From: H. Peter Anvin <hpa@zytor.com>
Date: Tue, 26 Nov 2013 17:58:17 +0000 (-0800)
Subject: isolinux: Clear upper half of EDX before using
X-Git-Tag: syslinux-6.03~86^2~2^2~7
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=88d17d136c21b8afb7d27e091cbb1f757ded80df;p=platform%2Fupstream%2Fsyslinux.git

isolinux: Clear upper half of EDX before using

In checkin:

    cb015497a4e4 isolinux: Update LBA in getlinsec loop

... we use EDX as a sector count, but the sector count is actually in
DX, and the upper half of EDX is uninitialized.  If the BIOS enters
with a nonzero value in the upper half of EDX, this breaks horribly.

At least one set of BIOSes has been identified where if the LBA > 64K
then the upper half of EDX will be nonzero.

Reported-by: Carl Duff <cdrw2400@gmail.com>
Reported-by: Philip Müller <philm@manjaro.org>
Tested-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---

diff --git a/core/isolinux.asm b/core/isolinux.asm
index db6d2d4..dd0fa89 100644
--- a/core/isolinux.asm
+++ b/core/isolinux.asm
@@ -430,7 +430,7 @@ MaxLMA		equ 384*1024		; Reasonable limit (384K)
 		call getlinsec
 		pop eax
 		pop cx
-		mov dx,cx
+		movzx edx,cx
 		pop bp
 		pop bx