From 428e789ddc814696ed7e7b46750125be050d5ef8 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Sat, 31 Aug 2019 09:04:59 +0300
Subject: [PATCH 1/2] vm: produce better error for ROLL with wrong index

Current VM implementation doesn't return errors for many operations, so the
only way to handle it here is to check for NULL. Refs. #96.
---
 pkg/vm/vm.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 19914cce2..eff7dac51 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -342,7 +342,11 @@ func (v *VM) execute(ctx *Context, op Instruction) {
 			panic("negative stack item returned")
 		}
 		if n > 0 {
-			v.estack.Push(v.estack.RemoveAt(n))
+			e := v.estack.RemoveAt(n)
+			if e == nil {
+				panic("bad index")
+			}
+			v.estack.Push(e)
 		}
 
 	case DROP:

From 42dfca47cfb8c212e5f099f8c2aae076801e2d33 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Sat, 31 Aug 2019 09:06:56 +0300
Subject: [PATCH 2/2] vm: fix double VM run from CLI

Fixes one more instruction being ran when VM FAULTs:

NEO-GO-VM > run
NEO-GO-VM > error encountered at instruction 6 (ROLL)
NEO-GO-VM > runtime error: invalid memory address or nil pointer dereference
FAULT
NEO-GO-VM > error encountered at instruction 7 (SETITEM)
NEO-GO-VM > interface conversion: interface {} is []vm.StackItem, not []uint8

Refs. #96.
---
 pkg/vm/cli/cli.go | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/pkg/vm/cli/cli.go b/pkg/vm/cli/cli.go
index b3d4efb36..84bc8ebcd 100644
--- a/pkg/vm/cli/cli.go
+++ b/pkg/vm/cli/cli.go
@@ -127,16 +127,13 @@ func (c *VMCLI) handleCommand(cmd string, args ...string) {
 		fmt.Printf("READY: loaded %d instructions\n", c.vm.Context().LenInstr())
 
 	case "run":
-		var (
-			method []byte
-			params []vm.StackItem
-			err    error
-			start  int
-		)
-
-		if len(args) == 0 {
-			c.vm.Run()
-		} else {
+		if len(args) != 0 {
+			var (
+				method []byte
+				params []vm.StackItem
+				err    error
+				start  int
+			)
 			if isMethodArg(args[0]) {
 				method = []byte(args[0])
 				start = 1
@@ -146,8 +143,8 @@ func (c *VMCLI) handleCommand(cmd string, args ...string) {
 				fmt.Println(err)
 				return
 			}
+			c.vm.LoadArgs(method, params)
 		}
-		c.vm.LoadArgs(method, params)
 		c.vm.Run()
 
 	case "cont":