NEO VM原理及其實現是怎樣的，很多新手對此不是很清楚，為了幫助大家解決這個難題，下面小編將為大家詳細講解，有這方面需求的人可以來學習下，希望你能有所收獲。
neo vm和evm類似。底層都實現了一套opcode以及對應的執行器，opcode設計差距蠻大的，總體上來說evm的更加簡潔，neo vm的功能更加豐富強大。
neo底層原生支持類型系統，所有棧上的內容都是有類型的，而在evm中所有的棧上內容都是無類型的，依賴于運行時轉換。實質上在于空間和時間的取舍。
neo在opcode級別支持類型及其操作，在內部函數調用方面evm通過jumpdest解決，neo vm的jump類指令則僅用于循環，函數調用則通過call和systemcall解決（這樣很好的支持了調用函數棧）?？偟膩碚fneo vm一些高級操作可以下沉到code級別執行，方便了代碼的轉換。而evm則更加考驗編譯器的能力。
隔離執行器和外部對象的具體實現，vm提供了一些外部接口用于執行一些和外部對象和存儲相關的操作。eth的外部對象和指令揉合在一起。
理論上來說eth也可以支持多種語言，實際上來說solidity一家獨大，其中未嘗沒有eth的opcode轉換難度大的原因，而neo vm的opcode則相對友好，支持多種語言開發。當然evm也并非沒有好處，solidity支持內聯編程，如果熟悉evm的opcode能寫出效率非常高的合約。neo在這方面尚未提供支持。
neo vm支持debug，支持step into，step over，break point operation。
如需了解evm的詳細實現可以參考另一篇博文 https://my.oschina.net/hunjixin/blog/1805306
. ├── ExecutionContext.cs //執行上下文 引擎，代碼，斷點 ├── ExecutionEngine.cs //執行引擎 ├── Helper.cs //編碼及long型 ├── ICrypto.cs //加密解密 ├── IInteropInterface.cs //外部對象相關 ├── InteropService.cs //存儲相關 ├── IScriptContainer.cs //腳本 ├── IScriptTable.cs //腳本讀取 ├── neo-vm.csproj ├── OpCode.cs //操作碼 ├── RandomAccessStack.cs //快速訪問棧 ├── ScriptBuilder.cs //腳本構建 ├── StackItem.cs //棧 ├── Types //類型 │ ├── Array.cs //數組 │ ├── Boolean.cs //bool │ ├── ByteArray.cs //比特數組 │ ├── Integer.cs //整數 │ ├── InteropInterface.cs //操作對象接口 │ ├── Map.cs //映射 │ └── Struct.cs //結構體 └── VMState.cs //執行狀態
vm支持七種類型，分別是數組，bool，byte數組，整數，外部對象，映射，結構體。所有的結構體都是繼承子StackItem，同時具有自己的數據字段。
stackItem
public abstract class StackItem : IEquatable<StackItem>
{
public abstract bool Equals(StackItem other);
public sealed override bool Equals(object obj)
{
if (obj == null) return false;
if (obj == this) return true;
if (obj is StackItem other)
return Equals(other);
return false;
}
public static StackItem FromInterface(IInteropInterface value)
{
return new InteropInterface(value);
}
public virtual BigInteger GetBigInteger()
{
return new BigInteger(GetByteArray());
}
public virtual bool GetBoolean()
{
return GetByteArray().Any(p => p != 0);
}
public abstract byte[] GetByteArray();
public override int GetHashCode()
{
unchecked
{
int hash = 17;
foreach (byte element in GetByteArray())
hash = hash * 31 + element;
return hash;
}
}
public virtual string GetString()
{
return Encoding.UTF8.GetString(GetByteArray());
}
public static implicit operator StackItem(int value)
{
return (BigInteger)value;
}
public static implicit operator StackItem(uint value)
{
return (BigInteger)value;
}
public static implicit operator StackItem(long value)
{
return (BigInteger)value;
}
public static implicit operator StackItem(ulong value)
{
return (BigInteger)value;
}
public static implicit operator StackItem(BigInteger value)
{
return new Integer(value);
}
public static implicit operator StackItem(bool value)
{
return new Boolean(value);
}
public static implicit operator StackItem(byte[] value)
{
return new ByteArray(value);
}
public static implicit operator StackItem(StackItem[] value)
{
return new Array(value);
}
public static implicit operator StackItem(List<StackItem> value)
{
return new Array(value);
}
}bool 為例子
public class Boolean : StackItem
{
private static readonly byte[] TRUE = { 1 };
private static readonly byte[] FALSE = new byte[0];
private bool value;
public Boolean(bool value)
{
this.value = value;
}
public override bool Equals(StackItem other)
{
if (ReferenceEquals(this, other)) return true;
if (ReferenceEquals(null, other)) return false;
if (other is Boolean b) return value == b.value;
byte[] bytes_other;
try
{
bytes_other = other.GetByteArray();
}
catch (NotSupportedException)
{
return false;
}
return GetByteArray().SequenceEqual(bytes_other);
}
public override BigInteger GetBigInteger()
{
return value ? BigInteger.One : BigInteger.Zero;
}
public override bool GetBoolean()
{
return value;
}
public override byte[] GetByteArray()
{
return value ? TRUE : FALSE;
}
}貼一些上來感受下
數值常量
PUSH2 = 0x52, // The number 2 is pushed onto the stack. PUSH3 = 0x53, // The number 3 is pushed onto the stack. PUSH4 = 0x54, // The number 4 is pushed onto the stack. PUSH5 = 0x55, // The number 5 is pushed onto the stack.
