From 241be5df8baa2089a635a2a373e5a219d184015d Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Mon, 25 Feb 2008 15:11:28 -0800
Subject: [PATCH] gptmbr: since %bx is advanced, we can test -2(%bx) ==
 (bootsec+510)

With %bx advanced to the end of the boot sector, we can use -2(%bx)
instead of (bootsec+510), thus saving one byte.
---
 mbr/gptmbr.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mbr/gptmbr.S b/mbr/gptmbr.S
index 49414e4..cca7b47 100644
--- a/mbr/gptmbr.S
+++ b/mbr/gptmbr.S
@@ -195,7 +195,7 @@ boot:
 	movl	(48+16)(%si),%edx
 	movw	$bootsec,%bx
 	call	read_sector
-	cmpw	$0xaa55, (bootsec+510)
+	cmpw	$0xaa55, -2(%bx)
 	jne	missing_os	/* Not a valid boot sector */
 	movw	$driveno, %sp	/* driveno == bootsec-6 */
 	popw	%dx		/* dl -> drive number */
-- 
2.7.4