vm: extract shared parts of the Context

Local calls reuse them, cross-contract calls create new ones. This allows to
avoid some allocations and use a little less memory.

pkg/core/interop/contract/call.go

@@ -27,7 +27,7 @@ func LoadToken(ic *interop.Context, id int32) error {
 	if !ctx.GetCallFlags().Has(callflag.ReadStates | callflag.AllowCall) {
 		return errors.New("invalid call flags")
 	}
-	tok := ctx.NEF.Tokens[id]
+	tok := ctx.GetNEF().Tokens[id]
 	if int(tok.ParamCount) > ctx.Estack().Len() {
 		return errors.New("stack is too small")
 	}

pkg/core/interop/runtime/engine.go

@@ -73,7 +73,7 @@ func Notify(ic *interop.Context) error {
 	if len(name) > MaxEventNameLen {
 		return fmt.Errorf("event name must be less than %d", MaxEventNameLen)
 	}
-	if ic.VM.Context().NEF == nil {
+	if !ic.VM.Context().IsDeployed() {
 		return errors.New("notifications are not allowed in dynamic scripts")
 	}
 

pkg/vm/context.go

@@ -16,14 +16,10 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
-// Context represents the current execution context of the VM.
+// scriptContext is a part of the Context that is shared between multiple Contexts,
-type Context struct {
+// it's created when a new script is loaded into the VM while regular
-	// Instruction pointer.
+// CALL/CALLL/CALLA internal invocations reuse it.
-	ip int
+type scriptContext struct {
-
-	// The next instruction pointer.
-	nextip int
-
 	// The raw program script.
 	prog []byte
 
@@ -33,12 +29,7 @@ type Context struct {
 	// Evaluation stack pointer.
 	estack *Stack
 
-	static    *slot
+	static slot
-	local     slot
-	arguments slot
-
-	// Exception context stack.
-	tryStack Stack
 
 	// Script hash of the prog.
 	scriptHash util.Uint160
@@ -49,17 +40,35 @@ type Context struct {
 	// Call flags this context was created with.
 	callFlag callflag.CallFlag
 
-	// retCount specifies the number of return values.
-	retCount int
 	// NEF represents a NEF file for the current contract.
 	NEF *nef.File
-	// invTree is an invocation tree (or branch of it) for this context.
+	// invTree is an invocation tree (or a branch of it) for this context.
 	invTree *invocations.Tree
 	// onUnload is a callback that should be called after current context unloading
 	// if no exception occurs.
 	onUnload ContextUnloadCallback
 }
 
+// Context represents the current execution context of the VM.
+type Context struct {
+	// Instruction pointer.
+	ip int
+
+	// The next instruction pointer.
+	nextip int
+
+	sc *scriptContext
+
+	local     slot
+	arguments slot
+
+	// Exception context stack.
+	tryStack Stack
+
+	// retCount specifies the number of return values.
+	retCount int
+}
+
 // ContextUnloadCallback is a callback method used on context unloading from istack.
 type ContextUnloadCallback func(commit bool) error
 
@@ -74,7 +83,9 @@ func NewContext(b []byte) *Context {
 // return value count and initial position in script.
 func NewContextWithParams(b []byte, rvcount int, pos int) *Context {
 	return &Context{
-		prog:     b,
+		sc: &scriptContext{
+			prog: b,
+		},
 		retCount: rvcount,
 		nextip:   pos,
 	}
@@ -82,7 +93,7 @@ func NewContextWithParams(b []byte, rvcount int, pos int) *Context {
 
 // Estack returns the evaluation stack of c.
 func (c *Context) Estack() *Stack {
-	return c.estack
+	return c.sc.estack
 }
 
 // NextIP returns the next instruction pointer.
@@ -92,7 +103,7 @@ func (c *Context) NextIP() int {
 
 // Jump unconditionally moves the next instruction pointer to the specified location.
 func (c *Context) Jump(pos int) {
-	if pos < 0 || pos >= len(c.prog) {
+	if pos < 0 || pos >= len(c.sc.prog) {
 		panic("instruction offset is out of range")
 	}
 	c.nextip = pos
@@ -105,11 +116,12 @@ func (c *Context) Next() (opcode.Opcode, []byte, error) {
 	var err error
 
 	c.ip = c.nextip
-	if c.ip >= len(c.prog) {
+	prog := c.sc.prog
+	if c.ip >= len(prog) {
 		return opcode.RET, nil, nil
 	}
 
