From e70a2b449160d651a898e46288d4e30cbcd3c737 Mon Sep 17 00:00:00 2001
From: Jeffrey Wilcke <jeffrey@ethereum.org>
Date: Sat, 19 Mar 2016 01:24:23 +0100
Subject: [PATCH] core/vm: fix possible jump table race

---
 core/vm/jump_table.go      | 23 ++++++++++++-----------
 core/vm/jump_table_test.go | 19 ++++---------------
 core/vm/vm.go              | 16 +++++++++++-----
 3 files changed, 27 insertions(+), 31 deletions(-)

diff --git a/core/vm/jump_table.go b/core/vm/jump_table.go
index 37d7bb160f..8a0f0a01c2 100644
--- a/core/vm/jump_table.go
+++ b/core/vm/jump_table.go
@@ -1,10 +1,6 @@
 package vm
 
-import (
-	"math/big"
-
-	"github.com/ethereum/go-ethereum/params"
-)
+import "math/big"
 
 type jumpPtr struct {
 	fn    instrFn
@@ -13,19 +9,22 @@ type jumpPtr struct {
 
 type vmJumpTable [256]jumpPtr
 
-func (jt vmJumpTable) init(blockNumber *big.Int) {
+var (
+	homesteadJumpTable = newJumpTable(true)
+	frontierJumpTable  = newJumpTable(false)
+)
+
+func newJumpTable(homestead bool) vmJumpTable {
+	var jumpTable vmJumpTable
+
 	// when initialising a new VM execution we must first check the homestead
 	// changes.
-	if params.IsHomestead(blockNumber) {
+	if homestead {
 		jumpTable[DELEGATECALL] = jumpPtr{opDelegateCall, true}
 	} else {
 		jumpTable[DELEGATECALL] = jumpPtr{nil, false}
 	}
-}
 
-var jumpTable vmJumpTable
-
-func init() {
 	jumpTable[ADD] = jumpPtr{opAdd, true}
 	jumpTable[SUB] = jumpPtr{opSub, true}
 	jumpTable[MUL] = jumpPtr{opMul, true}
@@ -156,4 +155,6 @@ func init() {
 	jumpTable[JUMP] = jumpPtr{nil, true}
 	jumpTable[JUMPI] = jumpPtr{nil, true}
 	jumpTable[STOP] = jumpPtr{nil, true}
+
+	return jumpTable
 }
diff --git a/core/vm/jump_table_test.go b/core/vm/jump_table_test.go
index 98d34bef20..71ffc25116 100644
--- a/core/vm/jump_table_test.go
+++ b/core/vm/jump_table_test.go
@@ -1,24 +1,13 @@
 package vm
 
-import (
-	"math/big"
-	"testing"
-
-	"github.com/ethereum/go-ethereum/params"
-)
+import "testing"
 
 func TestInit(t *testing.T) {
-	params.HomesteadBlock = big.NewInt(1)
-
-	jumpTable.init(big.NewInt(0))
-	if jumpTable[DELEGATECALL].valid {
+	if frontierJumpTable[DELEGATECALL].valid {
 		t.Error("Expected DELEGATECALL not to be present")
 	}
 
-	for _, n := range []int64{1, 2, 100} {
-		jumpTable.init(big.NewInt(n))
-		if !jumpTable[DELEGATECALL].valid {
-			t.Error("Expected DELEGATECALL to be present for block", n)
-		}
+	if !homesteadJumpTable[DELEGATECALL].valid {
+		t.Error("Expected DELEGATECALL not to be present")
 	}
 }
diff --git a/core/vm/vm.go b/core/vm/vm.go
index 4b502e3d81..8eb355f86a 100644
--- a/core/vm/vm.go
+++ b/core/vm/vm.go
@@ -30,15 +30,21 @@ import (
 
 // Vm is an EVM and implements VirtualMachine
 type Vm struct {
-	env Environment
+	env       Environment
+	jumpTable vmJumpTable
 }
 
 // New returns a new Vm
 func New(env Environment) *Vm {
-	// init the jump table. Also prepares the homestead changes
-	jumpTable.init(env.BlockNumber())
+	evm := &Vm{env: env}
 
-	return &Vm{env: env}
+	if params.IsHomestead(env.BlockNumber()) {
+		evm.jumpTable = homesteadJumpTable
+	} else {
+		evm.jumpTable = frontierJumpTable
+	}
+
+	return evm
 }
 
 // Run loops and evaluates the contract's code with the given input data
@@ -169,7 +175,7 @@ func (self *Vm) Run(contract *Contract, input []byte) (ret []byte, err error) {
 		mem.Resize(newMemSize.Uint64())
 		// Add a log message
 		self.log(pc, op, contract.Gas, cost, mem, stack, contract, nil)
-		if opPtr := jumpTable[op]; opPtr.valid {
+		if opPtr := self.jumpTable[op]; opPtr.valid {
 			if opPtr.fn != nil {
 				opPtr.fn(instruction{}, &pc, self.env, contract, mem, stack)
 			} else {