eth/tracers, core: use scopecontext in tracers, provide statedb in capturestart (#22333)

Fixes the CaptureStart api to include the EVM, thus being able to set the statedb early on. This pr also exposes the struct we used internally in the interpreter to encapsulate the contract, mem, stack, rstack, so we pass it as a single struct to the tracer, and removes the error returns on the capture methods. 

core/vm/eips.go

@@ -76,9 +76,9 @@ func enable1884(jt *JumpTable) {
 	}
 }
 
-func opSelfBalance(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byte, error) {
-	balance, _ := uint256.FromBig(interpreter.evm.StateDB.GetBalance(callContext.contract.Address()))
-	callContext.stack.push(balance)
+func opSelfBalance(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byte, error) {
+	balance, _ := uint256.FromBig(interpreter.evm.StateDB.GetBalance(scope.Contract.Address()))
+	scope.Stack.push(balance)
 	return nil, nil
 }
 
@@ -95,9 +95,9 @@ func enable1344(jt *JumpTable) {
 }
 
 // opChainID implements CHAINID opcode
-func opChainID(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byte, error) {
+func opChainID(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byte, error) {
 	chainId, _ := uint256.FromBig(interpreter.evm.chainConfig.ChainID)
-	callContext.stack.push(chainId)
+	scope.Stack.push(chainId)
 	return nil, nil
 }
 

core/vm/evm.go

@@ -239,7 +239,7 @@ func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas
 		if !isPrecompile && evm.chainRules.IsEIP158 && value.Sign() == 0 {
 			// Calling a non existing account, don't do anything, but ping the tracer
 			if evm.vmConfig.Debug && evm.depth == 0 {
-				evm.vmConfig.Tracer.CaptureStart(caller.Address(), addr, false, input, gas, value)
+				evm.vmConfig.Tracer.CaptureStart(evm, caller.Address(), addr, false, input, gas, value)
 				evm.vmConfig.Tracer.CaptureEnd(ret, 0, 0, nil)
 			}
 			return nil, gas, nil
@@ -250,7 +250,7 @@ func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas
 
 	// Capture the tracer start/end events in debug mode
 	if evm.vmConfig.Debug && evm.depth == 0 {
-		evm.vmConfig.Tracer.CaptureStart(caller.Address(), addr, false, input, gas, value)
+		evm.vmConfig.Tracer.CaptureStart(evm, caller.Address(), addr, false, input, gas, value)
 		defer func(startGas uint64, startTime time.Time) { // Lazy evaluation of the parameters
 			evm.vmConfig.Tracer.CaptureEnd(ret, startGas-gas, time.Since(startTime), err)
 		}(gas, time.Now())
@@ -472,7 +472,7 @@ func (evm *EVM) create(caller ContractRef, codeAndHash *codeAndHash, gas uint64,
 	}
 
 	if evm.vmConfig.Debug && evm.depth == 0 {
-		evm.vmConfig.Tracer.CaptureStart(caller.Address(), address, true, codeAndHash.code, gas, value)
+		evm.vmConfig.Tracer.CaptureStart(evm, caller.Address(), address, true, codeAndHash.code, gas, value)
 	}
 	start := time.Now()
 

