Refactor EIP-7702: delegation resolution in EVM instead of host function

lib/evmone/CMakeLists.txt

@@ -17,6 +17,7 @@ add_library(evmone
     baseline_instruction_table.cpp
     baseline_instruction_table.hpp
     constants.hpp
+    delegation.hpp
     eof.cpp
     eof.hpp
     instructions.hpp

lib/evmone/delegation.hpp

@@ -0,0 +1,42 @@
+// evmone: Fast Ethereum Virtual Machine implementation
+// Copyright 2025 The evmone Authors.
+// SPDX-License-Identifier: Apache-2.0
+#pragma once
+
+#include <evmc/bytes.hpp>
+#include <evmc/evmc.hpp>
+#include <cassert>
+
+namespace evmone
+{
+using evmc::bytes_view;
+
+/// Prefix of code for delegated accounts
+/// defined by [EIP-7702](https://eips.ethereum.org/EIPS/eip-7702)
+constexpr uint8_t DELEGATION_MAGIC_BYTES[] = {0xef, 0x01, 0x00};
+constexpr bytes_view DELEGATION_MAGIC{DELEGATION_MAGIC_BYTES, std::size(DELEGATION_MAGIC_BYTES)};
+
+/// Check if code contains EIP-7702 delegation designator
+inline constexpr bool is_code_delegated(bytes_view code) noexcept
+{
+    return code.starts_with(DELEGATION_MAGIC);
+}
+
+/// Get EIP-7702 delegate address from the code of addr, if it is delegated.
+inline std::optional<evmc::address> get_delegate_address(
+    const evmc::address& addr, const evmc::HostInterface& host) noexcept
+{
+    uint8_t prefix[std::size(DELEGATION_MAGIC)] = {};
+    host.copy_code(addr, 0, prefix, std::size(prefix));
+
+    if (!is_code_delegated(bytes_view{prefix, std::size(prefix)}))
+        return {};
+
+    evmc::address delegate_address;
+    assert(host.get_code_size(addr) ==
+           std::size(DELEGATION_MAGIC) + std::size(delegate_address.bytes));
+    host.copy_code(
+        addr, std::size(prefix), delegate_address.bytes, std::size(delegate_address.bytes));
+    return delegate_address;
+}
+}  // namespace evmone

lib/evmone/instructions_calls.cpp

@@ -2,6 +2,7 @@
 // Copyright 2019 The evmone Authors.
 // SPDX-License-Identifier: Apache-2.0
 
+#include "delegation.hpp"
 #include "eof.hpp"
 #include "instructions.hpp"
 
@@ -28,19 +29,19 @@ inline std::variant<evmc::address, Result> get_target_address(
     if (state.rev < EVMC_PRAGUE)
         return addr;
 
-    const auto delegate_addr = state.host.get_delegate_address(addr);
-    if (delegate_addr == evmc::address{})
+    const auto delegate_addr = get_delegate_address(addr, state.host);
+    if (!delegate_addr)
         return addr;
 
     const auto delegate_account_access_cost =
-        (state.host.access_account(delegate_addr) == EVMC_ACCESS_COLD ?
+        (state.host.access_account(*delegate_addr) == EVMC_ACCESS_COLD ?
                 instr::cold_account_access_cost :
                 instr::warm_storage_read_cost);
 
     if ((gas_left -= delegate_account_access_cost) < 0)
         return Result{EVMC_OUT_OF_GAS, gas_left};
 
-    return delegate_addr;
+    return *delegate_addr;
 }
 }  // namespace
 

test/state/host.cpp

@@ -552,17 +552,4 @@ void Host::set_transient_storage(
     m_state.journal_transient_storage_change(addr, key, slot);
     slot = value;
 }
-
-address Host::get_delegate_address(const address& addr) const noexcept
-{
-    const auto raw_code = m_state.get_code(addr);
-
-    if (!is_code_delegated(raw_code))
-        return {};
-
-    address delegate;
-    assert(raw_code.size() == std::size(DELEGATION_MAGIC) + sizeof(delegate));
-    std::copy_n(&raw_code[std::size(DELEGATION_MAGIC)], sizeof(delegate), delegate.bytes);
-    return delegate;
-}
 }  // namespace evmone::state

test/state/host.hpp

@@ -92,8 +92,6 @@ class Host : public evmc::Host
 public:
     evmc_access_status access_account(const address& addr) noexcept override;
 
-    address get_delegate_address(const address& addr) const noexcept override;
-
 private:
     evmc_access_status access_storage(const address& addr, const bytes32& key) noexcept override;
 

test/state/state.cpp

@@ -7,6 +7,7 @@
 #include "host.hpp"
 #include "state_view.hpp"
 #include <evmone/constants.hpp>
+#include <evmone/delegation.hpp>
 #include <evmone/eof.hpp>
 #include <algorithm>
 
@@ -604,9 +605,9 @@ TransactionReceipt transition(const StateView& state_view, const BlockInfo& bloc
     auto message = build_message(tx, tx_props.execution_gas_limit, rev);
     if (tx.to.has_value())
     {
-        if (const auto delegate = host.get_delegate_address(*tx.to))
+        if (const auto delegate = get_delegate_address(*tx.to, host))
         {
-            message.code_address = delegate;
+            message.code_address = *delegate;
             message.flags |= EVMC_DELEGATED;
             host.access_account(message.code_address);
         }

test/state/state.hpp

@@ -150,15 +150,4 @@ TransactionReceipt transition(const StateView& state, const BlockInfo& block,
 [[nodiscard]] std::variant<TransactionProperties, std::error_code> validate_transaction(
     const StateView& state_view, const BlockInfo& block, const Transaction& tx, evmc_revision rev,
     int64_t block_gas_left, int64_t blob_gas_left) noexcept;
-
-/// Prefix of code for delegated accounts
-/// defined by [EIP-7702](https://eips.ethereum.org/EIPS/eip-7702)
-constexpr uint8_t DELEGATION_MAGIC_BYTES[] = {0xef, 0x01, 0x00};
-constexpr bytes_view DELEGATION_MAGIC{DELEGATION_MAGIC_BYTES, std::size(DELEGATION_MAGIC_BYTES)};
-
-/// Check if code contains EIP-7702 delegation designator
-constexpr bool is_code_delegated(bytes_view code) noexcept
-{
-    return code.starts_with(DELEGATION_MAGIC);
-}
 }  // namespace evmone::state