core/vm: minor polishes, fix STATICCALL for precompiles

 * Fix STATICCALL so it is able to call precompiles too
 * Fix write detection to use the correct value argument of CALL
 * Fix write protection to ignore the value in CALLCODE

2 files changed, 33 insertions, 37 deletions

diff --git a/core/vm/evm.go b/core/vm/evm.go
index 97a9d3105..cc4214a16 100644
--- a/core/vm/evm.go
+++ b/core/vm/evm.go
@@ -123,19 +123,20 @@ func (evm *EVM) Cancel() {
 	atomic.StoreInt32(&evm.abort, 1)
 }
 
-// Call executes the contract associated with the addr with the given input as parameters. It also handles any
-// necessary value transfer required and takes the necessary steps to create accounts and reverses the state in
-// case of an execution error or failed value transfer.
+// Call executes the contract associated with the addr with the given input as
+// parameters. It also handles any necessary value transfer required and takes
+// the necessary steps to create accounts and reverses the state in case of an
+// execution error or failed value transfer.
 func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) {
 	if evm.vmConfig.NoRecursion && evm.depth > 0 {
 		return nil, gas, nil
 	}
 
-	// Depth check execution. Fail if we're trying to execute above the
-	// limit.
+	// Fail if we're trying to execute above the call depth limit
 	if evm.depth > int(params.CallCreateDepth) {
 		return nil, gas, ErrDepth
 	}
+	// Fail if we're trying to transfer more than the available balance
 	if !evm.Context.CanTransfer(evm.StateDB, caller.Address(), value) {
 		return nil, gas, ErrInsufficientBalance
 	}
@@ -173,21 +174,23 @@ func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas
 	return ret, contract.Gas, err
 }
 
-// CallCode executes the contract associated with the addr with the given input as parameters. It also handles any
-// necessary value transfer required and takes the necessary steps to create accounts and reverses the state in
-// case of an execution error or failed value transfer.
+// CallCode executes the contract associated with the addr with the given input
+// as parameters. It also handles any necessary value transfer required and takes
+// the necessary steps to create accounts and reverses the state in case of an
+// execution error or failed value transfer.
 //
-// CallCode differs from Call in the sense that it executes the given address' code with the caller as context.
+// CallCode differs from Call in the sense that it executes the given address'
+// code with the caller as context.
 func (evm *EVM) CallCode(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) {
 	if evm.vmConfig.NoRecursion && evm.depth > 0 {
 		return nil, gas, nil
 	}
 
-	// Depth check execution. Fail if we're trying to execute above the
-	// limit.
+	// Fail if we're trying to execute above the call depth limit
 	if evm.depth > int(params.CallCreateDepth) {
 		return nil, gas, ErrDepth
 	}
+	// Fail if we're trying to transfer more than the available balance
 	if !evm.CanTransfer(evm.StateDB, caller.Address(), value) {
 		return nil, gas, ErrInsufficientBalance
 	}
@@ -211,18 +214,16 @@ func (evm *EVM) CallCode(caller ContractRef, addr common.Address, input []byte,
 	return ret, contract.Gas, err
 }
 
-// DelegateCall executes the contract associated with the addr with the given input as parameters.
-// It reverses the state in case of an execution error.
+// DelegateCall executes the contract associated with the addr with the given input
+// as parameters. It reverses the state in case of an execution error.
 //
-// DelegateCall differs from CallCode in the sense that it executes the given address' code with the caller as context
-// and the caller is set to the caller of the caller.
+// DelegateCall differs from CallCode in the sense that it executes the given address'
+// code with the caller as context and the caller is set to the caller of the caller.
 func (evm *EVM) DelegateCall(caller ContractRef, addr common.Address, input []byte, gas uint64) (ret []byte, leftOverGas uint64, err error) {
 	if evm.vmConfig.NoRecursion && evm.depth > 0 {
 		return nil, gas, nil
 	}
-
-	// Depth check execution. Fail if we're trying to execute above the
-	// limit.
+	// Fail if we're trying to execute above the call depth limit
 	if evm.depth > int(params.CallCreateDepth) {
 		return nil, gas, ErrDepth
 	}
@@ -232,7 +233,7 @@ func (evm *EVM) DelegateCall(caller ContractRef, addr common.Address, input []by
 		to       = AccountRef(caller.Address())
 	)
 