core/vm/instructions_test.go

@@ -104,7 +104,7 @@ func testTwoOperandOp(t *testing.T, tests []TwoOperandTestcase, opFn executionFu
 		expected := new(uint256.Int).SetBytes(common.Hex2Bytes(test.Expected))
 		stack.push(x)
 		stack.push(y)
-		opFn(&pc, evmInterpreter, &callCtx{nil, stack, nil})
+		opFn(&pc, evmInterpreter, &ScopeContext{nil, stack, nil})
 		if len(stack.data) != 1 {
 			t.Errorf("Expected one item on stack after %v, got %d: ", name, len(stack.data))
 		}
@@ -219,7 +219,7 @@ func TestAddMod(t *testing.T) {
 		stack.push(z)
 		stack.push(y)
 		stack.push(x)
-		opAddmod(&pc, evmInterpreter, &callCtx{nil, stack, nil})
+		opAddmod(&pc, evmInterpreter, &ScopeContext{nil, stack, nil})
 		actual := stack.pop()
 		if actual.Cmp(expected) != 0 {
 			t.Errorf("Testcase %d, expected  %x, got %x", i, expected, actual)
@@ -241,7 +241,7 @@ func getResult(args []*twoOperandParams, opFn executionFunc) []TwoOperandTestcas
 		y := new(uint256.Int).SetBytes(common.Hex2Bytes(param.y))
 		stack.push(x)
 		stack.push(y)
-		opFn(&pc, interpreter, &callCtx{nil, stack, nil})
+		opFn(&pc, interpreter, &ScopeContext{nil, stack, nil})
 		actual := stack.pop()
 		result[i] = TwoOperandTestcase{param.x, param.y, fmt.Sprintf("%064x", actual)}
 	}
@@ -299,7 +299,7 @@ func opBenchmark(bench *testing.B, op executionFunc, args ...string) {
 			a.SetBytes(arg)
 			stack.push(a)
 		}
-		op(&pc, evmInterpreter, &callCtx{nil, stack, nil})
+		op(&pc, evmInterpreter, &ScopeContext{nil, stack, nil})
 		stack.pop()
 	}
 }
@@ -525,12 +525,12 @@ func TestOpMstore(t *testing.T) {
 	pc := uint64(0)
 	v := "abcdef00000000000000abba000000000deaf000000c0de00100000000133700"
 	stack.pushN(*new(uint256.Int).SetBytes(common.Hex2Bytes(v)), *new(uint256.Int))
-	opMstore(&pc, evmInterpreter, &callCtx{mem, stack, nil})
+	opMstore(&pc, evmInterpreter, &ScopeContext{mem, stack, nil})
 	if got := common.Bytes2Hex(mem.GetCopy(0, 32)); got != v {
 		t.Fatalf("Mstore fail, got %v, expected %v", got, v)
 	}
 	stack.pushN(*new(uint256.Int).SetUint64(0x1), *new(uint256.Int))
-	opMstore(&pc, evmInterpreter, &callCtx{mem, stack, nil})
+	opMstore(&pc, evmInterpreter, &ScopeContext{mem, stack, nil})
 	if common.Bytes2Hex(mem.GetCopy(0, 32)) != "0000000000000000000000000000000000000000000000000000000000000001" {
 		t.Fatalf("Mstore failed to overwrite previous value")
 	}
@@ -553,7 +553,7 @@ func BenchmarkOpMstore(bench *testing.B) {
 	bench.ResetTimer()
 	for i := 0; i < bench.N; i++ {
 		stack.pushN(*value, *memStart)
-		opMstore(&pc, evmInterpreter, &callCtx{mem, stack, nil})
+		opMstore(&pc, evmInterpreter, &ScopeContext{mem, stack, nil})
 	}
 }
 
@@ -572,7 +572,7 @@ func BenchmarkOpSHA3(bench *testing.B) {
 	bench.ResetTimer()
 	for i := 0; i < bench.N; i++ {
 		stack.pushN(*uint256.NewInt().SetUint64(32), *start)
-		opSha3(&pc, evmInterpreter, &callCtx{mem, stack, nil})
+		opSha3(&pc, evmInterpreter, &ScopeContext{mem, stack, nil})
 	}
 }
 

core/vm/interpreter.go

@@ -62,12 +62,12 @@ type Interpreter interface {
 	CanRun([]byte) bool
 }
 
-// callCtx contains the things that are per-call, such as stack and memory,
+// ScopeContext contains the things that are per-call, such as stack and memory,
 // but not transients like pc and gas
-type callCtx struct {
-	memory   *Memory
-	stack    *Stack
-	contract *Contract
+type ScopeContext struct {
+	Memory   *Memory
+	Stack    *Stack
+	Contract *Contract
 }
 
