Function syscall

freebsd/i386/i386/trap.c:1108–1149

* syscall - system call request C handler. A system call is * essentially treated as a trap by reusing the frame layout. */

 * essentially treated as a trap by reusing the frame layout.
 */
void
syscall(struct trapframe *frame)
{
	struct thread *td;
	register_t orig_tf_eflags;
	ksiginfo_t ksi;

#ifdef DIAGNOSTIC
	if (!(TRAPF_USERMODE(frame) &&
	    (curpcb->pcb_flags & PCB_VM86CALL) == 0)) {
		panic("syscall");
		/* NOT REACHED */
	}
#endif
	orig_tf_eflags = frame->tf_eflags;

	td = curthread;
	td->td_frame = frame;

	syscallenter(td);

	/*
	 * Traced syscall.
	 */
	if ((orig_tf_eflags & PSL_T) && !(orig_tf_eflags & PSL_VM)) {
		frame->tf_eflags &= ~PSL_T;
		ksiginfo_init_trap(&ksi);
		ksi.ksi_signo = SIGTRAP;
		ksi.ksi_code = TRAP_TRACE;
		ksi.ksi_addr = (void *)frame->tf_eip;
		trapsignal(td, &ksi);
	}

	KASSERT(PCB_USER_FPU(td->td_pcb),
	    ("System call %s returning with kernel FPU ctx leaked",
	     syscallname(td->td_proc, td->td_sa.code)));
	KASSERT(td->td_pcb->pcb_save == get_pcb_user_save_td(td),
	    ("System call %s returning with mangled pcb_save",
	     syscallname(td->td_proc, td->td_sa.code)));

	syscallret(td);
}