1// Copyright 2021 The go-ethereum Authors
2// This file is part of the go-ethereum library.
3//
4// The go-ethereum library is free software: you can redistribute it and/or modify
5// it under the terms of the GNU Lesser General Public License as published by
6// the Free Software Foundation, either version 3 of the License, or
7// (at your option) any later version.
8//
9// The go-ethereum library is distributed in the hope that it will be useful,
10// but WITHOUT ANY WARRANTY; without even the implied warranty of
11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12// GNU Lesser General Public License for more details.
13//
14// You should have received a copy of the GNU Lesser General Public License
15// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
16
17package native
18
19import (
20	"encoding/json"
21	"math/big"
22	"strconv"
23	"sync/atomic"
24	"time"
25
26	"github.com/ethereum/go-ethereum/common"
27	"github.com/ethereum/go-ethereum/core/vm"
28	"github.com/ethereum/go-ethereum/eth/tracers"
29)
30
31func init() {
32	register("4byteTracer", newFourByteTracer)
33}
34
35// fourByteTracer searches for 4byte-identifiers, and collects them for post-processing.
36// It collects the methods identifiers along with the size of the supplied data, so
37// a reversed signature can be matched against the size of the data.
38//
39// Example:
40//   > debug.traceTransaction( "0x214e597e35da083692f5386141e69f47e973b2c56e7a8073b1ea08fd7571e9de", {tracer: "4byteTracer"})
41//   {
42//     0x27dc297e-128: 1,
43//     0x38cc4831-0: 2,
44//     0x524f3889-96: 1,
45//     0xadf59f99-288: 1,
46//     0xc281d19e-0: 1
47//   }
48type fourByteTracer struct {
49	env               *vm.EVM
50	ids               map[string]int   // ids aggregates the 4byte ids found
51	interrupt         uint32           // Atomic flag to signal execution interruption
52	reason            error            // Textual reason for the interruption
53	activePrecompiles []common.Address // Updated on CaptureStart based on given rules
54}
55
56// newFourByteTracer returns a native go tracer which collects
57// 4 byte-identifiers of a tx, and implements vm.EVMLogger.
58func newFourByteTracer() tracers.Tracer {
59	t := &fourByteTracer{
60		ids: make(map[string]int),
61	}
62	return t
63}
64
65// isPrecompiled returns whether the addr is a precompile. Logic borrowed from newJsTracer in eth/tracers/js/tracer.go
66func (t *fourByteTracer) isPrecompiled(addr common.Address) bool {
67	for _, p := range t.activePrecompiles {
68		if p == addr {
69			return true
70		}
71	}
72	return false
73}
74
75// store saves the given identifier and datasize.
76func (t *fourByteTracer) store(id []byte, size int) {
77	key := bytesToHex(id) + "-" + strconv.Itoa(size)
78	t.ids[key] += 1
79}
80
81// CaptureStart implements the EVMLogger interface to initialize the tracing operation.
82func (t *fourByteTracer) CaptureStart(env *vm.EVM, from common.Address, to common.Address, create bool, input []byte, gas uint64, value *big.Int) {
83	t.env = env
84
85	// Update list of precompiles based on current block
86	rules := env.ChainConfig().Rules(env.Context.BlockNumber)
87	t.activePrecompiles = vm.ActivePrecompiles(rules)
88
89	// Save the outer calldata also
90	if len(input) >= 4 {
91		t.store(input[0:4], len(input)-4)
92	}
93}
94
95// CaptureState implements the EVMLogger interface to trace a single step of VM execution.
96func (t *fourByteTracer) CaptureState(pc uint64, op vm.OpCode, gas, cost uint64, scope *vm.ScopeContext, rData []byte, depth int, err error) {
97}
98
99// CaptureEnter is called when EVM enters a new scope (via call, create or selfdestruct).
100func (t *fourByteTracer) CaptureEnter(op vm.OpCode, from common.Address, to common.Address, input []byte, gas uint64, value *big.Int) {
101	// Skip if tracing was interrupted
102	if atomic.LoadUint32(&t.interrupt) > 0 {
103		t.env.Cancel()
104		return
105	}
106	if len(input) < 4 {
107		return
108	}
109	// primarily we want to avoid CREATE/CREATE2/SELFDESTRUCT
110	if op != vm.DELEGATECALL && op != vm.STATICCALL &&
111		op != vm.CALL && op != vm.CALLCODE {
112		return
113	}
114	// Skip any pre-compile invocations, those are just fancy opcodes
115	if t.isPrecompiled(to) {
116		return
117	}
118	t.store(input[0:4], len(input)-4)
119}
120
121// CaptureExit is called when EVM exits a scope, even if the scope didn't
122// execute any code.
123func (t *fourByteTracer) CaptureExit(output []byte, gasUsed uint64, err error) {
124}
125
126// CaptureFault implements the EVMLogger interface to trace an execution fault.
127func (t *fourByteTracer) CaptureFault(pc uint64, op vm.OpCode, gas, cost uint64, scope *vm.ScopeContext, depth int, err error) {
128}
129
130// CaptureEnd is called after the call finishes to finalize the tracing.
131func (t *fourByteTracer) CaptureEnd(output []byte, gasUsed uint64, _ time.Duration, err error) {
132}
133
134// GetResult returns the json-encoded nested list of call traces, and any
135// error arising from the encoding or forceful termination (via `Stop`).
136func (t *fourByteTracer) GetResult() (json.RawMessage, error) {
137	res, err := json.Marshal(t.ids)
138	if err != nil {
139		return nil, err
140	}
141	return res, t.reason
142}
143
144// Stop terminates execution of the tracer at the first opportune moment.
145func (t *fourByteTracer) Stop(err error) {
146	t.reason = err
147	atomic.StoreUint32(&t.interrupt, 1)
148}
149