 // keccakState wraps sha3.state. In addition to the usual hash methods, it also supports
@@ -163,10 +163,10 @@ func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (
 		op          OpCode        // current opcode
 		mem         = NewMemory() // bound memory
 		stack       = newstack()  // local stack
-		callContext = &callCtx{
-			memory:   mem,
-			stack:    stack,
-			contract: contract,
+		callContext = &ScopeContext{
+			Memory:   mem,
+			Stack:    stack,
+			Contract: contract,
 		}
 		// For optimisation reason we're using uint64 as the program counter.
 		// It's theoretically possible to go above 2^64. The YP defines the PC
@@ -191,9 +191,9 @@ func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (
 		defer func() {
 			if err != nil {
 				if !logged {
-					in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, mem, stack, in.returnData, contract, in.evm.depth, err)
+					in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, callContext, in.returnData, in.evm.depth, err)
 				} else {
-					in.cfg.Tracer.CaptureFault(in.evm, pcCopy, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
+					in.cfg.Tracer.CaptureFault(in.evm, pcCopy, op, gasCopy, cost, callContext, in.evm.depth, err)
 				}
 			}
 		}()
@@ -275,7 +275,7 @@ func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (
 		}
 
 		if in.cfg.Debug {
-			in.cfg.Tracer.CaptureState(in.evm, pc, op, gasCopy, cost, mem, stack, in.returnData, contract, in.evm.depth, err)
+			in.cfg.Tracer.CaptureState(in.evm, pc, op, gasCopy, cost, callContext, in.returnData, in.evm.depth, err)
 			logged = true
 		}
 

core/vm/jump_table.go

@@ -21,7 +21,7 @@ import (
 )
 
 type (
-	executionFunc func(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byte, error)
+	executionFunc func(pc *uint64, interpreter *EVMInterpreter, callContext *ScopeContext) ([]byte, error)
 	gasFunc       func(*EVM, *Contract, *Stack, *Memory, uint64) (uint64, error) // last parameter is the requested memory size as a uint64
 	// memorySizeFunc returns the required size, and whether the operation overflowed a uint64
 	memorySizeFunc func(*Stack) (size uint64, overflow bool)

core/vm/logger.go

@@ -18,7 +18,6 @@ package vm
 
 import (
 	"encoding/hex"
-	"errors"
 	"fmt"
 	"io"
 	"math/big"
@@ -32,8 +31,6 @@ import (
 	"github.com/ethereum/go-ethereum/params"
 )
 
-var errTraceLimitReached = errors.New("the number of logs reached the specified limit")
-
 // Storage represents a contract's storage.
 type Storage map[common.Hash]common.Hash
 
@@ -107,10 +104,10 @@ func (s *StructLog) ErrorString() string {
 // Note that reference types are actual VM data structures; make copies
 // if you need to retain them beyond the current call.
 type Tracer interface {
-	CaptureStart(from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) error
-	CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, rData []byte, contract *Contract, depth int, err error) error
-	CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, contract *Contract, depth int, err error) error
-	CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) error
+	CaptureStart(env *EVM, from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int)
+	CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, rData []byte, depth int, err error)
+	CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, depth int, err error)
+	CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error)
 }
 
 // StructLogger is an EVM state logger and implements Tracer.
@@ -139,17 +136,19 @@ func NewStructLogger(cfg *LogConfig) *StructLogger {
 }
 
 // CaptureStart implements the Tracer interface to initialize the tracing operation.
-func (l *StructLogger) CaptureStart(from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) error {
-	return nil
+func (l *StructLogger) CaptureStart(env *EVM, from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) {
 }
 
