Remove redundant gas checks in precompiles (paritytech#745)

* remove redundant gas checks * fmt * fix borrowing issue
boolnetwork · Jul 4, 2022 · da3f879 · da3f879
1 parent c52d5e8
commit da3f879
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Showing 3 changed files with 19 additions and 40 deletions.
diff --git a/frame/evm/precompile/blake2/src/lib.rs b/frame/evm/precompile/blake2/src/lib.rs
@@ -39,7 +39,6 @@ impl Precompile for Blake2F {
 		const BLAKE2_F_ARG_LEN: usize = 213;
 
 		let input = handle.input();
-		let target_gas = handle.gas_limit();
 
 		if input.len() != BLAKE2_F_ARG_LEN {
 			return Err(PrecompileFailure::Error {
@@ -54,15 +53,8 @@ impl Precompile for Blake2F {
 		let rounds: u32 = u32::from_be_bytes(rounds_buf);
 
 		let gas_cost: u64 = (rounds as u64) * Blake2F::GAS_COST_PER_ROUND;
-		if let Some(gas_left) = target_gas {
-			if gas_left < gas_cost {
-				return Err(PrecompileFailure::Error {
-					exit_status: ExitError::OutOfGas,
-				});
-			}
-		}
-
 		handle.record_cost(gas_cost)?;
+
 		let input = handle.input();
 
 		// we use from_le_bytes below to effectively swap byte order to LE if architecture is BE

diff --git a/frame/evm/precompile/bn128/src/lib.rs b/frame/evm/precompile/bn128/src/lib.rs
@@ -169,24 +169,19 @@ impl Precompile for Bn128Pairing {
 	fn execute(handle: &mut impl PrecompileHandle) -> PrecompileResult {
 		use bn::{pairing_batch, AffineG1, AffineG2, Fq, Fq2, Group, Gt, G1, G2};
 
-		let input = handle.input();
-		let target_gas = handle.gas_limit();
-
-		let (ret_val, gas_cost) = if input.is_empty() {
-			(U256::one(), Bn128Pairing::BASE_GAS_COST)
+		let ret_val = if handle.input().is_empty() {
+			handle.record_cost(Bn128Pairing::BASE_GAS_COST)?;
+			U256::one()
 		} else {
 			// (a, b_a, b_b - each 64-byte affine coordinates)
-			let elements = input.len() / 192;
+			let elements = handle.input().len() / 192;
 
 			let gas_cost: u64 = Bn128Pairing::BASE_GAS_COST
 				+ (elements as u64 * Bn128Pairing::GAS_COST_PER_PAIRING);
-			if let Some(gas_left) = target_gas {
-				if gas_left < gas_cost {
-					return Err(PrecompileFailure::Error {
-						exit_status: ExitError::OutOfGas,
-					});
-				}
-			}
+
+			handle.record_cost(gas_cost)?;
+
+			let input = handle.input();
 
 			let mut vals = Vec::new();
 			for idx in 0..elements {
@@ -268,14 +263,12 @@ impl Precompile for Bn128Pairing {
 			let mul = pairing_batch(&vals);
 
 			if mul == Gt::one() {
-				(U256::one(), gas_cost)
+				U256::one()
 			} else {
-				(U256::zero(), gas_cost)
+				U256::zero()
 			}
 		};
 
-		handle.record_cost(gas_cost)?;
-
 		let mut buf = [0u8; 32];
 		ret_val.to_big_endian(&mut buf);
 

diff --git a/frame/evm/precompile/modexp/src/lib.rs b/frame/evm/precompile/modexp/src/lib.rs
@@ -111,7 +111,6 @@ fn calculate_gas_cost(
 impl Precompile for Modexp {
 	fn execute(handle: &mut impl PrecompileHandle) -> PrecompileResult {
 		let input = handle.input();
-		let target_gas = handle.gas_limit();
 
 		if input.len() < 96 {
 			return Err(PrecompileFailure::Error {
@@ -161,8 +160,9 @@ impl Precompile for Modexp {
 		}
 
 		// Gas formula allows arbitrary large exp_len when base and modulus are empty, so we need to handle empty base first.
-		let (r, gas_cost) = if base_len == 0 && mod_len == 0 {
-			(BigUint::zero(), MIN_GAS_COST)
+		let r = if base_len == 0 && mod_len == 0 {
+			handle.record_cost(MIN_GAS_COST)?;
+			BigUint::zero()
 		} else {
 			// read the numbers themselves.
 			let base_start = 96; // previous 3 32-byte fields
@@ -174,26 +174,20 @@ impl Precompile for Modexp {
 			// do our gas accounting
 			let gas_cost =
 				calculate_gas_cost(base_len as u64, exp_len as u64, mod_len as u64, &exponent);
-			if let Some(gas_left) = target_gas {
-				if gas_left < gas_cost {
-					return Err(PrecompileFailure::Error {
-						exit_status: ExitError::OutOfGas,
-					});
-				}
-			};
+
+			handle.record_cost(gas_cost)?;
+			let input = handle.input();
 
 			let mod_start = exp_start + exp_len;
 			let modulus = BigUint::from_bytes_be(&input[mod_start..mod_start + mod_len]);
 
 			if modulus.is_zero() || modulus.is_one() {
-				(BigUint::zero(), gas_cost)
+				BigUint::zero()
 			} else {
-				(base.modpow(&exponent, &modulus), gas_cost)
+				base.modpow(&exponent, &modulus)
 			}
 		};
 
-		handle.record_cost(gas_cost)?;
-
 		// write output to given memory, left padded and same length as the modulus.
 		let bytes = r.to_bytes_be();