Rearchitected VM tracing to reflect existing tracing.

Should more or less work now.

ethcore/src/evm/ext.rs

@@ -40,9 +40,6 @@ pub enum MessageCallResult {
 	Failed
 }
 
-/// The trace function callback for VM tracing (*not* transaction tracing - that's different).
-pub type VMTraceFunctionBox = Box<FnMut(usize, u8, U256, U256) + Send>;
-
 /// Externalities interface for EVMs
 pub trait Ext {
 	/// Returns a value for given key.
@@ -109,6 +106,7 @@ pub trait Ext {
 	/// Increments sstore refunds count by 1.
 	fn inc_sstore_clears(&mut self);
 
-	/// Provide a tracer for VM tracing if the VM implementation supports it.
+	// TODO work out a way of not having this here but go via .
-	fn vm_tracer(&mut self) -> Option<&mut VMTraceFunctionBox>;
+	/// Prepare to trace an operation. Passthrough for the VM trace.
+	fn trace_prepare_execute(&mut self, _pc: usize, _instruction: u8, _gas_cost: &U256, _stack: &[U256]) {}
 }

ethcore/src/evm/interpreter.rs

@@ -17,6 +17,7 @@
 ///! Rust VM implementation
 
 use common::*;
+use trace::VMTracer;
 use super::instructions as instructions;
 use super::instructions::Instruction;
 use std::marker::Copy;
@@ -69,6 +70,8 @@ trait Stack<T> {
 	fn push(&mut self, elem: T);
 	/// Get number of elements on Stack
 	fn size(&self) -> usize;
+	/// Returns all data on stack.
+	fn peek_all(&mut self) -> &[T];
 }
 
 struct VecStack<S> {
@@ -131,6 +134,10 @@ impl<S : fmt::Display> Stack<S> for VecStack<S> {
 	fn size(&self) -> usize {
 		self.stack.len()
 	}
+
+	fn peek_all(&mut self) -> &[S] {
+		&self.stack
+	}
 }
 
 trait Memory {
@@ -297,6 +304,10 @@ impl evm::Evm for Interpreter {
 
 			// Calculate gas cost
 			let (gas_cost, mem_size) = try!(self.get_gas_cost_mem(ext, instruction, &mut mem, &stack));
+
+			// TODO: make compile-time removable if too much of a performance hit.
+			ext.trace_prepare_execute(reader.position, instruction, &gas_cost, stack.peek_all());
+
 			try!(self.verify_gas(&current_gas, &gas_cost));
 			mem.expand(mem_size);
 			current_gas = current_gas - gas_cost; //TODO: use operator -=
@@ -311,12 +322,6 @@ impl evm::Evm for Interpreter {
 				);
 			});
 
-			// Call trace
-			// TODO: allow to be disabled at build time for max speed
-			if let Some(ref mut trace_instruction) = ext.vm_tracer() {
-				(*trace_instruction.deref_mut())(reader.position, instruction, gas_cost, current_gas);
-			}
-
 			// Execute instruction
 			let result = try!(self.exec_instruction(
 					current_gas, &params, ext, instruction, &mut reader, &mut mem, &mut stack

ethcore/src/evm/jit.rs

@@ -16,6 +16,7 @@
 
 //! Just in time compiler execution environment.
 use common::*;
+use trace::VMTracer;
 use evmjit;
 use evm;
 

ethcore/src/evm/mod.rs

@@ -30,6 +30,6 @@ mod jit;
 mod tests;
 
 pub use self::evm::{Evm, Error, Result};
-pub use self::ext::{Ext, ContractCreateResult, MessageCallResult, VMTraceFunctionBox};
+pub use self::ext::{Ext, ContractCreateResult, MessageCallResult};
 pub use self::factory::{Factory, VMType};
 pub use self::schedule::Schedule;

ethcore/src/executive.rs

@@ -21,7 +21,7 @@ use engine::*;
 use evm::{self, Ext, Factory};
 use externalities::*;
 use substate::*;
-use trace::{Trace, Tracer, NoopTracer, ExecutiveTracer};
+use trace::{Trace, Tracer, NoopTracer, ExecutiveTracer, VMTrace, VMTracer, ExecutiveVMTracer, NoopVMTracer};
 use crossbeam;
 
 pub use types::executed::{Executed, ExecutionResult};
@@ -82,21 +82,40 @@ impl<'a> Executive<'a> {
 	}
 
