open my $fh, '<', 'test.elf' or die "can't do anything: $!";
binmode $fh;
read $fh, my $stuff, 1000 or die "read error: $!";
close $fh;

print length $stuff, " bytes in\n";
my $offs = 0;

my @tmp =
   map $_->[1],
      grep $_->[0] eq '7f',
         map [$_, $offs++],
            unpack "(H2)*", $stuff;

# prints "7f" offsets in binary file
print join':', @tmp;