 // CaptureState logs a new structured log message and pushes it out to the environment
 //
 // CaptureState also tracks SLOAD/SSTORE ops to track storage change.
-func (l *StructLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, rData []byte, contract *Contract, depth int, err error) error {
+func (l *StructLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, rData []byte, depth int, err error) {
+	memory := scope.Memory
+	stack := scope.Stack
+	contract := scope.Contract
 	// check if already accumulated the specified number of logs
 	if l.cfg.Limit != 0 && l.cfg.Limit <= len(l.logs) {
-		return errTraceLimitReached
+		return
 	}
 	// Copy a snapshot of the current memory state to a new buffer
 	var mem []byte
@@ -199,17 +198,15 @@ func (l *StructLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost ui
 	// create a new snapshot of the EVM.
 	log := StructLog{pc, op, gas, cost, mem, memory.Len(), stck, rdata, storage, depth, env.StateDB.GetRefund(), err}
 	l.logs = append(l.logs, log)
-	return nil
 }
 
 // CaptureFault implements the Tracer interface to trace an execution fault
 // while running an opcode.
-func (l *StructLogger) CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, contract *Contract, depth int, err error) error {
-	return nil
+func (l *StructLogger) CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, depth int, err error) {
 }
 
 // CaptureEnd is called after the call finishes to finalize the tracing.
-func (l *StructLogger) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) error {
+func (l *StructLogger) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) {
 	l.output = output
 	l.err = err
 	if l.cfg.Debug {
@@ -218,7 +215,6 @@ func (l *StructLogger) CaptureEnd(output []byte, gasUsed uint64, t time.Duration
 			fmt.Printf(" error: %v\n", err)
 		}
 	}
-	return nil
 }
 
 // StructLogs returns the captured log entries.
@@ -292,7 +288,7 @@ func NewMarkdownLogger(cfg *LogConfig, writer io.Writer) *mdLogger {
 	return l
 }
 
-func (t *mdLogger) CaptureStart(from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) error {
+func (t *mdLogger) CaptureStart(env *EVM, from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) {
 	if !create {
 		fmt.Fprintf(t.out, "From: `%v`\nTo: `%v`\nData: `0x%x`\nGas: `%d`\nValue `%v` wei\n",
 			from.String(), to.String(),
@@ -307,10 +303,11 @@ func (t *mdLogger) CaptureStart(from common.Address, to common.Address, create b
 |  Pc   |      Op     | Cost |   Stack   |   RStack  |  Refund |
 |-------|-------------|------|-----------|-----------|---------|
 `)
-	return nil
 }
 
-func (t *mdLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, rData []byte, contract *Contract, depth int, err error) error {
+// CaptureState also tracks SLOAD/SSTORE ops to track storage change.
+func (t *mdLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, rData []byte, depth int, err error) {
+	stack := scope.Stack
 	fmt.Fprintf(t.out, "| %4d  | %10v  |  %3d |", pc, op, cost)
 
 	if !t.cfg.DisableStack {
@@ -327,18 +324,13 @@ func (t *mdLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64
 	if err != nil {
 		fmt.Fprintf(t.out, "Error: %v\n", err)
 	}
-	return nil
 }
 
-func (t *mdLogger) CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, contract *Contract, depth int, err error) error {
-
+func (t *mdLogger) CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, depth int, err error) {
 	fmt.Fprintf(t.out, "\nError: at pc=%d, op=%v: %v\n", pc, op, err)
-
-	return nil
 }
 
-func (t *mdLogger) CaptureEnd(output []byte, gasUsed uint64, tm time.Duration, err error) error {
+func (t *mdLogger) CaptureEnd(output []byte, gasUsed uint64, tm time.Duration, err error) {
 	fmt.Fprintf(t.out, "\nOutput: `0x%x`\nConsumed gas: `%d`\nError: `%v`\n",
 		output, gasUsed, err)
-	return nil
 }

core/vm/logger_json.go

@@ -41,12 +41,16 @@ func NewJSONLogger(cfg *LogConfig, writer io.Writer) *JSONLogger {
 	return l
 }
 
-func (l *JSONLogger) CaptureStart(from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) error {
-	return nil
+func (l *JSONLogger) CaptureStart(env *EVM, from, to common.Address, create bool, input []byte, gas uint64, value *big.Int) {
 }
 
