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evmbytecode.go
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evmbytecode.go
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package evmbytecode
import (
"errors"
"strings"
)
// This function zeros-out the meta data stored in the bytecode. It is a hash
// of all compilation context, and is impractical to reproduce. Documented here;
// https://solidity.readthedocs.io/en/v0.5.1/metadata.html
func RemoveMetaData(bytecode string) string {
if len(bytecode) < 2 || !strings.HasPrefix(bytecode, "0x") {
panic(errors.New("Bytecode must start with 0x."))
}
if bytecode == "0x" || len(bytecode) < 18+64+4 {
return bytecode
}
metadataIndex := strings.Index(bytecode, "a165627a7a72305820")
if metadataIndex == -1 {
return bytecode
}
if bytecode[metadataIndex+18+64:metadataIndex+18+64+4] != "0029" {
panic(errors.New("Metadata malformed."))
}
// If everything looks fine, replace metadata hash with 0's
return bytecode[0:metadataIndex+18] +
strings.Repeat("0", 64) +
bytecode[metadataIndex+18+64:len(bytecode)]
}
// Stands for Get Program Counter--to--Operation Index mapping
func GetPcToOpIndex(bytecode string) map[int]int {
var pcToOpIndex = make(map[int]int)
var firstByteRune rune
var currentByte string
var byteIndex int
pushBytesRemaining := 0
opIndex := 0
for index, char := range strings.TrimPrefix(bytecode, "0x") {
if index%2 == 0 {
firstByteRune = char
continue
} else if index%2 == 1 {
currentByte = string(firstByteRune) + string(char)
byteIndex = index / 2
} else {
panic("This is logically impossible.")
}
// Now you have currentByte and byteIndex
if pushBytesRemaining != 0 {
pushBytesRemaining -= 1
continue
}
pcToOpIndex[byteIndex] = opIndex
if pushBytes := bytesPushed(currentByte); pushBytes != -1 {
pushBytesRemaining = pushBytes
}
opIndex += 1
continue
}
return pcToOpIndex
}
func bytesPushed(targetOpCode string) int {
var pushOps = [...]string{
"60",
"61",
"62",
"63",
"64",
"65",
"66",
"67",
"68",
"69",
"6a",
"6b",
"6c",
"6d",
"6e",
"6f",
"70",
"71",
"72",
"73",
"74",
"75",
"76",
"77",
"78",
"79",
"7a",
"7b",
"7c",
"7d",
"7e",
"7f",
}
for index, opCode := range pushOps {
if opCode == targetOpCode {
// Plus one because the first PUSH opcode pushes one byte onto the stack, not zero
return index + 1
}
}
return -1
}