package vm import ( "encoding/binary" "errors" "math/big" "github.com/nspcc-dev/neo-go/pkg/crypto/hash" "github.com/nspcc-dev/neo-go/pkg/smartcontract" "github.com/nspcc-dev/neo-go/pkg/util" "github.com/nspcc-dev/neo-go/pkg/vm/opcode" "github.com/nspcc-dev/neo-go/pkg/vm/stackitem" ) // Context represents the current execution context of the VM. type Context struct { // Instruction pointer. ip int // The next instruction pointer. nextip int // The raw program script. prog []byte // Breakpoints. breakPoints []int // Evaluation stack pointer. estack *Stack static *Slot local *Slot arguments *Slot // Exception context stack pointer. tryStack *Stack // Script hash of the prog. scriptHash util.Uint160 // Caller's contract script hash. callingScriptHash util.Uint160 // Call flags this context was created with. callFlag smartcontract.CallFlag } var errNoInstParam = errors.New("failed to read instruction parameter") // NewContext returns a new Context object. func NewContext(b []byte) *Context { return &Context{ prog: b, breakPoints: []int{}, } } // NextIP returns next instruction pointer. func (c *Context) NextIP() int { return c.nextip } // Next returns the next instruction to execute with its parameter if any. After // its invocation the instruction pointer points to the instruction being // returned. func (c *Context) Next() (opcode.Opcode, []byte, error) { var err error c.ip = c.nextip if c.ip >= len(c.prog) { return opcode.RET, nil, nil } var instrbyte = c.prog[c.ip] instr := opcode.Opcode(instrbyte) c.nextip++ var numtoread int switch instr { case opcode.PUSHDATA1: if c.nextip >= len(c.prog) { err = errNoInstParam } else { numtoread = int(c.prog[c.nextip]) c.nextip++ } case opcode.PUSHDATA2: if c.nextip+1 >= len(c.prog) { err = errNoInstParam } else { numtoread = int(binary.LittleEndian.Uint16(c.prog[c.nextip : c.nextip+2])) c.nextip += 2 } case opcode.PUSHDATA4: if c.nextip+3 >= len(c.prog) { err = errNoInstParam } else { var n = binary.LittleEndian.Uint32(c.prog[c.nextip : c.nextip+4]) if n > stackitem.MaxSize { return instr, nil, errors.New("parameter is too big") } numtoread = int(n) c.nextip += 4 } case opcode.JMP, opcode.JMPIF, opcode.JMPIFNOT, opcode.JMPEQ, opcode.JMPNE, opcode.JMPGT, opcode.JMPGE, opcode.JMPLT, opcode.JMPLE, opcode.CALL, opcode.ISTYPE, opcode.CONVERT, opcode.NEWARRAYT, opcode.ENDTRY, opcode.INITSSLOT, opcode.LDSFLD, opcode.STSFLD, opcode.LDARG, opcode.STARG, opcode.LDLOC, opcode.STLOC: numtoread = 1 case opcode.INITSLOT, opcode.TRY: numtoread = 2 case opcode.JMPL, opcode.JMPIFL, opcode.JMPIFNOTL, opcode.JMPEQL, opcode.JMPNEL, opcode.JMPGTL, opcode.JMPGEL, opcode.JMPLTL, opcode.JMPLEL, opcode.ENDTRYL, opcode.CALLL, opcode.SYSCALL, opcode.PUSHA: numtoread = 4 case opcode.TRYL: numtoread = 8 default: if instr <= opcode.PUSHINT256 { numtoread = 1 << instr } else { // No parameters, can just return. return instr, nil, nil } } if c.nextip+numtoread-1 >= len(c.prog) { err = errNoInstParam } if err != nil { return instr, nil, err } parameter := make([]byte, numtoread) copy(parameter, c.prog[c.nextip:c.nextip+numtoread]) c.nextip += numtoread return instr, parameter, nil } // IP returns the absolute instruction without taking 0 into account. // If that program starts the ip = 0 but IP() will return 1, cause its // the first instruction. func (c *Context) IP() int { return c.ip + 1 } // LenInstr returns the number of instructions loaded. func (c *Context) LenInstr() int { return len(c.prog) } // CurrInstr returns the current instruction and opcode. func (c *Context) CurrInstr() (int, opcode.Opcode) { return c.ip, opcode.Opcode(c.prog[c.ip]) } // Copy returns an new exact copy of c. func (c *Context) Copy() *Context { ctx := new(Context) *ctx = *c return ctx } // GetCallFlags returns calling flags context was created with. func (c *Context) GetCallFlags() smartcontract.CallFlag { return c.callFlag } // Program returns the loaded program. func (c *Context) Program() []byte { return c.prog } // ScriptHash returns a hash of the script in the current context. func (c *Context) ScriptHash() util.Uint160 { if c.scriptHash.Equals(util.Uint160{}) { c.scriptHash = hash.Hash160(c.prog) } return c.scriptHash } // Value implements stackitem.Item interface. func (c *Context) Value() interface{} { return c } // Dup implements stackitem.Item interface. func (c *Context) Dup() stackitem.Item { return c } // Bool implements stackitem.Item interface. func (c *Context) Bool() bool { panic("can't convert Context to Bool") } // TryBytes implements stackitem.Item interface. func (c *Context) TryBytes() ([]byte, error) { return nil, errors.New("can't convert Context to ByteArray") } // TryInteger implements stackitem.Item interface. func (c *Context) TryInteger() (*big.Int, error) { return nil, errors.New("can't convert Context to Integer") } // Type implements stackitem.Item interface. func (c *Context) Type() stackitem.Type { panic("Context cannot appear on evaluation stack") } // Convert implements stackitem.Item interface. func (c *Context) Convert(_ stackitem.Type) (stackitem.Item, error) { panic("Context cannot be converted to anything") } // Equals implements stackitem.Item interface. func (c *Context) Equals(s stackitem.Item) bool { return c == s } func (c *Context) atBreakPoint() bool { for _, n := range c.breakPoints { if n == c.ip { return true } } return false } func (c *Context) String() string { return "execution context" } // getContextScriptHash returns script hash of the invocation stack element // number n. func (v *VM) getContextScriptHash(n int) util.Uint160 { element := v.Istack().Peek(n) if element == nil { return util.Uint160{} } ctxIface := element.Value() ctx := ctxIface.(*Context) return ctx.ScriptHash() } // PushContextScriptHash pushes to evaluation stack the script hash of the // invocation stack element number n. func (v *VM) PushContextScriptHash(n int) error { h := v.getContextScriptHash(n) v.Estack().PushVal(h.BytesBE()) return nil }