Remove pass-by-reference return data value from executive (#9211)

* Remove pass-by-reference return data value from executive

* Fix tests

* Fix a missing test output

* typo: wasm_activation_test

* Tracing change in output

* json_tests: fix compile

* typo: 0..32 -> ..32 to keep it consistent with other occurance

* Fix tests

ethcore/evm/src/evm.rs

@@ -45,7 +45,7 @@ impl Finalize for Result<GasLeft> {
 	fn finalize<E: Ext>(self, ext: E) -> Result<FinalizationResult> {
 		match self {
 			Ok(GasLeft::Known(gas_left)) => Ok(FinalizationResult { gas_left: gas_left, apply_state: true, return_data: ReturnData::empty() }),
-			Ok(GasLeft::NeedsReturn {gas_left, data, apply_state}) => ext.ret(&gas_left, &data, apply_state).map(|gas_left| FinalizationResult {
+			Ok(GasLeft::NeedsReturn { gas_left, data, apply_state }) => ext.ret(&gas_left, &data, apply_state).map(|gas_left| FinalizationResult {
 				gas_left: gas_left,
 				apply_state: apply_state,
 				return_data: data,

ethcore/evm/src/interpreter/mod.rs

@@ -523,20 +523,25 @@ impl<Cost: CostType> Interpreter<Cost> {
 				}
 
 				let call_result = {
-					// we need to write and read from memory in the same time
+					let input = self.mem.read_slice(in_off, in_size);
-					// and we don't want to copy
+					ext.call(&call_gas.as_u256(), sender_address, receive_address, value, input, &code_address, call_type)
-					let input = unsafe { ::std::mem::transmute(self.mem.read_slice(in_off, in_size)) };
-					let output = self.mem.writeable_slice(out_off, out_size);
-					ext.call(&call_gas.as_u256(), sender_address, receive_address, value, input, &code_address, output, call_type)
 				};
 
+				let output = self.mem.writeable_slice(out_off, out_size);
+
 				return match call_result {
 					MessageCallResult::Success(gas_left, data) => {
+						let len = cmp::min(output.len(), data.len());
+						(&mut output[..len]).copy_from_slice(&data[..len]);
+
 						self.stack.push(U256::one());
 						self.return_data = data;
 						Ok(InstructionResult::UnusedGas(Cost::from_u256(gas_left).expect("Gas left cannot be greater than current one")))
 					},
 					MessageCallResult::Reverted(gas_left, data) => {
+						let len = cmp::min(output.len(), data.len());
+						(&mut output[..len]).copy_from_slice(&data[..len]);
+
 						self.stack.push(U256::zero());
 						self.return_data = data;
 						Ok(InstructionResult::UnusedGas(Cost::from_u256(gas_left).expect("Gas left cannot be greater than current one")))

ethcore/src/client/evm_test_client.rs

@@ -19,7 +19,7 @@
 use std::fmt;
 use std::sync::Arc;
 use ethereum_types::{H256, U256, H160};
-use {factory, journaldb, trie, kvdb_memorydb, bytes};
+use {factory, journaldb, trie, kvdb_memorydb};
 use kvdb::{self, KeyValueDB};
 use {state, state_db, client, executive, trace, transaction, db, spec, pod_state, log_entry, receipt};
 use factory::Factories;
@@ -183,14 +183,12 @@ impl<'a> EvmTestClient<'a> {
 			gas_limit: *genesis.gas_limit(),
 		};
 		let mut substate = state::Substate::new();
-		let mut output = vec![];
 		let machine = self.spec.engine.machine();
 		let schedule = machine.schedule(info.number);
 		let mut executive = executive::Executive::new(&mut self.state, &info, &machine, &schedule);
 		executive.call(
 			params,
 			&mut substate,
-			bytes::BytesRef::Flexible(&mut output),
 			tracer,
 			vm_tracer,
 		).map_err(EvmTestError::Evm)