+func (l *JSONLogger) CaptureFault(*EVM, uint64, OpCode, uint64, uint64, *ScopeContext, int, error) {}
+
 // CaptureState outputs state information on the logger.
-func (l *JSONLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, rData []byte, contract *Contract, depth int, err error) error {
+func (l *JSONLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint64, scope *ScopeContext, rData []byte, depth int, err error) {
+	memory := scope.Memory
+	stack := scope.Stack
+
 	log := StructLog{
 		Pc:            pc,
 		Op:            op,
@@ -72,16 +76,11 @@ func (l *JSONLogger) CaptureState(env *EVM, pc uint64, op OpCode, gas, cost uint
 	if !l.cfg.DisableReturnData {
 		log.ReturnData = rData
 	}
-	return l.encoder.Encode(log)
-}
-
-// CaptureFault outputs state information on the logger.
-func (l *JSONLogger) CaptureFault(env *EVM, pc uint64, op OpCode, gas, cost uint64, memory *Memory, stack *Stack, contract *Contract, depth int, err error) error {
-	return nil
+	l.encoder.Encode(log)
 }
 
 // CaptureEnd is triggered at end of execution.
-func (l *JSONLogger) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) error {
+func (l *JSONLogger) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) {
 	type endLog struct {
 		Output  string              `json:"output"`
 		GasUsed math.HexOrDecimal64 `json:"gasUsed"`
@@ -89,7 +88,7 @@ func (l *JSONLogger) CaptureEnd(output []byte, gasUsed uint64, t time.Duration,
 		Err     string              `json:"error,omitempty"`
 	}
 	if err != nil {
-		return l.encoder.Encode(endLog{common.Bytes2Hex(output), math.HexOrDecimal64(gasUsed), t, err.Error()})
+		l.encoder.Encode(endLog{common.Bytes2Hex(output), math.HexOrDecimal64(gasUsed), t, err.Error()})
 	}
-	return l.encoder.Encode(endLog{common.Bytes2Hex(output), math.HexOrDecimal64(gasUsed), t, ""})
+	l.encoder.Encode(endLog{common.Bytes2Hex(output), math.HexOrDecimal64(gasUsed), t, ""})
 }

core/vm/logger_test.go

@@ -53,16 +53,20 @@ func TestStoreCapture(t *testing.T) {
 	var (
 		env      = NewEVM(BlockContext{}, TxContext{}, &dummyStatedb{}, params.TestChainConfig, Config{})
 		logger   = NewStructLogger(nil)
-		mem      = NewMemory()
-		stack    = newstack()
 		contract = NewContract(&dummyContractRef{}, &dummyContractRef{}, new(big.Int), 0)
+		scope    = &ScopeContext{
+			Memory:   NewMemory(),
+			Stack:    newstack(),
+			Contract: contract,
+		}
 	)
-	stack.push(uint256.NewInt().SetUint64(1))
-	stack.push(uint256.NewInt())
+	scope.Stack.push(uint256.NewInt().SetUint64(1))
+	scope.Stack.push(uint256.NewInt())
 	var index common.Hash
-	logger.CaptureState(env, 0, SSTORE, 0, 0, mem, stack, nil, contract, 0, nil)
+	logger.CaptureState(env, 0, SSTORE, 0, 0, scope, nil, 0, nil)
 	if len(logger.storage[contract.Address()]) == 0 {
-		t.Fatalf("expected exactly 1 changed value on address %x, got %d", contract.Address(), len(logger.storage[contract.Address()]))
+		t.Fatalf("expected exactly 1 changed value on address %x, got %d", contract.Address(),
+			len(logger.storage[contract.Address()]))
 	}
 	exp := common.BigToHash(big.NewInt(1))
 	if logger.storage[contract.Address()][index] != exp {

core/vm/runtime/runtime_test.go

@@ -326,23 +326,18 @@ type stepCounter struct {
 	steps int
 }
 
-func (s *stepCounter) CaptureStart(from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) error {
-	return nil
+func (s *stepCounter) CaptureStart(env *vm.EVM, from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) {
 }
 