-	var instrbyte = c.prog[c.ip]
+	var instrbyte = prog[c.ip]
 	instr := opcode.Opcode(instrbyte)
 	if !opcode.IsValid(instr) {
 		return instr, nil, fmt.Errorf("incorrect opcode %s", instr.String())
@@ -119,24 +131,24 @@ func (c *Context) Next() (opcode.Opcode, []byte, error) {
 	var numtoread int
 	switch instr {
 	case opcode.PUSHDATA1:
-		if c.nextip >= len(c.prog) {
+		if c.nextip >= len(prog) {
 			err = errNoInstParam
 		} else {
-			numtoread = int(c.prog[c.nextip])
+			numtoread = int(prog[c.nextip])
 			c.nextip++
 		}
 	case opcode.PUSHDATA2:
-		if c.nextip+1 >= len(c.prog) {
+		if c.nextip+1 >= len(prog) {
 			err = errNoInstParam
 		} else {
-			numtoread = int(binary.LittleEndian.Uint16(c.prog[c.nextip : c.nextip+2]))
+			numtoread = int(binary.LittleEndian.Uint16(prog[c.nextip : c.nextip+2]))
 			c.nextip += 2
 		}
 	case opcode.PUSHDATA4:
-		if c.nextip+3 >= len(c.prog) {
+		if c.nextip+3 >= len(prog) {
 			err = errNoInstParam
 		} else {
-			var n = binary.LittleEndian.Uint32(c.prog[c.nextip : c.nextip+4])
+			var n = binary.LittleEndian.Uint32(prog[c.nextip : c.nextip+4])
 			if n > stackitem.MaxSize {
 				return instr, nil, errors.New("parameter is too big")
 			}
@@ -166,13 +178,13 @@ func (c *Context) Next() (opcode.Opcode, []byte, error) {
 			return instr, nil, nil
 		}
 	}
-	if c.nextip+numtoread-1 >= len(c.prog) {
+	if c.nextip+numtoread-1 >= len(prog) {
 		err = errNoInstParam
 	}
 	if err != nil {
 		return instr, nil, err
 	}
-	parameter := c.prog[c.nextip : c.nextip+numtoread]
+	parameter := prog[c.nextip : c.nextip+numtoread]
 	c.nextip += numtoread
 	return instr, parameter, nil
 }
@@ -184,46 +196,44 @@ func (c *Context) IP() int {
 
 // LenInstr returns the number of instructions loaded.
 func (c *Context) LenInstr() int {
-	return len(c.prog)
+	return len(c.sc.prog)
 }
 
 // CurrInstr returns the current instruction and opcode.
 func (c *Context) CurrInstr() (int, opcode.Opcode) {
-	return c.ip, opcode.Opcode(c.prog[c.ip])
+	return c.ip, opcode.Opcode(c.sc.prog[c.ip])
 }
 
 // NextInstr returns the next instruction and opcode.
 func (c *Context) NextInstr() (int, opcode.Opcode) {
 	op := opcode.RET
-	if c.nextip < len(c.prog) {
+	if c.nextip < len(c.sc.prog) {
-		op = opcode.Opcode(c.prog[c.nextip])
+		op = opcode.Opcode(c.sc.prog[c.nextip])
 	}
 	return c.nextip, op
 }
 
-// Copy returns an new exact copy of c.
-func (c *Context) Copy() *Context {
-	ctx := new(Context)
-	*ctx = *c
-	return ctx
-}
-
 // GetCallFlags returns the calling flags which the context was created with.
 func (c *Context) GetCallFlags() callflag.CallFlag {
-	return c.callFlag
+	return c.sc.callFlag
 }
 
 // Program returns the loaded program.
 func (c *Context) Program() []byte {
-	return c.prog
+	return c.sc.prog
 }
 
 // ScriptHash returns a hash of the script in the current context.
 func (c *Context) ScriptHash() util.Uint160 {
-	if c.scriptHash.Equals(util.Uint160{}) {
+	if c.sc.scriptHash.Equals(util.Uint160{}) {
-		c.scriptHash = hash.Hash160(c.prog)
+		c.sc.scriptHash = hash.Hash160(c.sc.prog)
 	}
-	return c.scriptHash
+	return c.sc.scriptHash
+}
+
+// GetNEF returns NEF structure used by this context if it's present.
+func (c *Context) GetNEF() *nef.File {
+	return c.sc.NEF
 }
 
 // Value implements the stackitem.Item interface.
@@ -263,7 +273,7 @@ func (c *Context) Equals(s stackitem.Item) bool {
 }
 
 func (c *Context) atBreakPoint() bool {
-	for _, n := range c.breakPoints {
+	for _, n := range c.sc.breakPoints {
 		if n == c.nextip {
 			return true
 		}
@@ -277,12 +287,12 @@ func (c *Context) String() string {
 