ethcore/src/executive.rs

@@ -204,7 +204,7 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 		&'any mut self,
 		origin_info: OriginInfo,
 		substate: &'any mut Substate,
-		output: OutputPolicy<'any, 'any>,
+		output: OutputPolicy,
 		tracer: &'any mut T,
 		vm_tracer: &'any mut V,
 		static_call: bool,
@@ -312,8 +312,12 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 					call_type: CallType::None,
 					params_type: vm::ParamsType::Embedded,
 				};
-				let mut out = if output_from_create { Some(vec![]) } else { None };
+				let res = self.create(params, &mut substate, &mut tracer, &mut vm_tracer);
-				(self.create(params, &mut substate, &mut out, &mut tracer, &mut vm_tracer), out.unwrap_or_else(Vec::new))
+				let out = match &res {
+					Ok(res) if output_from_create => res.return_data.to_vec(),
+					_ => Vec::new(),
+				};
+				(res, out)
 			},
 			Action::Call(ref address) => {
 				let params = ActionParams {
@@ -330,8 +334,12 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 					call_type: CallType::Call,
 					params_type: vm::ParamsType::Separate,
 				};
-				let mut out = vec![];
+				let res = self.call(params, &mut substate, &mut tracer, &mut vm_tracer);
-				(self.call(params, &mut substate, BytesRef::Flexible(&mut out), &mut tracer, &mut vm_tracer), out)
+				let out = match &res {
+					Ok(res) => res.return_data.to_vec(),
+					_ => Vec::new(),
+				};
+				(res, out)
 			}
 		};
 
@@ -382,7 +390,6 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 		&mut self,
 		params: ActionParams,
 		substate: &mut Substate,
-		mut output: BytesRef,
 		tracer: &mut T,
 		vm_tracer: &mut V
 	) -> vm::Result<FinalizationResult> where T: Tracer, V: VMTracer {
@@ -432,7 +439,6 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 					Err(evm_err)
 				} else {
 					self.state.discard_checkpoint();
-					output.write(0, &builtin_out_buffer);
 
 					// Trace only top level calls and calls with balance transfer to builtins. The reason why we don't
 					// trace all internal calls to builtin contracts is that memcpy (IDENTITY) is a heavily used
@@ -444,7 +450,7 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 					if self.depth == 0 || is_transferred {
 						let mut trace_output = tracer.prepare_trace_output();
 						if let Some(out) = trace_output.as_mut() {
-							*out = output.to_owned();
+							*out = builtin_out_buffer.clone();
 						}
 
 						tracer.trace_call(
@@ -485,7 +491,7 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 				let mut subvmtracer = vm_tracer.prepare_subtrace(params.code.as_ref().expect("scope is conditional on params.code.is_some(); qed"));
 
 				let res = {
-					self.exec_vm(params, &mut unconfirmed_substate, OutputPolicy::Return(output, trace_output.as_mut()), &mut subtracer, &mut subvmtracer)
+					self.exec_vm(params, &mut unconfirmed_substate, OutputPolicy::Return, &mut subtracer, &mut subvmtracer)
 				};
 
 				vm_tracer.done_subtrace(subvmtracer);
@@ -494,12 +500,15 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 
 				let traces = subtracer.drain();
 				match res {
-					Ok(ref res) if res.apply_state => tracer.trace_call(
+					Ok(ref res) if res.apply_state => {
-						trace_info,
+						trace_output.as_mut().map(|d| *d = res.return_data.to_vec());
-						gas - res.gas_left,
+						tracer.trace_call(
-						trace_output,
+							trace_info,
-						traces
+							gas - res.gas_left,
-					),
+							trace_output,
+							traces
+						);
+					},
 					Ok(_) => tracer.trace_failed_call(trace_info, traces, vm::Error::Reverted.into()),
 					Err(ref e) => tracer.trace_failed_call(trace_info, traces, e.into()),
 				};
@@ -530,7 +539,6 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 		&mut self,
 		params: ActionParams,
 		substate: &mut Substate,
-		output: &mut Option<Bytes>,
 		tracer: &mut T,
 		vm_tracer: &mut V,
 	) -> vm::Result<FinalizationResult> where T: Tracer, V: VMTracer {
@@ -579,7 +587,7 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 		let res = self.exec_vm(
 			params,
 			&mut unconfirmed_substate,
-			OutputPolicy::InitContract(output.as_mut().or(trace_output.as_mut())),
+			OutputPolicy::InitContract,
 			&mut subtracer,
 			&mut subvmtracer
 		);
@@ -587,13 +595,16 @@ impl<'a, B: 'a + StateBackend> Executive<'a, B> {
 		vm_tracer.done_subtrace(subvmtracer);
 
