core/vm: track 63/64 call gas off stack (#15563)

* core/vm: track 63/64 call gas off stack

Gas calculations in gasCall* relayed the available gas for calls by
replacing it on the stack. This lead to inconsistent traces, which we
papered over by copying the pre-execution stack in trace mode.

This change relays available gas using a temporary variable, off the
stack, and allows removing the weird copy.

* core/vm: remove stackCopy

* core/vm: pop call gas into pool

* core/vm: to -> addr

4 files changed, 55 insertions, 99 deletions

diff --git a/core/vm/evm.go b/core/vm/evm.go
index 093c7d4c1..344435f73 100644
--- a/core/vm/evm.go
+++ b/core/vm/evm.go
@@ -104,6 +104,10 @@ type EVM struct {
 	// abort is used to abort the EVM calling operations
 	// NOTE: must be set atomically
 	abort int32
+	// callGasTemp holds the gas available for the current call. This is needed because the
+	// available gas is calculated in gasCall* according to the 63/64 rule and later
+	// applied in opCall*.
+	callGasTemp uint64
 }
 
 // NewEVM retutrns a new EVM . The returned EVM is not thread safe and should
diff --git a/core/vm/gas_table.go b/core/vm/gas_table.go
index 0d8e295a5..ff109af57 100644
--- a/core/vm/gas_table.go
+++ b/core/vm/gas_table.go
@@ -342,19 +342,11 @@ func gasCall(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem
 		return 0, errGasUintOverflow
 	}
 
-	cg, err := callGas(gt, contract.Gas, gas, stack.Back(0))
+	evm.callGasTemp, err = callGas(gt, contract.Gas, gas, stack.Back(0))
 	if err != nil {
 		return 0, err
 	}
-	// Replace the stack item with the new gas calculation. This means that
-	// either the original item is left on the stack or the item is replaced by:
-	// (availableGas - gas) * 63 / 64
-	// We replace the stack item so that it's available when the opCall instruction is
-	// called. This information is otherwise lost due to the dependency on *current*
-	// available gas.
-	stack.data[stack.len()-1] = new(big.Int).SetUint64(cg)
-
-	if gas, overflow = math.SafeAdd(gas, cg); overflow {
+	if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
 		return 0, errGasUintOverflow
 	}
 	return gas, nil
@@ -374,19 +366,11 @@ func gasCallCode(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack,
 		return 0, errGasUintOverflow
 	}
 
-	cg, err := callGas(gt, contract.Gas, gas, stack.Back(0))
+	evm.callGasTemp, err = callGas(gt, contract.Gas, gas, stack.Back(0))
 	if err != nil {
 		return 0, err
 	}
-	// Replace the stack item with the new gas calculation. This means that
-	// either the original item is left on the stack or the item is replaced by:
-	// (availableGas - gas) * 63 / 64
-	// We replace the stack item so that it's available when the opCall instruction is
-	// called. This information is otherwise lost due to the dependency on *current*
-	// available gas.
-	stack.data[stack.len()-1] = new(big.Int).SetUint64(cg)
-
-	if gas, overflow = math.SafeAdd(gas, cg); overflow {
+	if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
 		return 0, errGasUintOverflow
 	}
 	return gas, nil
@@ -436,18 +420,11 @@ func gasDelegateCall(gt params.GasTable, evm *EVM, contract *Contract, stack *St
 		return 0, errGasUintOverflow
 	}
 
-	cg, err := callGas(gt, contract.Gas, gas, stack.Back(0))
+	evm.callGasTemp, err = callGas(gt, contract.Gas, gas, stack.Back(0))
 	if err != nil {
 		return 0, err
 	}
-	// Replace the stack item with the new gas calculation. This means that
-	// either the original item is left on the stack or the item is replaced by:
-	// (availableGas - gas) * 63 / 64
-	// We replace the stack item so that it's available when the opCall instruction is
-	// called.
-	stack.data[stack.len()-1] = new(big.Int).SetUint64(cg)
-
-	if gas, overflow = math.SafeAdd(gas, cg); overflow {
+	if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
 		return 0, errGasUintOverflow
 	}
 	return gas, nil
@@ -463,18 +440,11 @@ func gasStaticCall(gt params.GasTable, evm *EVM, contract *Contract, stack *Stac
 		return 0, errGasUintOverflow
 	}
 