-func (s *stepCounter) CaptureState(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, memory *vm.Memory, stack *vm.Stack, rData []byte, contract *vm.Contract, depth int, err error) error {
-	s.steps++
-	// Enable this for more output
-	//s.inner.CaptureState(env, pc, op, gas, cost, memory, stack, rStack, contract, depth, err)
-	return nil
+func (s *stepCounter) CaptureFault(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, scope *vm.ScopeContext, depth int, err error) {
 }
 
-func (s *stepCounter) CaptureFault(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, memory *vm.Memory, stack *vm.Stack, contract *vm.Contract, depth int, err error) error {
-	return nil
-}
+func (s *stepCounter) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) {}
 
-func (s *stepCounter) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) error {
-	return nil
+func (s *stepCounter) CaptureState(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, scope *vm.ScopeContext, rData []byte, depth int, err error) {
+	s.steps++
+	// Enable this for more output
+	//s.inner.CaptureState(env, pc, op, gas, cost, memory, stack, rStack, contract, depth, err)
 }
 
 // benchmarkNonModifyingCode benchmarks code, but if the code modifies the

eth/tracers/tracer.go

@@ -287,8 +287,6 @@ func (cw *contractWrapper) pushObject(vm *duktape.Context) {
 // Tracer provides an implementation of Tracer that evaluates a Javascript
 // function for each VM execution step.
 type Tracer struct {
-	inited bool // Flag whether the context was already inited from the EVM
-
 	vm *duktape.Context // Javascript VM instance
 
 	tracerObject int // Stack index of the tracer JavaScript object
@@ -529,7 +527,7 @@ func wrapError(context string, err error) error {
 }
 
 // CaptureStart implements the Tracer interface to initialize the tracing operation.
-func (jst *Tracer) CaptureStart(from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) error {
+func (jst *Tracer) CaptureStart(env *vm.EVM, from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) {
 	jst.ctx["type"] = "CALL"
 	if create {
 		jst.ctx["type"] = "CREATE"
@@ -540,77 +538,67 @@ func (jst *Tracer) CaptureStart(from common.Address, to common.Address, create b
 	jst.ctx["gas"] = gas
 	jst.ctx["value"] = value
 
-	return nil
+	// Initialize the context
+	jst.ctx["block"] = env.Context.BlockNumber.Uint64()
+	jst.dbWrapper.db = env.StateDB
+	// Compute intrinsic gas
+	isHomestead := env.ChainConfig().IsHomestead(env.Context.BlockNumber)
+	isIstanbul := env.ChainConfig().IsIstanbul(env.Context.BlockNumber)
+	intrinsicGas, err := core.IntrinsicGas(input, nil, jst.ctx["type"] == "CREATE", isHomestead, isIstanbul)
+	if err != nil {
+		return
+	}
+	jst.ctx["intrinsicGas"] = intrinsicGas
 }
 
