feat: replace DIFFICULTY with PREVRANDAO since merge (EIP-4399)

Author: vimpunk

benches/loop.rs

@@ -19,6 +19,7 @@ fn run_loop_contract() {
 		block_gas_limit: Default::default(),
 		chain_id: U256::one(),
 		block_base_fee_per_gas: U256::zero(),
+		block_randomness: None,
 	};
 
 	let mut state = BTreeMap::new();

core/src/error.rs

@@ -127,9 +127,6 @@ pub enum ExitError {
 	/// Create init code exceeds limit (runtime).
 	#[cfg_attr(feature = "with-codec", codec(index = 7))]
 	CreateContractLimit,
-	/// Invalid opcode during execution or starting byte is 0xef. See [EIP-3541](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-3541.md).
-	#[cfg_attr(feature = "with-codec", codec(index = 15))]
-	InvalidCode(Opcode),
 
 	/// An opcode accesses external information, but the request is off offset
 	/// limit (runtime).
@@ -154,6 +151,10 @@ pub enum ExitError {
 	/// Other normal errors.
 	#[cfg_attr(feature = "with-codec", codec(index = 13))]
 	Other(Cow<'static, str>),
+
+	/// Invalid opcode during execution or starting byte is 0xef. See [EIP-3541](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-3541.md).
+	#[cfg_attr(feature = "with-codec", codec(index = 15))]
+	InvalidCode(Opcode),
 }
 
 impl From<ExitError> for ExitReason {

runtime/src/eval/mod.rs

@@ -40,7 +40,13 @@ pub fn eval<H: Handler>(state: &mut Runtime, opcode: Opcode, handler: &mut H) ->
 		Opcode::COINBASE => system::coinbase(state, handler),
 		Opcode::TIMESTAMP => system::timestamp(state, handler),
 		Opcode::NUMBER => system::number(state, handler),
-		Opcode::DIFFICULTY => system::difficulty(state, handler),
+		Opcode::DIFFICULTY => {
+			if let Some(rand) = handler.block_randomness() {
+				system::prevrandao(state, &rand)
+			} else {
+				system::difficulty(state, handler)
+			}
+		}
 		Opcode::GASLIMIT => system::gaslimit(state, handler),
 		Opcode::SLOAD => system::sload(state, handler),
 		Opcode::SSTORE => system::sstore(state, handler),

runtime/src/eval/system.rs

@@ -185,6 +185,20 @@ pub fn difficulty<H: Handler>(runtime: &mut Runtime, handler: &H) -> Control<H>
 	Control::Continue
 }
 
+pub fn prevrandao<H: Handler>(runtime: &mut Runtime, randomness: &U256) -> Control<H> {
+	// Convert between U256 and H256. U256 is in little-endian but since H256 is just
+	// a string-like byte array, it's big endian (MSB is the first element of the array).
+	//
+	// Byte order here is important because this opcode has the same value as DIFFICULTY
+	// (0x44), and so for older forks of Ethereum, the threshold value of 2^64 is used to
+	// distinguish between the two: if it's below, the value corresponds to the DIFFICULTY
+	// opcode, otherwise to the PREVRANDAO opcode.
+	let mut buf = [0u8; 32];
+	randomness.to_big_endian(&mut buf);
+	push!(runtime, H256(buf));
+	Control::Continue
+}
+
 pub fn gaslimit<H: Handler>(runtime: &mut Runtime, handler: &H) -> Control<H> {
 	push_u256!(runtime, handler.block_gas_limit());
 	Control::Continue

runtime/src/handler.rs

@@ -54,6 +54,8 @@ pub trait Handler {
 	fn block_timestamp(&self) -> U256;
 	/// Get environmental block difficulty.
 	fn block_difficulty(&self) -> U256;
+	/// Get environmental block randomness.
+	fn block_randomness(&self) -> Option<U256>;
 	/// Get environmental gas limit.
 	fn block_gas_limit(&self) -> U256;
 	/// Environmental block base fee.

