vm, core: push Null return value only if no exception occurs

Close https://github.com/nspcc-dev/neo-go/issues/2509.

pkg/core/blockchain.go

@@ -2247,7 +2247,7 @@ func (bc *Blockchain) InitVerificationContext(ic *interop.Context, hash util.Uin
 		}
 		ic.Invocations[cs.Hash]++
 		ic.VM.LoadNEFMethod(&cs.NEF, util.Uint160{}, hash, callflag.ReadOnly,
-			true, verifyOffset, initOffset)
+			true, verifyOffset, initOffset, nil)
 	}
 	if len(witness.InvocationScript) != 0 {
 		err := vm.IsScriptCorrect(witness.InvocationScript, nil)

pkg/core/interop/contract/call.go

@@ -40,7 +40,7 @@ func LoadToken(ic *interop.Context) func(id int32) error {
 		if err != nil {
 			return fmt.Errorf("token contract %s not found: %w", tok.Hash.StringLE(), err)
 		}
-		return callInternal(ic, cs, tok.Method, tok.CallFlag, tok.HasReturn, args)
+		return callInternal(ic, cs, tok.Method, tok.CallFlag, tok.HasReturn, args, nil)
 	}
 }
 
@@ -69,14 +69,17 @@ func Call(ic *interop.Context) error {
 		return fmt.Errorf("method not found: %s/%d", method, len(args))
 	}
 	hasReturn := md.ReturnType != smartcontract.VoidType
+	var cb vm.ContextUnloadCallback
 	if !hasReturn {
-		ic.VM.Estack().PushItem(stackitem.Null{})
+		cb = func(estack *vm.Stack) {
+			estack.PushItem(stackitem.Null{})
+		}
 	}
-	return callInternal(ic, cs, method, fs, hasReturn, args)
+	return callInternal(ic, cs, method, fs, hasReturn, args, cb)
 }
 
 func callInternal(ic *interop.Context, cs *state.Contract, name string, f callflag.CallFlag,
-	hasReturn bool, args []stackitem.Item) error {
+	hasReturn bool, args []stackitem.Item, cb vm.ContextUnloadCallback) error {
 	md := cs.Manifest.ABI.GetMethod(name, len(args))
 	if md.Safe {
 		f &^= (callflag.WriteStates | callflag.AllowNotify)
@@ -88,12 +91,12 @@ func callInternal(ic *interop.Context, cs *state.Contract, name string, f callfl
 			}
 		}
 	}
-	return callExFromNative(ic, ic.VM.GetCurrentScriptHash(), cs, name, args, f, hasReturn)
+	return callExFromNative(ic, ic.VM.GetCurrentScriptHash(), cs, name, args, f, hasReturn, cb)
 }
 
 // callExFromNative calls a contract with flags using the provided calling hash.
 func callExFromNative(ic *interop.Context, caller util.Uint160, cs *state.Contract,
-	name string, args []stackitem.Item, f callflag.CallFlag, hasReturn bool) error {
+	name string, args []stackitem.Item, f callflag.CallFlag, hasReturn bool, cb vm.ContextUnloadCallback) error {
 	for _, nc := range ic.Natives {
 		if nc.Metadata().Name == nativenames.Policy {
 			var pch = nc.(policyChecker)
@@ -120,7 +123,7 @@ func callExFromNative(ic *interop.Context, caller util.Uint160, cs *state.Contra
 	}
 	ic.Invocations[cs.Hash]++
 	ic.VM.LoadNEFMethod(&cs.NEF, caller, cs.Hash, ic.VM.Context().GetCallFlags()&f,
-		hasReturn, methodOff, initOff)
+		hasReturn, methodOff, initOff, cb)
 
