From 3a9288fab031a820afa7be96e355c28ded1546bf Mon Sep 17 00:00:00 2001 From: Glauber Costa Date: Wed, 24 Jun 2009 14:31:41 +0100 Subject: [PATCH 2/7] compute checksum for roms bigger than a segment Some option roms (e1000 provided by gpxe project as an example) are bigger than a segment. The current algorithm to compute the checksum fails in such case. To proper compute the checksum, this patch deals with the possibility of the rom's size crossing a segment border. We don't need to worry about it crossing more than one segment border, since the option roms format only save one byte to store the image size (thus, maximum size = 0xff = 128k = 2 segments) [ including improvements suggested by malc ] Signed-off-by: Glauber Costa Signed-off-by: Mark McLoughlin --- kvm/bios/rombios.c | 33 +++++++++++++++++++++++++++------ 1 files changed, 27 insertions(+), 6 deletions(-) diff --git a/kvm/bios/rombios.c b/kvm/bios/rombios.c index 6186199..fc289c0 100644 --- a/kvm/bios/rombios.c +++ b/kvm/bios/rombios.c @@ -10170,22 +10170,43 @@ no_serial: ret rom_checksum: - push ax - push bx - push cx + pusha + push ds + xor ax, ax xor bx, bx xor cx, cx + xor dx, dx + mov ch, [2] shl cx, #1 + + jnc checksum_loop + xchg dx, cx + dec cx + checksum_loop: add al, [bx] inc bx loop checksum_loop + + test dx, dx + je checksum_out + + add al, [bx] + mov cx, dx + mov dx, ds + add dh, #0x10 + mov ds, dx + xor dx, dx + xor bx, bx + + jmp checksum_loop + +checksum_out: and al, #0xff - pop cx - pop bx - pop ax + pop ds + popa ret -- 1.6.2.2