 // IsDeployed returns whether this context contains a deployed contract.
 func (c *Context) IsDeployed() bool {
-	return c.NEF != nil
+	return c.sc.NEF != nil
 }
 
 // DumpStaticSlot returns json formatted representation of the given slot.
 func (c *Context) DumpStaticSlot() string {
-	return dumpSlot(c.static)
+	return dumpSlot(&c.sc.static)
 }
 
 // DumpLocalSlot returns json formatted representation of the given slot.

pkg/vm/interop.go

@@ -36,8 +36,9 @@ func defaultSyscallHandler(v *VM, id uint32) error {
 		return errors.New("syscall not found")
 	}
 	d := defaultVMInterops[n]
-	if !v.Context().callFlag.Has(d.RequiredFlags) {
+	ctxFlag := v.Context().sc.callFlag
-		return fmt.Errorf("missing call flags: %05b vs %05b", v.Context().callFlag, d.RequiredFlags)
+	if !ctxFlag.Has(d.RequiredFlags) {
+		return fmt.Errorf("missing call flags: %05b vs %05b", ctxFlag, d.RequiredFlags)
 	}
 	return d.Func(v)
 }

pkg/vm/json_test.go

@@ -115,7 +115,7 @@ func testSyscallHandler(v *VM, id uint32) error {
 	case 0x77777777:
 		v.Estack().PushVal(stackitem.NewInterop(new(int)))
 	case 0x66666666:
-		if !v.Context().callFlag.Has(callflag.ReadOnly) {
+		if !v.Context().sc.callFlag.Has(callflag.ReadOnly) {
 			return errors.New("invalid call flags")
 		}
 		v.Estack().PushVal(stackitem.NewInterop(new(int)))
@@ -167,14 +167,14 @@ func testFile(t *testing.T, filename string) {
 					if len(result.InvocationStack) > 0 {
 						for i, s := range result.InvocationStack {
 							ctx := vm.istack.Peek(i).Value().(*Context)
-							if ctx.nextip < len(ctx.prog) {
+							if ctx.nextip < len(ctx.sc.prog) {
 								require.Equal(t, s.InstructionPointer, ctx.nextip)
 								op, err := opcode.FromString(s.Instruction)
 								require.NoError(t, err)
-								require.Equal(t, op, opcode.Opcode(ctx.prog[ctx.nextip]))
+								require.Equal(t, op, opcode.Opcode(ctx.sc.prog[ctx.nextip]))
 							}
 							compareStacks(t, s.EStack, vm.estack)
-							compareSlots(t, s.StaticFields, ctx.static)
+							compareSlots(t, s.StaticFields, ctx.sc.static)
 						}
 					}
 
@@ -240,8 +240,8 @@ func compareStacks(t *testing.T, expected []vmUTStackItem, actual *Stack) {
 	compareItemArrays(t, expected, actual.Len(), func(i int) stackitem.Item { return actual.Peek(i).Item() })
 }
 
-func compareSlots(t *testing.T, expected []vmUTStackItem, actual *slot) {
+func compareSlots(t *testing.T, expected []vmUTStackItem, actual slot) {
-	if (actual == nil || *actual == nil) && len(expected) == 0 {
+	if actual == nil && len(expected) == 0 {
 		return
 	}
 	require.NotNil(t, actual)

pkg/vm/opcodebench_test.go

@@ -56,7 +56,7 @@ func opParamSlotsPushVM(op opcode.Opcode, param []byte, sslot int, slotloc int,
 			return nil
 		}
 		if sslot != 0 {
-			v.Context().static.init(sslot, &v.refs)
+			v.Context().sc.static.init(sslot, &v.refs)
 		}
 		if slotloc != 0 && slotarg != 0 {
 			v.Context().local.init(slotloc, &v.refs)

pkg/vm/vm.go

@@ -171,9 +171,7 @@ func (v *VM) PrintOps(out io.Writer) {
 	w := tabwriter.NewWriter(out, 0, 0, 4, ' ', 0)
 	fmt.Fprintln(w, "INDEX\tOPCODE\tPARAMETER")
 	realctx := v.Context()
-	ctx := realctx.Copy()
+	ctx := &Context{sc: realctx.sc}
-	ctx.ip = 0
-	ctx.nextip = 0
 	for {
 		cursor := ""
 		instr, parameter, err := ctx.Next()
@@ -228,7 +226,7 @@ func (v *VM) PrintOps(out io.Writer) {
 		}
 
 		fmt.Fprintf(w, "%d\t%s\t%s%s\n", ctx.ip, instr, desc, cursor)
-		if ctx.nextip >= len(ctx.prog) {
+		if ctx.nextip >= len(ctx.sc.prog) {
 			break
 		}
 	}
@@ -246,7 +244,7 @@ func getOffsetDesc(ctx *Context, parameter []byte) string {
 // AddBreakPoint adds a breakpoint to the current context.
 func (v *VM) AddBreakPoint(n int) {
 	ctx := v.Context()
-	ctx.breakPoints = append(ctx.breakPoints, n)
+	ctx.sc.breakPoints = append(ctx.sc.breakPoints, n)
 }
 
