Subcoded System Calls

Some system calls as presented in man page section 2 are implemented as suboperations of an undocumented system call. For example, the system calls related to System V semaphores, such as semctl, semget, semids, semop, and semtimedop are implemented as suboperations of a single system call, semsys. The semsys system call takes as its first argument an implementation-specific subcode denoting the specific system call required: SEMCTL, SEMGET, SEMIDS, SEMOP, or SEMTIMEDOP, respectively. As a result of overloading a single system call to implement multiple system calls, there is only a single pair of syscall probes for System V semaphores:

syscall::semsys:entry and syscall::semsys:return