eth/tracers/native: add keccak256preimage tracer (#32569)

Introduces a new tracer which returns the preimages
of evm KECCAK256 hashes.

See #32570.

---------

Co-authored-by: Sina M <[email protected]>
Co-authored-by: Sina Mahmoodi <[email protected]>

Author: draganm

eth/tracers/native/keccak256_preimage.go

@@ -0,0 +1,86 @@
+package native
+
+// Copyright 2021 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+import (
+	"encoding/json"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/core/tracing"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/eth/tracers"
+	"github.com/ethereum/go-ethereum/eth/tracers/internal"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+func init() {
+	tracers.DefaultDirectory.Register("keccak256PreimageTracer", newKeccak256PreimageTracer, false)
+}
+
+// keccak256PreimageTracer is a native tracer that collects preimages of all KECCAK256 operations.
+// This tracer is particularly useful for analyzing smart contract execution patterns,
+// especially when debugging storage access in Solidity mappings and dynamic arrays.
+type keccak256PreimageTracer struct {
+	computedHashes map[common.Hash]hexutil.Bytes
+}
+
+// newKeccak256PreimageTracer returns a new keccak256PreimageTracer instance.
+func newKeccak256PreimageTracer(ctx *tracers.Context, cfg json.RawMessage, chainConfig *params.ChainConfig) (*tracers.Tracer, error) {
+	t := &keccak256PreimageTracer{
+		computedHashes: make(map[common.Hash]hexutil.Bytes),
+	}
+	return &tracers.Tracer{
+		Hooks: &tracing.Hooks{
+			OnOpcode: t.OnOpcode,
+		},
+		GetResult: t.GetResult,
+	}, nil
+}
+
+func (t *keccak256PreimageTracer) OnOpcode(pc uint64, op byte, gas, cost uint64, scope tracing.OpContext, rData []byte, depth int, err error) {
+	if op == byte(vm.KECCAK256) {
+		sd := scope.StackData()
+		// it turns out that sometimes the stack is empty, evm will fail in this case, but we should not panic here
+		if len(sd) < 2 {
+			return
+		}
+
+		dataOffset := internal.StackBack(sd, 0).Uint64()
+		dataLength := internal.StackBack(sd, 1).Uint64()
+		preimage, err := internal.GetMemoryCopyPadded(scope.MemoryData(), int64(dataOffset), int64(dataLength))
+		if err != nil {
+			log.Warn("keccak256PreimageTracer: failed to copy keccak preimage from memory", "err", err)
+			return
+		}
+
+		hash := crypto.Keccak256(preimage)
+
+		t.computedHashes[common.Hash(hash)] = hexutil.Bytes(preimage)
+	}
+}
+
+// GetResult returns the collected keccak256 preimages as a JSON object mapping hashes to preimages.
+func (t *keccak256PreimageTracer) GetResult() (json.RawMessage, error) {
+	msg, err := json.Marshal(t.computedHashes)
+	if err != nil {
+		return nil, err
+	}
+	return msg, nil
+}