 		match res {
-			Ok(ref res) if res.apply_state => tracer.trace_create(
+			Ok(ref res) if res.apply_state => {
-				trace_info,
+				trace_output.as_mut().map(|trace| *trace = res.return_data.to_vec());
-				gas - res.gas_left,
+				tracer.trace_create(
-				trace_output.map(|data| output.as_ref().map(|out| out.to_vec()).unwrap_or(data)),
+					trace_info,
-				created,
+					gas - res.gas_left,
-				subtracer.drain()
+					trace_output,
-			),
+					created,
+					subtracer.drain()
+				);
+			}
 			Ok(_) => tracer.trace_failed_create(trace_info, subtracer.drain(), vm::Error::Reverted.into()),
 			Err(ref e) => tracer.trace_failed_create(trace_info, subtracer.drain(), e.into())
 		};
@@ -715,7 +726,6 @@ mod tests {
 	use ethkey::{Generator, Random};
 	use super::*;
 	use ethereum_types::{H256, U256, U512, Address};
-	use bytes::BytesRef;
 	use vm::{ActionParams, ActionValue, CallType, EnvInfo, CreateContractAddress};
 	use evm::{Factory, VMType};
 	use error::ExecutionError;
@@ -766,7 +776,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.create(params, &mut substate, &mut None, &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(79_975));
@@ -824,7 +834,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.create(params, &mut substate, &mut None, &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(62_976));
@@ -868,8 +878,7 @@ mod tests {
 		let mut vm_tracer = ExecutiveVMTracer::toplevel();
 
 		let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-		let output = BytesRef::Fixed(&mut[0u8;0]);
+		ex.call(params, &mut substate, &mut tracer, &mut vm_tracer).unwrap();
-		ex.call(params, &mut substate, output, &mut tracer, &mut vm_tracer).unwrap();
 
 		assert_eq!(tracer.drain(), vec![FlatTrace {
 			action: trace::Action::Call(trace::Call {
@@ -896,7 +905,7 @@ mod tests {
 				call_type: CallType::Call
 			}), result: trace::Res::Call(trace::CallResult {
 				gas_used: 600.into(),
-				output: vec![]
+				output: vec![0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 156, 17, 133, 165, 197, 233, 252, 84, 97, 40, 8, 151, 126, 232, 245, 72, 178, 37, 141, 49]
 			}),
 			subtraces: 0,
 			trace_address: vec![0].into_iter().collect(),
@@ -954,8 +963,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			let output = BytesRef::Fixed(&mut[0u8;0]);
+			ex.call(params, &mut substate, &mut tracer, &mut vm_tracer).unwrap()
-			ex.call(params, &mut substate, output, &mut tracer, &mut vm_tracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(44_752));
@@ -1071,8 +1079,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			let output = BytesRef::Fixed(&mut[0u8;0]);
+			ex.call(params, &mut substate, &mut tracer, &mut vm_tracer).unwrap()
-			ex.call(params, &mut substate, output, &mut tracer, &mut vm_tracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(62967));
@@ -1144,7 +1151,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.create(params.clone(), &mut substate, &mut None, &mut tracer, &mut vm_tracer).unwrap()
+			ex.create(params.clone(), &mut substate, &mut tracer, &mut vm_tracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(96_776));
@@ -1230,7 +1237,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.create(params, &mut substate, &mut None, &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(62_976));
@@ -1282,7 +1289,7 @@ mod tests {
 
