Go back to using the transfer's sender in Tobin tax calculation. (#1611)

Even though the Tobin tax calculation doesn't depend on the sender, the change (in PR #1465) of the sender from the transaction's sender to the zero account led to a bad block error (i.e. a hard fork change).  This was due to a conjunction of factors including the upstream implementation of EIP-161 not being quite correct for the case of Celo (because of the existence of system EVM calls made from celo-blockchain).  This commit reverts the change, by adding an `ExecuteFrom()` method to the EVMRunner type.

Author: Or Neeman

contracts/reserve/tobin_tax.go

@@ -31,7 +31,7 @@ func TobinTax(vmRunner vm.EVMRunner, sender common.Address) (tax Ratio, reserveA
 		return Ratio{}, common.ZeroAddress, err
 	}
 
-	ret, err := vmRunner.Execute(reserveAddress, params.TobinTaxFunctionSelector, params.MaxGasForGetOrComputeTobinTax, big.NewInt(0))
+	ret, err := vmRunner.ExecuteFrom(sender, reserveAddress, params.TobinTaxFunctionSelector, params.MaxGasForGetOrComputeTobinTax, big.NewInt(0))
 	if err != nil {
 		return Ratio{}, common.ZeroAddress, err
 	}

contracts/testutil/fail_runner.go

@@ -18,6 +18,10 @@ func (fvm FailingVmRunner) Execute(recipient common.Address, input []byte, gas u
 	return nil, ErrFailingRunner
 }
 
+func (fvm FailingVmRunner) ExecuteFrom(sender, recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	return nil, ErrFailingRunner
+}
+
 func (fvm FailingVmRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	return nil, ErrFailingRunner
 }

contracts/testutil/runner.go

@@ -45,6 +45,11 @@ func (ev *MockEVMRunner) Execute(recipient common.Address, input []byte, gas uin
 	return mock.Call(input)
 }
 
+func (ev *MockEVMRunner) ExecuteFrom(sender, recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	// No difference necessary for the mock runner between Execute() and ExecuteFrom()
+	return ev.Execute(recipient, input, gas, value)
+}
+
 func (ev *MockEVMRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	mock, ok := ev.contracts[recipient]
 	if !ok {

core/vm/interface.go

@@ -89,6 +89,11 @@ type EVMRunner interface {
 	// It can be seen as a message (input,value) from sender to recipient that returns `ret`
 	Execute(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error)
 
+	// ExecuteFrom is like Execute, but lets you specify the sender to use for the EVM call.
+	// It exists only for use in the Tobin tax calculation done as part of TobinTransfer, because that
+	// originally used the transaction's sender instead of the zero address.
+	ExecuteFrom(sender, recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error)
+
 	// Query performs a read operation over the runner's state
 	// It can be seen as a message (input,value) from sender to recipient that returns `ret`
 	Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error)

core/vm/vmcontext/runner.go

@@ -25,7 +25,7 @@ type evmRunnerContext interface {
 }
 
 type evmRunner struct {
-	newEVM func() *vm.EVM
+	newEVM func(from common.Address) *vm.EVM
 	state  vm.StateDB
 
 	dontMeterGas bool
@@ -35,26 +35,35 @@ func NewEVMRunner(chain evmRunnerContext, header *types.Header, state vm.StateDB
 
 	return &evmRunner{
 		state: state,
-		newEVM: func() *vm.EVM {
+		newEVM: func(from common.Address) *vm.EVM {
 			// The EVM Context requires a msg, but the actual field values don't really matter for this case.
-			// Putting in zero values.
-			context := New(VMAddress, common.Big0, header, chain, nil)
+			// Putting in zero values for gas price and tx fee recipient
+			context := New(from, common.Big0, header, chain, nil)
 			return vm.NewEVM(context, state, chain.Config(), *chain.GetVMConfig())
 		},
 	}
 }
 
 func (ev *evmRunner) Execute(recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
-	evm := ev.newEVM()
+	evm := ev.newEVM(VMAddress)
 	if ev.dontMeterGas {
 		evm.StopGasMetering()
 	}
 	ret, _, err = evm.Call(vm.AccountRef(evm.Origin), recipient, input, gas, value)
 	return ret, err
 }
 
+func (ev *evmRunner) ExecuteFrom(sender, recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	evm := ev.newEVM(sender)
+	if ev.dontMeterGas {
+		evm.StopGasMetering()
+	}
+	ret, _, err = evm.Call(vm.AccountRef(sender), recipient, input, gas, value)
+	return ret, err
+}
+
 func (ev *evmRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
-	evm := ev.newEVM()
+	evm := ev.newEVM(VMAddress)
 	if ev.dontMeterGas {
 		evm.StopGasMetering()
 	}
@@ -85,6 +94,11 @@ func (sev *SharedEVMRunner) Execute(recipient common.Address, input []byte, gas
 	return ret, err
 }
 
+func (sev *SharedEVMRunner) ExecuteFrom(sender, recipient common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, err error) {
+	ret, _, err = sev.Call(vm.AccountRef(sender), recipient, input, gas, value)
+	return ret, err
+}
+
 func (sev *SharedEVMRunner) Query(recipient common.Address, input []byte, gas uint64) (ret []byte, err error) {
 	ret, _, err = sev.StaticCall(vm.AccountRef(VMAddress), recipient, input, gas)
 	return ret, err