contrib/mntnbi/mntnbi.pl

   1 #!/usr/bin/perl -w
   2 #
   3 # Quick Perl program to decode and display details about
   4 # tagged images created by mknbi, and then mount the contained
   5 # DOS filesystem using a loop-back mount
   6 #
   7 # Martin Atkins, November 1998
   8 # by hacking disnbi by
   9 # Ken Yap, September 1998
  10 #
  11 #
  12
  13 sub getvendordata {
  14         my ($flags) = @_;
  15
  16         my $vendordata = '';
  17         my $vendorlen = ($flags & 0xff) >> 4;
  18         if ($vendorlen > 0) {
  19                 $vendorlen *= 4;
  20                 $vendordata = unpack("A$vendorlen", substr($imageheader, $curoffset));
  21                 $curoffset += $vendorlen;
  22         }
  23         return ($vendordata);
  24 }
  25
  26 sub decodesegmentflags {
  27         my ($flags) = @_;
  28
  29         $flags >>= 24;
  30         $flags &= 0x3;
  31         ($flags == 0) and $type = "Absolute";
  32         ($flags == 1) and $type = "Follows last segment";
  33         ($flags == 2) and $type = "Below end of memory";
  34         ($flags == 3) and $type = "Below last segment loaded";
  35         return ($type);
  36 }
  37
  38 sub onesegment
  39 {
  40         my ($segnum) = @_;
  41         my ($type, $vendordata);
  42
  43         my ($flags, $loadaddr, $imagelen, $memlength) = unpack("V4", substr($imageheader, $curoffset));
  44         $curoffset += 16;
  45         print "Segment number $segnum\n";
  46         printf "Load address:\t\t%08x\n", $loadaddr;
  47         printf "Image length:\t\t%d\n", $imagelen;
  48         printf "Memory length:\t\t%d\n", $memlength;
  49         $type = &decodesegmentflags($flags);
  50         printf "Position:\t\t$type\n";
  51         printf "Vendor tag:\t\t%d\n", ($flags >> 8) & 0xff;
  52         if (($vendordata = &getvendordata($flags)) ne '') {
  53                 print "Vendor data:\t\t", $vendordata, "\n";
  54         }
  55         print "\n";
  56         push (@seglengths, $imagelen);
  57         return (($flags >> 26) & 1);
  58 }
  59
  60 @seglengths = ();
  61 $#ARGV == 1 or die "Usage: mntnbi tagged-image-file dir\n";
  62 $imagefile= $ARGV[0];
  63 open(I, $ARGV[0]) or die "$imagefile: $!\n";
  64 (defined($status = sysread(I, $imageheader, 512)) and $status == 512)
  65         or die "$imagefile: Cannot read header\n";
  66 $headerrecord = substr($imageheader, 0, 16);
  67 ($magic, $flags, $bx, $ds, $ip, $cs) = unpack("a4Vv4", $headerrecord);
  68 $magic eq "\x36\x13\x03\x1B" or die "$imagefile: Not a tagged image file\n";
  69 $curoffset = 16;
  70
  71 # Now decode the header
  72
  73 printf "Header location:\t%04x:%04x\n", $ds, $bx;
  74 printf "Start address:\t\t%04x:%04x\n", $cs, $ip;
  75 printf "Flags:\n";
  76         print "Return to loader after execution (extension)\n" if (($flags >> 8) &  1);
  77 if (($vendordata = &getvendordata($flags)) ne '') {
  78         print "Vendor data:\t\t", $vendordata, "\n";
  79 }
  80 print "\n";
  81
  82 # Now decode each segment record
  83
  84 $segnum = 1;
  85 do {
  86         $lastrecord = &onesegment($segnum);
  87         ++$segnum;
  88 } while (!$lastrecord);
  89
  90 if ($#seglengths != 1) {
  91         die "This is not a DOS image $#seglengths\n";
  92 }
  93 $offset = 512 + $seglengths[0];
  94 print "mounting filesystem at offset $offset in $ARGV[0] on $ARGV[1]\n";
  95 $rc = system "mount $ARGV[0] $ARGV[1] -t msdos -o loop,offset=$offset";
  96 print "Done\n" if ($rc == 0);
  97 exit(0);