core/vm: customisable jump table

core/vm/jump_table.go

@@ -48,7 +48,10 @@ type operation struct {
 	valid bool
 }
 
-var jumpTable = [256]operation{
+var defaultJumpTable = NewJumpTable()
+
+func NewJumpTable() [256]operation {
+	return [256]operation{
 		ADD: operation{
 			execute:       opAdd,
 			gasCost:       constGasFunc(GasFastestStep),
@@ -852,4 +855,5 @@ var jumpTable = [256]operation{
 			validateStack: makeStackFunc(16, 1),
 			valid:         true,
 		},
+	}
 }

core/vm/vm.go

@@ -44,6 +44,10 @@ type Config struct {
 	NoRecursion bool
 	// Disable gas metering
 	DisableGasMetering bool
+	// JumpTable contains the EVM instruction table. This
+	// may me left uninitialised and will be set the default
+	// table.
+	JumpTable [256]operation
 }
 
 // Interpreter is used to run Ethereum based contracts and will utilise the
@@ -58,6 +62,13 @@ type Interpreter struct {
 
 // NewInterpreter returns a new instance of the Interpreter.
 func NewInterpreter(env *EVM, cfg Config) *Interpreter {
+	// We use the STOP instruction whether to see
+	// the jump table was initialised. If it was not
+	// we'll set the default jump table.
+	if !cfg.JumpTable[STOP].valid {
+		cfg.JumpTable = defaultJumpTable
+	}
+
 	return &Interpreter{
 		env:      env,
 		cfg:      cfg,
@@ -121,7 +132,7 @@ func (evm *Interpreter) Run(contract *Contract, input []byte) (ret []byte, err e
 		op = contract.GetOp(pc)
 
 		// get the operation from the jump table matching the opcode
-		operation := jumpTable[op]
+		operation := evm.cfg.JumpTable[op]
 
 		// if the op is invalid abort the process and return an error
 		if !operation.valid {