path: root/core/vm/interpreter.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
    "fmt"
    "sync/atomic"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/math"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/params"
)

// Config are the configuration options for the Interpreter
type Config struct {
    // Debug enabled debugging Interpreter options
    Debug bool
    // EnableJit enabled the JIT VM
    EnableJit bool
    // ForceJit forces the JIT VM
    ForceJit bool
    // Tracer is the op code logger
    Tracer Tracer
    // NoRecursion disabled Interpreter call, callcode,
    // delegate call and create.
    NoRecursion bool
    // Disable gas metering
    DisableGasMetering bool
    // Enable recording of SHA3/keccak preimages
    EnablePreimageRecording bool
    // JumpTable contains the EVM instruction table. This
    // may be left uninitialised and will be set to the default
    // table.
    JumpTable [256]operation
}

// Interpreter is used to run Ethereum based contracts and will utilise the
// passed evmironment to query external sources for state information.
// The Interpreter will run the byte code VM or JIT VM based on the passed
// configuration.
type Interpreter struct {
    evm      *EVM
    cfg      Config
    gasTable params.GasTable
    intPool  *intPool

    readOnly   bool   // Whether to throw on stateful modifications
    returnData []byte // Last CALL's return data for subsequent reuse
}

// NewInterpreter returns a new instance of the Interpreter.
func NewInterpreter(evm *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 {
        switch {
        case evm.ChainConfig().IsMetropolis(evm.BlockNumber):
            cfg.JumpTable = metropolisInstructionSet
        case evm.ChainConfig().IsHomestead(evm.BlockNumber):
            cfg.JumpTable = homesteadInstructionSet
        default:
            cfg.JumpTable = frontierInstructionSet
        }
    }

    return &Interpreter{
        evm:      evm,
        cfg:      cfg,
        gasTable: evm.ChainConfig().GasTable(evm.BlockNumber),
        intPool:  newIntPool(),
    }
}

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 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 && stack.Back(2).BitLen() > 0) {
                return errWriteProtection
            }
        }
    }
    return nil
}

// Run loops and evaluates the contract's code with the given input data and returns
// the return byte-slice and an error if one occurred.
//
// It's important to note that any errors returned by the interpreter should be
// considered a revert-and-consume-all-gas operation. No error specific checks
// should be handled to reduce complexity and errors further down the in.
func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret []byte, err error) {
    // Increment the call depth which is restricted to 1024
    in.evm.depth++
    defer func() { in.evm.depth-- }()

    // Reset the previous call's return data. It's unimportant to preserve the old buffer
    // as every returning call will return new data anyway.
    in.returnData = nil

    // Don't bother with the execution if there's no code.
    if len(contract.Code) == 0 {
        return nil, nil
    }

    codehash := contract.CodeHash // codehash is used when doing jump dest caching
    if codehash == (common.Hash{}) {
        codehash = crypto.Keccak256Hash(contract.Code)
    }

    var (
        op    OpCode        // current opcode
        mem   = NewMemory() // bound memory
        stack = newstack()  // local stack
        // For optimisation reason we're using uint64 as the program counter.
        // It's theoretically possible to go above 2^64. The YP defines the PC
        // to be uint256. Practically much less so feasible.
        pc   = uint64(0) // program counter
        cost uint64
    )
    contract.Input = input

    defer func() {
        if err != nil && in.cfg.Debug {
            in.cfg.Tracer.CaptureState(in.evm, pc, op, contract.Gas, cost, mem, stack, contract, in.evm.depth, err)
        }
    }()

    // The Interpreter main run loop (contextual). This loop runs until either an
    // explicit STOP, RETURN or SELFDESTRUCT is executed, an error occurred during
    // 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)

        // get the operation from the jump table matching the opcode
        operation := in.cfg.JumpTable[op]
        if err := in.enforceRestrictions(op, operation, stack); err != nil {
            return nil, err
        }

        // if the op is invalid abort the process and return an error
        if !operation.valid {
            return nil, fmt.Errorf("invalid opcode 0x%x", int(op))
        }

        // validate the stack and make sure there enough stack items available
        // to perform the operation
        if err := operation.validateStack(stack); err != nil {
            return nil, err
        }

        var memorySize uint64
        // calculate the new memory size and expand the memory to fit
        // the operation
        if operation.memorySize != nil {
            memSize, overflow := bigUint64(operation.memorySize(stack))
            if overflow {
                return nil, errGasUintOverflow
            }
            // memory is expanded in words of 32 bytes. Gas
            // is also calculated in words.
            if memorySize, overflow = math.SafeMul(toWordSize(memSize), 32); overflow {
                return nil, errGasUintOverflow
            }
        }

        if !in.cfg.DisableGasMetering {
            // consume the gas and return an error if not enough gas is available.
            // cost is explicitly set so that the capture state defer method cas get the proper cost
            cost, err = operation.gasCost(in.gasTable, in.evm, contract, stack, mem, memorySize)
            if err != nil || !contract.UseGas(cost) {
                return nil, ErrOutOfGas
            }
        }
        if memorySize > 0 {
            mem.Resize(memorySize)
        }

        if in.cfg.Debug {
            in.cfg.Tracer.CaptureState(in.evm, pc, op, contract.Gas, cost, mem, stack, contract, in.evm.depth, err)
        }

        // execute the operation
        res, err := operation.execute(&pc, in.evm, contract, mem, stack)
        // verifyPool is a build flag. Pool verification makes sure the integrity
        // of the integer pool by comparing values to a default value.
        if verifyPool {
            verifyIntegerPool(in.intPool)
        }
        // checks whether the operation should revert state.
        if operation.reverts {
            in.evm.StateDB.RevertToSnapshot(snapshot)
        }

        switch {
        case err != nil:
            return nil, err
        case operation.halts:
            return res, nil
        case !operation.jumps:
            pc++
        }
        // if the operation clears the return data (e.g. it has returning data)
        // set the last return to the result of the operation.
        if operation.returns {
            in.returnData = res
        }
    }
    return nil, nil
}