From bbf71d454c24adceb0a9f94d78b8d83e7c36439f Mon Sep 17 00:00:00 2001
From: Benjamen Keroack <benjamen.keroack@dollarshaveclub.com>
Date: Wed, 3 Jan 2018 09:36:39 -0800
Subject: [PATCH] disasm: fix incorrect stack depth for end/discard

End/Discard ops were being misencoded with incorrect stack depths which caused stack underflows that manifested as slice index out of bounds runtime panics.
---
 disasm/disasm.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/disasm/disasm.go b/disasm/disasm.go
index 66cda640..d2b9488b 100644
--- a/disasm/disasm.go
+++ b/disasm/disasm.go
@@ -184,7 +184,7 @@ func Disassemble(fn wasm.Function, module *wasm.Module) (*Disassembly, error) {
 			// Same with ops.Br/BrIf, we subtract 2 instead of 1
 			// to get the depth of the *parent* block of the branch
 			// we want to take.
-			prevDepthIndex := stackDepths.Len() - 2
+			prevDepthIndex := stackDepths.Len() - 1
 			prevDepth := stackDepths.Get(prevDepthIndex)
 
 			if op != ops.Else && blockSig != wasm.BlockTypeEmpty && !instr.Unreachable {