 	/// Creates `Externalities` from `Executive`.
-	pub fn as_externalities<'_, T>(&'_ mut self, origin_info: OriginInfo, substate: &'_ mut Substate, output: OutputPolicy<'_, '_>, tracer: &'_ mut T) -> Externalities<'_, T> where T: Tracer {
+	pub fn as_externalities<'_, T, V>(
-		Externalities::new(self.state, self.info, self.engine, self.vm_factory, self.depth, origin_info, substate, output, tracer)
+		&'_ mut self,
+		origin_info: OriginInfo,
+		substate: &'_ mut Substate,
+		output: OutputPolicy<'_, '_>,
+		tracer: &'_ mut T,
+		vm_tracer: &'_ mut V
+	) -> Externalities<'_, T, V> where T: Tracer, V: VMTracer {
+		Externalities::new(self.state, self.info, self.engine, self.vm_factory, self.depth, origin_info, substate, output, tracer, vm_tracer)
 	}
 
 	/// This function should be used to execute transaction.
 	pub fn transact(&'a mut self, t: &SignedTransaction, options: TransactOptions) -> Result<Executed, ExecutionError> {
 		let check = options.check_nonce;
 		match options.tracing {
-			true => self.transact_with_tracer(t, check, ExecutiveTracer::default()),
+			true => match options.vm_tracing {
-			false => self.transact_with_tracer(t, check, NoopTracer),
+				true => self.transact_with_tracer(t, check, ExecutiveTracer::default(), ExecutiveVMTracer::default()),
+				false => self.transact_with_tracer(t, check, ExecutiveTracer::default(), NoopVMTracer),
+			},
+			false => match options.vm_tracing {
+				true => self.transact_with_tracer(t, check, NoopTracer, ExecutiveVMTracer::default()),
+				false => self.transact_with_tracer(t, check, NoopTracer, NoopVMTracer),
+			},
 		}
 	}
 
 	/// Execute transaction/call with tracing enabled
-	pub fn transact_with_tracer<T>(&'a mut self, t: &SignedTransaction, check_nonce: bool, mut tracer: T) -> Result<Executed, ExecutionError> where T: Tracer {
+	pub fn transact_with_tracer<T, V>(
+		&'a mut self,
+		t: &SignedTransaction,
+		check_nonce: bool,
+		mut tracer: T,
+		mut vm_tracer: V
+	) -> Result<Executed, ExecutionError> where T: Tracer, V: VMTracer {
 		let sender = try!(t.sender().map_err(|e| {
 			let message = format!("Transaction malformed: {:?}", e);
 			ExecutionError::TransactionMalformed(message)
@@ -156,7 +175,7 @@ impl<'a> Executive<'a> {
 					code: Some(t.data.clone()),
 					data: None,
 				};
-				(self.create(params, &mut substate, &mut tracer), vec![])
+				(self.create(params, &mut substate, &mut tracer, &mut vm_tracer), vec![])
 			},
 			Action::Call(ref address) => {
 				let params = ActionParams {
@@ -172,20 +191,26 @@ impl<'a> Executive<'a> {
 				};
 				// TODO: move output upstream
 				let mut out = vec![];
-				(self.call(params, &mut substate, BytesRef::Flexible(&mut out), &mut tracer), out)
+				(self.call(params, &mut substate, BytesRef::Flexible(&mut out), &mut tracer, &mut vm_tracer), out)
 			}
 		};
 
 		// finalize here!
-		Ok(try!(self.finalize(t, substate, gas_left, output, tracer.traces().pop())))
+		Ok(try!(self.finalize(t, substate, gas_left, output, tracer.traces().pop(), vm_tracer.drain())))
 	}
 
-	fn exec_vm<T>(&mut self, params: ActionParams, unconfirmed_substate: &mut Substate, output_policy: OutputPolicy, tracer: &mut T)
+	fn exec_vm<T, V>(
-		-> evm::Result where T: Tracer {
+		&mut self,
+		params: ActionParams,
+		unconfirmed_substate: &mut Substate,
+		output_policy: OutputPolicy,
+		tracer: &mut T,
+		vm_tracer: &mut V
+	) -> evm::Result where T: Tracer, V: VMTracer {
 		// Ordinary execution - keep VM in same thread
 		if (self.depth + 1) % MAX_VM_DEPTH_FOR_THREAD != 0 {
 			let vm_factory = self.vm_factory;
-			let mut ext = self.as_externalities(OriginInfo::from(&params), unconfirmed_substate, output_policy, tracer);
+			let mut ext = self.as_externalities(OriginInfo::from(&params), unconfirmed_substate, output_policy, tracer, vm_tracer);
 			trace!(target: "executive", "ext.schedule.have_delegate_call: {}", ext.schedule().have_delegate_call);
 			return vm_factory.create().exec(params, &mut ext);
 		}
@@ -195,7 +220,7 @@ impl<'a> Executive<'a> {
 		// https://github.com/aturon/crossbeam/issues/16
 		crossbeam::scope(|scope| {
 			let vm_factory = self.vm_factory;
-			let mut ext = self.as_externalities(OriginInfo::from(&params), unconfirmed_substate, output_policy, tracer);
+			let mut ext = self.as_externalities(OriginInfo::from(&params), unconfirmed_substate, output_policy, tracer, vm_tracer);
 