 		{
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.create(params, &mut substate, &mut None, &mut NoopTracer, &mut NoopVMTracer).unwrap();
+			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap();
 		}
 
 		assert_eq!(substate.contracts_created.len(), 1);
@@ -1343,7 +1350,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.call(params, &mut substate, BytesRef::Fixed(&mut []), &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.call(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(73_237));
@@ -1388,7 +1395,7 @@ mod tests {
 
 		let FinalizationResult { gas_left, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.call(params, &mut substate, BytesRef::Fixed(&mut []), &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.call(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
 
 		assert_eq!(gas_left, U256::from(59_870));
@@ -1562,7 +1569,7 @@ mod tests {
 
 		let result = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.create(params, &mut substate, &mut None, &mut NoopTracer, &mut NoopVMTracer)
+			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer)
 		};
 
 		match result {
@@ -1595,10 +1602,11 @@ mod tests {
 		let mut substate = Substate::new();
 
 		let mut output = [0u8; 14];
-		let FinalizationResult { gas_left: result, .. } = {
+		let FinalizationResult { gas_left: result, return_data, .. } = {
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.call(params, &mut substate, BytesRef::Fixed(&mut output), &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.call(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
+		(&mut output).copy_from_slice(&return_data[..(cmp::min(14, return_data.len()))]);
 
 		assert_eq!(result, U256::from(1));
 		assert_eq!(output[..], returns[..]);
@@ -1638,11 +1646,12 @@ mod tests {
 		let machine = ::ethereum::new_kovan_wasm_test_machine();
 
 		let mut output = [0u8; 20];
-		let FinalizationResult { gas_left: result, .. } = {
+		let FinalizationResult { gas_left: result, return_data, .. } = {
 			let schedule = machine.schedule(info.number);
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.call(params.clone(), &mut Substate::new(), BytesRef::Fixed(&mut output), &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.call(params.clone(), &mut Substate::new(), &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
+		(&mut output).copy_from_slice(&return_data[..(cmp::min(20, return_data.len()))]);
 
 		assert_eq!(result, U256::from(18433));
 		// Transaction successfully returned sender
@@ -1652,11 +1661,12 @@ mod tests {
 		info.number = 1;
 
 		let mut output = [0u8; 20];
-		let FinalizationResult { gas_left: result, .. } = {
+		let FinalizationResult { gas_left: result, return_data, .. } = {
 			let schedule = machine.schedule(info.number);
 			let mut ex = Executive::new(&mut state, &info, &machine, &schedule);
-			ex.call(params, &mut Substate::new(), BytesRef::Fixed(&mut output), &mut NoopTracer, &mut NoopVMTracer).unwrap()
+			ex.call(params, &mut Substate::new(), &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
+		(&mut output[..((cmp::min(20, return_data.len())))]).copy_from_slice(&return_data[..(cmp::min(20, return_data.len()))]);
 
 		assert_eq!(result, U256::from(20025));
 		// Since transaction errored due to wasm was not activated, result is just empty

ethcore/src/externalities.rs

@@ -18,7 +18,7 @@
 use std::cmp;
 use std::sync::Arc;
 use ethereum_types::{H256, U256, Address};
-use bytes::{Bytes, BytesRef};
+use bytes::Bytes;
 use state::{Backend as StateBackend, State, Substate, CleanupMode};
 use machine::EthereumMachine as Machine;
 use executive::*;
@@ -32,12 +32,12 @@ use transaction::UNSIGNED_SENDER;
 use trace::{Tracer, VMTracer};
 
 /// Policy for handling output data on `RETURN` opcode.
-pub enum OutputPolicy<'a, 'b> {
+pub enum OutputPolicy {
 	/// Return reference to fixed sized output.
 	/// Used for message calls.
-	Return(BytesRef<'a>, Option<&'b mut Bytes>),
+	Return,
 	/// Init new contract as soon as `RETURN` is called.
-	InitContract(Option<&'b mut Bytes>),
+	InitContract,
 }
 
 /// Transaction properties that externalities need to know about.
@@ -71,7 +71,7 @@ pub struct Externalities<'a, T: 'a, V: 'a, B: 'a> {
 	substate: &'a mut Substate,
 	machine: &'a Machine,
 	schedule: &'a Schedule,
-	output: OutputPolicy<'a, 'a>,
+	output: OutputPolicy,
 	tracer: &'a mut T,
 	vm_tracer: &'a mut V,
 	static_flag: bool,
@@ -89,7 +89,7 @@ impl<'a, T: 'a, V: 'a, B: 'a> Externalities<'a, T, V, B>
 		depth: usize,
 		origin_info: OriginInfo,
 		substate: &'a mut Substate,
-		output: OutputPolicy<'a, 'a>,
+		output: OutputPolicy,
 		tracer: &'a mut T,
 		vm_tracer: &'a mut V,
 		static_flag: bool,
@@ -171,9 +171,12 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 				params_type: vm::ParamsType::Separate,
 			};
 
