Constant HELLO64 

pub const HELLO64: i64 = _; // 39i64

getpid on the host’s 64-bit ABI (x86_64 39, aarch64 172). The exec shim makes it from the notify gate once it runs, with HELLO_MARK as its argument, telling the supervisor that the exec it planned has happened. A real syscall that every seccomp profile allows: a container runtime’s filter refuses unknown numbers, and its refusal outranks the notification.