[syslinux:master] mbr: Make sure the MBR code starts with the byte 0x33

[syslinux-bot for H. Peter Anvin]

Commit-ID:  d0f275981c9289dc4b8df64e72cd9902bf85aebe
Gitweb:     http://syslinux.zytor.com/commit/d0f275981c9289dc4b8df64e72cd9902bf85aebe
Author:     H. Peter Anvin <hpa at zytor.com>
AuthorDate: Thu, 23 Dec 2010 12:02:52 -0800
Committer:  H. Peter Anvin <hpa at zytor.com>
CommitDate: Thu, 23 Dec 2010 12:02:52 -0800

mbr: Make sure the MBR code starts with the byte 0x33

Apparently some BIOSes (including some Acer Travelmate machines)
require an MBR to start with 0x33; apparently Micro$oft MBRs start
with 33 C0, an alternate coding of the "xorw %ax,%ax" instruction.  As
such, follow suit to work on these braindead BIOSes.

Signed-off-by: H. Peter Anvin <hpa at zytor.com>


---
 mbr/altmbr.S   |    2 +-
 mbr/gptmbr.S   |    2 +-
 mbr/isohdpfx.S |    3 +--
 mbr/mbr.S      |    2 +-
 4 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/mbr/altmbr.S b/mbr/altmbr.S
index 794ab62..1b60905 100644
--- a/mbr/altmbr.S
+++ b/mbr/altmbr.S
@@ -49,8 +49,8 @@ bootsec:
 	.text
 	.globl	_start
 _start:
+	.byte	0x33, 0xc0	/* xorw	%ax, %ax */
 	cli
-	xorw	%ax, %ax
 	movw	%ax, %ds
 	movw	%ax, %ss
 	movw	$stack, %sp
diff --git a/mbr/gptmbr.S b/mbr/gptmbr.S
index 8ed4cf4..ae0549f 100644
--- a/mbr/gptmbr.S
+++ b/mbr/gptmbr.S
@@ -55,8 +55,8 @@ bootsec:
 	.text
 	.globl	_start
 _start:
+	.byte	0x33, 0xc0	/* xorw	%ax, %ax */
 	cli
-	xorw	%ax, %ax
 	movw	%ax, %ds
 	movw	%ax, %ss
 	movw	$stack, %sp
diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S
index 0bf807e..2784fb8 100644
--- a/mbr/isohdpfx.S
+++ b/mbr/isohdpfx.S
@@ -65,9 +65,8 @@ bootsec:
 	.text
 	.globl	_start
 _start:
-
+	.byte	0x33, 0xed	/* xorw	%bp, %bp */
 	cli
-	xorw	%bp, %bp
 	movw	%bp, %ss
 	movw	$stack, %sp
 	sti
diff --git a/mbr/mbr.S b/mbr/mbr.S
index 7caf4fc..b71cfb7 100644
--- a/mbr/mbr.S
+++ b/mbr/mbr.S
@@ -49,8 +49,8 @@ bootsec:
 	.text
 	.globl	_start
 _start:
+	.byte	0x33, 0xc0	/* xorw	%ax, %ax */
 	cli
-	xorw	%ax, %ax
 	movw	%ax, %ds
 	movw	%ax, %ss
 	movw	$stack, %sp