 			scope.spawn(move || {
 				vm_factory.create().exec(params, &mut ext)
@@ -207,8 +232,14 @@ impl<'a> Executive<'a> {
 	/// NOTE. It does not finalize the transaction (doesn't do refunds, nor suicides).
 	/// Modifies the substate and the output.
 	/// Returns either gas_left or `evm::Error`.
-	pub fn call<T>(&mut self, params: ActionParams, substate: &mut Substate, mut output: BytesRef, tracer: &mut T)
+	pub fn call<T, V>(
-		-> evm::Result where T: Tracer {
+		&mut self,
+		params: ActionParams,
+		substate: &mut Substate,
+		mut output: BytesRef,
+		tracer: &mut T,
+		vm_tracer: &mut V
+	) -> evm::Result where T: Tracer, V: VMTracer {
 		// backup used in case of running out of gas
 		self.state.snapshot();
 
@@ -266,16 +297,22 @@ impl<'a> Executive<'a> {
 			let trace_info = tracer.prepare_trace_call(&params);
 			let mut trace_output = tracer.prepare_trace_output();
 			let mut subtracer = tracer.subtracer();
+
 			let gas = params.gas;
 
 			if params.code.is_some() {
 				// part of substate that may be reverted
 				let mut unconfirmed_substate = Substate::new();
 
+				// TODO: make ActionParams pass by ref then avoid copy altogether.
+				let mut subvmtracer = vm_tracer.prepare_subtrace(params.code.as_ref().expect("scope is protected by params.code.is_some condition"));
+
 				let res = {
-					self.exec_vm(params, &mut unconfirmed_substate, OutputPolicy::Return(output, trace_output.as_mut()), &mut subtracer)
+					self.exec_vm(params, &mut unconfirmed_substate, OutputPolicy::Return(output, trace_output.as_mut()), &mut subtracer, &mut subvmtracer)
 				};
 
+				vm_tracer.done_subtrace(subvmtracer);
+
 				trace!(target: "executive", "res={:?}", res);
 
 				let traces = subtracer.traces();
@@ -309,8 +346,13 @@ impl<'a> Executive<'a> {
 	/// Creates contract with given contract params.
 	/// NOTE. It does not finalize the transaction (doesn't do refunds, nor suicides).
 	/// Modifies the substate.
-	pub fn create<T>(&mut self, params: ActionParams, substate: &mut Substate, tracer: &mut T) -> evm::Result where T:
+	pub fn create<T, V>(
-		Tracer {
+		&mut self,
+		params: ActionParams,
+		substate: &mut Substate,
+		tracer: &mut T,
+		vm_tracer: &mut V
+	) -> evm::Result where T: Tracer, V: VMTracer {
 		// backup used in case of running out of gas
 		self.state.snapshot();
 
@@ -332,10 +374,14 @@ impl<'a> Executive<'a> {
 		let gas = params.gas;
 		let created = params.address.clone();
 
+		let mut subvmtracer = vm_tracer.prepare_subtrace(&params.code.as_ref().expect("two ways into create (Externalities::create and Executive::transact_with_tracer); both place `Some(...)` `code` in `params`; qed"));
+
 		let res = {
-			self.exec_vm(params, &mut unconfirmed_substate, OutputPolicy::InitContract(trace_output.as_mut()), &mut subtracer)
+			self.exec_vm(params, &mut unconfirmed_substate, OutputPolicy::InitContract(trace_output.as_mut()), &mut subtracer, &mut subvmtracer)
 		};
 
+		vm_tracer.done_subtrace(subvmtracer);
+
 		match res {
 			Ok(gas_left) => tracer.trace_create(
 				trace_info,
@@ -353,7 +399,15 @@ impl<'a> Executive<'a> {
 	}
 