-			let mut output = H256::new();
 			let mut ex = Executive::new(self.state, self.env_info, self.machine, self.schedule);
-			let r = ex.call(params, self.substate, BytesRef::Fixed(&mut output), self.tracer, self.vm_tracer);
+			let r = ex.call(params, self.substate, self.tracer, self.vm_tracer);
+			let output = match &r {
+				Ok(ref r) => H256::from(&r.return_data[..32]),
+				_ => H256::new(),
+			};
 			trace!("ext: blockhash contract({}) -> {:?}({}) self.env_info.number={}\n", number, r, output, self.env_info.number);
 			output
 		} else {
@@ -194,7 +197,13 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 		}
 	}
 
-	fn create(&mut self, gas: &U256, value: &U256, code: &[u8], address_scheme: CreateContractAddress) -> ContractCreateResult {
+	fn create(
+		&mut self,
+		gas: &U256,
+		value: &U256,
+		code: &[u8],
+		address_scheme: CreateContractAddress
+	) -> ContractCreateResult {
 		// create new contract address
 		let (address, code_hash) = match self.state.nonce(&self.origin_info.address) {
 			Ok(nonce) => contract_address(address_scheme, &self.origin_info.address, &nonce, &code),
@@ -231,7 +240,7 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 		let mut ex = Executive::from_parent(self.state, self.env_info, self.machine, self.schedule, self.depth, self.static_flag);
 
 		// TODO: handle internal error separately
-		match ex.create(params, self.substate, &mut None, self.tracer, self.vm_tracer) {
+		match ex.create(params, self.substate, self.tracer, self.vm_tracer) {
 			Ok(FinalizationResult{ gas_left, apply_state: true, .. }) => {
 				self.substate.contracts_created.push(address.clone());
 				ContractCreateResult::Created(address, gas_left)
@@ -243,14 +252,14 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 		}
 	}
 
-	fn call(&mut self,
+	fn call(
+		&mut self,
 		gas: &U256,
 		sender_address: &Address,
 		receive_address: &Address,
 		value: Option<U256>,
 		data: &[u8],
 		code_address: &Address,
-		output: &mut [u8],
 		call_type: CallType
 	) -> MessageCallResult {
 		trace!(target: "externalities", "call");
@@ -284,7 +293,7 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 
 		let mut ex = Executive::from_parent(self.state, self.env_info, self.machine, self.schedule, self.depth, self.static_flag);
 
-		match ex.call(params, self.substate, BytesRef::Fixed(output), self.tracer, self.vm_tracer) {
+		match ex.call(params, self.substate, self.tracer, self.vm_tracer) {
 			Ok(FinalizationResult{ gas_left, return_data, apply_state: true }) => MessageCallResult::Success(gas_left, return_data),
 			Ok(FinalizationResult{ gas_left, return_data, apply_state: false }) => MessageCallResult::Reverted(gas_left, return_data),
 			_ => MessageCallResult::Failed
@@ -303,27 +312,13 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 		Ok(self.state.code_size(address)?)
 	}
 
