core/vm: review changes (gas, comments)

* Changed the gas for RETURNDATASIZE
* Added comments for read only check
* Fixed opReturnDataCopy

core/vm/instructions.go

@@ -30,7 +30,8 @@ import (
 
 var (
  bigZero = new(big.Int)
- errWriteProtection = errors.New("evm write protection")
+ errWriteProtection = errors.New("evm: write protection")
+ errReadOutOfBound = errors.New("evm: read out of bound")
 )
 
 func opAdd(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
@@ -778,9 +779,14 @@ func opReturnDataCopy(pc *uint64, evm *EVM, contract *Contract, memory *Memory,
  cOff = stack.pop()
  l = stack.pop()
  )
- memory.Set(mOff.Uint64(), l.Uint64(), getData(evm.interpreter.returnData, cOff, l))
+ defer evm.interpreter.intPool.put(mOff, cOff, l)
+
+ cEnd := new(big.Int).Add(cOff, l)
+ if cEnd.BitLen() > 64 || uint64(len(evm.interpreter.returnData)) < cEnd.Uint64() {
+ return nil, errReadOutOfBound
+ }
+ memory.Set(mOff.Uint64(), l.Uint64(), evm.interpreter.returnData[cOff.Uint64():cEnd.Uint64()])
 
- evm.interpreter.intPool.put(mOff, cOff, l)
  return nil, nil
 }
 

core/vm/interpreter.go

@@ -93,7 +93,10 @@ func (in *Interpreter) enforceRestrictions(op OpCode, operation operation, stack
  if in.evm.chainRules.IsMetropolis {
  if in.readonly {
  // if the interpreter is operating in readonly mode, make sure no
- // state-modifying operation is performed.
+ // state-modifying operation is performed. The 4th stack item
+ // for a call operation is the value. Transfering value from one
+ // account to the others means the state is modified and should also
+ // return with an error.
  if operation.writes ||
  ((op == CALL || op == CALLCODE) && stack.Back(3).BitLen() > 0) {
  return errWriteProtection

core/vm/jump_table.go

@@ -84,7 +84,7 @@ func NewMetropolisInstructionSet() [256]operation {
  }
  instructionSet[RETURNDATASIZE] = operation{
  execute: opReturnDataSize,
- gasCost: constGasFunc(0), // TODO
+ gasCost: constGasFunc(GasQuickStep),
  validateStack: makeStackFunc(0, 1),
  valid: true,
  }