[PATCH] [MIPS] Use lwpid from lwp_info instead of inferior_ptid

[Yao Qi <qiyaoltc@gmail.com>]

RAJESH reported that GDB gets "Couldn't write debug register: No such
process." on mips64 when GDB attaches to a multi threaded application.

Looks GDB nows PTRACE_GET_WATCH_REGS for inferior_ptid but
PTRACE_SET_WATCH_REGS for lwp->ptid, they may be different.

gdb:

2017-04-27  Yao Qi  <yao.qi@linaro.org>

	* mips-linux-nat.c (mips_linux_new_thread): Get lwpid from
	lwp_info instead of getting from inferior_ptid.
---
 gdb/mips-linux-nat.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/gdb/mips-linux-nat.c b/gdb/mips-linux-nat.c
index 9596b49..c5c18fd 100644
--- a/gdb/mips-linux-nat.c
+++ b/gdb/mips-linux-nat.c
@@ -624,14 +624,13 @@ write_watchpoint_regs (void)
 static void
 mips_linux_new_thread (struct lwp_info *lp)
 {
-  int tid;
+  long tid = ptid_get_lwp (lp->ptid);
 
-  if (!mips_linux_read_watch_registers (ptid_get_lwp (inferior_ptid),
+  if (!mips_linux_read_watch_registers (tid,
 					&watch_readback,
 					&watch_readback_valid, 0))
     return;
 
-  tid = ptid_get_lwp (lp->ptid);
   if (ptrace (PTRACE_SET_WATCH_REGS, tid, &watch_mirror, NULL) == -1)
     perror_with_name (_("Couldn't write debug register"));
 }
-- 
1.9.1