-	fn ret(mut self, gas: &U256, data: &ReturnData, apply_state: bool) -> vm::Result<U256>
+	fn ret(self, gas: &U256, data: &ReturnData, apply_state: bool) -> vm::Result<U256>
 		where Self: Sized {
-		let handle_copy = |to: &mut Option<&mut Bytes>| {
-			to.as_mut().map(|b| **b = data.to_vec());
-		};
 		match self.output {
-			OutputPolicy::Return(BytesRef::Fixed(ref mut slice), ref mut copy) => {
+			OutputPolicy::Return => {
-				handle_copy(copy);
-
-				let len = cmp::min(slice.len(), data.len());
-				(&mut slice[..len]).copy_from_slice(&data[..len]);
 				Ok(*gas)
 			},
-			OutputPolicy::Return(BytesRef::Flexible(ref mut vec), ref mut copy) => {
+			OutputPolicy::InitContract if apply_state => {
-				handle_copy(copy);
-
-				vec.clear();
-				vec.extend_from_slice(&*data);
-				Ok(*gas)
-			},
-			OutputPolicy::InitContract(ref mut copy) if apply_state => {
 				let return_cost = U256::from(data.len()) * U256::from(self.schedule.create_data_gas);
 				if return_cost > *gas || data.len() > self.schedule.create_data_limit {
 					return match self.schedule.exceptional_failed_code_deposit {
@@ -331,11 +326,10 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for Externalities<'a, T, V, B>
 						false => Ok(*gas)
 					}
 				}
-				handle_copy(copy);
 				self.state.init_code(&self.origin_info.address, data.to_vec())?;
 				Ok(*gas - return_cost)
 			},
-			OutputPolicy::InitContract(_) => {
+			OutputPolicy::InitContract => {
 				Ok(*gas)
 			},
 		}
@@ -479,7 +473,7 @@ mod tests {
 		let mut tracer = NoopTracer;
 		let mut vm_tracer = NoopVMTracer;
 
-		let ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+		let ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
 
 		assert_eq!(ext.env_info().number, 100);
 	}
@@ -491,7 +485,7 @@ mod tests {
 		let mut tracer = NoopTracer;
 		let mut vm_tracer = NoopVMTracer;
 
-		let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+		let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
 
 		let hash = ext.blockhash(&"0000000000000000000000000000000000000000000000000000000000120000".parse::<U256>().unwrap());
 
@@ -515,7 +509,7 @@ mod tests {
 		let mut tracer = NoopTracer;
 		let mut vm_tracer = NoopVMTracer;
 
-		let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+		let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
 
 		let hash = ext.blockhash(&"0000000000000000000000000000000000000000000000000000000000120000".parse::<U256>().unwrap());
 
@@ -530,9 +524,7 @@ mod tests {
 		let mut tracer = NoopTracer;
 		let mut vm_tracer = NoopVMTracer;
 
-		let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+		let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
-
-		let mut output = vec![];
 
 		// this should panic because we have no balance on any account
 		ext.call(
@@ -542,7 +534,6 @@ mod tests {
 			Some("0000000000000000000000000000000000000000000000000000000000150000".parse::<U256>().unwrap()),
 			&[],
 			&Address::new(),
-			&mut output,
 			CallType::Call
 		);
 	}
@@ -558,7 +549,7 @@ mod tests {
 		let mut vm_tracer = NoopVMTracer;
 
 		{
-			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
 			ext.log(log_topics, &log_data).unwrap();
 		}
 
@@ -575,7 +566,7 @@ mod tests {
 		let mut vm_tracer = NoopVMTracer;
 
 		{
-			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
 			ext.suicide(refund_account).unwrap();
 		}
 
@@ -592,7 +583,7 @@ mod tests {
 		let mut vm_tracer = NoopVMTracer;
 
 		let address = {
-			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
 			match ext.create(&U256::max_value(), &U256::zero(), &[], CreateContractAddress::FromSenderAndNonce) {
 				ContractCreateResult::Created(address, _) => address,
 				_ => panic!("Test create failed; expected Created, got Failed/Reverted."),
@@ -612,8 +603,8 @@ mod tests {
 		let mut vm_tracer = NoopVMTracer;
 
 		let address = {
-			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract(None), &mut tracer, &mut vm_tracer, false);
+			let mut ext = Externalities::new(state, &setup.env_info, &setup.machine, &setup.schedule, 0, get_test_origin(), &mut setup.sub_state, OutputPolicy::InitContract, &mut tracer, &mut vm_tracer, false);
-	
+
 			match ext.create(&U256::max_value(), &U256::zero(), &[], CreateContractAddress::FromSenderSaltAndCodeHash(H256::default())) {
 				ContractCreateResult::Created(address, _) => address,
 				_ => panic!("Test create failed; expected Created, got Failed/Reverted."),

