Re: Cannot execute this command without a live selected thread.

[Pedro Alves <palves at redhat dot com>]

On 10/24/2014 06:23 PM, Pedro Alves wrote:
> On 10/24/2014 06:07 PM, Sandra Loosemore wrote:
>> Sending packet: $?#3f...Packet received: S00
>> Sending packet: $qfThreadInfo#bb...Packet received: l
> 
> Huh, I think this is the problem.
> 
> So this target supports qfThreadInfo, but then it's returning
> an empty thread list...  remote_update_thread_list will delete
> threads from GDB's list that are not found in the thread list that
> the target reported.  Why is the target reporting that empty list?
> 
> See ab970af19746364a4f236bebc238ebb036adc898.
> 
> We may be able add a workaround for this.  :-/  Just in case,
> can you confirm that the current thread's ptid (inferior_ptid)
> is magic_null_ptid?

Please give this a try.

>From 2062235a91a3c69e73c39b0f8a4f78f4ec396931 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Fri, 24 Oct 2014 18:27:14 +0100
Subject: [PATCH] gdb/ 2014-10-24  Pedro Alves  <palves@redhat.com>

	* remote.c (remote_thread_alive): New, factored out from ...
	(remote_thread_alive): ... this.
	(remote_update_thread_list): Bail out before deleting threads if
	the target returned an empty list, and, the current thread has a
	magic/fake ptid.
---
 gdb/remote.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/gdb/remote.c b/gdb/remote.c
index 20f2988..affc7c2 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1842,11 +1842,11 @@ set_general_process (void)
 }
 
 
-/*  Return nonzero if the thread PTID is still alive on the remote
-    system.  */
+/* Return nonzero if this is the main thread that we made up ourselves
+   to model non-threaded targets as single-threaded.  */
 
 static int
-remote_thread_alive (struct target_ops *ops, ptid_t ptid)
+remote_thread_always_alive (struct target_ops *ops, ptid_t ptid)
 {
   struct remote_state *rs = get_remote_state ();
   char *p, *endp;
@@ -1861,6 +1861,23 @@ remote_thread_alive (struct target_ops *ops, ptid_t ptid)
        multi-threading.  */
     return 1;
 
+  return 0;
+}
+
+/*  Return nonzero if the thread PTID is still alive on the remote
+    system.  */
+
+static int
+remote_thread_alive (struct target_ops *ops, ptid_t ptid)
+{
+  struct remote_state *rs = get_remote_state ();
+  char *p, *endp;
+
+  /* Check if this is a thread that we made up ourselves to model
+     non-threaded targets as single-threaded.  */
+  if (remote_thread_always_alive (ops, ptid))
+    return 1;
+
   p = rs->buf;
   endp = rs->buf + get_remote_packet_size ();
 
@@ -2780,6 +2797,18 @@ remote_update_thread_list (struct target_ops *ops)
 
       got_list = 1;
 
+      if (VEC_empty (thread_item_t, context.items)
+	  && remote_thread_always_alive (ops, inferior_ptid))
+	{
+	  /* Some targets don't really support threads, but still
+	     reply an (empty) thread list in response to the thread
+	     listing packets, instead of replying "packet not
+	     supported".  Exit early so we don't delete the main
+	     thread.  */
+	  do_cleanups (old_chain);
+	  return;
+	}
+
       /* CONTEXT now holds the current thread list on the remote
 	 target end.  Delete GDB-side threads no longer found on the
 	 target.  */
-- 
1.9.3