 	/// Finalizes the transaction (does refunds and suicides).
-	fn finalize(&mut self, t: &SignedTransaction, substate: Substate, result: evm::Result, output: Bytes, trace: Option<Trace>) -> ExecutionResult {
+	fn finalize(
+		&mut self,
+		t: &SignedTransaction,
+		substate: Substate,
+		result: evm::Result,
+		output: Bytes,
+		trace: Option<Trace>,
+		vm_trace: Option<VMTrace>
+	) -> ExecutionResult {
 		let schedule = self.engine.schedule(self.info);
 
 		// refunds from SSTORE nonzero -> zero
@@ -396,7 +450,7 @@ impl<'a> Executive<'a> {
 					contracts_created: vec![],
 					output: output,
 					trace: trace,
-					vm_trace: None,
+					vm_trace: vm_trace,
 				})
 			},
 			_ => {
@@ -409,7 +463,7 @@ impl<'a> Executive<'a> {
 					contracts_created: substate.contracts_created,
 					output: output,
 					trace: trace,
-					vm_trace: None,
+					vm_trace: vm_trace,
 				})
 			},
 		}

ethcore/src/externalities.rs

@@ -19,9 +19,9 @@ use common::*;
 use state::*;
 use engine::*;
 use executive::*;
-use evm::{self, Schedule, Ext, ContractCreateResult, MessageCallResult, Factory, VMTraceFunctionBox};
+use evm::{self, Schedule, Ext, ContractCreateResult, MessageCallResult, Factory};
 use substate::*;
-use trace::Tracer;
+use trace::{Tracer, VMTracer};
 
 /// Policy for handling output data on `RETURN` opcode.
 pub enum OutputPolicy<'a, 'b> {
@@ -55,7 +55,7 @@ impl OriginInfo {
 }
 
 /// Implementation of evm Externalities.
-pub struct Externalities<'a, T> where T: 'a + Tracer {
+pub struct Externalities<'a, T, V> where T: 'a + Tracer, V: 'a + VMTracer {
 	state: &'a mut State,
 	env_info: &'a EnvInfo,
 	engine: &'a Engine,
@@ -66,10 +66,10 @@ pub struct Externalities<'a, T> where T: 'a + Tracer {
 	schedule: Schedule,
 	output: OutputPolicy<'a, 'a>,
 	tracer: &'a mut T,
-	vm_tracer: Option<VMTraceFunctionBox>,
+	vm_tracer: &'a mut V,
 }
 
-impl<'a, T> Externalities<'a, T> where T: 'a + Tracer {
+impl<'a, T, V> Externalities<'a, T, V> where T: 'a + Tracer, V: 'a + VMTracer {
 	#[cfg_attr(feature="dev", allow(too_many_arguments))]
 	/// Basic `Externalities` constructor.
 	pub fn new(state: &'a mut State,
@@ -81,6 +81,7 @@ impl<'a, T> Externalities<'a, T> where T: 'a + Tracer {
 		substate: &'a mut Substate,
 		output: OutputPolicy<'a, 'a>,
 		tracer: &'a mut T,
+		vm_tracer: &'a mut V,
 	) -> Self {
 		Externalities {
 			state: state,
@@ -93,40 +94,12 @@ impl<'a, T> Externalities<'a, T> where T: 'a + Tracer {
 			schedule: engine.schedule(env_info),
 			output: output,
 			tracer: tracer,
-			vm_tracer: None,
+			vm_tracer: vm_tracer,
-		}
-	}
-
-	#[cfg_attr(feature="dev", allow(too_many_arguments))]
-	/// Basic `Externalities` constructor.
-	pub fn with_vm_tracer(state: &'a mut State,
-		env_info: &'a EnvInfo,
-		engine: &'a Engine,
-		vm_factory: &'a Factory,
-		depth: usize,
-		origin_info: OriginInfo,
-		substate: &'a mut Substate,
-		output: OutputPolicy<'a, 'a>,
-		tracer: &'a mut T,
-		vm_tracer: VMTraceFunctionBox,
-	) -> Self {
-		Externalities {
-			state: state,
-			env_info: env_info,
-			engine: engine,
-			vm_factory: vm_factory,
-			depth: depth,
-			origin_info: origin_info,
-			substate: substate,
-			schedule: engine.schedule(env_info),
-			output: output,
-			tracer: tracer,
-			vm_tracer: Some(vm_tracer),
 		}
 	}
 }
 
