From: Markus Metzger <markus.t.metzger@intel.com>
Date: Fri, 1 Aug 2025 09:53:44 +0000 (+0000)
Subject: gdb, remote: fix set_thread () in start_remote ()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ef706f09f1e53715810903a1aad5cdd4dc57d249;p=thirdparty%2Fbinutils-gdb.git

gdb, remote: fix set_thread () in start_remote ()

remote_target::start_remote_1 () calls set_continue_thread (minus_one_ptid)
with the intent to

      /* Let the stub know that we want it to return the thread.  */
      set_continue_thread (minus_one_ptid);

I interpret it such that it expects a later get_current_thread () to
return the thread selected by the target:

          /* We have thread information; select the thread the target
             says should be current.  If we're reconnecting to a
             multi-threaded program, this will ideally be the thread
             that last reported an event before GDB disconnected.  */
          ptid_t curr_thread = get_current_thread (wait_status);

This results in the packet sequence Hc-1, qC.

Hc simply sets cont_thread:

          else if (cs.own_buf[1] == 'c')
            cs.cont_thread = thread_id;

          write_ok (cs.own_buf);

and qC returns the general thread.  This doesn't match.

It also has some special treatment for null_ptid and minus_one_ptid:

    if (cs.general_thread != null_ptid && cs.general_thread != minus_one_ptid)
      ptid = cs.general_thread;
    else
      {
        init_thread_iter ();
        ptid = thread_iter->id;
      }

Similarly, Hg has some special treatment for null_ptid:

    if (cs.own_buf[1] == 'g')
      {
        if (thread_id == null_ptid)
          {
            /* GDB is telling us to choose any thread.  Check if
               the currently selected thread is still valid. If
               it is not, select the first available.  */
            thread_info *thread = find_thread_ptid (cs.general_thread);
            if (thread == NULL)
              thread = get_first_thread ();
            thread_id = thread->id;
          }

        cs.general_thread = thread_id;

The comment at Hg matches the intent of GDB for sending Hc-1.

Change the set_thread () call in remote_target::start_remote_1 () to

    set_general_thread (any_thread_ptid);

This results in GDB sending Hg0 and gdbserver preserving the currently
selected thread that is later returned in response to qC.

CC: Thiago Jung Bauermann  <thiago.bauermann@linaro.org>
Approved-By: Tom Tromey <tom@tromey.com>
---

diff --git a/gdb/remote.c b/gdb/remote.c
index 4db83bc6c35..80d47c16551 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -5661,7 +5661,7 @@ remote_target::start_remote_1 (int from_tty, int extended_p)
       target_update_thread_list ();
 
       /* Let the stub know that we want it to return the thread.  */
-      set_continue_thread (minus_one_ptid);
+      set_general_thread (any_thread_ptid);
 
       if (thread_count (this) == 0)
 	{