I made a system call and recompiled the kernel, however upon running the system call it returned Killed. So, to trace it, I used strace, which shows the following message:
syscall_0x224(0x7ffda7199738, 0x7ffda7199748, 0x55743750a6d0, 0x7f9f20df7d80, 0x7f9f20df7d80, 0x7ffda7199730) = ?
What does this mean (not the hex, the question mark)?