in src/producer.rs [115:120]
fn is_gcno_llvm(reader: &mut dyn Read) -> bool {
let mut bytes: [u8; 8] = [0; 8];
reader.read_exact(&mut bytes).is_ok()
&& &bytes[..5] == b"oncg*"
&& (&bytes[5..] == b"204" || &bytes[5..] == b"804")
}