 	for e, i := ic.VM.Estack(), len(args)-1; i >= 0; i-- {
 		e.PushItem(args[i])
@@ -134,7 +137,7 @@ var ErrNativeCall = errors.New("failed native call")
 // CallFromNative performs synchronous call from native contract.
 func CallFromNative(ic *interop.Context, caller util.Uint160, cs *state.Contract, method string, args []stackitem.Item, hasReturn bool) error {
 	startSize := ic.VM.Istack().Len()
-	if err := callExFromNative(ic, caller, cs, method, args, callflag.All, hasReturn); err != nil {
+	if err := callExFromNative(ic, caller, cs, method, args, callflag.All, hasReturn, nil); err != nil {
 		return err
 	}
 

pkg/core/interop_system_neotest_test.go

@@ -507,3 +507,150 @@ func TestSnapshotIsolation_CallToItself(t *testing.T) {
 	// unwrapped and persisted during the previous call.
 	ctrInvoker.Invoke(t, stackitem.Null{}, "check")
 }
+
+// This test is written to check https://github.com/nspcc-dev/neo-go/issues/2509
+// and https://github.com/neo-project/neo/pull/2745#discussion_r879167180.
+func TestRET_after_FINALLY_PanicInsideVoidMethod(t *testing.T) {
+	bc, acc := chain.NewSingle(t)
+	e := neotest.NewExecutor(t, bc, acc, acc)
+
+	// Contract A throws catchable exception. It also has a non-void method.
+	srcA := `package contractA
+		func Panic() {
+			panic("panic from A")
+		}
+		func ReturnSomeValue() int {
+			return 5
+		}`
+	ctrA := neotest.CompileSource(t, acc.ScriptHash(), strings.NewReader(srcA), &compiler.Options{
+		NoEventsCheck:      true,
+		NoPermissionsCheck: true,
+		Name:               "contractA",
+	})
+	e.DeployContract(t, ctrA, nil)
+
+	var hashAStr string
+	for i := 0; i < util.Uint160Size; i++ {
+		hashAStr += fmt.Sprintf("%#x", ctrA.Hash[i])
+		if i != util.Uint160Size-1 {
+			hashAStr += ", "
+		}
+	}
+	// Contract B calls A and catches the exception thrown by A.
+	srcB := `package contractB
+		import (
+			"github.com/nspcc-dev/neo-go/pkg/interop"
+			"github.com/nspcc-dev/neo-go/pkg/interop/contract"
+		)
+		func Catch() {
+			defer func() {
+				if r := recover(); r != nil {
+					// Call method with return value to check https://github.com/neo-project/neo/pull/2745#discussion_r879167180.
+					contract.Call(interop.Hash160{` + hashAStr + `}, "returnSomeValue", contract.All)
+				}
+			}()
+			contract.Call(interop.Hash160{` + hashAStr + `}, "panic", contract.All)
+		}`
+	ctrB := neotest.CompileSource(t, acc.ScriptHash(), strings.NewReader(srcB), &compiler.Options{
+		Name:               "contractB",
+		NoEventsCheck:      true,
+		NoPermissionsCheck: true,
+		Permissions: []manifest.Permission{
+			{
+				Methods: manifest.WildStrings{Value: nil},
+			},
+		},
+	})
+	e.DeployContract(t, ctrB, nil)
+
+	ctrInvoker := e.NewInvoker(ctrB.Hash, e.Committee)
+	ctrInvoker.Invoke(t, stackitem.Null{}, "catch")
+}
+
+// This test is written to check https://github.com/neo-project/neo/pull/2745#discussion_r879125733.
