[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH] compute checksum for roms bigger than a segment
From: |
Glauber Costa |
Subject: |
[Qemu-devel] [PATCH] compute checksum for roms bigger than a segment |
Date: |
Wed, 25 Mar 2009 12:06:46 -0300 |
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 <address@hidden>
---
bios/rombios.c | 33 +++++++++++++++++++++++++++------
1 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/bios/rombios.c b/bios/rombios.c
index bc43251..5e7ad24 100644
--- a/bios/rombios.c
+++ b/bios/rombios.c
@@ -10162,22 +10162,43 @@ 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
[Qemu-devel] [PATCH] compute checksum for roms bigger than a segment,
Glauber Costa <=