host: Make EOF opaque for EXTCODE* instructions

test/state/host.cpp

@@ -77,24 +77,35 @@ uint256be Host::get_balance(const address& addr) const noexcept
     return (acc != nullptr) ? intx::be::store<uint256be>(acc->balance) : uint256be{};
 }
 
+namespace
+{
+/// For EXTCODE* instructions if the target is an EOF account, then only return EF00.
+/// While we only do this if the caller is legacy, it is not a problem doing this
+/// unconditionally, because EOF contracts dot no have EXTCODE* instructions.
+bytes_view extcode(bytes_view code) noexcept
+{
+    return is_eof_container(code) ? code.substr(0, 2) : code;
+}
+}  // namespace
+
 size_t Host::get_code_size(const address& addr) const noexcept
 {
     const auto* const acc = m_state.find(addr);
-    return (acc != nullptr) ? acc->code.size() : 0;
+    return (acc != nullptr) ? extcode(acc->code).size() : 0;
 }
 
 bytes32 Host::get_code_hash(const address& addr) const noexcept
 {
     // TODO: Cache code hash. It will be needed also to compute the MPT hash.
     const auto* const acc = m_state.find(addr);
-    return (acc != nullptr && !acc->is_empty()) ? keccak256(acc->code) : bytes32{};
+    return (acc != nullptr && !acc->is_empty()) ? keccak256(extcode(acc->code)) : bytes32{};
 }
 
 size_t Host::copy_code(const address& addr, size_t code_offset, uint8_t* buffer_data,
     size_t buffer_size) const noexcept
 {
     const auto* const acc = m_state.find(addr);
-    const auto code = (acc != nullptr) ? bytes_view{acc->code} : bytes_view{};
+    const auto code = (acc != nullptr) ? extcode(acc->code) : bytes_view{};
     const auto code_slice = code.substr(std::min(code_offset, code.size()));
     const auto num_bytes = std::min(buffer_size, code_slice.size());
     std::copy_n(code_slice.begin(), num_bytes, buffer_data);