runtime/src/lib.rs

@@ -409,6 +409,11 @@ impl Config {
 		Self::config_with_derived_values(DerivedConfigInputs::london())
 	}
 
+	/// The Merge (Paris) hard fork configuration.
+	pub const fn merge() -> Config {
+		Self::config_with_derived_values(DerivedConfigInputs::merge())
+	}
+
 	/// Shanghai hard fork configuration.
 	pub const fn shanghai() -> Config {
 		Self::config_with_derived_values(DerivedConfigInputs::shanghai())
@@ -535,6 +540,20 @@ impl DerivedConfigInputs {
 		}
 	}
 
+	const fn merge() -> Self {
+		Self {
+			gas_storage_read_warm: 100,
+			gas_sload_cold: 2100,
+			gas_access_list_storage_key: 1900,
+			decrease_clears_refund: true,
+			has_base_fee: true,
+			has_push0: false,
+			disallow_executable_format: true,
+			warm_coinbase_address: false,
+			max_initcode_size: None,
+		}
+	}
+
 	const fn shanghai() -> Self {
 		Self {
 			gas_storage_read_warm: 100,

src/backend/memory.rs

@@ -31,6 +31,11 @@ pub struct MemoryVicinity {
 	pub block_gas_limit: U256,
 	/// Environmental base fee per gas.
 	pub block_base_fee_per_gas: U256,
+	/// Environmental randomness.
+	///
+	/// In Ethereum, this is the randomness beacon provided by the beacon
+	/// chain and is only enabled post Merge.
+	pub block_randomness: Option<U256>,
 }
 
 /// Account information of a memory backend.
@@ -110,6 +115,9 @@ impl<'vicinity> Backend for MemoryBackend<'vicinity> {
 	fn block_difficulty(&self) -> U256 {
 		self.vicinity.block_difficulty
 	}
+	fn block_randomness(&self) -> Option<U256> {
+		self.vicinity.block_randomness
+	}
 	fn block_gas_limit(&self) -> U256 {
 		self.vicinity.block_gas_limit
 	}

src/backend/mod.rs

@@ -66,6 +66,8 @@ pub trait Backend {
 	fn block_timestamp(&self) -> U256;
 	/// Environmental block difficulty.
 	fn block_difficulty(&self) -> U256;
+	/// Get environmental block randomness.
+	fn block_randomness(&self) -> Option<U256>;
 	/// Environmental block gas limit.
 	fn block_gas_limit(&self) -> U256;
 	/// Environmental block base fee.

src/executor/stack/executor.rs

@@ -304,7 +304,7 @@ impl<'config, 'precompiles, S: StackState<'config>, P: PrecompileSet>
 	/// Execute using Runtimes on the call_stack until it returns.
 	fn execute_with_call_stack(
 		&mut self,
-		call_stack: &mut Vec<TaggedRuntime>,
+		call_stack: &mut Vec<TaggedRuntime<'_>>,
 	) -> (ExitReason, Option<H160>, Vec<u8>) {
 		// This `interrupt_runtime` is used to pass the runtime obtained from the
 		// `Capture::Trap` branch in the match below back to the top of the call stack.
@@ -1108,6 +1108,9 @@ impl<'config, 'precompiles, S: StackState<'config>, P: PrecompileSet> Handler
 	fn block_difficulty(&self) -> U256 {
 		self.state.block_difficulty()
 	}
+	fn block_randomness(&self) -> Option<U256> {
+		self.state.block_randomness()
+	}
 	fn block_gas_limit(&self) -> U256 {
 		self.state.block_gas_limit()
 	}

src/executor/stack/memory.rs

@@ -421,6 +421,9 @@ impl<'backend, 'config, B: Backend> Backend for MemoryStackState<'backend, 'conf
 	fn block_difficulty(&self) -> U256 {
 		self.backend.block_difficulty()
 	}
+	fn block_randomness(&self) -> Option<U256> {
+		self.backend.block_randomness()
+	}
 	fn block_gas_limit(&self) -> U256 {
 		self.backend.block_gas_limit()
 	}