LoongArch: Fix watchpoint setting error

commit f63a47b3

 upstream.

In the current code, when debugging the following code using gdb,
"invalid argument ..." message will be displayed.

lihui@bogon:~$ cat test.c
  #include <stdio.h>
  int a = 0;
  int main()
  {
	a = 1;
	return 0;
  }
lihui@bogon:~$ gcc -g test.c -o test
lihui@bogon:~$ gdb test
...
(gdb) watch a
Hardware watchpoint 1: a
(gdb) r
...
Invalid argument setting hardware debug registers

There are mainly two types of issues.

1. Some incorrect judgment condition existed in user_watch_state
   argument parsing, causing -EINVAL to be returned.

When setting up a watchpoint, gdb uses the ptrace interface,
ptrace(PTRACE_SETREGSET, tid, NT_LOONGARCH_HW_WATCH, (void *) &iov)).
Register values in user_watch_state as follows:

  addr[0] = 0x0, mask[0] = 0x0, ctrl[0] = 0x0
  addr[1] = 0x0, mask[1] = 0x0, ctrl[1] = 0x0
  addr[2] = 0x0, mask[2] = 0x0, ctrl[2] = 0x0
  addr[3] = 0x0, mask[3] = 0x0, ctrl[3] = 0x0
  addr[4] = 0x0, mask[4] = 0x0, ctrl[4] = 0x0
  addr[5] = 0x0, mask[5] = 0x0, ctrl[5] = 0x0
  addr[6] = 0x0, mask[6] = 0x0, ctrl[6] = 0x0
  addr[7] = 0x12000803c, mask[7] = 0x0, ctrl[7] = 0x610

In arch_bp_generic_fields(), return -EINVAL when ctrl.len is
LOONGARCH_BREAKPOINT_LEN_8(0b00). So delete the incorrect judgment here.

In ptrace_hbp_fill_attr_ctrl(), when note_type is NT_LOONGARCH_HW_WATCH
and ctrl[0] == 0x0, if ((type & HW_BREAKPOINT_RW) != type) will return
-EINVAL. Here ctrl.type should be set based on note_type, and unnecessary
judgments can be removed.

2. The watchpoint argument was not set correctly due to unnecessary
   offset and alignment_mask.

Modify ptrace_hbp_fill_attr_ctrl() and hw_breakpoint_arch_parse(), which
ensure the watchpont argument is set correctly.

All changes according to the LoongArch Reference Manual:
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#control-and-status-registers-related-to-watchpoints

Cc: stable@vger.kernel.org
Signed-off-by: Hui Li <lihui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>