ethcore/src/json_tests/executive.rs

@@ -30,7 +30,7 @@ use test_helpers::get_temp_state;
 use ethjson;
 use trace::{Tracer, NoopTracer};
 use trace::{VMTracer, NoopVMTracer};
-use bytes::{Bytes, BytesRef};
+use bytes::Bytes;
 use ethtrie;
 use rlp::RlpStream;
 use hash::keccak;
@@ -90,7 +90,7 @@ impl<'a, T: 'a, V: 'a, B: 'a> TestExt<'a, T, V, B>
 		depth: usize,
 		origin_info: OriginInfo,
 		substate: &'a mut Substate,
-		output: OutputPolicy<'a, 'a>,
+		output: OutputPolicy,
 		address: Address,
 		tracer: &'a mut T,
 		vm_tracer: &'a mut V,
@@ -154,7 +154,6 @@ impl<'a, T: 'a, V: 'a, B: 'a> Ext for TestExt<'a, T, V, B>
 		value: Option<U256>,
 		data: &[u8],
 		_code_address: &Address,
-		_output: &mut [u8],
 		_call_type: CallType
 	) -> MessageCallResult {
 		self.callcreates.push(CallCreate {
@@ -262,7 +261,6 @@ fn do_json_test_for<H: FnMut(&str, HookType)>(vm_type: &VMType, json_data: &[u8]
 		let mut substate = Substate::new();
 		let mut tracer = NoopTracer;
 		let mut vm_tracer = NoopVMTracer;
-		let mut output = vec![];
 		let vm_factory = state.vm_factory();
 
 		// execute
@@ -276,7 +274,7 @@ fn do_json_test_for<H: FnMut(&str, HookType)>(vm_type: &VMType, json_data: &[u8]
 				0,
 				OriginInfo::from(&params),
 				&mut substate,
-				OutputPolicy::Return(BytesRef::Flexible(&mut output), None),
+				OutputPolicy::Return,
 				params.address.clone(),
 				&mut tracer,
 				&mut vm_tracer,
@@ -288,6 +286,11 @@ fn do_json_test_for<H: FnMut(&str, HookType)>(vm_type: &VMType, json_data: &[u8]
 			(res.finalize(ex), callcreates)
 		};
 
+		let output = match &res {
+			Ok(res) => res.return_data.to_vec(),
+			Err(_) => Vec::new(),
+		};
+
 		let log_hash = {
 			let mut rlp = RlpStream::new_list(substate.logs.len());
 			for l in &substate.logs {

ethcore/src/machine.rs

@@ -33,7 +33,6 @@ use transaction::{self, SYSTEM_ADDRESS, UnverifiedTransaction, SignedTransaction
 use tx_filter::TransactionFilter;
 
 use ethereum_types::{U256, Address};
-use bytes::BytesRef;
 use rlp::Rlp;
 use vm::{CallType, ActionParams, ActionValue, ParamsType};
 use vm::{EnvInfo, Schedule, CreateContractAddress};
@@ -148,10 +147,14 @@ impl EthereumMachine {
 		let schedule = self.schedule(env_info.number);
 		let mut ex = Executive::new(&mut state, &env_info, self, &schedule);
 		let mut substate = Substate::new();
-		let mut output = Vec::new();
+		let res = ex.call(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer);
-		if let Err(e) = ex.call(params, &mut substate, BytesRef::Flexible(&mut output), &mut NoopTracer, &mut NoopVMTracer) {
+		let output = match res {
-			warn!("Encountered error on making system call: {}", e);
+			Ok(res) => res.return_data.to_vec(),
-		}
+			Err(e) => {
+				warn!("Encountered error on making system call: {}", e);
+				Vec::new()
+			}
+		};
 
