#!/usr/bin/perl

use strict;
use warnings;
use XML::LibXML;
use Data::Dumper 'Dumper';

my $xml = XML::LibXML->new();
my $doc = $xml->parse_file( "j.xml" );
my $pth = XML::LibXML::XPathContext->new( $doc );

my @subblocks;
for my $sbnode ( $pth->findnodes( "/itpslsig/itpslbody/mainblock/subblock" )) {
    for my $sbchild ( $sbnode->childNodes ) {
        next unless ( $sbchild->nodeName =~ /fileexists|userexec/ );
        my %feitem = ( STARTOP => $sbchild->nodeName );
        for my $fechild ( $sbchild->childNodes ) {
            $feitem{$fechild->nodeName} = $fechild->textContent;
        }
        my @features = map { "$_ => $feitem{$_}" } sort grep /^\w/, keys %feitem;
        push @subblocks, [ @features ];
    }
}

print Dumper( \@subblocks );