 // AddBreakPointRel adds a breakpoint relative to the current
@@ -337,31 +335,28 @@ func (v *VM) LoadNEFMethod(exe *nef.File, caller util.Uint160, hash util.Uint160
 // It should be used for calling from native contracts.
 func (v *VM) loadScriptWithCallingHash(b []byte, exe *nef.File, caller util.Uint160,
 	hash util.Uint160, f callflag.CallFlag, rvcount int, offset int, onContextUnload ContextUnloadCallback) {
-	var sl slot
-
 	v.checkInvocationStackSize()
 	ctx := NewContextWithParams(b, rvcount, offset)
 	if rvcount != -1 || v.estack.Len() != 0 {
 		v.estack = subStack(v.estack)
 	}
-	ctx.estack = v.estack
+	ctx.sc.estack = v.estack
 	initStack(&ctx.tryStack, "exception", nil)
-	ctx.callFlag = f
+	ctx.sc.callFlag = f
-	ctx.static = &sl
+	ctx.sc.scriptHash = hash
-	ctx.scriptHash = hash
+	ctx.sc.callingScriptHash = caller
-	ctx.callingScriptHash = caller
+	ctx.sc.NEF = exe
-	ctx.NEF = exe
 	if v.invTree != nil {
 		curTree := v.invTree
 		parent := v.Context()
 		if parent != nil {
-			curTree = parent.invTree
+			curTree = parent.sc.invTree
 		}
 		newTree := &invocations.Tree{Current: ctx.ScriptHash()}
 		curTree.Calls = append(curTree.Calls, newTree)
-		ctx.invTree = newTree
+		ctx.sc.invTree = newTree
 	}
-	ctx.onUnload = onContextUnload
+	ctx.sc.onUnload = onContextUnload
 	v.istack.PushItem(ctx)
 }
 
@@ -481,7 +476,7 @@ func (v *VM) StepInto() error {
 		return nil
 	}
 
-	if ctx != nil && ctx.prog != nil {
+	if ctx != nil && ctx.sc.prog != nil {
 		op, param, err := ctx.Next()
 		if err != nil {
 			v.state = vmstate.Fault
@@ -584,7 +579,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		}
 	}()
 
-	if v.getPrice != nil && ctx.ip < len(ctx.prog) {
+	if v.getPrice != nil && ctx.ip < len(ctx.sc.prog) {
 		v.gasConsumed += v.getPrice(op, parameter)
 		if v.GasLimit >= 0 && v.gasConsumed > v.GasLimit {
 			panic("gas limit is exceeded")
@@ -610,7 +605,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.PUSHA:
 		n := getJumpOffset(ctx, parameter)
-		ptr := stackitem.NewPointerWithHash(n, ctx.prog, ctx.ScriptHash())
+		ptr := stackitem.NewPointerWithHash(n, ctx.sc.prog, ctx.ScriptHash())
 		v.estack.PushItem(ptr)
 
 	case opcode.PUSHNULL:
@@ -637,7 +632,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		if parameter[0] == 0 {
 			panic("zero argument")
 		}
-		ctx.static.init(int(parameter[0]), &v.refs)
+		ctx.sc.static.init(int(parameter[0]), &v.refs)
 
 	case opcode.INITSLOT:
 		if ctx.local != nil || ctx.arguments != nil {
@@ -658,20 +653,20 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		}
 
 	case opcode.LDSFLD0, opcode.LDSFLD1, opcode.LDSFLD2, opcode.LDSFLD3, opcode.LDSFLD4, opcode.LDSFLD5, opcode.LDSFLD6:
-		item := ctx.static.Get(int(op - opcode.LDSFLD0))
+		item := ctx.sc.static.Get(int(op - opcode.LDSFLD0))
 		v.estack.PushItem(item)
 
 	case opcode.LDSFLD:
-		item := ctx.static.Get(int(parameter[0]))
+		item := ctx.sc.static.Get(int(parameter[0]))
 		v.estack.PushItem(item)
 
