RFC: don't call add_target for thread_db_ops

[Tom Tromey <tromey@redhat.com>]

Right now, "help target" will include this line:

    target multi-thread -- Threads and pthreads support

However, it doesn't make sense to invoke "target multi-thread".

This patch fixes the problem by not registering the multi-thread
target.  add_target does some needed initialization of the target_ops,
so I broke this out into a new function.

It isn't clear to me whether this patch requires a test case or not.
I'm not sure whether there are other unregistered targets; but if
there are, it seems unlikely that we test for their absence from the
help.

Built and regtested on x86-64 Fedora 18.

	* linux-thread-db.c (init_thread_db_ops): Call
	complete_target_initialization.
	(_initialize_thread_db): Don't call add_target.
	* target.c (complete_target_initialization): New function.
	(add_target_with_completer): Call it.
	* target.h (complete_target_initialization): Declare.
---
 gdb/linux-thread-db.c |  3 ++-
 gdb/target.c          | 23 ++++++++++++++++-------
 gdb/target.h          |  5 +++++
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index 23c29c9..3696827 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -2057,6 +2057,8 @@ init_thread_db_ops (void)
   thread_db_ops.to_extra_thread_info = thread_db_extra_thread_info;
   thread_db_ops.to_get_ada_task_ptid = thread_db_get_ada_task_ptid;
   thread_db_ops.to_magic = OPS_MAGIC;
+
+  complete_target_initialization (&thread_db_ops);
 }
 
 /* Provide a prototype to silence -Wmissing-prototypes.  */
@@ -2066,7 +2068,6 @@ void
 _initialize_thread_db (void)
 {
   init_thread_db_ops ();
-  add_target (&thread_db_ops);
 
   /* Defer loading of libthread_db.so until inferior is running.
      This allows gdb to load correct libthread_db for a given
diff --git a/gdb/target.c b/gdb/target.c
index 920f916..5bf8059 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -381,16 +381,12 @@ target_has_execution_current (void)
   return target_has_execution_1 (inferior_ptid);
 }
 
-/* Add possible target architecture T to the list and add a new
-   command 'target T->to_shortname'.  Set COMPLETER as the command's
-   completer if not NULL.  */
+/* Complete initialization of T.  This ensures that various fields in
+   T are set, if needed by the target implementation.  */
 
 void
-add_target_with_completer (struct target_ops *t,
-			   completer_ftype *completer)
+complete_target_initialization (struct target_ops *t)
 {
-  struct cmd_list_element *c;
-
   /* Provide default values for all "must have" methods.  */
   if (t->to_xfer_partial == NULL)
     t->to_xfer_partial = default_xfer_partial;
@@ -409,6 +405,19 @@ add_target_with_completer (struct target_ops *t,
 
   if (t->to_has_execution == NULL)
     t->to_has_execution = (int (*) (struct target_ops *, ptid_t)) return_zero;
+}
+
+/* Add possible target architecture T to the list and add a new
+   command 'target T->to_shortname'.  Set COMPLETER as the command's
+   completer if not NULL.  */
+
+void
+add_target_with_completer (struct target_ops *t,
+			   completer_ftype *completer)
+{
+  struct cmd_list_element *c;
+
+  complete_target_initialization (t);
 
   if (!target_structs)
     {
diff --git a/gdb/target.h b/gdb/target.h
index 1bf716e..00dad64 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -1837,6 +1837,9 @@ int target_verify_memory (const gdb_byte *data,
 
 /* Routines for maintenance of the target structures...
 
+   complete_target_initialization: Finalize a target_ops by filling in
+   any fields needed by the target implementation.
+
    add_target:   Add a target to the list of all possible targets.
 
    push_target:  Make this target the top of the stack of currently used
@@ -1855,6 +1858,8 @@ extern void add_target (struct target_ops *);
 extern void add_target_with_completer (struct target_ops *t,
 				       completer_ftype *completer);
 
+extern void complete_target_initialization (struct target_ops *t);
+
 /* Adds a command ALIAS for target T and marks it deprecated.  This is useful
    for maintaining backwards compatibility when renaming targets.  */
 
-- 
1.8.1.4