 // CaptureState implements the Tracer interface to trace a single step of VM execution.
-func (jst *Tracer) CaptureState(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, memory *vm.Memory, stack *vm.Stack, rdata []byte, contract *vm.Contract, depth int, err error) error {
-	if jst.err == nil {
-		// Initialize the context if it wasn't done yet
-		if !jst.inited {
-			jst.ctx["block"] = env.Context.BlockNumber.Uint64()
-			// Compute intrinsic gas
-			isHomestead := env.ChainConfig().IsHomestead(env.Context.BlockNumber)
-			isIstanbul := env.ChainConfig().IsIstanbul(env.Context.BlockNumber)
-			var input []byte
-			if data, ok := jst.ctx["input"].([]byte); ok {
-				input = data
-			}
-			intrinsicGas, err := core.IntrinsicGas(input, nil, jst.ctx["type"] == "CREATE", isHomestead, isIstanbul)
-			if err != nil {
-				return err
-			}
-			jst.ctx["intrinsicGas"] = intrinsicGas
-			jst.inited = true
-		}
-		// If tracing was interrupted, set the error and stop
-		if atomic.LoadUint32(&jst.interrupt) > 0 {
-			jst.err = jst.reason
-			return nil
-		}
-		jst.opWrapper.op = op
-		jst.stackWrapper.stack = stack
-		jst.memoryWrapper.memory = memory
-		jst.contractWrapper.contract = contract
-		jst.dbWrapper.db = env.StateDB
-
-		*jst.pcValue = uint(pc)
-		*jst.gasValue = uint(gas)
-		*jst.costValue = uint(cost)
-		*jst.depthValue = uint(depth)
-		*jst.refundValue = uint(env.StateDB.GetRefund())
-
-		jst.errorValue = nil
-		if err != nil {
-			jst.errorValue = new(string)
-			*jst.errorValue = err.Error()
-		}
-		_, err := jst.call("step", "log", "db")
-		if err != nil {
-			jst.err = wrapError("step", err)
-		}
+func (jst *Tracer) CaptureState(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, scope *vm.ScopeContext, rData []byte, depth int, err error) {
+	if jst.err != nil {
+		return
+	}
+	// If tracing was interrupted, set the error and stop
+	if atomic.LoadUint32(&jst.interrupt) > 0 {
+		jst.err = jst.reason
+		return
+	}
+	jst.opWrapper.op = op
+	jst.stackWrapper.stack = scope.Stack
+	jst.memoryWrapper.memory = scope.Memory
+	jst.contractWrapper.contract = scope.Contract
+
+	*jst.pcValue = uint(pc)
+	*jst.gasValue = uint(gas)
+	*jst.costValue = uint(cost)
+	*jst.depthValue = uint(depth)
+	*jst.refundValue = uint(env.StateDB.GetRefund())
+
+	jst.errorValue = nil
+	if err != nil {
+		jst.errorValue = new(string)
+		*jst.errorValue = err.Error()
+	}
+
+	if _, err := jst.call("step", "log", "db"); err != nil {
+		jst.err = wrapError("step", err)
 	}
-	return nil
 }
 
 // CaptureFault implements the Tracer interface to trace an execution fault
-// while running an opcode.
-func (jst *Tracer) CaptureFault(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, memory *vm.Memory, stack *vm.Stack, contract *vm.Contract, depth int, err error) error {
-	if jst.err == nil {
-		// Apart from the error, everything matches the previous invocation
-		jst.errorValue = new(string)
-		*jst.errorValue = err.Error()
+func (jst *Tracer) CaptureFault(env *vm.EVM, pc uint64, op vm.OpCode, gas, cost uint64, scope *vm.ScopeContext, depth int, err error) {
+	if jst.err != nil {
+		return
+	}
+	// Apart from the error, everything matches the previous invocation
+	jst.errorValue = new(string)
+	*jst.errorValue = err.Error()
 
-		_, err := jst.call("fault", "log", "db")
-		if err != nil {
-			jst.err = wrapError("fault", err)
-		}
+	if _, err := jst.call("fault", "log", "db"); err != nil {
+		jst.err = wrapError("fault", err)
 	}
-	return nil
 }
 
 // CaptureEnd is called after the call finishes to finalize the tracing.
-func (jst *Tracer) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) error {
+func (jst *Tracer) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, err error) {
 	jst.ctx["output"] = output
 	jst.ctx["time"] = t.String()
 	jst.ctx["gasUsed"] = gasUsed
@@ -618,7 +606,6 @@ func (jst *Tracer) CaptureEnd(output []byte, gasUsed uint64, t time.Duration, er
 	if err != nil {
 		jst.ctx["error"] = err.Error()
 	}
-	return nil
 }
 
