Feat(xcc): Estimate EVM gas cost for xcc precompile (#564)

engine-precompiles/src/xcc.rs

@@ -19,8 +19,27 @@ use evm_core::ExitError;
 pub mod costs {
     use crate::prelude::types::{EthGas, NearGas};
 
-    // TODO(#483): Determine the correct amount of gas
-    pub(super) const CROSS_CONTRACT_CALL: EthGas = EthGas::new(0);
+    /// Base EVM gas cost for calling this precompile.
+    /// Value obtained from the following methodology:
+    /// 1. Estimate the cost of calling this precompile in terms of NEAR gas.
+    ///    This is done by calling the precompile with inputs of different lengths
+    ///    and performing a linear regression to obtain a function
+    ///    `NEAR_gas = CROSS_CONTRACT_CALL_BASE + (input_length) * (CROSS_CONTRACT_CALL_BYTE)`.
+    /// 2. Convert the NEAR gas cost into an EVM gas cost using the conversion ratio below
+    ///    (`CROSS_CONTRACT_CALL_NEAR_GAS`).
+    ///
+    /// This process is done in the `test_xcc_eth_gas_cost` test in
+    /// `engine-tests/src/tests/xcc.rs`.
+    pub const CROSS_CONTRACT_CALL_BASE: EthGas = EthGas::new(115_000);
+    /// Additional EVM gas cost per bytes of input given.
+    /// See `CROSS_CONTRACT_CALL_BASE` for estimation methodology.
+    pub const CROSS_CONTRACT_CALL_BYTE: EthGas = EthGas::new(2);
+    /// EVM gas cost per NEAR gas attached to the created promise.
+    /// This value is derived from the gas report https://hackmd.io/@birchmd/Sy4piXQ29
+    /// The units on this quantity are `NEAR Gas / EVM Gas`.
+    /// The report gives a value `0.175 T(NEAR_gas) / k(EVM_gas)`. To convert the units to
+    /// `NEAR Gas / EVM Gas`, we simply multiply `0.175 * 10^12 / 10^3 = 175 * 10^6`.
+    pub const CROSS_CONTRACT_CALL_NEAR_GAS: u64 = 175_000_000;
 
     pub const ROUTER_EXEC: NearGas = NearGas::new(7_000_000_000_000);
     pub const ROUTER_SCHEDULE: NearGas = NearGas::new(5_000_000_000_000);
@@ -61,8 +80,10 @@ pub mod cross_contract_call {
 }
 
 impl<I: IO> Precompile for CrossContractCall<I> {
-    fn required_gas(_input: &[u8]) -> Result<EthGas, ExitError> {
-        Ok(costs::CROSS_CONTRACT_CALL)
+    fn required_gas(input: &[u8]) -> Result<EthGas, ExitError> {
+        // This only includes the cost we can easily derive without parsing the input.
+        // The other cost is added in later to avoid parsing the input more than once.
+        Ok(costs::CROSS_CONTRACT_CALL_BASE + costs::CROSS_CONTRACT_CALL_BYTE * input.len())
     }
 
     fn run(
@@ -72,11 +93,16 @@ impl<I: IO> Precompile for CrossContractCall<I> {
         context: &Context,
         is_static: bool,
     ) -> EvmPrecompileResult {
-        if let Some(target_gas) = target_gas {
-            if Self::required_gas(input)? > target_gas {
-                return Err(ExitError::OutOfGas);
+        let mut cost = Self::required_gas(input)?;
+        let check_cost = |cost: EthGas| -> Result<(), ExitError> {
+            if let Some(target_gas) = target_gas {
+                if cost > target_gas {
+                    return Err(ExitError::OutOfGas);
+                }
             }
-        }
+            Ok(())
+        };
+        check_cost(cost)?;
 
         // It's not allowed to call cross contract call precompile in static or delegate mode
         if is_static {
@@ -114,6 +140,8 @@ impl<I: IO> Precompile for CrossContractCall<I> {
                 attached_gas: costs::ROUTER_SCHEDULE,
             },
         };
+        cost += EthGas::new(promise.attached_gas.as_u64() / costs::CROSS_CONTRACT_CALL_NEAR_GAS);
+        check_cost(cost)?;
 
         let promise_log = Log {
             address: cross_contract_call::ADDRESS.raw(),
@@ -125,6 +153,7 @@ impl<I: IO> Precompile for CrossContractCall<I> {
 
         Ok(PrecompileOutput {
             logs: vec![promise_log],
+            cost,
             ..Default::default()
         }
         .into())

engine-tests/src/tests/xcc.rs

@@ -3,14 +3,105 @@ use crate::tests::erc20_connector::sim_tests;
 use crate::tests::state_migration::deploy_evm;
 use aurora_engine_precompiles::xcc::{costs, cross_contract_call};
 use aurora_engine_transactions::legacy::TransactionLegacy;
-use aurora_engine_types::parameters::{CrossContractCallArgs, PromiseArgs, PromiseCreateArgs};
-use aurora_engine_types::types::{NearGas, Wei, Yocto};
+use aurora_engine_types::parameters::{
+    CrossContractCallArgs, PromiseArgs, PromiseCreateArgs, PromiseWithCallbackArgs,
+};
+use aurora_engine_types::types::{Address, EthGas, NearGas, Wei, Yocto};
+use aurora_engine_types::U256;
 use borsh::BorshSerialize;
 use near_primitives::transaction::Action;
 use near_primitives_core::contract::ContractCode;
 use std::fs;
 use std::path::Path;
 
