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optionrom: fix bugs in signrom.sh

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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>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Avi Kivity 2010-11-16 16:33:17 +02:00 committed by Anthony Liguori
parent e71e00ed25
commit 33bbd1de5e
1 changed files with 3 additions and 4 deletions
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7
pc-bios/optionrom/signrom.sh
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@ -31,14 +31,13 @@ x=`dd if="$1" bs=1 count=1 skip=2 2>/dev/null | od -t u1 -A n`
size=$(( $x * 512 - 1 )) size=$(( $x * 512 - 1 ))
# now get the checksum # 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 for i in ${nums}; do
# add each byte's value to sum # add each byte's value to sum
sum=`expr $sum + $i` sum=`expr \( $sum + $i \) % 256`
done done
sum=$(( $sum % 256 )) sum=$(( (256 - $sum) % 256 ))
sum=$(( 256 - $sum ))
sum_octal=$( printf "%o" $sum ) sum_octal=$( printf "%o" $sum )
# and write the output file # and write the output file