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