// Copyright 2015 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 (
"math/big"
"github.com/ethereum/go-ethereum/common"
"github.com/holiman/uint256"
)
// ContractRef is a reference to the contract's backing object
type ContractRef interface {
Address() common.Address
}
// AccountRef implements ContractRef.
//
// Account references are used during EVM initialisation and
// it's primary use is to fetch addresses. Removing this object
// proves difficult because of the cached jump destinations which
// are fetched from the parent contract (i.e. the caller), which
// is a ContractRef.
type AccountRef common.Address
// Address casts AccountRef to a Address
func (ar AccountRef) Address() common.Address { return (common.Address)(ar) }
// Contract represents an ethereum contract in the state database. It contains
// the contract code, calling arguments. Contract implements ContractRef
type Contract struct {
// CallerAddress is the result of the caller which initialised this
// contract. However when the "call method" is delegated this value
// needs to be initialised to that of the caller's caller.
CallerAddress common.Address
caller ContractRef
self ContractRef
jumpdests map[common.Hash]bitvec // Aggregated result of JUMPDEST analysis.
analysis bitvec // Locally cached result of JUMPDEST analysis
Code []byte
CodeHash common.Hash
CodeAddr *common.Address
Input []byte
Gas uint64
value *big.Int
}
// NewContract returns a new contract environment for the execution of EVM.
func NewContract(caller ContractRef, object ContractRef, value *big.Int, gas uint64) *Contract {
c := &Contract{CallerAddress: caller.Address(), caller: caller, self: object}
if parent, ok := caller.(*Contract); ok {
// Reuse JUMPDEST analysis from parent context if available.
c.jumpdests = parent.jumpdests
} else {
c.jumpdests = make(map[common.Hash]bitvec)
}
// Gas should be a pointer so it can safely be reduced through the run
// This pointer will be off the state transition
c.Gas = gas
// ensures a value is set
c.value = value
return c
}
func (c *Contract) validJumpdest(dest *uint256.Int) bool {
udest, overflow := dest.Uint64WithOverflow()
// PC cannot go beyond len(code) and certainly can't be bigger than 63bits.
// Don't bother checking for JUMPDEST in that case.
if overflow || udest >= uint64(len(c.Code)) {
return false
}
// Only JUMPDESTs allowed for destinations
if OpCode(c.Code[udest]) != JUMPDEST {
return false
}
return c.isCode(udest)
}
func (c *Contract) validJumpSubdest(udest uint64) bool {
// PC cannot go beyond len(code) and certainly can't be bigger than 63 bits.
// Don't bother checking for BEGINSUB in that case.
if int64(udest) < 0 || udest >= uint64(len(c.Code)) {
return false
}
// Only BEGINSUBs allowed for destinations
if OpCode(c.Code[udest]) != BEGINSUB {
return false
}
return c.isCode(udest)
}
// isCode returns true if the provided PC location is an actual opcode, as
// opposed to a data-segment following a PUSHN operation.
func (c *Contract) isCode(udest uint64) bool {
// Do we already have an analysis laying around?
if c.analysis != nil {
return c.analysis.codeSegment(udest)
}
// Do we have a contract hash already?
// If we do have a hash, that means it's a 'regular' contract. For regular
// contracts ( not temporary initcode), we store the analysis in a map
if c.CodeHash != (common.Hash{}) {
// Does parent context have the analysis?
analysis, exist := c.jumpdests[c.CodeHash]
if !exist {
// Do the analysis and save in parent context
// We do not need to store it in c.analysis
analysis = codeBitmap(c.Code)
c.jumpdests[c.CodeHash] = analysis
}
// Also stash it in current contract for faster access
c.analysis = analysis
return analysis.codeSegment(udest)
}
// We don't have the code hash, most likely a piece of initcode not already
// in state trie. In that case, we do an analysis, and save it locally, so
// we don't have to recalculate it for every JUMP instruction in the execution
// However, we don't save it within the parent context
if c.analysis == nil {
c.analysis = codeBitmap(c.Code)
}
return c.analysis.codeSegment(udest)
}
// AsDelegate sets the contract to be a delegate call and returns the current
// contract (for chaining calls)
func (c *Contract) AsDelegate() *Contract {
// NOTE: caller must, at all times be a contract. It should never happen
// that caller is something other than a Contract.
parent := c.caller.(*Contract)
c.CallerAddress = parent.CallerAddress
c.value = parent.value
return c
}
// GetOp returns the n'th element in the contract's byte array
func (c *Contract) GetOp(n uint64) OpCode {
return OpCode(c.GetByte(n))
}
// GetByte returns the n'th byte in the contract's byte array
func (c *Contract) GetByte(n uint64) byte {
if n < uint64(len(c.Code)) {
return c.Code[n]
}
return 0
}
// Caller returns the caller of the contract.
//
// Caller will recursively call caller when the contract is a delegate
// call, including that of caller's caller.
func (c *Contract) Caller() common.Address {
return c.CallerAddress
}
// UseGas attempts the use gas and subtracts it and returns true on success
func (c *Contract) UseGas(gas uint64) (ok bool) {
if c.Gas < gas {
return false
}
c.Gas -= gas
return true
}
// Address returns the contracts address
func (c *Contract) Address() common.Address {
return c.self.Address()
}
// Value returns the contract's value (sent to it from it's caller)
func (c *Contract) Value() *big.Int {
return c.value
}
// SetCallCode sets the code of the contract and address of the backing data
// object
func (c *Contract) SetCallCode(addr *common.Address, hash common.Hash, code []byte) {
c.Code = code
c.CodeHash = hash
c.CodeAddr = addr
}
// SetCodeOptionalHash can be used to provide code, but it's optional to provide hash.
// In case hash is not provided, the jumpdest analysis will not be saved to the parent context
func (c *Contract) SetCodeOptionalHash(addr *common.Address, codeAndHash *codeAndHash) {
c.Code = codeAndHash.code
c.CodeHash = codeAndHash.hash
c.CodeAddr = addr
}