[pallet-revive] implement the base fee API (#6964)

This PR implements the base fee syscall API method. Currently this is
implemented as a compile time constant in the revive compiler, returning
0. However, since this is an opocde, if we ever need to implement it for
compatibility reasons with
[EIP-1559](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1559.md),
it would break already deployed contracts. Thus we provide a syscall
method instead.

---------

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

prdoc/pr_6964.prdoc

@@ -0,0 +1,15 @@
+title: '[pallet-revive] implement the base fee API'
+doc:
+- audience: Runtime Dev
+  description: This PR implements the base fee syscall API method. Currently this
+    is implemented as a compile time constant in the revive compiler, returning 0.
+    However, since this is an opocde, if we ever need to implement it for compatibility
+    reasons with [EIP-1559](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1559.md),
+    it would break already deployed contracts. Thus we provide a syscall method instead.
+crates:
+- name: pallet-revive-fixtures
+  bump: minor
+- name: pallet-revive
+  bump: minor
+- name: pallet-revive-uapi
+  bump: minor

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

@@ -0,0 +1,36 @@
+// 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 base fee 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() {
+	let mut buf = [0; 32];
+	api::base_fee(&mut buf);
+	api::return_value(ReturnFlags::empty(), &buf);
+}

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

@@ -832,6 +832,18 @@ mod benchmarks {
 		assert_eq!(result.unwrap(), u64::from(GAS_PRICE));
 	}
 
+	#[benchmark(pov_mode = Measured)]
+	fn seal_base_fee() {
+		build_runtime!(runtime, memory: [[1u8;32], ]);
+		let result;
+		#[block]
+		{
+			result = runtime.bench_base_fee(memory.as_mut_slice(), 0);
+		}
+		assert_ok!(result);
+		assert_eq!(U256::from_little_endian(&memory[..]), U256::zero());
+	}
+
 	#[benchmark(pov_mode = Measured)]
 	fn seal_block_number() {
 		build_runtime!(runtime, memory: [[0u8;32], ]);

substrate/frame/revive/src/tests.rs

@@ -4382,6 +4382,24 @@ fn gas_price_api_works() {
 	});
 }
 
+#[test]
+fn base_fee_api_works() {
+	let (code, _) = compile_module("base_fee").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 base fee API.
+		let received = builder::bare_call(addr).build_and_unwrap_result();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(U256::from_little_endian(received.data[..].try_into().unwrap()), U256::zero());
+	});
+}
+
 #[test]
 fn call_data_size_api_works() {
 	let (code, _) = compile_module("call_data_size").unwrap();

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

@@ -327,6 +327,8 @@ pub enum RuntimeCosts {
 	BlockHash,
 	/// Weight of calling `seal_gas_price`.
 	GasPrice,
+	/// Weight of calling `seal_base_fee`.
+	BaseFee,
 	/// Weight of calling `seal_now`.
 	Now,
 	/// Weight of calling `seal_gas_limit`.
@@ -481,6 +483,7 @@ impl<T: Config> Token<T> for RuntimeCosts {
 			BlockNumber => T::WeightInfo::seal_block_number(),
 			BlockHash => T::WeightInfo::seal_block_hash(),
 			GasPrice => T::WeightInfo::seal_gas_price(),
+			BaseFee => T::WeightInfo::seal_base_fee(),
 			Now => T::WeightInfo::seal_now(),
 			GasLimit => T::WeightInfo::seal_gas_limit(),
 			WeightToFee => T::WeightInfo::seal_weight_to_fee(),
@@ -1575,6 +1578,20 @@ pub mod env {
 		Ok(GAS_PRICE.into())
 	}
 
+	/// Returns the simulated ethereum `BASEFEE` value.
+	/// See [`pallet_revive_uapi::HostFn::base_fee`].
+	#[stable]
+	fn base_fee(&mut self, memory: &mut M, out_ptr: u32) -> Result<(), TrapReason> {
+		self.charge_gas(RuntimeCosts::BaseFee)?;
+		Ok(self.write_fixed_sandbox_output(
+			memory,
+			out_ptr,
+			&U256::zero().to_little_endian(),
+			false,
+			already_charged,
+		)?)
+	}
+
 	/// Load the latest block timestamp into the supplied buffer
 	/// See [`pallet_revive_uapi::HostFn::now`].
 	#[stable]