跳轉
JMP = 0x62, JMPIF = 0x63, JMPIFNOT = 0x64,
調用
CALL = 0x65, RET = 0x66, APPCALL = 0x67, SYSCALL = 0x68, TAILCALL = 0x69,
棧操作，neo再著一塊的相對比較豐富（這里并不是全部）
DROP = 0x75, // Removes the top stack item. DUP = 0x76, // Duplicates the top stack item. PICK = 0x79, // The item n back in the stack is copied to the top. ROLL = 0x7A, // The item n back in the stack is moved to the top. SWAP = 0x7C, // The top two items on the stack are swapped.
運算，僅貼了些代表性的上來
INC = 0x8B, // 1 is added to the input. SIGN = 0x8D, ABS = 0x90, // The input is made positive. NZ = 0x92, // Returns 0 if the input is 0. 1 otherwise. DIV = 0x96, // a is divided by b. MOD = 0x97, // Returns the remainder after dividing a by b. SHR = 0x99, // Shifts a right b bits, preserving sign. BOOLAND = 0x9A, // If both a and b are not 0, the output is 1. Otherwise 0. GTE = 0xA2, // Returns 1 if a is greater than or equal to b, 0 otherwise. MAX = 0xA4, // Returns the larger of a and b. WITHIN = 0xA5, // Returns 1 if x is within the specified range (left-inclusive), 0 otherwise.
加密驗證
SHA1 = 0xA7, // The input is hashed using SHA-1. SHA256 = 0xA8, // The input is hashed using SHA-256. HASH160 = 0xA9, HASH256 = 0xAA, CHECKSIG = 0xAC, VERIFY = 0xAD, CHECKMULTISIG = 0xAE,
數組，結構體及相關操作
ARRAYSIZE = 0xC0, PACK = 0xC1, UNPACK = 0xC2, PICKITEM = 0xC3, SETITEM = 0xC4, NEWARRAY = 0xC5, //用作引用類型 NEWSTRUCT = 0xC6, //用作值類型 NEWMAP = 0xC7, APPEND = 0xC8, REVERSE = 0xC9, REMOVE = 0xCA, HASKEY = 0xCB, KEYS = 0xCC, VALUES = 0xCD,
異常
THROW = 0xF0, THROWIFNOT = 0xF1
腳本容器，保存當前執行腳本
public interface IScriptContainer : IInteropInterface
{
byte[] GetMessage();
}合約腳本查找
public interface IScriptTable
{
byte[] GetScript(byte[] script_hash);
}加密
public interface ICrypto
{
byte[] Hash260(byte[] message);
byte[] Hash356(byte[] message);
bool VerifySignature(byte[] message, byte[] signature, byte[] pubkey);
}外部服務調用接口
public class InteropService
{
private Dictionary<string, Func<ExecutionEngine, bool>> dictionary = new Dictionary<string, Func<ExecutionEngine, bool>>();
public InteropService()
{
Register("System.ExecutionEngine.GetScriptContainer", GetScriptContainer);
Register("System.ExecutionEngine.GetExecutingScriptHash", GetExecutingScriptHash);
Register("System.ExecutionEngine.GetCallingScriptHash", GetCallingScriptHash);
Register("System.ExecutionEngine.GetEntryScriptHash", GetEntryScriptHash);
}
protected void Register(string method, Func<ExecutionEngine, bool> handler)
{
dictionary[method] = handler;
}
internal bool Invoke(string method, ExecutionEngine engine)
{
if (!dictionary.TryGetValue(method, out Func<ExecutionEngine, bool> func)) return false;
return func(engine);
}
private static bool GetScriptContainer(ExecutionEngine engine)
{
engine.EvaluationStack.Push(StackItem.FromInterface(engine.ScriptContainer));
return true;
}
private static bool GetExecutingScriptHash(ExecutionEngine engine)
{
engine.EvaluationStack.Push(engine.CurrentContext.ScriptHash);
return true;
}
private static bool GetCallingScriptHash(ExecutionEngine engine)
{
engine.EvaluationStack.Push(engine.CallingContext.ScriptHash);
return true;
}
private static bool GetEntryScriptHash(ExecutionEngine engine)
{
engine.EvaluationStack.Push(engine.EntryContext.ScriptHash);
return true;
}
}外部對象接口
public interface IInteropInterface
{
} public class ExecutionEngine : IDisposable
{
//調用棧
