From 182619548e9c215f61083e3c4932d8aff6901cac Mon Sep 17 00:00:00 2001
From: David Major <dmajor@mozilla.com>
Date: Tue, 3 Jun 2014 16:47:43 +1200
Subject: [PATCH] Bug 1018477: Fix R/M check in x86 detour code. r=m_kato

---
 xpcom/build/nsWindowsDllInterceptor.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/xpcom/build/nsWindowsDllInterceptor.h b/xpcom/build/nsWindowsDllInterceptor.h
index 9c6e3300dd2..afedc2aeda7 100644
--- a/xpcom/build/nsWindowsDllInterceptor.h
+++ b/xpcom/build/nsWindowsDllInterceptor.h
@@ -355,9 +355,14 @@ protected:
         {
           // REG=r, R/M=r or REG=r, R/M=[r]
           nBytes += 2;
-        } else if (((b & 0xc0) == 0x40) && ((b & 0x38) != 0x20)) {
-          // REG=r, R/M=[r + disp8]
-          nBytes += 3;
+        } else if ((b & 0xc0) == 0x40) {
+          if ((b & 0x07) == 0x04) {
+            // REG=r, R/M=[SIB + disp8]
+            nBytes += 4;
+          } else {
+            // REG=r, R/M=[r + disp8]
+            nBytes += 3;
+          }
         } else {
           // complex MOV, bail
           return;