 	case opcode.STSFLD0, opcode.STSFLD1, opcode.STSFLD2, opcode.STSFLD3, opcode.STSFLD4, opcode.STSFLD5, opcode.STSFLD6:
 		item := v.estack.Pop().Item()
-		ctx.static.Set(int(op-opcode.STSFLD0), item, &v.refs)
+		ctx.sc.static.Set(int(op-opcode.STSFLD0), item, &v.refs)
 
 	case opcode.STSFLD:
 		item := v.estack.Pop().Item()
-		ctx.static.Set(int(parameter[0]), item, &v.refs)
+		ctx.sc.static.Set(int(parameter[0]), item, &v.refs)
 
 	case opcode.LDLOC0, opcode.LDLOC1, opcode.LDLOC2, opcode.LDLOC3, opcode.LDLOC4, opcode.LDLOC5, opcode.LDLOC6:
 		item := ctx.local.Get(int(op - opcode.LDLOC0))
@@ -1475,7 +1470,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 			break
 		}
 
-		newEstack := v.Context().estack
+		newEstack := v.Context().sc.estack
 		if oldEstack != newEstack {
 			if oldCtx.retCount >= 0 && oldEstack.Len() != oldCtx.retCount {
 				panic(fmt.Errorf("invalid return values count: expected %d, got %d",
@@ -1631,17 +1626,19 @@ func (v *VM) unloadContext(ctx *Context) {
 		ctx.arguments.ClearRefs(&v.refs)
 	}
 	currCtx := v.Context()
-	if ctx.static != nil && (currCtx == nil || ctx.static != currCtx.static) {
+	if currCtx == nil || ctx.sc != currCtx.sc {
-		ctx.static.ClearRefs(&v.refs)
+		if ctx.sc.static != nil {
-	}
+			ctx.sc.static.ClearRefs(&v.refs)
-	if ctx.onUnload != nil {
+		}
-		err := ctx.onUnload(v.uncaughtException == nil)
+		if ctx.sc.onUnload != nil {
-		if err != nil {
+			err := ctx.sc.onUnload(v.uncaughtException == nil)
-			errMessage := fmt.Sprintf("context unload callback failed: %s", err)
+			if err != nil {
-			if v.uncaughtException != nil {
+				errMessage := fmt.Sprintf("context unload callback failed: %s", err)
-				errMessage = fmt.Sprintf("%s, uncaught exception: %s", errMessage, v.uncaughtException)
+				if v.uncaughtException != nil {
+					errMessage = fmt.Sprintf("%s, uncaught exception: %s", errMessage, v.uncaughtException)
+				}
+				panic(errors.New(errMessage))
 			}
-			panic(errors.New(errMessage))
 		}
 	}
 }
@@ -1691,17 +1688,13 @@ func (v *VM) Call(offset int) {
 // package.
 func (v *VM) call(ctx *Context, offset int) {
 	v.checkInvocationStackSize()
-	newCtx := ctx.Copy()
+	newCtx := &Context{
-	newCtx.retCount = -1
+		sc:       ctx.sc,
-	newCtx.local = nil
+		retCount: -1,
-	newCtx.arguments = nil
+		tryStack: ctx.tryStack,
-	// If memory for `elems` is reused, we can end up
+	}
-	// with an incorrect exception context state in the caller.
+	// New context -> new exception handlers.
-	newCtx.tryStack.elems = nil
+	newCtx.tryStack.elems = ctx.tryStack.elems[len(ctx.tryStack.elems):]
-	initStack(&newCtx.tryStack, "exception", nil)
-	newCtx.NEF = ctx.NEF
-	// Do not clone unloading callback, new context does not require any actions to perform on unloading.
-	newCtx.onUnload = nil
 	v.istack.PushItem(newCtx)
 	newCtx.Jump(offset)
 }
@@ -1732,7 +1725,7 @@ func calcJumpOffset(ctx *Context, parameter []byte) (int, int, error) {
 		return 0, 0, fmt.Errorf("invalid %s parameter length: %d", curr, l)
 	}
 	offset := ctx.ip + int(rOffset)
-	if offset < 0 || offset > len(ctx.prog) {
+	if offset < 0 || offset > len(ctx.sc.prog) {
 		return 0, 0, fmt.Errorf("invalid offset %d ip at %d", offset, ctx.ip)
 	}
 
@@ -1955,7 +1948,7 @@ func bytesToPublicKey(b []byte, curve elliptic.Curve) *keys.PublicKey {
 
 // GetCallingScriptHash implements the ScriptHashGetter interface.
 func (v *VM) GetCallingScriptHash() util.Uint160 {
-	return v.Context().callingScriptHash
+	return v.Context().sc.callingScriptHash
 }
 
 // GetEntryScriptHash implements the ScriptHashGetter interface.