ACC SHELL

#! /usr/bin/perl

#
# Install MBR on Thinkpads.
#
# TPs have a special boot loader to manage the rescue stuff. It keeps the
# orignal MBR stored somewhere and uses it to boot the normal OSes.
#
# MBR[6]: 1 byte CRC over original MBR
# MBR[7]: sector number of original MBR
#

sub crc;

# mbr from master-boot-code package
$new_mbr =
  "\x31\xc0\x8e\xd0\x66\xbc\x00\x7c\x00\x00\x8e\xc0\x8e\xd8\x89\xe6" .
  "\x66\xbf\x00\x06\x00\x00\x66\xb9\x00\x01\x00\x00\xf3\xa5\xea\x23" .
  "\x06\x00\x00\x80\xfa\x80\x7c\x05\x80\xfa\x87\x7e\x02\xb2\x80\x88" .
  "\x16\x49\x07\x66\xbf\xbe\x07\x00\x00\x31\xf6\x66\xb9\x04\x00\x00" .
  "\x00\x67\x80\x3f\x80\x75\x07\x85\xf6\x75\x0c\x66\x89\xfe\x83\xc7" .
  "\x10\xe2\xee\x85\xf6\x75\x0b\x66\xbe\x4a\x07\x00\x00\xe9\x8d\x00" .
  "\x00\x00\x8a\x16\x49\x07\x66\x31\xc9\x66\x31\xc0\xb4\x08\xcd\x13" .
  "\xc1\xea\x08\x42\x89\xc8\x83\xe0\x3f\x89\xcb\xc1\xe9\x08\x81\xe3" .
  "\xc0\x00\x00\x00\xc1\xe3\x02\x09\xd9\x41\xf7\xe2\x66\xf7\xe1\x8a" .
  "\x16\x49\x07\x66\x67\x8b\x5e\x08\x66\x39\xc3\x66\x7c\x63\x66\x56" .
  "\x52\x66\xbb\xaa\x55\x00\x00\xb4\x41\xcd\x13\x5a\x66\x5e\x72\x51" .
  "\x66\xb8\x55\xaa\x00\x00\x39\xc3\x75\x47\xf6\xc1\x01\x74\x42\x67" .
  "\x66\xc7\x06\x10\x00\x01\x00\x67\x66\xc7\x46\x04\x00\x7c\x00\x00" .
  "\x67\x66\xc7\x46\x0c\x00\x00\x00\x00\xb6\x05\x56\x52\xb4\x42\xcd" .
  "\x13\x5a\x5e\x73\x45\xfe\xce\x75\xf2\x66\xbe\x76\x07\x00\x00\xac" .
  "\x84\xc0\x74\x0a\xb4\x0e\xb3\x07\x56\xcd\x10\x5e\xeb\xf1\xfb\xeb" .
  "\xfd\x67\x8a\x76\x01\x67\x8b\x4e\x02\x66\xbf\x05\x00\x00\x00\x66" .
  "\xbb\x00\x7c\x00\x00\x66\xb8\x01\x02\x00\x00\x57\x52\x51\xcd\x13" .
  "\x59\x5a\x5f\x73\x05\x4f\x75\xe7\xeb\xbf\x66\xbe\x62\x07\x00\x00" .
  "\x67\xa1\xfe\x7d\x00\x00\x66\xbb\x55\xaa\x00\x00\x39\xc3\x75\xaf" .
  "\x8a\x16\x49\x07\xea\x00\x7c\x00\x00\x80\x49\x6e\x76\x61\x6c\x69" .
  "\x64\x20\x70\x61\x72\x74\x69\x74\x69\x6f\x6e\x20\x74\x61\x62\x6c" .
  "\x65\x00\x4e\x6f\x20\x6f\x70\x65\x72\x61\x74\x69\x6e\x67\x20\x73" .
  "\x79\x73\x74\x65\x6d\x00\x45\x72\x72\x6f\x72\x20\x6c\x6f\x61\x64" .
  "\x69\x6e\x67\x20\x6f\x70\x65\x72\x61\x74\x69\x6e\x67\x20\x73\x79" .
  "\x73\x74\x65\x6d\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00" .
  "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00" .
  "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00";


$disk = shift;

die "usage: tp_mbr device\n" unless $disk && (-f($disk) || -b($disk));

open F, $disk;
sysread F, $mbr, 0x200;

@mbr = unpack "C512", $mbr;

die "$disk: no mbr\n" unless @mbr == 0x200 && $mbr[0x1fe] == 0x55 && $mbr[0x1ff] == 0xaa;

$old_mbr_sec = $mbr[7];

=cut
# just a quick check
die "$disk: np tp mbr\n" unless
  $mbr[0x17b] == 0x50 &&
  $mbr[0x17c] == 0xe4 &&
  $mbr[0x17d] == 0x61 &&
  $mbr[0x17e] == 0x24 &&
  $old_mbr_sec > 1;
=cut

# read original mbr

seek F, ($old_mbr_sec - 1) << 9, 0 or die "$disk: $!\n";
print "number $old_mbr_sec : seek ".(($old_mbr_sec-1)<<9);

sysread F, $old_mbr, 0x200;

@old_mbr = unpack "C512", $old_mbr;

die "$disk: no orig mbr\n" unless @old_mbr == 0x200 && $old_mbr[0x1fe] == 0x55 && $mbr[0x1ff] == 0xaa;

close F;

# verify crc

if($mbr[6] == 0) {
  print STDERR "$disk: orig mbr crc not checked\n" if $mbr[6] == 0;
}
else {
  die "$disk: orig mbr crc failure\n" unless crc(\@old_mbr) == $mbr[6];
}

# store new mbr & update crc

substr($old_mbr, 0, length $new_mbr) = $new_mbr;

@old_mbr = unpack "C512", $old_mbr;

$mbr[6] = crc \@old_mbr;

$mbr = pack "C512", @mbr;


# write it

open F, "+<$disk";
syswrite F, $mbr, 0x200;
seek F, ($old_mbr_sec - 1) << 9, 0;
syswrite F, $old_mbr;
close F;


# crc function
sub crc
{
  my $c = 0;
  local $_;

  $c ^= $_ for @{$_[0]};

  return $c;
}