LoongArch: Extend the maximum number of watchpoints

commit 531936de upstream.

The maximum number of load/store watchpoints and fetch instruction
watchpoints is 14 each according to LoongArch Reference Manual, so
extend the maximum number of watchpoints from 8 to 14 for ptrace.

By the way, just simply change 8 to 14 for the definition in struct
user_watch_state at the beginning, but it may corrupt uapi, then add
a new struct user_watch_state_v2 directly.

As far as I can tell, the only users for this struct in the userspace
are GDB and LLDB, there are no any problems of software compatibility
between the application and kernel according to the analysis.

The compatibility problem has been considered while developing and
testing. When the applications in the userspace get watchpoint state,
the length will be specified which is no bigger than the sizeof struct
user_watch_state or user_watch_state_v2, the actual length is assigned
as the minimal value of the application and kernel in the generic code
of ptrace:

kernel/ptrace.c: ptrace_regset():

	kiov->iov_len = min(kiov->iov_len,
			   (__kernel_size_t) (regset->n * regset->size));

	if (req == PTRACE_GETREGSET)
		return copy_regset_to_user(task, view, regset_no, 0,
					  kiov->iov_len, kiov->iov_base);
	else
		return copy_regset_from_user(task, view, regset_no, 0,
					  kiov->iov_len, kiov->iov_base);

For example, there are four kind of combinations, all of them work well.

(1) "older kernel + older gdb", the actual length is 8+(8+8+4+4)*8=200;
(2) "newer kernel + newer gdb", the actual length is 8+(8+8+4+4)*14=344;
(3) "older kernel + newer gdb", the actual length is 8+(8+8+4+4)*8=200;
(4) "newer kernel + older gdb", the actual length is 8+(8+8+4+4)*8=200.

Link: https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#control-and-status-registers-related-to-watchpoints


Cc: stable@vger.kernel.org
Fixes: 1a69f7a1 ("LoongArch: ptrace: Expose hardware breakpoints to debuggers")
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>