From: Matthew Dempsky <mdempsky@google.com>
Date: Mon, 11 Aug 2014 17:53:38 +0000 (-0400)
Subject: cmd/link: fix zig-zag decoding
X-Git-Tag: go1.4beta1~861
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=eae9fee3bf8c58c7403bcd103050ef2196fdfed1;p=gostls13.git

cmd/link: fix zig-zag decoding

The >>1 shift needs to happen before converting to int32, otherwise
large values will decode with an incorrect sign bit.

The <<31 shift can happen before or after, but before is consistent
with liblink and the go12symtab doc.

Bug demo at http://play.golang.org/p/jLrhPUakIu

LGTM=rsc
R=golang-codereviews, minux, rsc
CC=golang-codereviews
https://golang.org/cl/119630043
---

diff --git a/src/cmd/link/pclntab.go b/src/cmd/link/pclntab.go
index b0b19ad53c..a950895aa5 100644
--- a/src/cmd/link/pclntab.go
+++ b/src/cmd/link/pclntab.go
@@ -437,7 +437,7 @@ func (it *PCIter) Next() {
 		return
 	}
 	it.start = false
-	sv := int32(uv)>>1 ^ int32(uv)<<31>>31
+	sv := int32(uv>>1) ^ int32(uv<<31)>>31
 	it.Value += sv
 
 	// pc delta