[Qemu-devel] [PATCH] optionrom: fix bugs in signrom.sh

[Qemu-devel] [PATCH] optionrom: fix bugs in signrom.sh

[Avi Kivity]

signrom.sh has multiple bugs:

- the last byte is considered when calculating the existing checksum, but not
  when computing the correction
- apprently the 'expr' expression overflows and produces incorrect results with
  larger roms
- if the checksum happened to be zero, we calculated the correction byte to be
  256

Instead of rewriting this in half a line of python, this patch fixes the bugs.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 pc-bios/optionrom/signrom.sh |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/pc-bios/optionrom/signrom.sh b/pc-bios/optionrom/signrom.sh
index 975b27d..9dc5c63 100755
--- a/pc-bios/optionrom/signrom.sh
+++ b/pc-bios/optionrom/signrom.sh
@@ -31,14 +31,13 @@ x=`dd if="$1" bs=1 count=1 skip=2 2>/dev/null | od -t u1 -A n`
 size=$(( $x * 512 - 1 ))
 
 # now get the checksum
-nums=`od -A n -t u1 -v "$1"`
+nums=`od -A n -t u1 -v -N $size "$1"`
 for i in ${nums}; do
     # add each byte's value to sum
-    sum=`expr $sum + $i`
+    sum=`expr \( $sum + $i \) % 256`
 done
 
-sum=$(( $sum % 256 ))
-sum=$(( 256 - $sum ))
+sum=$(( (256 - $sum) % 256 ))
 sum_octal=$( printf "%o" $sum )
 
 # and write the output file
-- 
1.7.3.1

Re: [Qemu-devel] [PATCH] optionrom: fix bugs in signrom.sh

[Anthony Liguori]

On 11/16/2010 08:33 AM, Avi Kivity wrote:
> signrom.sh has multiple bugs:
>
> - the last byte is considered when calculating the existing checksum, but not
>    when computing the correction
> - apprently the 'expr' expression overflows and produces incorrect results with
>    larger roms
> - if the checksum happened to be zero, we calculated the correction byte to be
>    256
>
> Instead of rewriting this in half a line of python, this patch fixes the bugs.
>
> Signed-off-by: Avi Kivity<avi@redhat.com>
>    

Applied.   Thanks.

Regards,

Anthony Liguori

> ---
>   pc-bios/optionrom/signrom.sh |    7 +++----
>   1 files changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/pc-bios/optionrom/signrom.sh b/pc-bios/optionrom/signrom.sh
> index 975b27d..9dc5c63 100755
> --- a/pc-bios/optionrom/signrom.sh
> +++ b/pc-bios/optionrom/signrom.sh
> @@ -31,14 +31,13 @@ x=`dd if="$1" bs=1 count=1 skip=2 2>/dev/null | od -t u1 -A n`
>   size=$(( $x * 512 - 1 ))
>
>   # now get the checksum
> -nums=`od -A n -t u1 -v "$1"`
> +nums=`od -A n -t u1 -v -N $size "$1"`
>   for i in ${nums}; do
>       # add each byte's value to sum
> -    sum=`expr $sum + $i`
> +    sum=`expr \( $sum + $i \) % 256`
>   done
>
> -sum=$(( $sum % 256 ))
> -sum=$(( 256 - $sum ))
> +sum=$(( (256 - $sum) % 256 ))
>   sum_octal=$( printf "%o" $sum )
>
>   # and write the output file
>