[RFA] Fix for PR mi/15863

[Keith Seitz <keiths@redhat.com>]

If an MI client creates a varobj and attempts to update the root
/before/ the inferior is started, gdb will throw an internal error:

(gdb)
-var-create * - batch_flag
^done,name="var1",numchild="0",value="0",type="int",has_more="0"
(gdb) 
-var-update var1
^done,changelist=[]
(gdb) 
-var-update *
~"../../src/gdb/thread.c:628: internal-error: is_thread_state: Assertion `tp' failed.\nA problem internal to GDB has been detected,\nfurther debugging may prove unreliable.\nQuit this debugging session? "
~"(y or n) "

The function that handles the varobj update in the failing case,
mi_cmd_var_udpate_iter, checks if the thread/inferior is stopped before
attempting to update the varobj. It calls is_stopped (inferior_ptid)
which calls is_thread_state:

    tp = find_thread_ptid (ptid);
    gdb_assert (tp);

When there is no inferior, ptid is null_ptid, and find_thread_ptid (null_ptid)
returns NULL and the assertion is triggered.

This patch changes mi_cmd_var_update_iter to behave the same way
"-var-update var1" does: by calling the thread "stopped" if
there is no inferior (and thereby calling varobj_update_one).

ChangeLog
2014-06-13  Keith Seitz  <keiths@redhat.com>

	PR mi/15863
	* mi/mi-cmd-var.c (mi_cmd_var_update_iter): Do not attempt
	to update the varobj if inferior_ptid is null_ptid.

testsuite/ChangeLog
2014-06-13  Keith Seitz  <keiths@redhat.com>

	PR mi/15863
	* gdb.mi/mi-var-cmd.exp: Add test for -var-update before
	the inferior is started.

---
 gdb/mi/mi-cmd-var.c                 | 4 +++-
 gdb/testsuite/gdb.mi/mi-var-cmd.exp | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gdb/mi/mi-cmd-var.c b/gdb/mi/mi-cmd-var.c
index 9059616..08a87bf 100644
--- a/gdb/mi/mi-cmd-var.c
+++ b/gdb/mi/mi-cmd-var.c
@@ -642,7 +642,9 @@ mi_cmd_var_update_iter (struct varobj *var, void *data_pointer)
 
   thread_id = varobj_get_thread_id (var);
 
-  if (thread_id == -1 && is_stopped (inferior_ptid))
+  if (thread_id == -1
+      && (ptid_equal (inferior_ptid, null_ptid)
+	  || is_stopped (inferior_ptid)))
     thread_stopped = 1;
   else
     {
diff --git a/gdb/testsuite/gdb.mi/mi-var-cmd.exp b/gdb/testsuite/gdb.mi/mi-var-cmd.exp
index 46a4e9e..03e1b4c 100644
--- a/gdb/testsuite/gdb.mi/mi-var-cmd.exp
+++ b/gdb/testsuite/gdb.mi/mi-var-cmd.exp
@@ -50,6 +50,12 @@ mi_gdb_load ${binfile}
 
 mi_create_varobj "global_simple" "global_simple" "create global variable"
 
+# PR mi/15863
+# Attempt to update the varobj before running the inferior.
+mi_gdb_test "-var-update *" \
+	"\\^done,changelist=\\\[\\\]" \
+	"update varobj before running inferior"
+
 # Test: c_variable-1.2
 # Desc: Create non-existent variable
 
-- 
1.9.3