-	// Iinitialise a new contract and make initialise the delegate values
+	// Initialise a new contract and make initialise the delegate values
 	contract := NewContract(caller, to, nil, gas).AsDelegate()
 	contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))
 
@@ -245,18 +246,19 @@ func (evm *EVM) DelegateCall(caller ContractRef, addr common.Address, input []by
 	return ret, contract.Gas, err
 }
 
+// StaticCall executes the contract associated with the addr with the given input
+// as parameters while disallowing any modifications to the state during the call.
+// Opcodes that attempt to perform such modifications will result in exceptions
+// instead of performing the modifications.
 func (evm *EVM) StaticCall(caller ContractRef, addr common.Address, input []byte, gas uint64) (ret []byte, leftOverGas uint64, err error) {
 	if evm.vmConfig.NoRecursion && evm.depth > 0 {
 		return nil, gas, nil
 	}
-
-	// Depth check execution. Fail if we're trying to execute above the
-	// limit.
+	// Fail if we're trying to execute above the call depth limit
 	if evm.depth > int(params.CallCreateDepth) {
 		return nil, gas, ErrDepth
 	}
-
-	// make sure the readonly is only set if we aren't in readonly yet
+	// Make sure the readonly is only set if we aren't in readonly yet
 	// this makes also sure that the readonly flag isn't removed for
 	// child calls.
 	if !evm.interpreter.readonly {
@@ -268,23 +270,18 @@ func (evm *EVM) StaticCall(caller ContractRef, addr common.Address, input []byte
 		to       = AccountRef(addr)
 		snapshot = evm.StateDB.Snapshot()
 	)
-	if !evm.StateDB.Exist(addr) {
-		return nil, gas, nil
-	}
-
-	// initialise a new contract and set the code that is to be used by the
-	// EVM. The contract is a scoped evmironment for this execution context
+	// Initialise a new contract and set the code that is to be used by the
+	// EVM. The contract is a scoped environment for this execution context
 	// only.
 	contract := NewContract(caller, to, new(big.Int), gas)
 	contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))
 
-	ret, err = evm.interpreter.Run(snapshot, contract, input)
 	// When an error was returned by the EVM or when setting the creation code
 	// above we revert to the snapshot and consume any gas remaining. Additionally
-	// when we're in homestead this also counts for code storage gas errors.
+	// when we're in Homestead this also counts for code storage gas errors.
+	ret, err = run(evm, snapshot, contract, input)
 	if err != nil {
 		contract.UseGas(contract.Gas)
-
 		evm.StateDB.RevertToSnapshot(snapshot)
 	}
 	return ret, contract.Gas, err
diff --git a/core/vm/interpreter.go b/core/vm/interpreter.go
index 32d764b9f..661ada691 100644
--- a/core/vm/interpreter.go
+++ b/core/vm/interpreter.go
@@ -89,13 +89,12 @@ func NewInterpreter(evm *EVM, cfg Config) *Interpreter {
 func (in *Interpreter) enforceRestrictions(op OpCode, operation operation, stack *Stack) error {
 	if in.evm.chainRules.IsMetropolis {
 		if in.readonly {
-			// if the interpreter is operating in readonly mode, make sure no
-			// state-modifying operation is performed. The 4th stack item
+			// If the interpreter is operating in readonly mode, make sure no
+			// state-modifying operation is performed. The 3rd 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) {
+			if operation.writes || (op == CALL && stack.Back(2).BitLen() > 0) {
 				return errWriteProtection
 			}
 		}