int copy_thread()

in kernel/process.c [204:315]

• 65 lines of code
• 9 McCabe index (conditional complexity)

int copy_thread(unsigned long clone_flags, unsigned long usp_thread_fn,
		unsigned long thread_fn_arg, struct task_struct *p,
		unsigned long tls)
{
	struct pt_regs *childregs = task_pt_regs(p);

#if (XTENSA_HAVE_COPROCESSORS || XTENSA_HAVE_IO_PORTS)
	struct thread_info *ti;
#endif

#if defined(__XTENSA_WINDOWED_ABI__)
	/* Create a call4 dummy-frame: a0 = 0, a1 = childregs. */
	SPILL_SLOT(childregs, 1) = (unsigned long)childregs;
	SPILL_SLOT(childregs, 0) = 0;

	p->thread.sp = (unsigned long)childregs;
#elif defined(__XTENSA_CALL0_ABI__)
	/* Reserve 16 bytes for the _switch_to stack frame. */
	p->thread.sp = (unsigned long)childregs - 16;
#else
#error Unsupported Xtensa ABI
#endif

	if (!(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
		struct pt_regs *regs = current_pt_regs();
		unsigned long usp = usp_thread_fn ?
			usp_thread_fn : regs->areg[1];

		p->thread.ra = MAKE_RA_FOR_CALL(
				(unsigned long)ret_from_fork, 0x1);

		/* This does not copy all the regs.
		 * In a bout of brilliance or madness,
		 * ARs beyond a0-a15 exist past the end of the struct.
		 */
		*childregs = *regs;
		childregs->areg[1] = usp;
		childregs->areg[2] = 0;

		/* When sharing memory with the parent thread, the child
		   usually starts on a pristine stack, so we have to reset
		   windowbase, windowstart and wmask.
		   (Note that such a new thread is required to always create
		   an initial call4 frame)
		   The exception is vfork, where the new thread continues to
		   run on the parent's stack until it calls execve. This could
		   be a call8 or call12, which requires a legal stack frame
		   of the previous caller for the overflow handlers to work.
		   (Note that it's always legal to overflow live registers).
		   In this case, ensure to spill at least the stack pointer
		   of that frame. */

		if (clone_flags & CLONE_VM) {
			/* check that caller window is live and same stack */
			int len = childregs->wmask & ~0xf;
			if (regs->areg[1] == usp && len != 0) {
				int callinc = (regs->areg[0] >> 30) & 3;
				int caller_ars = XCHAL_NUM_AREGS - callinc * 4;
				put_user(regs->areg[caller_ars+1],
					 (unsigned __user*)(usp - 12));
			}
			childregs->wmask = 1;
			childregs->windowstart = 1;
			childregs->windowbase = 0;
		} else {
			int len = childregs->wmask & ~0xf;
			memcpy(&childregs->areg[XCHAL_NUM_AREGS - len/4],
			       &regs->areg[XCHAL_NUM_AREGS - len/4], len);
		}

		childregs->syscall = regs->syscall;

		if (clone_flags & CLONE_SETTLS)
			childregs->threadptr = tls;
	} else {
		p->thread.ra = MAKE_RA_FOR_CALL(
				(unsigned long)ret_from_kernel_thread, 1);

		/* pass parameters to ret_from_kernel_thread: */
#if defined(__XTENSA_WINDOWED_ABI__)
		/*
		 * a2 = thread_fn, a3 = thread_fn arg.
		 * Window underflow will load registers from the
		 * spill slots on the stack on return from _switch_to.
		 */
		SPILL_SLOT(childregs, 2) = usp_thread_fn;
		SPILL_SLOT(childregs, 3) = thread_fn_arg;
#elif defined(__XTENSA_CALL0_ABI__)
		/*
		 * a12 = thread_fn, a13 = thread_fn arg.
		 * _switch_to epilogue will load registers from the stack.
		 */
		((unsigned long *)p->thread.sp)[0] = usp_thread_fn;
		((unsigned long *)p->thread.sp)[1] = thread_fn_arg;
#else
#error Unsupported Xtensa ABI
#endif

		/* Childregs are only used when we're going to userspace
		 * in which case start_thread will set them up.
		 */
	}

#if (XTENSA_HAVE_COPROCESSORS || XTENSA_HAVE_IO_PORTS)
	ti = task_thread_info(p);
	ti->cpenable = 0;
#endif

	clear_ptrace_hw_breakpoint(p);

	return 0;
}