 		Ok(output)
 	}

ethcore/src/spec/spec.rs

@@ -655,7 +655,7 @@ impl Spec {
 					let machine = self.engine.machine();
 					let schedule = machine.schedule(env_info.number);
 					let mut exec = Executive::new(&mut state, &env_info, &machine, &schedule);
-					if let Err(e) = exec.create(params, &mut substate, &mut None, &mut NoopTracer, &mut NoopVMTracer) {
+					if let Err(e) = exec.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer) {
 						warn!(target: "spec", "Genesis constructor execution at {} failed: {}.", address, e);
 					}
 				}

ethcore/src/tests/evm.rs

@@ -29,7 +29,6 @@ use transaction::SYSTEM_ADDRESS;
 use rustc_hex::FromHex;
 
 use ethereum_types::{H256, Address};
-use bytes::BytesRef;
 
 evm_test!{test_blockhash_eip210: test_blockhash_eip210_int}
 fn test_blockhash_eip210(factory: Factory) {
@@ -65,8 +64,7 @@ fn test_blockhash_eip210(factory: Factory) {
 		let schedule = machine.schedule(env_info.number);
 		let mut ex = Executive::new(&mut state, &env_info, &machine, &schedule);
 		let mut substate = Substate::new();
-		let mut output = [];
+		if let Err(e) = ex.call(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer) {
-		if let Err(e) = ex.call(params, &mut substate, BytesRef::Fixed(&mut output), &mut NoopTracer, &mut NoopVMTracer) {
 			panic!("Encountered error on updating last hashes: {}", e);
 		}
 	}
@@ -89,9 +87,12 @@ fn test_blockhash_eip210(factory: Factory) {
 	let schedule = machine.schedule(env_info.number);
 	let mut ex = Executive::new(&mut state, &env_info, &machine, &schedule);
 	let mut substate = Substate::new();
-	let mut output = H256::new();
+	let res = ex.call(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer);
-	if let Err(e) = ex.call(params, &mut substate, BytesRef::Fixed(&mut output), &mut NoopTracer, &mut NoopVMTracer) {
+	let output = match res {
-		panic!("Encountered error on getting last hash: {}", e);
+		Ok(res) => H256::from(&res.return_data[..32]),
-	}
+		Err(e) => {
+			panic!("Encountered error on getting last hash: {}", e);
+		},
+	};
 	assert_eq!(output, 255.into());
 }

ethcore/vm/src/ext.rs

@@ -101,7 +101,6 @@ pub trait Ext {
 		value: Option<U256>,
 		data: &[u8],
 		code_address: &Address,
-		output: &mut [u8],
 		call_type: CallType
 	) -> MessageCallResult;
 

ethcore/vm/src/tests.rs

@@ -155,7 +155,6 @@ impl Ext for FakeExt {
 			value: Option<U256>,
 			data: &[u8],
 			code_address: &Address,
-			_output: &mut [u8],
 			_call_type: CallType
 		) -> MessageCallResult {
 

ethcore/wasm/src/runtime.rs

@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
+use std::cmp;
 use ethereum_types::{U256, H256, Address};
 use vm::{self, CallType};
 use wasmi::{self, MemoryRef, RuntimeArgs, RuntimeValue, Error as InterpreterError, Trap, TrapKind};
@@ -447,12 +448,14 @@ impl<'a> Runtime<'a> {
 			val,
 			&payload,
 			&address,
-			&mut result[..],
 			call_type,
 		);
 
 		match call_result {
-			vm::MessageCallResult::Success(gas_left, _) => {
+			vm::MessageCallResult::Success(gas_left, data) => {
+				let len = cmp::min(result.len(), data.len());
+				(&mut result[..len]).copy_from_slice(&data[..len]);
+
 				// cannot overflow, before making call gas_counter was incremented with gas, and gas_left < gas
 				self.gas_counter = self.gas_counter -
 					gas_left.low_u64() * self.ext.schedule().wasm().opcodes_div as u64
@@ -461,7 +464,10 @@ impl<'a> Runtime<'a> {
 				self.memory.set(result_ptr, &result)?;
 				Ok(0i32.into())
 			},
-			vm::MessageCallResult::Reverted(gas_left, _) => {
+			vm::MessageCallResult::Reverted(gas_left, data) => {
+				let len = cmp::min(result.len(), data.len());
+				(&mut result[..len]).copy_from_slice(&data[..len]);
+
 				// cannot overflow, before making call gas_counter was incremented with gas, and gas_left < gas
 				self.gas_counter = self.gas_counter -
 					gas_left.low_u64() * self.ext.schedule().wasm().opcodes_div as u64