-	cg, err := callGas(gt, contract.Gas, gas, stack.Back(0))
+	evm.callGasTemp, err = callGas(gt, contract.Gas, gas, stack.Back(0))
 	if err != nil {
 		return 0, err
 	}
-	// Replace the stack item with the new gas calculation. This means that
-	// either the original item is left on the stack or the item is replaced by:
-	// (availableGas - gas) * 63 / 64
-	// We replace the stack item so that it's available when the opCall instruction is
-	// called.
-	stack.data[stack.len()-1] = new(big.Int).SetUint64(cg)
-
-	if gas, overflow = math.SafeAdd(gas, cg); overflow {
+	if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
 		return 0, errGasUintOverflow
 	}
 	return gas, nil
diff --git a/core/vm/instructions.go b/core/vm/instructions.go
index b6d6e22c4..1d1585fca 100644
--- a/core/vm/instructions.go
+++ b/core/vm/instructions.go
@@ -603,24 +603,20 @@ func opCreate(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *S
 }
 
 func opCall(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
-	gas := stack.pop().Uint64()
-	// pop gas and value of the stack.
-	addr, value := stack.pop(), stack.pop()
+	// Pop gas. The actual gas in in evm.callGasTemp.
+	evm.interpreter.intPool.put(stack.pop())
+	gas := evm.callGasTemp
+	// Pop other call parameters.
+	addr, value, inOffset, inSize, retOffset, retSize := stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop()
+	toAddr := common.BigToAddress(addr)
 	value = math.U256(value)
-	// pop input size and offset
-	inOffset, inSize := stack.pop(), stack.pop()
-	// pop return size and offset
-	retOffset, retSize := stack.pop(), stack.pop()
-
-	address := common.BigToAddress(addr)
-
-	// Get the arguments from the memory
+	// Get the arguments from the memory.
 	args := memory.Get(inOffset.Int64(), inSize.Int64())
 
 	if value.Sign() != 0 {
 		gas += params.CallStipend
 	}
-	ret, returnGas, err := evm.Call(contract, address, args, gas, value)
+	ret, returnGas, err := evm.Call(contract, toAddr, args, gas, value)
 	if err != nil {
 		stack.push(new(big.Int))
 	} else {
@@ -636,25 +632,20 @@ func opCall(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Sta
 }
 
 func opCallCode(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
-	gas := stack.pop().Uint64()
-	// pop gas and value of the stack.
-	addr, value := stack.pop(), stack.pop()
+	// Pop gas. The actual gas is in evm.callGasTemp.
+	evm.interpreter.intPool.put(stack.pop())
+	gas := evm.callGasTemp
+	// Pop other call parameters.
+	addr, value, inOffset, inSize, retOffset, retSize := stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop()
+	toAddr := common.BigToAddress(addr)
 	value = math.U256(value)
-	// pop input size and offset
-	inOffset, inSize := stack.pop(), stack.pop()
-	// pop return size and offset
-	retOffset, retSize := stack.pop(), stack.pop()
-
-	address := common.BigToAddress(addr)
-
-	// Get the arguments from the memory
+	// Get arguments from the memory.
 	args := memory.Get(inOffset.Int64(), inSize.Int64())
 
 	if value.Sign() != 0 {
 		gas += params.CallStipend
 	}
-
-	ret, returnGas, err := evm.CallCode(contract, address, args, gas, value)
+	ret, returnGas, err := evm.CallCode(contract, toAddr, args, gas, value)
 	if err != nil {
 		stack.push(new(big.Int))
 	} else {
@@ -670,9 +661,13 @@ func opCallCode(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack
 }
 
 func opDelegateCall(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
-	gas, to, inOffset, inSize, outOffset, outSize := stack.pop().Uint64(), stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop()
-
-	toAddr := common.BigToAddress(to)
+	// Pop gas. The actual gas is in evm.callGasTemp.
+	evm.interpreter.intPool.put(stack.pop())
+	gas := evm.callGasTemp
+	// Pop other call parameters.
+	addr, inOffset, inSize, retOffset, retSize := stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop()
+	toAddr := common.BigToAddress(addr)
+	// Get arguments from the memory.
 	args := memory.Get(inOffset.Int64(), inSize.Int64())
 
 	ret, returnGas, err := evm.DelegateCall(contract, toAddr, args, gas)
@@ -682,30 +677,25 @@ func opDelegateCall(pc *uint64, evm *EVM, contract *Contract, memory *Memory, st
 		stack.push(big.NewInt(1))
 	}
 	if err == nil || err == errExecutionReverted {
-		memory.Set(outOffset.Uint64(), outSize.Uint64(), ret)
+		memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
 	}
 	contract.Gas += returnGas
 