+func TestRET_after_FINALLY_CallNonVoidAfterVoidMethod(t *testing.T) {
+	bc, acc := chain.NewSingle(t)
+	e := neotest.NewExecutor(t, bc, acc, acc)
+
+	// Contract A has two methods. One of them has no return value, and the other has it.
+	srcA := `package contractA
+		import "github.com/nspcc-dev/neo-go/pkg/interop/runtime"
+		func NoRet() {
+			runtime.Notify("no ret")
+		}
+		func HasRet() int {
+			runtime.Notify("ret")
+			return 5
+		}`
+	ctrA := neotest.CompileSource(t, acc.ScriptHash(), strings.NewReader(srcA), &compiler.Options{
+		NoEventsCheck:      true,
+		NoPermissionsCheck: true,
+		Name:               "contractA",
+	})
+	e.DeployContract(t, ctrA, nil)
+
+	var hashAStr string
+	for i := 0; i < util.Uint160Size; i++ {
+		hashAStr += fmt.Sprintf("%#x", ctrA.Hash[i])
+		if i != util.Uint160Size-1 {
+			hashAStr += ", "
+		}
+	}
+	// Contract B calls A in try-catch block.
+	srcB := `package contractB
+		import (
+			"github.com/nspcc-dev/neo-go/pkg/interop"
+			"github.com/nspcc-dev/neo-go/pkg/interop/contract"
+			"github.com/nspcc-dev/neo-go/pkg/interop/util"
+		)
+		func CallAInTryCatch() {
+			defer func() {
+				if r := recover(); r != nil {
+					util.Abort() // should never happen
+				}
+			}()
+			contract.Call(interop.Hash160{` + hashAStr + `}, "noRet", contract.All)
+			contract.Call(interop.Hash160{` + hashAStr + `}, "hasRet", contract.All)
+		}`
+	ctrB := neotest.CompileSource(t, acc.ScriptHash(), strings.NewReader(srcB), &compiler.Options{
+		Name:               "contractB",
+		NoEventsCheck:      true,
+		NoPermissionsCheck: true,
+		Permissions: []manifest.Permission{
+			{
+				Methods: manifest.WildStrings{Value: nil},
+			},
+		},
+	})
+	e.DeployContract(t, ctrB, nil)
+
+	ctrInvoker := e.NewInvoker(ctrB.Hash, e.Committee)
+	h := ctrInvoker.Invoke(t, stackitem.Null{}, "callAInTryCatch")
+	aer := e.GetTxExecResult(t, h)
+
+	require.Equal(t, 1, len(aer.Stack))
+}
+
+// This test is created to check https://github.com/neo-project/neo/pull/2755#discussion_r880087983.
+func TestCALLL_from_VoidContext(t *testing.T) {
+	bc, acc := chain.NewSingle(t)
+	e := neotest.NewExecutor(t, bc, acc, acc)
+
+	// Contract A has void method `CallHasRet` which calls non-void method `HasRet`.
+	srcA := `package contractA
+		func CallHasRet() { // Creates a context with non-nil onUnload.
+			HasRet()
+		}
+		func HasRet() int { // CALL_L clones parent context, check that onUnload is not cloned.
+			return 5
+		}`
+	ctrA := neotest.CompileSource(t, acc.ScriptHash(), strings.NewReader(srcA), &compiler.Options{
+		NoEventsCheck:      true,
+		NoPermissionsCheck: true,
+		Name:               "contractA",
+	})
+	e.DeployContract(t, ctrA, nil)
+
+	ctrInvoker := e.NewInvoker(ctrA.Hash, e.Committee)
+	ctrInvoker.Invoke(t, stackitem.Null{}, "callHasRet")
+}

