#!/usr/bin/env perl
#This is a utility to scrape out the EFI boot image from an el torito enabled disk
use strict;
use Fcntl qw/SEEK_SET/;
my $iso;
my $outfile;
GetOptions("out=s" => \$outfile,
    "iso=s" => \$iso);
my $emul;
my $blksize = 2048;
my $istream;
use Getopt::Long;

sub grabimage {
    my $bootcat = shift;
    my $image;
    my @recdata = unpack("C2vC2vV", $bootcat);
    unless ($recdata[0] == 0x88) { printf "Error: EFI torito record not bootable\n"; exit; }
    $emul = $recdata[1];

    #for now, ignore load segment, system type
    seek($istream, $recdata[6] * $blksize, SEEK_SET);
    my $size = $recdata[5];
    if ($size == 0) { $size = 1; }    #if 0/1, it's auto-detect time
    my $readbytes = read($istream, $image, $size * 512);
    if ($size == 1) {  #we have to interpret the FAT header to get the real size
        seek($istream, $recdata[6] * $blksize, SEEK_SET); # go back to beginning
        my @fatheader = unpack("C11vCvC3vC11V", $image);
        my $secsize = $fatheader[11];
        if ($fatheader[17]) {
            $size = $secsize * ($fatheader[17]);
        } else {
            die "Unsupported FAT header, requires test of commented code segment";
        }

        #		} elsif ($fatheader[-1]) {
        #			$size=$secsize*$fatheader[-1];
        #		}
        $readbytes = read($istream, $image, $size);
    }
    my $outh;
    open($outh, ">", $outfile);
    print $outh $image;
    close($outh);
}
if (!-r $iso) {
    printf "Error, $iso does not seem to exist or is not readable";
    exit 1;
}
open($istream, "<", $iso) || die "Error opening $iso";
my $bootsect;
seek($istream, 17 * $blksize, SEEK_SET);
my $readbytes = read($istream, $bootsect, 0x4b);
unless ($readbytes == 0x4b) {
    printf "Error reading boot record volume from $iso\n";
    exit 1;
}
my @recdata;
@recdata = unpack("CA5CA32C32V", $bootsect); #it would have been nice if the el torito actually said little endian on it..
unless ($recdata[0] == 0 and $recdata[1] eq 'CD001'
    and $recdata[2] == 1 and $recdata[3] eq "EL TORITO SPECIFICATION") {
    printf "Error: Boot record volume format invalid\n";
    exit 1;
}
my $bootcatidx = $recdata[-1];
my $bootcat;
seek($istream, $bootcatidx * $blksize, SEEK_SET);
$readbytes = read($istream, $bootcat, 0x20);
unless ($readbytes == 0x20) { printf "Error reading boot catalog at $bootcatidx\n"; exit 1; }
@recdata = unpack("C*", $bootcat);
unless ($recdata[0] == 1 and $recdata[0x1e] == 0x55 and $recdata[0x1f] == 0xaa) {
    printf "Boot catalog has invalid header\n"; exit 1;
}
$readbytes = read($istream, $bootcat, 0x20);
my $image;
unless ($readbytes == 0x20) { printf "Error reading default El torito record\n"; exit; }
if ($recdata[1] == 0xef) { #wow, the efi record came first, actually interpret that first record
    grabimage($bootcat);
} else {                   # keep looking for an *EFI* record
                           #read in first header
    read($istream, $bootcat, 0x20);
    @recdata = unpack("CCv", $bootcat);
    while ($recdata[0] == 0x90 and $recdata[1] != 0xef) {
        my $additionalrecords = $recdata[2];
        while ($additionalrecords) {
            read($istream, $bootcat, 0x20);    #throw away irrelevant sectors
            $additionalrecords -= 1;
        }
        read($istream, $bootcat, 0x20);        #throw away irrelevant sectors
        @recdata = unpack("CCv", $bootcat);
    }
    if ($recdata[1] != 0xef) {
        printf "No EFI boot image found\n";
        exit 1;
    }
    $readbytes = read($istream, $bootcat, 0x20);
    grabimage($bootcat);
}