disasm: print invalid opcodes as #bytes

Author: fjl

disasm/disassembler.go

@@ -90,16 +90,11 @@ func (d *Disassembler) Disassemble(bytecode []byte, outW io.Writer) error {
 			d.printInvalid(out, bytecode[pc])
 		} else {
 			d.printPrefix(out, pc)
-			d.printOp(out, op)
-			if op.Push && op.Name != "PUSH0" {
-				size := op.PushSize()
-				if len(bytecode)-1-pc < size {
-					d.newline(out, op, nil)
-					return fmt.Errorf("bytecode truncated, ends within %s", op.Name)
-				}
-				data := bytecode[pc+1 : pc+size+1]
-				d.printPushData(out, data)
+			if op.Push {
+				size := d.printPush(out, op, bytecode[pc:])
 				pc += size
+			} else {
+				d.printOp(out, op)
 			}
 		}
 
@@ -120,7 +115,7 @@ func (d *Disassembler) printPrefix(out io.Writer, pc int) {
 }
 
 func (d *Disassembler) printInvalid(out io.Writer, b byte) {
-	fmt.Fprintf(out, "<invalid %x>\n", b)
+	fmt.Fprintf(out, "#bytes %#x\n", b)
 }
 
 func (d *Disassembler) printOp(out io.Writer, op *evm.Op) {
@@ -131,8 +126,21 @@ func (d *Disassembler) printOp(out io.Writer, op *evm.Op) {
 	fmt.Fprint(out, name)
 }
 
-func (d *Disassembler) printPushData(out io.Writer, data []byte) {
+func (d *Disassembler) printPush(out io.Writer, op *evm.Op, code []byte) (dataSize int) {
+	size := op.PushSize()
+	if size == 0 {
+		d.printOp(out, op)
+		return 0
+	}
+	if size > len(code)-1 {
+		// Handle truncated PUSH at end of code.
+		fmt.Fprintf(out, "#bytes %#x", code)
+		return len(code) - 1
+	}
+	d.printOp(out, op)
+	data := code[1 : size+1]
 	fmt.Fprintf(out, " %#x", data)
+	return len(data)
 }
 
 func (d *Disassembler) newline(out io.Writer, prevOp *evm.Op, nextOp *evm.Op) {

disasm/disassembler_test.go

@@ -0,0 +1,94 @@
+// Copyright 2025 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/>.
+
+package disasm
+
+import (
+	"bytes"
+	"encoding/hex"
+	"strings"
+	"testing"
+
+	"github.com/fjl/geas/asm"
+)
+
+func TestIncompletePush(t *testing.T) {
+	bytecode, _ := hex.DecodeString("6080604052348015600e575f80fd5b50603e80601a5f395ff3fe60806040525f80fdfea2646970667358221220ba4339602dd535d09d71fae3164f7aa7f6e098ec879fc9e8f36bd912d4877c5264736f6c63430008190033")
+	expectedOutput := strings.TrimSpace(`
+push1 0x80
+push1 0x40
+mstore
+callvalue
+dup1
+iszero
+push1 0x0e
+jumpi
+push0
+dup1
+revert
+jumpdest
+pop
+push1 0x3e
+dup1
+push1 0x1a
+push0
+codecopy
+push0
+return
+#bytes 0xfe
+push1 0x80
+push1 0x40
+mstore
+push0
+dup1
+revert
+#bytes 0xfe
+log2
+push5 0x6970667358
+#bytes 0x22
+slt
+keccak256
+#bytes 0xba
+number
+codecopy
+push1 0x2d
+#bytes 0xd5
+calldataload
+#bytes 0xd0
+swap14
+push18 0xfae3164f7aa7f6e098ec879fc9e8f36bd912
+#bytes 0xd4
+dup8
+#bytes 0x7c5264736f6c63430008190033
+`)
+
+	var buf strings.Builder
+	d := New()
+	d.SetShowBlocks(false)
+	d.SetTarget("cancun")
+	d.Disassemble(bytecode, &buf)
+	output := strings.TrimSpace(buf.String())
+	if output != expectedOutput {
+		t.Fatal("wrong output:", output)
+	}
+
+	// try round trip
+	a := asm.New(nil)
+	rtcode := a.CompileString(output)
+	if !bytes.Equal(rtcode, bytecode) {
+		t.Error("disassembly did not round-trip")
+	}
+}