pkg/vm/context.go

@@ -63,8 +63,14 @@ type Context struct {
 	// isWrapped tells whether the context's DAO was wrapped into another layer of
 	// MemCachedStore on creation and whether it should be unwrapped on context unloading.
 	isWrapped bool
+	// onUnload is a callback that should be called after current context unloading
+	// if no exception occurs.
+	onUnload ContextUnloadCallback
 }
 
+// ContextUnloadCallback is a callback method used on context unloading from istack.
+type ContextUnloadCallback func(parentEstack *Stack)
+
 var errNoInstParam = errors.New("failed to read instruction parameter")
 
 // NewContext returns a new Context object.

pkg/vm/vm.go

@@ -311,7 +311,7 @@ func (v *VM) LoadScript(b []byte) {
 
 // LoadScriptWithFlags loads script and sets call flag to f.
 func (v *VM) LoadScriptWithFlags(b []byte, f callflag.CallFlag) {
-	v.loadScriptWithCallingHash(b, nil, v.GetCurrentScriptHash(), util.Uint160{}, f, -1, 0)
+	v.loadScriptWithCallingHash(b, nil, v.GetCurrentScriptHash(), util.Uint160{}, f, -1, 0, nil)
 }
 
 // LoadScriptWithHash is similar to the LoadScriptWithFlags method, but it also loads
@@ -321,19 +321,19 @@ func (v *VM) LoadScriptWithFlags(b []byte, f callflag.CallFlag) {
 // accordingly). It's up to the user of this function to make sure the script and hash match
 // each other.
 func (v *VM) LoadScriptWithHash(b []byte, hash util.Uint160, f callflag.CallFlag) {
-	v.loadScriptWithCallingHash(b, nil, v.GetCurrentScriptHash(), hash, f, 1, 0)
+	v.loadScriptWithCallingHash(b, nil, v.GetCurrentScriptHash(), hash, f, 1, 0, nil)
 }
 
 // LoadNEFMethod allows to create a context to execute a method from the NEF
 // file with the specified caller and executing hash, call flags, return value,
 // method and _initialize offsets.
 func (v *VM) LoadNEFMethod(exe *nef.File, caller util.Uint160, hash util.Uint160, f callflag.CallFlag,
-	hasReturn bool, methodOff int, initOff int) {
+	hasReturn bool, methodOff int, initOff int, onContextUnload ContextUnloadCallback) {
 	var rvcount int
 	if hasReturn {
 		rvcount = 1
 	}
-	v.loadScriptWithCallingHash(exe.Script, exe, caller, hash, f, rvcount, methodOff)
+	v.loadScriptWithCallingHash(exe.Script, exe, caller, hash, f, rvcount, methodOff, onContextUnload)
 	if initOff >= 0 {
 		v.Call(initOff)
 	}
@@ -342,7 +342,7 @@ func (v *VM) LoadNEFMethod(exe *nef.File, caller util.Uint160, hash util.Uint160
 // loadScriptWithCallingHash is similar to LoadScriptWithHash but sets calling hash explicitly.
 // 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) {
+	hash util.Uint160, f callflag.CallFlag, rvcount int, offset int, onContextUnload ContextUnloadCallback) {
 	var sl slot
 
 	v.checkInvocationStackSize()
@@ -384,6 +384,7 @@ func (v *VM) loadScriptWithCallingHash(b []byte, exe *nef.File, caller util.Uint
 		}
 	}
 	ctx.persistNotificationsCountOnUnloading = true
+	ctx.onUnload = onContextUnload
 	v.istack.PushItem(ctx)
 }
 
@@ -1651,6 +1652,12 @@ func (v *VM) unloadContext(ctx *Context) {
 	if currCtx != nil && ctx.persistNotificationsCountOnUnloading && !(ctx.isWrapped && v.uncaughtException != nil) {
 		*currCtx.notificationsCount += *ctx.notificationsCount
 	}
+	if currCtx != nil && ctx.onUnload != nil {
+		if v.uncaughtException == nil {
+			ctx.onUnload(currCtx.Estack()) // Use the estack of current context.
+		}
+		ctx.onUnload = nil
+	}
 }
 
 // getTryParams splits TRY(L) instruction parameter into offsets for catch and finally blocks.
@@ -1713,6 +1720,7 @@ func (v *VM) call(ctx *Context, offset int) {
 	newCtx.notificationsCount = ctx.notificationsCount
 	newCtx.isWrapped = false
 	newCtx.persistNotificationsCountOnUnloading = false
+	newCtx.onUnload = nil
 	v.istack.PushItem(newCtx)
 	newCtx.Jump(offset)
 }