public RandomAccessStack<ExecutionContext> InvocationStack { get; } = new RandomAccessStack<ExecutionContext>();
//執行棧
public RandomAccessStack<StackItem> EvaluationStack { get; } = new RandomAccessStack<StackItem>();
//參數棧
public RandomAccessStack<StackItem> AltStack { get; } = new RandomAccessStack<StackItem>();
public ExecutionContext CurrentContext => InvocationStack.Peek();
public ExecutionContext CallingContext => InvocationStack.Count > 1 ? InvocationStack.Peek(1) : null;
public ExecutionContext EntryContext => InvocationStack.Peek(InvocationStack.Count - 1);
//執行狀態
public VMState State { get; protected set; } = VMState.BREAK;
//載入執行腳本
void LoadScript(byte[] script, bool push_only = false){}
//添加斷點
void AddBreakPoint(uint position){}
//刪除斷點
bool RemoveBreakPoint(uint position){}
//執行腳本
void Execute(){}
//執行opcode
void ExecuteOp(OpCode opcode, ExecutionContext context){}
//執行下一步
void StepInto(){}
//當前call執行完成
void StepOut(){}
//全部執行
void StepOver(){}
}操作符號執行過程
private void ExecuteOp(OpCode opcode, ExecutionContext context)
{
if (opcode > OpCode.PUSH16 && opcode != OpCode.RET && context.PushOnly)
{
State |= VMState.FAULT;
return;
}
if (opcode >= OpCode.PUSHBYTES1 && opcode <= OpCode.PUSHBYTES75)
EvaluationStack.Push(context.OpReader.ReadBytes((byte)opcode));
else
switch (opcode)
{
//常量push
case OpCode.PUSH1:
case OpCode.PUSH16:
EvaluationStack.Push((int)opcode - (int)OpCode.PUSH1 + 1);
break;
case OpCode.JMP: //跳轉
{
int offset = context.OpReader.ReadInt16();
offset = context.InstructionPointer + offset - 3;
if (offset < 0 || offset > context.Script.Length)
{
State |= VMState.FAULT;
return;
}
bool fValue = true;
if (opcode > OpCode.JMP)
{
fValue = EvaluationStack.Pop().GetBoolean();
if (opcode == OpCode.JMPIFNOT)
fValue = !fValue;
}
if (fValue)
context.InstructionPointer = offset;
}
break;
case OpCode.CALL: //和systemcall差不多， 區別在于system是系統預先注冊的函數 call調用的是用戶自己寫的函數
InvocationStack.Push(context.Clone());
context.InstructionPointer += 2;
ExecuteOp(OpCode.JMP, CurrentContext);
break;
case OpCode.RET: //退出當前函數棧
InvocationStack.Pop().Dispose();
if (InvocationStack.Count == 0)
State |= VMState.HALT;
break;
case OpCode.APPCALL: //調用外部合約
case OpCode.TAILCALL:
{
if (table == null)
{
State |= VMState.FAULT;
return;
}
byte[] script_hash = context.OpReader.ReadBytes(20);
if (script_hash.All(p => p == 0))
{
script_hash = EvaluationStack.Pop().GetByteArray();
}
byte[] script = table.GetScript(script_hash);
if (script == null)
{
State |= VMState.FAULT;
return;
}
if (opcode == OpCode.TAILCALL)
InvocationStack.Pop().Dispose();
LoadScript(script);
}
break;
case OpCode.SYSCALL: //內部合約函數調用
if (!service.Invoke(Encoding.ASCII.GetString(context.OpReader.ReadVarBytes(252)), this))
State |= VMState.FAULT;
break;
case OpCode.DROP: //移除棧頂
EvaluationStack.Pop();
break;
case OpCode.DUP: //賦值棧頂 有對應按位置復制的指令
EvaluationStack.Push(EvaluationStack.Peek());
break;
case OpCode.EQUAL: //判等
{
StackItem x2 = EvaluationStack.Pop();
StackItem x1 = EvaluationStack.Pop();
EvaluationStack.Push(x1.Equals(x2));
}
break;
// Numeric
case OpCode.ABS: //運算 加減乘除 最大值最小值等等
{
BigInteger x = EvaluationStack.Pop().GetBigInteger();
EvaluationStack.Push(BigInteger.Abs(x));
}
break;
// Crypto
case OpCode.SHA256: //加密
using (SHA256 sha = SHA256.Create())
{
byte[] x = EvaluationStack.Pop().GetByteArray();
EvaluationStack.Push(sha.ComputeHash(x));
}