-	evm.interpreter.intPool.put(to, inOffset, inSize, outOffset, outSize)
+	evm.interpreter.intPool.put(addr, inOffset, inSize, retOffset, retSize)
 	return ret, nil
 }
 
 func opStaticCall(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
-	// pop gas
-	gas := stack.pop().Uint64()
-	// pop address
-	addr := stack.pop()
-	// pop input size and offset
-	inOffset, inSize := stack.pop(), stack.pop()
-	// pop return size and offset
-	retOffset, retSize := stack.pop(), stack.pop()
-
-	address := common.BigToAddress(addr)
-
-	// Get the arguments from the memory
+	// Pop gas. The actual gas is in evm.callGasTemp.
+	evm.interpreter.intPool.put(stack.pop())
+	gas := evm.callGasTemp
+	// Pop other call parameters.
+	addr, inOffset, inSize, retOffset, retSize := stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop()
+	toAddr := common.BigToAddress(addr)
+	// Get arguments from the memory.
 	args := memory.Get(inOffset.Int64(), inSize.Int64())
 
-	ret, returnGas, err := evm.StaticCall(contract, address, args, gas)
+	ret, returnGas, err := evm.StaticCall(contract, toAddr, args, gas)
 	if err != nil {
 		stack.push(new(big.Int))
 	} else {
diff --git a/core/vm/interpreter.go b/core/vm/interpreter.go
index ea5468f90..ac6000f97 100644
--- a/core/vm/interpreter.go
+++ b/core/vm/interpreter.go
@@ -138,16 +138,15 @@ func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret
 		pc   = uint64(0) // program counter
 		cost uint64
 		// copies used by tracer
-		stackCopy = newstack() // stackCopy needed for Tracer since stack is mutated by 63/64 gas rule
-		pcCopy    uint64       // needed for the deferred Tracer
-		gasCopy   uint64       // for Tracer to log gas remaining before execution
-		logged    bool         // deferred Tracer should ignore already logged steps
+		pcCopy  uint64 // needed for the deferred Tracer
+		gasCopy uint64 // for Tracer to log gas remaining before execution
+		logged  bool   // deferred Tracer should ignore already logged steps
 	)
 	contract.Input = input
 
 	defer func() {
 		if err != nil && !logged && in.cfg.Debug {
-			in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, mem, stackCopy, contract, in.evm.depth, err)
+			in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
 		}
 	}()
 
@@ -156,21 +155,14 @@ func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret
 	// the execution of one of the operations or until the done flag is set by the
 	// parent context.
 	for atomic.LoadInt32(&in.evm.abort) == 0 {
-		// Get the memory location of pc
-		op = contract.GetOp(pc)
-
 		if in.cfg.Debug {
-			logged = false
-			pcCopy = pc
-			gasCopy = contract.Gas
-			stackCopy = newstack()
-			for _, val := range stack.data {
-				stackCopy.push(val)
-			}
+			// Capture pre-execution values for tracing.
+			logged, pcCopy, gasCopy = false, pc, contract.Gas
 		}
 
-		// Get the operation from the jump table matching the opcode and validate the
-		// stack and make sure there enough stack items available to perform the operation
+		// Get the operation from the jump table and validate the stack to ensure there are
+		// enough stack items available to perform the operation.
+		op = contract.GetOp(pc)
 		operation := in.cfg.JumpTable[op]
 		if !operation.valid {
 			return nil, fmt.Errorf("invalid opcode 0x%x", int(op))
@@ -211,7 +203,7 @@ func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret
 		}
 
 		if in.cfg.Debug {
-			in.cfg.Tracer.CaptureState(in.evm, pc, op, gasCopy, cost, mem, stackCopy, contract, in.evm.depth, err)
+			in.cfg.Tracer.CaptureState(in.evm, pc, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
 			logged = true
 		}