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

// Config are the configuration options for the Interpreter
type Config struct {
    // Debug enabled debugging Interpreter options
    Debug bool
    // Tracer is the op code logger
    Tracer Tracer
    // NoRecursion disabled Interpreter call, callcode,
    // delegate call and create.
    NoRecursion 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 environment to query external sources for state information.
// The Interpreter will run the byte code VM based on the passed
// configuration.
type Interpreter interface {
    // 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.
    Run(contract *Contract, input []byte, static bool) ([]byte, error)
    // CanRun tells if the contract, passed as an argument, can be
    // run by the current interpreter. This is meant so that the
    // caller can do something like:
    //
    // ```golang
    // for _, interpreter := range interpreters {
    //   if interpreter.CanRun(contract.code) {
    //     interpreter.Run(contract.code, input)
    //   }
    // }
    // ```
    CanRun([]byte) bool
}

// EVMInterpreter represents an EVM interpreter
type EVMInterpreter 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
}

// NewEVMInterpreter returns a new instance of the Interpreter.
func NewEVMInterpreter(evm *EVM, cfg Config) *EVMInterpreter {
    // 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().IsConstantinople(evm.BlockNumber):
            cfg.JumpTable = constantinopleInstructionSet
        case evm.ChainConfig().IsByzantium(evm.BlockNumber):
            cfg.JumpTable = byzantiumInstructionSet
        case evm.ChainConfig().IsHomestead(evm.BlockNumber):
            cfg.JumpTable = homesteadInstructionSet
        default:
            cfg.JumpTable = frontierInstructionSet
        }
    }

    return &EVMInterpreter{
        evm:      evm,
        cfg:      cfg,
        gasTable: evm.ChainConfig().GasTable(evm.BlockNumber),
    }
}

func (in *EVMInterpreter) enforceRestrictions(op OpCode, operation operation, stack *Stack) error {
    if in.evm.chainRules.IsByzantium {
        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. Transferring 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 except for
// errExecutionReverted which means revert-and-keep-gas-left.
func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (ret []byte, err error) {
    if in.intPool == nil {
        in.intPool = poolOfIntPools.get()
        defer func() {
            poolOfIntPools.put(in.intPool)
            in.intPool = nil
        }()
    }

    // Increment the call depth which is restricted to 1024
    in.evm.depth++
    defer func() { in.evm.depth-- }()

    // 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 readOnly && !in.readOnly {
        in.readOnly = true
        defer func() { in.readOnly = false }()
    }

    // 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
    }

    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
        // copies used by tracer
        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

    // Reclaim the stack as an int pool when the execution stops
    defer func() { in.intPool.put(stack.data...) }()

    if in.cfg.Debug {
        defer func() {
            if err != nil {
                if !logged {
                    in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
                } else {
                    in.cfg.Tracer.CaptureFault(in.evm, pcCopy, op, gasCopy, 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 {
        if in.cfg.Debug {
            // Capture pre-execution values for tracing.
            logged, pcCopy, gasCopy = false, pc, contract.Gas
        }

        // 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))
        }
        if err := operation.validateStack(stack); err != nil {
            return nil, err
        }
        // If the operation is valid, enforce and write restrictions
        if err := in.enforceRestrictions(op, operation, 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
            }
        }
        // consume the gas and return an error if not enough gas is available.
        // cost is explicitly set so that the capture state defer method can 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, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
            logged = true
        }

        // execute the operation
        res, err := operation.execute(&pc, in, 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)
        }
        // 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
        }

        switch {
        case err != nil:
            return nil, err
        case operation.reverts:
            return res, errExecutionReverted
        case operation.halts:
            return res, nil
        case !operation.jumps:
            pc++
        }
    }
    return nil, nil
}

// CanRun tells if the contract, passed as an argument, can be
// run by the current interpreter.
func (in *EVMInterpreter) CanRun(code []byte) bool {
    return true
}