int copy_thread()

in kernel/process.c [53:112]

• 30 lines of code
• 4 McCabe index (conditional complexity)

int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
		struct task_struct *p, unsigned long tls)
{
	struct thread_info *ti = task_thread_info(p);
	struct hexagon_switch_stack *ss;
	struct pt_regs *childregs;
	asmlinkage void ret_from_fork(void);

	childregs = (struct pt_regs *) (((unsigned long) ti + THREAD_SIZE) -
					sizeof(*childregs));

	ti->regs = childregs;

	/*
	 * Establish kernel stack pointer and initial PC for new thread
	 * Note that unlike the usual situation, we do not copy the
	 * parent's callee-saved here; those are in pt_regs and whatever
	 * we leave here will be overridden on return to userland.
	 */
	ss = (struct hexagon_switch_stack *) ((unsigned long) childregs -
						    sizeof(*ss));
	ss->lr = (unsigned long)ret_from_fork;
	p->thread.switch_sp = ss;
	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
		memset(childregs, 0, sizeof(struct pt_regs));
		/* r24 <- fn, r25 <- arg */
		ss->r24 = usp;
		ss->r25 = arg;
		pt_set_kmode(childregs);
		return 0;
	}
	memcpy(childregs, current_pt_regs(), sizeof(*childregs));
	ss->r2524 = 0;

	if (usp)
		pt_set_rte_sp(childregs, usp);

	/* Child sees zero return value */
	childregs->r00 = 0;

	/*
	 * The clone syscall has the C signature:
	 * int [r0] clone(int flags [r0],
	 *           void *child_frame [r1],
	 *           void *parent_tid [r2],
	 *           void *child_tid [r3],
	 *           void *thread_control_block [r4]);
	 * ugp is used to provide TLS support.
	 */
	if (clone_flags & CLONE_SETTLS)
		childregs->ugp = tls;

	/*
	 * Parent sees new pid -- not necessary, not even possible at
	 * this point in the fork process
	 * Might also want to set things like ti->addr_limit
	 */

	return 0;
}