[pallet-revive] implement the gas price API (#6954)

This PR implements the EVM gas price syscall API method. Currently this
is a compile time constant in revive, but in the EVM it is an opcode.
Thus we should provide an opcode for this in the pallet.

---------

Signed-off-by: Cyrill Leutwiler <[email protected]>
Signed-off-by: xermicus <[email protected]>
Co-authored-by: command-bot <>

prdoc/pr_6954.prdoc

@@ -0,0 +1,13 @@
+title: '[pallet-revive] implement the gas price API'
+doc:
+- audience: Runtime Dev
+  description: This PR implements the EVM gas price syscall API method. Currently
+    this is a compile time constant in revive, but in the EVM it is an opcode. Thus
+    we should provide an opcode for this in the pallet.
+crates:
+- name: pallet-revive-fixtures
+  bump: minor
+- name: pallet-revive
+  bump: minor
+- name: pallet-revive-uapi
+  bump: minor

substrate/frame/revive/fixtures/contracts/gas_price.rs

@@ -0,0 +1,34 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Returns the gas price back to the caller.
+
+#![no_std]
+#![no_main]
+
+extern crate common;
+use uapi::{HostFn, HostFnImpl as api, ReturnFlags};
+
+#[no_mangle]
+#[polkavm_derive::polkavm_export]
+pub extern "C" fn deploy() {}
+
+#[no_mangle]
+#[polkavm_derive::polkavm_export]
+pub extern "C" fn call() {
+	api::return_value(ReturnFlags::empty(), &api::gas_price().to_le_bytes());
+}

substrate/frame/revive/src/benchmarking/mod.rs

@@ -23,6 +23,7 @@ mod call_builder;
 mod code;
 use self::{call_builder::CallSetup, code::WasmModule};
 use crate::{
+	evm::runtime::GAS_PRICE,
 	exec::{Key, MomentOf},
 	limits,
 	storage::WriteOutcome,
@@ -820,6 +821,17 @@ mod benchmarks {
 		assert_eq!(result.unwrap(), T::BlockWeights::get().max_block.ref_time());
 	}
 
+	#[benchmark(pov_mode = Measured)]
+	fn seal_gas_price() {
+		build_runtime!(runtime, memory: []);
+		let result;
+		#[block]
+		{
+			result = runtime.bench_gas_price(memory.as_mut_slice());
+		}
+		assert_eq!(result.unwrap(), u64::from(GAS_PRICE));
+	}
+
 	#[benchmark(pov_mode = Measured)]
 	fn seal_block_number() {
 		build_runtime!(runtime, memory: [[0u8;32], ]);

substrate/frame/revive/src/tests.rs

@@ -29,7 +29,7 @@ use crate::{
 		ChainExtension, Environment, Ext, RegisteredChainExtension, Result as ExtensionResult,
 		RetVal, ReturnFlags,
 	},
-	evm::GenericTransaction,
+	evm::{runtime::GAS_PRICE, GenericTransaction},
 	exec::Key,
 	limits,
 	primitives::CodeUploadReturnValue,
@@ -4364,6 +4364,24 @@ fn create1_with_value_works() {
 	});
 }
 
+#[test]
+fn gas_price_api_works() {
+	let (code, _) = compile_module("gas_price").unwrap();
+
+	ExtBuilder::default().existential_deposit(100).build().execute_with(|| {
+		let _ = <Test as Config>::Currency::set_balance(&ALICE, 1_000_000);
+
+		// Create fixture: Constructor does nothing
+		let Contract { addr, .. } =
+			builder::bare_instantiate(Code::Upload(code)).build_and_unwrap_contract();
+
+		// Call the contract: It echoes back the value returned by the gas price API.
+		let received = builder::bare_call(addr).build_and_unwrap_result();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(u64::from_le_bytes(received.data[..].try_into().unwrap()), u64::from(GAS_PRICE));
+	});
+}
+
 #[test]
 fn call_data_size_api_works() {
 	let (code, _) = compile_module("call_data_size").unwrap();

substrate/frame/revive/src/wasm/runtime.rs

@@ -19,6 +19,7 @@
 
 use crate::{
 	address::AddressMapper,
+	evm::runtime::GAS_PRICE,
 	exec::{ExecError, ExecResult, Ext, Key},
 	gas::{ChargedAmount, Token},
 	limits,
@@ -324,6 +325,8 @@ pub enum RuntimeCosts {
 	BlockNumber,
 	/// Weight of calling `seal_block_hash`.
 	BlockHash,
+	/// Weight of calling `seal_gas_price`.
+	GasPrice,
 	/// Weight of calling `seal_now`.
 	Now,
 	/// Weight of calling `seal_gas_limit`.
@@ -477,6 +480,7 @@ impl<T: Config> Token<T> for RuntimeCosts {
 			MinimumBalance => T::WeightInfo::seal_minimum_balance(),
 			BlockNumber => T::WeightInfo::seal_block_number(),
 			BlockHash => T::WeightInfo::seal_block_hash(),
+			GasPrice => T::WeightInfo::seal_gas_price(),
 			Now => T::WeightInfo::seal_now(),
 			GasLimit => T::WeightInfo::seal_gas_limit(),
 			WeightToFee => T::WeightInfo::seal_weight_to_fee(),
@@ -1563,6 +1567,14 @@ pub mod env {
 		)?)
 	}
 
+	/// Returns the simulated ethereum `GASPRICE` value.
+	/// See [`pallet_revive_uapi::HostFn::gas_price`].
+	#[stable]
+	fn gas_price(&mut self, memory: &mut M) -> Result<u64, TrapReason> {
+		self.charge_gas(RuntimeCosts::GasPrice)?;
+		Ok(GAS_PRICE.into())
+	}
+
 	/// Load the latest block timestamp into the supplied buffer
 	/// See [`pallet_revive_uapi::HostFn::now`].
 	#[stable]