 // GetResult calls the Javascript 'result' function and returns its value, or any accumulated error

eth/tracers/tracer_test.go

@@ -47,7 +47,8 @@ type dummyStatedb struct {
 	state.StateDB
 }
 
-func (*dummyStatedb) GetRefund() uint64 { return 1337 }
+func (*dummyStatedb) GetRefund() uint64                       { return 1337 }
+func (*dummyStatedb) GetBalance(addr common.Address) *big.Int { return new(big.Int) }
 
 type vmContext struct {
 	blockCtx vm.BlockContext
@@ -67,7 +68,7 @@ func runTrace(tracer *Tracer, vmctx *vmContext) (json.RawMessage, error) {
 	contract := vm.NewContract(account{}, account{}, value, startGas)
 	contract.Code = []byte{byte(vm.PUSH1), 0x1, byte(vm.PUSH1), 0x1, 0x0}
 
-	tracer.CaptureStart(contract.Caller(), contract.Address(), false, []byte{}, startGas, value)
+	tracer.CaptureStart(env, contract.Caller(), contract.Address(), false, []byte{}, startGas, value)
 	ret, err := env.Interpreter().Run(contract, []byte{}, false)
 	tracer.CaptureEnd(ret, startGas-contract.Gas, 1, err)
 	if err != nil {
@@ -150,14 +151,55 @@ func TestHaltBetweenSteps(t *testing.T) {
 		t.Fatal(err)
 	}
 	env := vm.NewEVM(vm.BlockContext{BlockNumber: big.NewInt(1)}, vm.TxContext{}, &dummyStatedb{}, params.TestChainConfig, vm.Config{Debug: true, Tracer: tracer})
-	contract := vm.NewContract(&account{}, &account{}, big.NewInt(0), 0)
+	scope := &vm.ScopeContext{
+		Contract: vm.NewContract(&account{}, &account{}, big.NewInt(0), 0),
+	}
 
-	tracer.CaptureState(env, 0, 0, 0, 0, nil, nil, nil, contract, 0, nil)
+	tracer.CaptureState(env, 0, 0, 0, 0, scope, nil, 0, nil)
 	timeout := errors.New("stahp")
 	tracer.Stop(timeout)
-	tracer.CaptureState(env, 0, 0, 0, 0, nil, nil, nil, contract, 0, nil)
+	tracer.CaptureState(env, 0, 0, 0, 0, scope, nil, 0, nil)
 
 	if _, err := tracer.GetResult(); err.Error() != timeout.Error() {
 		t.Errorf("Expected timeout error, got %v", err)
 	}
 }
+
+// TestNoStepExec tests a regular value transfer (no exec), and accessing the statedb
+// in 'result'
+func TestNoStepExec(t *testing.T) {
+	runEmptyTrace := func(tracer *Tracer, vmctx *vmContext) (json.RawMessage, error) {
+		env := vm.NewEVM(vmctx.blockCtx, vmctx.txCtx, &dummyStatedb{}, params.TestChainConfig, vm.Config{Debug: true, Tracer: tracer})
+		startGas := uint64(10000)
+		contract := vm.NewContract(account{}, account{}, big.NewInt(0), startGas)
+		tracer.CaptureStart(env, contract.Caller(), contract.Address(), false, []byte{}, startGas, big.NewInt(0))
+		tracer.CaptureEnd(nil, startGas-contract.Gas, 1, nil)
+		return tracer.GetResult()
+	}
+	execTracer := func(code string) []byte {
+		t.Helper()
+		ctx := &vmContext{blockCtx: vm.BlockContext{BlockNumber: big.NewInt(1)}, txCtx: vm.TxContext{GasPrice: big.NewInt(100000)}}
+		tracer, err := New(code, ctx.txCtx)
+		if err != nil {
+			t.Fatal(err)
+		}
+		ret, err := runEmptyTrace(tracer, ctx)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return ret
+	}
+	for i, tt := range []struct {
+		code string
+		want string
+	}{
+		{ // tests that we don't panic on accessing the db methods
+			code: "{depths: [], step: function() {}, fault: function() {},  result: function(ctx, db){ return db.getBalance(ctx.to)} }",
+			want: `"0"`,
+		},
+	} {
+		if have := execTracer(tt.code); tt.want != string(have) {
+			t.Errorf("testcase %d: expected return value to be %s got %s\n\tcode: %v", i, tt.want, string(have), tt.code)
+		}
+	}
+}