[pallet-revive] implement the call data load API (#6835)

This PR implements the call data load API akin to [how it works on
ethereum](https://www.evm.codes/?fork=cancun#35).

There will also be a second PR to adjust the input function to resemble
the call data copy opcode on EVM.

---------

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

prdoc/pr_6835.prdoc

@@ -0,0 +1,12 @@
+title: '[pallet-revive] implement the call data load API'
+doc:
+- audience: Runtime Dev
+  description: |-
+    This PR implements the call data load API akin to [how it works on ethereum](https://www.evm.codes/?fork=cancun#35).
+crates:
+- name: pallet-revive-fixtures
+  bump: minor
+- name: pallet-revive
+  bump: minor
+- name: pallet-revive-uapi
+  bump: minor

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

@@ -0,0 +1,44 @@
+// 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.
+
+//! This uses the call data load API to first the first input byte.
+//! This single input byte is used as the offset for a second call
+//! to the call data load API.
+//! The output of the second API call is returned.
+
+#![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::call_data_load(&mut buf, 0);
+
+	let offset = buf[31] as u32;
+	let mut buf = [0; 32];
+	api::call_data_load(&mut buf, offset);
+
+	api::return_value(ReturnFlags::empty(), &buf);
+}

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

@@ -838,6 +838,21 @@ mod benchmarks {
 		assert_eq!(U256::from_little_endian(&memory[..]), runtime.ext().get_weight_price(weight));
 	}
 
+	#[benchmark(pov_mode = Measured)]
+	fn seal_call_data_load() {
+		let mut setup = CallSetup::<T>::default();
+		let (mut ext, _) = setup.ext();
+		let mut runtime = crate::wasm::Runtime::new(&mut ext, vec![42u8; 32]);
+		let mut memory = memory!(vec![0u8; 32],);
+		let result;
+		#[block]
+		{
+			result = runtime.bench_call_data_load(memory.as_mut_slice(), 0, 0);
+		}
+		assert_ok!(result);
+		assert_eq!(&memory[..], &vec![42u8; 32]);
+	}
+
 	#[benchmark(pov_mode = Measured)]
 	fn seal_input(n: Linear<0, { limits::code::BLOB_BYTES - 4 }>) {
 		let mut setup = CallSetup::<T>::default();

substrate/frame/revive/src/tests.rs

@@ -4407,6 +4407,48 @@ fn chain_id_works() {
 	});
 }
 
+#[test]
+fn call_data_load_api_works() {
+	let (code, _) = compile_module("call_data_load").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 reads a byte for the offset and then returns
+		// what call data load returned using this byte as the offset.
+		let input = (3u8, U256::max_value(), U256::max_value()).encode();
+		let received = builder::bare_call(addr).data(input).build().result.unwrap();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(U256::from_little_endian(&received.data), U256::max_value());
+
+		// Edge case
+		let input = (2u8, U256::from(255).to_big_endian()).encode();
+		let received = builder::bare_call(addr).data(input).build().result.unwrap();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(U256::from_little_endian(&received.data), U256::from(65280));
+
+		// Edge case
+		let received = builder::bare_call(addr).data(vec![1]).build().result.unwrap();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(U256::from_little_endian(&received.data), U256::zero());
+
+		// OOB case
+		let input = (42u8).encode();
+		let received = builder::bare_call(addr).data(input).build().result.unwrap();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(U256::from_little_endian(&received.data), U256::zero());
+
+		// No calldata should return the zero value
+		let received = builder::bare_call(addr).build().result.unwrap();
+		assert_eq!(received.flags, ReturnFlags::empty());
+		assert_eq!(U256::from_little_endian(&received.data), U256::zero());
+	});
+}
+
 #[test]
 fn return_data_api_works() {
 	let (code_return_data_api, _) = compile_module("return_data_api").unwrap();

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

@@ -267,6 +267,8 @@ pub enum RuntimeCosts {
 	CopyFromContract(u32),
 	/// Weight charged for copying data to the sandbox.
 	CopyToContract(u32),
+	/// Weight of calling `seal_call_data_load``.
+	CallDataLoad,
 	/// Weight of calling `seal_caller`.
 	Caller,
 	/// Weight of calling `seal_origin`.
@@ -429,6 +431,7 @@ impl<T: Config> Token<T> for RuntimeCosts {
 			HostFn => cost_args!(noop_host_fn, 1),
 			CopyToContract(len) => T::WeightInfo::seal_input(len),
 			CopyFromContract(len) => T::WeightInfo::seal_return(len),
+			CallDataLoad => T::WeightInfo::seal_call_data_load(),
 			Caller => T::WeightInfo::seal_caller(),
 			Origin => T::WeightInfo::seal_origin(),
 			IsContract => T::WeightInfo::seal_is_contract(),
@@ -1319,6 +1322,37 @@ pub mod env {
 		}
 	}
 
+	/// Stores the U256 value at given call input `offset` into the supplied buffer.
+	/// See [`pallet_revive_uapi::HostFn::call_data_load`].
+	#[stable]
+	fn call_data_load(
+		&mut self,
+		memory: &mut M,
+		out_ptr: u32,
+		offset: u32,
+	) -> Result<(), TrapReason> {
+		self.charge_gas(RuntimeCosts::CallDataLoad)?;
+
+		let Some(input) = self.input_data.as_ref() else {
+			return Err(Error::<E::T>::InputForwarded.into());
+		};
+
+		let mut data = [0; 32];
+		let start = offset as usize;
+		let data = if start >= input.len() {
+			data // Any index is valid to request; OOB offsets return zero.
+		} else {
+			let end = start.saturating_add(32).min(input.len());
+			data[..end - start].copy_from_slice(&input[start..end]);
+			data.reverse();
+			data // Solidity expects right-padded data
+		};
+
+		self.write_fixed_sandbox_output(memory, out_ptr, &data, false, already_charged)?;
+
+		Ok(())
+	}
+
 	/// Cease contract execution and save a data buffer as a result of the execution.
 	/// See [`pallet_revive_uapi::HostFn::return_value`].
 	#[stable]