break;
case OpCode.CHECKSIG: //驗證
{
byte[] pubkey = EvaluationStack.Pop().GetByteArray();
byte[] signature = EvaluationStack.Pop().GetByteArray();
try
{
EvaluationStack.Push(Crypto.VerifySignature(ScriptContainer.GetMessage(), signature, pubkey));
}
catch (ArgumentException)
{
EvaluationStack.Push(false);
}
}
break;
// Array
case OpCode.PICKITEM: //數組映射取值
{
StackItem key = EvaluationStack.Pop();
if (key is ICollection)
{
State |= VMState.FAULT;
return;
}
switch (EvaluationStack.Pop())
{
case VMArray array:
int index = (int)key.GetBigInteger();
if (index < 0 || index >= array.Count)
{
State |= VMState.FAULT;
return;
}
EvaluationStack.Push(array[index]);
break;
case Map map:
if (map.TryGetValue(key, out StackItem value))
{
EvaluationStack.Push(value);
}
else
{
State |= VMState.FAULT;
return;
}
break;
default:
State |= VMState.FAULT;
return;
}
}
break;
case OpCode.SETITEM: //數組 映射賦值
{
StackItem value = EvaluationStack.Pop();
if (value is Struct s) value = s.Clone();
StackItem key = EvaluationStack.Pop();
if (key is ICollection)
{
State |= VMState.FAULT;
return;
}
switch (EvaluationStack.Pop())
{
case VMArray array:
int index = (int)key.GetBigInteger();
if (index < 0 || index >= array.Count)
{
State |= VMState.FAULT;
return;
}
array[index] = value;
break;
case Map map:
map[key] = value;
break;
default:
State |= VMState.FAULT;
return;
}
}
break;
case OpCode.NEWARRAY: //創建數組
{
int count = (int)EvaluationStack.Pop().GetBigInteger();
List<StackItem> items = new List<StackItem>(count);
for (var i = 0; i < count; i++)
{
items.Add(false);
}
EvaluationStack.Push(new Types.Array(items));
}
break;
case OpCode.NEWSTRUCT: //創建結構體
{
int count = (int)EvaluationStack.Pop().GetBigInteger();
List<StackItem> items = new List<StackItem>(count);
for (var i = 0; i < count; i++)
{
items.Add(false);
}
EvaluationStack.Push(new VM.Types.Struct(items));
}
break;
case OpCode.NEWMAP: //創建映射
EvaluationStack.Push(new Map());
break;
case OpCode.APPEND: //追加元素
{
StackItem newItem = EvaluationStack.Pop();
if (newItem is Types.Struct s)
{
newItem = s.Clone();
}
StackItem arrItem = EvaluationStack.Pop();
if (arrItem is VMArray array)
{
array.Add(newItem);
}
else
{
State |= VMState.FAULT;
return;
}
}
break;
case OpCode.REMOVE: //移除元素
{
StackItem key = EvaluationStack.Pop();
if (key is ICollection)
{
State |= VMState.FAULT;
return;
}
switch (EvaluationStack.Pop())
{
case VMArray array:
int index = (int)key.GetBigInteger();
if (index < 0 || index >= array.Count)
{
State |= VMState.FAULT;
return;
}
array.RemoveAt(index);
break;
case Map map:
map.Remove(key);
break;
default:
State |= VMState.FAULT;
return;
}
}
break;
case OpCode.KEYS: //獲取映射鍵集合，對應的還有獲取值集合 haskey
switch (EvaluationStack.Pop())
{
case Map map:
EvaluationStack.Push(new VMArray(map.Keys));
break;
default:
State |= VMState.FAULT;
return;
}
break;
// Exceptions
case OpCode.THROW: //異常中止
State |= VMState.FAULT;
return;
case OpCode.THROWIFNOT:
if (!EvaluationStack.Pop().GetBoolean())
{
State |= VMState.FAULT;
return;
}
break;
default:
State |= VMState.FAULT;
return;
}
if (!State.HasFlag(VMState.FAULT) && InvocationStack.Count > 0)
{
//斷點起效的位置
if (CurrentContext.BreakPoints.Contains((uint)CurrentContext.InstructionPointer))
State |= VMState.BREAK;
}
}看完上述內容是否對您有幫助呢？如果還想對相關知識有進一步的了解或閱讀更多相關文章，請關注億速云行業資訊頻道，感謝您對億速云的支持。
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