open(my $fh1, '<', $file1) or die $!;
binmode($fh1);

open(my $fh2, '<', $file2) or die $!;
binmode($fh2);

local $/ = \(64*1024);  # Tweak as desired.
for (;;) {
   my $blk1 = <$fh1>;
   my $blk2 = <$fh2>;

   last if !defined($blk1) && !defined($blk2);

   die("diff\n")
      if !defined($blk1)
      || !defined($blk2)
      || $blk1 ne $blk2;
}