From 3d62db4f34a5c5e84b4d373f49df3a566b316aec Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Thu, 16 Jul 2020 11:47:42 +0300
Subject: [PATCH] vm: clear altstack on CALL, fix #1158

neo-vm doesn't copy altstack on CALL, so it effectively is cleared. But we
need to copy things back on return if there are any.
---
 pkg/vm/vm.go | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 0312f01a6..3276ae567 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -258,8 +258,9 @@ func (v *VM) Load(prog []byte) {
 func (v *VM) LoadScript(b []byte) {
 	ctx := NewContext(b)
 	ctx.estack = v.estack
-	ctx.astack = v.astack
+	ctx.astack = v.newItemStack("alt")
 	v.istack.PushVal(ctx)
+	v.astack = ctx.astack
 }
 
 // loadScriptWithHash if similar to the LoadScript method, but it also loads
@@ -1138,6 +1139,8 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 		newCtx := ctx.Copy()
 		newCtx.rvcount = -1
+		newCtx.astack = v.newItemStack("alt")
+		v.astack = newCtx.astack
 		v.istack.PushVal(newCtx)
 
 		offset := v.getJumpOffset(newCtx, parameter, 0)
@@ -1202,8 +1205,15 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 				newEstack.Push(elem)
 			}
 			v.estack = newEstack
-			v.astack = v.Context().astack
 		}
+		newAstack := v.Context().astack
+		if rvcount == -1 && newAstack != oldCtx.astack {
+			for i := oldCtx.astack.Len(); i > 0; i-- {
+				elem := oldCtx.astack.RemoveAt(i - 1)
+				newAstack.Push(elem)
+			}
+		}
+		v.astack = newAstack
 
 	case opcode.CHECKSIG, opcode.VERIFY:
 		var hashToCheck []byte