core/asm: assembly parser label fixes (ethereum#20210)

* core/asm: Fix encoding of pushed labels

EVM uses big-endian byte-order, so to pad a label value to 4 bytes,
zeros must be added to the front, not the end.

* core/asm: Fix PC calculations when a label is pushed

Incrementing PC by 5 is only correct if the label appears after a jump,
in which case there is an implicit push. When it appears after an explicit
push, PC should only be incremented by 4.

* core/asm: Allow JUMP with no argument

This way, a label can be pushed explicitly, or loaded from memory to
implement a jump table.

core/asm/compiler.go

@@ -57,6 +57,7 @@ func NewCompiler(debug bool) *Compiler {
 // second stage to push labels and determine the right
 // position.
 func (c *Compiler) Feed(ch <-chan token) {
+	var prev token
 	for i := range ch {
 		switch i.typ {
 		case number:
@@ -73,10 +74,14 @@ func (c *Compiler) Feed(ch <-chan token) {
 			c.labels[i.text] = c.pc
 			c.pc++
 		case label:
-			c.pc += 5
+			c.pc += 4
+			if prev.typ == element && isJump(prev.text) {
+				c.pc++
+			}
 		}
 
 		c.tokens = append(c.tokens, i)
+		prev = i
 	}
 	if c.debug {
 		fmt.Fprintln(os.Stderr, "found", len(c.labels), "labels")
@@ -181,6 +186,8 @@ func (c *Compiler) compileElement(element token) error {
 			pos := big.NewInt(int64(c.labels[rvalue.text])).Bytes()
 			pos = append(make([]byte, 4-len(pos)), pos...)
 			c.pushBin(pos)
+		case lineEnd:
+			c.pos--
 		default:
 			return compileErr(rvalue, rvalue.text, "number, string or label")
 		}
@@ -201,8 +208,8 @@ func (c *Compiler) compileElement(element token) error {
 		case stringValue:
 			value = []byte(rvalue.text[1 : len(rvalue.text)-1])
 		case label:
-			value = make([]byte, 4)
-			copy(value, big.NewInt(int64(c.labels[rvalue.text])).Bytes())
+			value = big.NewInt(int64(c.labels[rvalue.text])).Bytes()
+			value = append(make([]byte, 4-len(value)), value...)
 		default:
 			return compileErr(rvalue, rvalue.text, "number, string or label")
 		}

core/asm/compiler_test.go

@@ -0,0 +1,71 @@
+// Copyright 2019 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 asm
+
+import (
+	"testing"
+)
+
+func TestCompiler(t *testing.T) {
+	tests := []struct {
+		input, output string
+	}{
+		{
+			input: `
+	GAS
+	label:
+	PUSH @label
+`,
+			output: "5a5b6300000001",
+		},
+		{
+			input: `
+	PUSH @label
+	label:
+`,
+			output: "63000000055b",
+		},
+		{
+			input: `
+	PUSH @label
+	JUMP
+	label:
+`,
+			output: "6300000006565b",
+		},
+		{
+			input: `
+	JUMP @label
+	label:
+`,
+			output: "6300000006565b",
+		},
+	}
+	for _, test := range tests {
+		ch := Lex([]byte(test.input), false)
+		c := NewCompiler(false)
+		c.Feed(ch)
+		output, err := c.Compile()
+		if len(err) != 0 {
+			t.Errorf("compile error: %v\ninput: %s", err, test.input)
+			continue
+		}
+		if output != test.output {
+			t.Errorf("incorrect output\ninput: %sgot:  %s\nwant: %s\n", test.input, output, test.output)
+		}
+	}
+}