93 lines
2.8 KiB
Go
93 lines
2.8 KiB
Go
// Copyright 2014 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package vm
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import (
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"math/big"
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"github.com/ethereum/go-ethereum/common"
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)
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// destinations stores one map per contract (keyed by hash of code).
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// The maps contain an entry for each location of a JUMPDEST
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// instruction.
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type destinations map[common.Hash]bitvec
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// has checks whether code has a JUMPDEST at dest.
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func (d destinations) has(codehash common.Hash, code []byte, dest *big.Int) bool {
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// PC cannot go beyond len(code) and certainly can't be bigger than 63bits.
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// Don't bother checking for JUMPDEST in that case.
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udest := dest.Uint64()
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if dest.BitLen() >= 63 || udest >= uint64(len(code)) {
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return false
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}
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m, analysed := d[codehash]
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if !analysed {
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m = jumpdests(code)
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d[codehash] = m
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}
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return OpCode(code[udest]) == JUMPDEST && m.codeSegment(udest)
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// return (m[udest/8] & (1 << (udest % 8))) != 0
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}
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// bitvec is a bit vector which maps bytes in a program
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// An unset bit means the byte is a code-segemnt, a set bit means it's data-segment
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type bitvec []byte
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func (bits *bitvec) set(pos uint64) {
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(*bits)[pos/8] |= 0x80 >> (pos % 8)
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}
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func (bits *bitvec) set8(pos uint64) {
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(*bits)[pos/8] |= 0xFF >> (pos % 8)
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(*bits)[pos/8+1] |= ^(0xFF >> (pos % 8))
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}
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// codeSegment checks if the position is in a code segment
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func (bits *bitvec) codeSegment(pos uint64) bool {
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return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0
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}
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// jumpdests creates a map that contains an entry for each
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// PC location that is a JUMPDEST instruction.
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func jumpdests(code []byte) []byte {
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//The map is 4 bytes longer than necessary, in case the code
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// ends with a PUSH32, the algorithm will push zeroes onto the
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// bitvector outside the bounds of the actual code.
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m := make([]byte, len(code)/8+1+4)
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bits := bitvec(m)
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for pc := uint64(0); pc < uint64(len(code)); {
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op := OpCode(code[pc])
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if op >= PUSH1 && op <= PUSH32 {
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numbits := op - PUSH1 + 1
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pc++
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for ; numbits >= 8; numbits -= 8 {
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bits.set8(pc) // 8
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pc += 8
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}
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for ; numbits > 0; numbits-- {
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bits.set(pc)
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pc++
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}
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} else {
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pc++
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}
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}
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return bits
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}
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