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core/vm: Use a bitmap instead of a map for jumpdest analysis

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This commit is contained in:
Nick Johnson 2017-06-01 18:42:20 +01:00
parent 0424192e61
commit d5a79934dc
1 changed files with 12 additions and 14 deletions
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26
core/vm/analysis.go
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@ -22,41 +22,39 @@ import (
"github.com/ethereum/go-ethereum/common" "github.com/ethereum/go-ethereum/common"
) )
var bigMaxUint64 = new(big.Int).SetUint64(^uint64(0))
// destinations stores one map per contract (keyed by hash of code). // destinations stores one map per contract (keyed by hash of code).
// The maps contain an entry for each location of a JUMPDEST // The maps contain an entry for each location of a JUMPDEST
// instruction. // instruction.
type destinations map[common.Hash]map[uint64]struct{} type destinations map[common.Hash][]byte
// has checks whether code has a JUMPDEST at dest. // has checks whether code has a JUMPDEST at dest.
func (d destinations) has(codehash common.Hash, code []byte, dest *big.Int) bool { func (d destinations) has(codehash common.Hash, code []byte, dest *big.Int) bool {
// PC cannot go beyond len(code) and certainly can't be bigger than 64bits. // PC cannot go beyond len(code) and certainly can't be bigger than 63bits.
// Don't bother checking for JUMPDEST in that case. // Don't bother checking for JUMPDEST in that case.
if dest.Cmp(bigMaxUint64) > 0 { udest := dest.Uint64()
if dest.BitLen() >= 63 || udest >= uint64(len(code)) {
return false return false
} }
m, analysed := d[codehash] m, analysed := d[codehash]
if !analysed { if !analysed {
m = jumpdests(code) m = jumpdests(code)
d[codehash] = m d[codehash] = m
} }
_, ok := m[dest.Uint64()] return (m[udest/8] & (1 << (udest % 8))) != 0
return ok
} }
// jumpdests creates a map that contains an entry for each // jumpdests creates a map that contains an entry for each
// PC location that is a JUMPDEST instruction. // PC location that is a JUMPDEST instruction.
func jumpdests(code []byte) map[uint64]struct{} { func jumpdests(code []byte) []byte {
m := make(map[uint64]struct{}) m := make([]byte, len(code)/8+1)
for pc := uint64(0); pc < uint64(len(code)); pc++ { for pc := uint64(0); pc < uint64(len(code)); pc++ {
var op OpCode = OpCode(code[pc]) op := OpCode(code[pc])
switch op { if op == JUMPDEST {
case PUSH1, PUSH2, PUSH3, PUSH4, PUSH5, PUSH6, PUSH7, PUSH8, PUSH9, PUSH10, PUSH11, PUSH12, PUSH13, PUSH14, PUSH15, PUSH16, PUSH17, PUSH18, PUSH19, PUSH20, PUSH21, PUSH22, PUSH23, PUSH24, PUSH25, PUSH26, PUSH27, PUSH28, PUSH29, PUSH30, PUSH31, PUSH32: m[pc/8] |= 1 << (pc % 8)
} else if op >= PUSH1 && op <= PUSH32 {
a := uint64(op) - uint64(PUSH1) + 1 a := uint64(op) - uint64(PUSH1) + 1
pc += a pc += a
case JUMPDEST:
m[pc] = struct{}{}
} }
} }
return m return m