-impl<'a, T> Ext for Externalities<'a, T> where T: 'a + Tracer {
+impl<'a, T, V> Ext for Externalities<'a, T, V> where T: 'a + Tracer, V: 'a + VMTracer {
 	fn storage_at(&self, key: &H256) -> H256 {
 		self.state.storage_at(&self.origin_info.address, key)
 	}
@@ -181,7 +154,7 @@ impl<'a, T> Ext for Externalities<'a, T> where T: 'a + Tracer {
 		let mut ex = Executive::from_parent(self.state, self.env_info, self.engine, self.vm_factory, self.depth);
 
 		// TODO: handle internal error separately
-		match ex.create(params, self.substate, self.tracer) {
+		match ex.create(params, self.substate, self.tracer, self.vm_tracer) {
 			Ok(gas_left) => {
 				self.substate.contracts_created.push(address.clone());
 				ContractCreateResult::Created(address, gas_left)
@@ -219,7 +192,7 @@ impl<'a, T> Ext for Externalities<'a, T> where T: 'a + Tracer {
 
 		let mut ex = Executive::from_parent(self.state, self.env_info, self.engine, self.vm_factory, self.depth);
 
-		match ex.call(params, self.substate, BytesRef::Fixed(output), self.tracer) {
+		match ex.call(params, self.substate, BytesRef::Fixed(output), self.tracer, self.vm_tracer) {
 			Ok(gas_left) => MessageCallResult::Success(gas_left),
 			_ => MessageCallResult::Failed
 		}
@@ -316,7 +289,9 @@ impl<'a, T> Ext for Externalities<'a, T> where T: 'a + Tracer {
 		self.substate.sstore_clears_count = self.substate.sstore_clears_count + U256::one();
 	}
 
-	fn vm_tracer(&mut self) -> Option<&mut VMTraceFunctionBox> { self.vm_tracer.as_mut() }
+	fn trace_prepare_execute(&mut self, pc: usize, instruction: u8, gas_cost: &U256, stack: &[U256]) {
+		self.vm_tracer.trace_prepare_execute(pc, instruction, gas_cost, stack);
+	}
 }
 
 #[cfg(test)]

ethcore/src/trace/executive_tracer.rs

@@ -18,13 +18,13 @@
 
 use util::{Bytes, Address, U256};
 use action_params::ActionParams;
-use trace::trace::{Trace, Call, Create, Action, Res, CreateResult, CallResult};
+use trace::trace::{Trace, Call, Create, Action, Res, CreateResult, CallResult, VMTrace, VMOperation};
-use trace::Tracer;
+use trace::{Tracer, VMTracer};
 
 /// Simple executive tracer. Traces all calls and creates. Ignores delegatecalls.
 #[derive(Default)]
 pub struct ExecutiveTracer {
-	traces: Vec<Trace>
+	traces: Vec<Trace>,
 }
 
 impl Tracer for ExecutiveTracer {
@@ -105,3 +105,35 @@ impl Tracer for ExecutiveTracer {
 		self.traces
 	}
 }
+
+/// Simple VM tracer. Traces all operations. Ignores delegatecalls.
+#[derive(Default)]
+pub struct ExecutiveVMTracer {
+	data: VMTrace,
+}
+
+impl VMTracer for ExecutiveVMTracer {
+	fn trace_prepare_execute(&mut self, pc: usize, instruction: u8, gas_cost: &U256, stack: &[U256]) {
+		self.data.operations.push(VMOperation {
+			pc: pc,
+			instruction: instruction,
+			gas_cost: gas_cost.clone(),
+			stack: stack.iter().cloned().collect(),
+		})
+	}
+
+	fn prepare_subtrace(&self, code: &Bytes) -> Self {
+		ExecutiveVMTracer { data: VMTrace {
+			parent_step: self.data.operations.len(),
+			code: code.clone(),
+			operations: vec![],
+			subs: vec![],
+		}}
+	}
+
+	fn done_subtrace(&mut self, sub: Self) {
+		self.data.subs.push(sub.data);
+	}
+
+	fn drain(self) -> Option<VMTrace> { Some(self.data) }
+}

