[binutils-gdb] Ensure selected thread after thread exit stop

[binutils-gdb] Ensure selected thread after thread exit stop

[Pedro Alves]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d0b591497952db37ed7a5545ced7aad64433f79a

commit d0b591497952db37ed7a5545ced7aad64433f79a
Author: Pedro Alves <pedro@palves.net>
Date:   Mon Nov 20 17:49:08 2023 +0000

    Ensure selected thread after thread exit stop
    
    While making step over thread exit work properly on AMDGPU, I noticed
    that if there's a breakpoint on top of the exit syscall, and,
    displaced stepping is off, then when GDB reports "Command aborted,
    thread exited.", GDB also switches focus to a random thread, instead
    of leaving the exited thread as selected:
    
     (gdb) thread
     [Current thread is 6, lane 0 (AMDGPU Lane 1:4:1:1/0 (0,0,0)[0,0,0])]
     (gdb) si
     Command aborted, thread exited.
     (gdb) thread
     [Current thread is 5 (Thread 0x7ffff626f640 (LWP 3248392))]
     (gdb)
    
    The previous patch extended gdb.threads/step-over-thread-exit.exp to
    exercise this on GNU/Linux (on the CPU side), and there, after that
    "si", we always end up with the exiting thread as selected even
    without this fix, but that's just a concidence, there's a code path
    that happens to select the exiting thread for an unrelated reason.
    
    This commit add the explict switch, fixing the latent problem for
    GNU/Linux, and the actual problem on AMDGPU.  I wrote a gdb.rocm/
    testcase for this, but it can't be upstreamed yet, until more pieces
    of the DWARF machinery are upstream as well.
    
    Approved-By: Simon Marchi <simon.marchi@efficios.com>
    Change-Id: I6ff57a79514ac0142bba35c749fe83d53d9e4e51

Diff:
---
 gdb/infrun.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 45c1b4a79bb..6dc0a2bb9a5 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5895,7 +5895,14 @@ handle_thread_exited (execution_control_state *ecs)
 
   if (abort_cmd)
     {
+      /* We're stopping for the thread exit event.  Switch to the
+	 event thread again, as finish_step_over may have switched
+	 threads.  */
+      switch_to_thread (ecs->event_thread);
+
+      /* Emit [Thread ... exited] notification.  */
       delete_thread (ecs->event_thread);
+
       ecs->event_thread = nullptr;
       return false;
     }