vmcli: set breakpoint before the instruction

Breakpoint should occur before actual instruction execution.

pkg/vm/cli/cli.go

@@ -226,8 +226,13 @@ func handleIP(c *ishell.Context) {
 		return
 	}
 	v := getVMFromContext(c)
-	ip, opcode := v.Context().CurrInstr()
-	c.Printf("instruction pointer at %d (%s)\n", ip, opcode)
+	ctx := v.Context()
+	if ctx.NextIP() < ctx.LenInstr() {
+		ip, opcode := v.Context().NextInstr()
+		c.Printf("instruction pointer at %d (%s)\n", ip, opcode)
+	} else {
+		c.Println("execution has finished")
+	}
 }
 
 func handleBreak(c *ishell.Context) {
@@ -341,22 +346,25 @@ func runVMWithHandling(c *ishell.Context, v *vm.VM) {
 	err := v.Run()
 	if err != nil {
 		c.Err(err)
-		return
 	}
 
 	var message string
 	switch {
 	case v.HasFailed():
-		message = "FAILED"
+		message = "" // the error will be printed on return
 	case v.HasHalted():
 		message = v.Stack("estack")
 	case v.AtBreakpoint():
 		ctx := v.Context()
-		i, op := ctx.CurrInstr()
-		message = fmt.Sprintf("at breakpoint %d (%s)\n", i, op.String())
+		if ctx.NextIP() < ctx.LenInstr() {
+			i, op := ctx.NextInstr()
+			message = fmt.Sprintf("at breakpoint %d (%s)", i, op)
+		} else {
+			message = "execution has finished"
+		}
 	}
 	if message != "" {
-		c.Printf(message)
+		c.Println(message)
 	}
 }
 
@@ -419,8 +427,9 @@ func handleStepType(c *ishell.Context, stepType string) {
 	}
 	if err != nil {
 		c.Err(err)
+	} else {
+		handleIP(c)
 	}
-	handleIP(c)
 	changePrompt(c, v)
 }
 
@@ -435,8 +444,8 @@ func handleOps(c *ishell.Context) {
 }
 
 func changePrompt(c ishell.Actions, v *vm.VM) {
-	if v.Ready() && v.Context().IP() >= 0 {
-		c.SetPrompt(fmt.Sprintf("NEO-GO-VM %d > ", v.Context().IP()))
+	if v.Ready() && v.Context().NextIP() >= 0 && v.Context().NextIP() < v.Context().LenInstr() {
+		c.SetPrompt(fmt.Sprintf("NEO-GO-VM %d > ", v.Context().NextIP()))
 	} else {
 		c.SetPrompt("NEO-GO-VM > ")
 	}

pkg/vm/context.go

@@ -185,6 +185,15 @@ func (c *Context) CurrInstr() (int, opcode.Opcode) {
 	return c.ip, opcode.Opcode(c.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) {
+		op = opcode.Opcode(c.prog[c.nextip])
+	}
+	return c.nextip, op
+}
+
 // Copy returns an new exact copy of c.
 func (c *Context) Copy() *Context {
 	ctx := new(Context)

pkg/vm/vm.go

@@ -241,7 +241,7 @@ func (v *VM) AddBreakPoint(n int) {
 // instruction pointer.
 func (v *VM) AddBreakPointRel(n int) {
 	ctx := v.Context()
-	v.AddBreakPoint(ctx.ip + n)
+	v.AddBreakPoint(ctx.nextip + n)
 }
 
 // LoadFile loads a program in NEF format from the given path, ready to execute it.