Function linux_set_thread_area

freebsd/i386/linux/linux_machdep.c:568–638

}

int
linux_set_thread_area(struct thread *td, struct linux_set_thread_area_args *args)
{
	struct l_user_desc info;
	int error;
	int idx;
	int a[2];
	struct segment_descriptor sd;

	error = copyin(args->desc, &info, sizeof(struct l_user_desc));
	if (error)
		return (error);

	idx = info.entry_number;
	/*
	 * Semantics of Linux version: every thread in the system has array of
	 * 3 tls descriptors. 1st is GLIBC TLS, 2nd is WINE, 3rd unknown. This
	 * syscall loads one of the selected tls decriptors with a value and
	 * also loads GDT descriptors 6, 7 and 8 with the content of the
	 * per-thread descriptors.
	 *
	 * Semantics of FreeBSD version: I think we can ignore that Linux has 3
	 * per-thread descriptors and use just the 1st one. The tls_array[]
	 * is used only in set/get-thread_area() syscalls and for loading the
	 * GDT descriptors. In FreeBSD we use just one GDT descriptor for TLS
	 * so we will load just one.
	 *
	 * XXX: this doesn't work when a user space process tries to use more
	 * than 1 TLS segment. Comment in the Linux sources says wine might do
	 * this.
	 */

	/*
	 * we support just GLIBC TLS now
	 * we should let 3 proceed as well because we use this segment so
	 * if code does two subsequent calls it should succeed
	 */
	if (idx != 6 && idx != -1 && idx != 3)
		return (EINVAL);

	/*
	 * we have to copy out the GDT entry we use
	 * FreeBSD uses GDT entry #3 for storing %gs so load that
	 *
	 * XXX: what if a user space program doesn't check this value and tries
	 * to use 6, 7 or 8?
	 */
	idx = info.entry_number = 3;
	error = copyout(&info, args->desc, sizeof(struct l_user_desc));
	if (error)
		return (error);

	if (LINUX_LDT_empty(&info)) {
		a[0] = 0;
		a[1] = 0;
	} else {
		a[0] = LINUX_LDT_entry_a(&info);
		a[1] = LINUX_LDT_entry_b(&info);