ethcore/src/trace/mod.rs

@@ -32,8 +32,8 @@ pub use self::config::{Config, Switch};
 pub use self::db::TraceDB;
 pub use self::error::Error;
 pub use types::trace_types::trace::{Trace, VMTrace};
-pub use self::noop_tracer::NoopTracer;
+pub use self::noop_tracer::{NoopTracer, NoopVMTracer};
-pub use self::executive_tracer::ExecutiveTracer;
+pub use self::executive_tracer::{ExecutiveTracer, ExecutiveVMTracer};
 pub use types::trace_types::filter::{Filter, AddressesFilter};
 pub use self::import::ImportRequest;
 pub use self::localized::LocalizedTrace;
@@ -91,13 +91,16 @@ pub trait Tracer: Send {
 /// Used by executive to build VM traces.
 pub trait VMTracer: Send {
 	/// Trace the preparation to execute a single instruction.
-	fn trace_prepare_execute(pc: usize, instruction: u8, gas_cost: &U256, stack: &Vec<U256>);
+	fn trace_prepare_execute(&mut self, pc: usize, instruction: u8, gas_cost: &U256, stack: &[U256]);
 
 	/// Spawn subtracer which will be used to trace deeper levels of execution.
-	fn subtracer(&self) -> Self where Self: Sized;
+	fn prepare_subtrace(&self, code: &Bytes) -> Self where Self: Sized;
 
-	/// Consumes self and returns all VM traces.
+	/// Spawn subtracer which will be used to trace deeper levels of execution.
-	fn traces(self) -> Vec<VMTrace>;
+	fn done_subtrace(&mut self, sub: Self) where Self: Sized;
+
+	/// Consumes self and returns the VM trace.
+	fn drain(self) -> Option<VMTrace>;
 }
 
 /// `DbExtras` provides an interface to query extra data which is not stored in tracesdb,

ethcore/src/trace/noop_tracer.rs

@@ -18,8 +18,8 @@
 
 use util::{Bytes, Address, U256};
 use action_params::ActionParams;
-use trace::Tracer;
+use trace::{Tracer, VMTracer};
-use trace::trace::{Trace, Call, Create};
+use trace::trace::{Trace, Call, Create, VMTrace};
 
 /// Nonoperative tracer. Does not trace anything.
 pub struct NoopTracer;
@@ -63,3 +63,20 @@ impl Tracer for NoopTracer {
 		vec![]
 	}
 }
+
+/// Nonoperative VM tracer. Does not trace anything.
+pub struct NoopVMTracer;
+
+impl VMTracer for NoopVMTracer {
+	/// Trace the preparation to execute a single instruction.
+	fn trace_prepare_execute(&mut self, _pc: usize, _instruction: u8, _gas_cost: &U256, _stack: &[U256]) {}
+
+	/// Spawn subtracer which will be used to trace deeper levels of execution.
+	fn prepare_subtrace(&self, _code: &Bytes) -> Self { NoopVMTracer }
+
+	/// Spawn subtracer which will be used to trace deeper levels of execution.
+	fn done_subtrace(&mut self, _sub: Self) {}
+
+	/// Consumes self and returns all VM traces.
+	fn drain(self) -> Option<VMTrace> { None }
+}

ethcore/src/types/trace_types/trace.rs

@@ -397,12 +397,11 @@ impl Decodable for VMOperation {
 	}
 }
 
-#[derive(Debug, Clone, PartialEq, Binary)]
+#[derive(Debug, Clone, PartialEq, Binary, Default)]
 /// A record of a full VM trace for a CALL/CREATE.
 pub struct VMTrace {
-	/// The number of EVM execution environments active when this action happened; 0 if it's
+	/// The step (i.e. index into operations) at which this trace corresponds.
-	/// the outer action of the transaction.
+	pub parent_step: usize,
-	pub depth: usize,
 	/// The code to be executed.
 	pub code: Bytes,
 	/// The operations executed.
@@ -415,7 +414,7 @@ pub struct VMTrace {
 impl Encodable for VMTrace {
 	fn rlp_append(&self, s: &mut RlpStream) {
 		s.begin_list(4);
-		s.append(&self.depth);
+		s.append(&self.parent_step);
 		s.append(&self.code);
 		s.append(&self.operations);
 		s.append(&self.subs);
@@ -426,7 +425,7 @@ impl Decodable for VMTrace {
 	fn decode<D>(decoder: &D) -> Result<Self, DecoderError> where D: Decoder {
 		let d = decoder.as_rlp();
 		let res = VMTrace {
-			depth: try!(d.val_at(0)),
+			parent_step: try!(d.val_at(0)),
 			code: try!(d.val_at(1)),
 			operations: try!(d.val_at(2)),
 			subs: try!(d.val_at(3)),