+#[test]
+fn test_xcc_eth_gas_cost() {
+    let mut runner = test_utils::deploy_evm();
+    runner.standalone_runner = None;
+    let xcc_wasm_bytes = contract_bytes();
+    let _ = runner.call("factory_update", "aurora", xcc_wasm_bytes);
+    let mut signer = test_utils::Signer::random();
+    runner.context.block_index = aurora_engine::engine::ZERO_ADDRESS_FIX_HEIGHT + 1;
+
+    // Baseline transaction that does essentially nothing.
+    let (_, baseline) = runner
+        .submit_with_signer_profiled(&mut signer, |nonce| TransactionLegacy {
+            nonce,
+            gas_price: U256::zero(),
+            gas_limit: u64::MAX.into(),
+            to: Some(Address::from_array([0; 20])),
+            value: Wei::zero(),
+            data: Vec::new(),
+        })
+        .unwrap();
+
+    let mut profile_for_promise = |p: PromiseArgs| -> (u64, u64) {
+        let data = CrossContractCallArgs::Eager(p).try_to_vec().unwrap();
+        let input_length = data.len();
+        let (_, profile) = runner
+            .submit_with_signer_profiled(&mut signer, |nonce| TransactionLegacy {
+                nonce,
+                gas_price: U256::zero(),
+                gas_limit: u64::MAX.into(),
+                to: Some(cross_contract_call::ADDRESS),
+                value: Wei::zero(),
+                data,
+            })
+            .unwrap();
+        // Subtract off baseline transaction to isolate just precompile things
+        (
+            u64::try_from(input_length).unwrap(),
+            profile.all_gas() - baseline.all_gas(),
+        )
+    };
+
+    let promise = PromiseCreateArgs {
+        target_account_id: "some_account.near".parse().unwrap(),
+        method: "some_method".into(),
+        args: b"hello_world".to_vec(),
+        attached_balance: Yocto::new(56),
+        attached_gas: NearGas::new(0),
+    };
+    // Shorter input
+    let (x1, y1) = profile_for_promise(PromiseArgs::Create(promise.clone()));
+    // longer input
+    let (x2, y2) = profile_for_promise(PromiseArgs::Callback(PromiseWithCallbackArgs {
+        base: promise.clone(),
+        callback: promise,
+    }));
+
+    // NEAR costs (inferred from a line through (x1, y1) and (x2, y2))
+    let xcc_cost_per_byte = (y2 - y1) / (x2 - x1);
+    let xcc_base_cost = NearGas::new(y1 - xcc_cost_per_byte * x1);
+
+    // Convert to EVM cost using conversion ratio
+    let xcc_base_cost = EthGas::new(xcc_base_cost.as_u64() / costs::CROSS_CONTRACT_CALL_NEAR_GAS);
+    let xcc_cost_per_byte = xcc_cost_per_byte / costs::CROSS_CONTRACT_CALL_NEAR_GAS;
+
+    let within_5_percent = |a: u64, b: u64| -> bool {
+        let x = a.max(b);
+        let y = a.min(b);
+
+        20 * (x - y) <= x
+    };
+    assert!(
+        within_5_percent(
+            xcc_base_cost.as_u64(),
+            costs::CROSS_CONTRACT_CALL_BASE.as_u64()
+        ),
+        "Incorrect xcc base cost. Expected: {} Actual: {}",
+        xcc_base_cost,
+        costs::CROSS_CONTRACT_CALL_BASE
+    );
+
+    assert!(
+        within_5_percent(xcc_cost_per_byte, costs::CROSS_CONTRACT_CALL_BYTE.as_u64()),
+        "Incorrect xcc per byte cost. Expected: {} Actual: {}",
+        xcc_cost_per_byte,
+        costs::CROSS_CONTRACT_CALL_BYTE
+    );
+}
+
 #[test]
 fn test_xcc_precompile_eager() {
     test_xcc_precompile_common(false)

engine-types/src/lib.rs

@@ -25,8 +25,8 @@ mod v0 {
         vec::Vec,
     };
     pub use core::{
-        cmp::Ordering, fmt::Display, marker::PhantomData, mem, ops::Add, ops::Div, ops::Mul,
-        ops::Sub, ops::SubAssign,
+        cmp::Ordering, fmt::Display, marker::PhantomData, mem, ops::Add, ops::AddAssign, ops::Div,
+        ops::Mul, ops::Sub, ops::SubAssign,
     };
     pub use primitive_types::{H160, H256, U256};
 }

engine-types/src/types/gas.rs

@@ -1,5 +1,5 @@
 use crate::fmt::Formatter;
-use crate::{Add, Display, Div, Mul, Sub};
+use crate::{Add, AddAssign, Display, Div, Mul, Sub};
 use borsh::{BorshDeserialize, BorshSerialize};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
@@ -75,6 +75,12 @@ impl Add<EthGas> for EthGas {
     }
 }
 
+impl AddAssign<EthGas> for EthGas {
+    fn add_assign(&mut self, rhs: EthGas) {
+        self.0 += rhs.0
+    }
+}
+
 impl Div<u64> for EthGas {
     type Output = EthGas;