syscall - indirect system call
syscall (number, arg, ...)
The syscall system call performs the system call whose assembly language interface has the specified number, register arguments r0 and r1, and further arguments arg.
The r0 value of the system call is returned.
This interface is not recommended. An alternative interface is documented
There is no way to simulate system calls such as pipe,
which return values in register r1.
When the C-bit is set, syscall returns -1 and sets the external variable errno.
Functions: errno(2), pipe(2)