_tx};
+            const auto& code = acc->code;
+            [[maybe_unused]] const auto res = vm.execute(host, rev, msg, code.data(), code.size());
+            assert(res.status_code == EVMC_SUCCESS);
+            assert(acc->access_status == EVMC_ACCESS_COLD);
+
+            // Reset storage status.
+            for (auto& [_, val] : acc->storage)
+            {
+                val.access_status = EVMC_ACCESS_COLD;
+                val.original = val.current;
+            }
+        }
+    }
+}
+
 void finalize(State& state, evmc_revision rev, const address& coinbase,
     std::optional<uint64_t> block_reward, std::span<const Ommer> ommers,
     std::span<const Withdrawal> withdrawals)

test/state/state.hpp

@@ -97,6 +97,7 @@ struct BlockInfo
     int64_t parent_difficulty = 0;
     hash256 parent_ommers_hash;
     bytes32 prev_randao;
+    hash256 parent_beacon_block_root;
     uint64_t base_fee = 0;
     std::vector<Ommer> ommers;
     std::vector<Withdrawal> withdrawals;
@@ -190,6 +191,12 @@ std::variant<int64_t, std::error_code> validate_transaction(const Account& sende
     const BlockInfo& block, const Transaction& tx, evmc_revision rev,
     int64_t block_gas_left) noexcept;
 
+/// Performs the system call.
+///
+/// Executes code at pre-defined accounts from the system sender (0xff...fe).
+/// The sender's nonce is not increased.
+void system_call(State& state, const BlockInfo& block, evmc_revision rev, evmc::VM& vm);
+
 /// Defines how to RLP-encode a Transaction.
 [[nodiscard]] bytes rlp_encode(const Transaction& tx);
 

test/statetest/statetest_loader.cpp

@@ -231,6 +231,7 @@ state::BlockInfo from_json<state::BlockInfo>(const json::json& j)
         .parent_difficulty = parent_difficulty,
         .parent_ommers_hash = parent_uncle_hash,
         .prev_randao = prev_randao,
+        .parent_beacon_block_root = {},
         .base_fee = base_fee,
         .ommers = std::move(ommers),
         .withdrawals = std::move(withdrawals),

test/unittests/CMakeLists.txt

@@ -46,6 +46,7 @@ target_sources(
     state_new_account_address_test.cpp
     state_precompiles_test.cpp
     state_rlp_test.cpp
+    state_system_call_test.cpp
     state_transition.hpp
     state_transition.cpp
     state_transition_block_test.cpp

test/unittests/state_system_call_test.cpp

@@ -0,0 +1,40 @@
+// evmone: Fast Ethereum Virtual Machine implementation
+// Copyright 2023 The evmone Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+#include <evmone/evmone.h>
+#include <gtest/gtest.h>
+#include <test/state/state.hpp>
+#include <test/utils/bytecode.hpp>
+
+using namespace evmc;
+using namespace evmone::state;
+
+TEST(state_system_call, non_existient)
+{
+    evmc::VM vm;
+    State state;
+
+    system_call(state, {}, EVMC_CANCUN, vm);
+
+    EXPECT_EQ(state.get_accounts().size(), 0);
+}
+
+TEST(state_system_call, sstore_timestamp)
+{
+    static constexpr auto BeaconRootsAddress = 0x000F3df6D732807Ef1319fB7B8bB8522d0Beac02_address;
+
+    evmc::VM vm{evmc_create_evmone()};
+    const BlockInfo block{.number = 1, .timestamp = 404};
+    State state;
+    state.insert(BeaconRootsAddress, {.code = sstore(OP_NUMBER, OP_TIMESTAMP)});
+
+    system_call(state, block, EVMC_CANCUN, vm);
+
+    ASSERT_EQ(state.get_accounts().size(), 1);
+    EXPECT_EQ(state.get(BeaconRootsAddress).nonce, 0);
+    EXPECT_EQ(state.get(BeaconRootsAddress).balance, 0);
+    const auto& storage = state.get(BeaconRootsAddress).storage;
+    ASSERT_EQ(storage.size(), 1);
+    EXPECT_EQ(storage.at(0x01_bytes32).current, 404);
+}