From 3bc37d6e2a7b7eb0f6e31dfa333d244f52e8c4bc Mon Sep 17 00:00:00 2001
From: Joel Dice <joel.dice@gmail.com>
Date: Tue, 2 Feb 2010 11:37:08 -0700
Subject: [PATCH] fix encoding of single byte register-to-memory moves on
 x86_64

We need to prefix instructions of the form "mov R,M" with a REX byte
when R is %spl, %bpl, %sil, or %dil.  Such moves are unencodable on
32-bit x86, and, because of the order in which we pick registers,
pretty rare on 64-bit systems, which is why this took so long to
notice.
---
 src/x86.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/x86.cpp b/src/x86.cpp
index 4021c86e6d..2d4d3e55f7 100644
--- a/src/x86.cpp
+++ b/src/x86.cpp
@@ -518,7 +518,7 @@ void
 maybeRex(Context* c, unsigned size, Assembler::Register* a,
          Assembler::Memory* b)
 {
-  maybeRex(c, size, a->low, b->index, b->base, false);
+  maybeRex(c, size, a->low, b->index, b->base, size == 1 and (a->low & 4));
 }
 
 void