[Bug gdb/27710] remote-notif.c:113: internal-error: void remote_async_get_pending_events_handler(gdb_client_data): Assertion `target_is_non_stop_p ()' failed

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27710

--- Comment #6 from Tom de Vries <vries at gcc dot gnu.org> ---
Backtrace:
...
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007fd1b7b43a01 in __GI_abort () at abort.c:79
#2  0x0000000000b1db10 in dump_core () at
/home/vries/gdb_versions/devel/src/gdb/utils.c:204
#3  0x0000000000b1e022 in internal_vproblem(internal_problem *, const char *,
int, const char *, typedef __va_list_tag __va_list_tag *) (problem=0x16d7bc0
<internal_error_problem>, 
    file=0xf4c5b0 "/home/vries/gdb_versions/devel/src/gdb/remote-notif.c",
line=113, 
    fmt=0xf4c584 "%s: Assertion `%s' failed.", ap=0x7ffe5cb2a788)
    at /home/vries/gdb_versions/devel/src/gdb/utils.c:414
#4  0x0000000000b1e0ea in internal_verror (
    file=0xf4c5b0 "/home/vries/gdb_versions/devel/src/gdb/remote-notif.c",
line=113, 
    fmt=0xf4c584 "%s: Assertion `%s' failed.", ap=0x7ffe5cb2a788)
    at /home/vries/gdb_versions/devel/src/gdb/utils.c:439
#5  0x0000000000df5b79 in internal_error (
    file=0xf4c5b0 "/home/vries/gdb_versions/devel/src/gdb/remote-notif.c",
line=113, 
    fmt=0xf4c584 "%s: Assertion `%s' failed.")
    at /home/vries/gdb_versions/devel/src/gdbsupport/errors.cc:55
#6  0x000000000094be95 in remote_async_get_pending_events_handler
(data=0x40e34b0)
    at /home/vries/gdb_versions/devel/src/gdb/remote-notif.c:113
#7  0x00000000004d29e5 in check_async_event_handlers ()
    at /home/vries/gdb_versions/devel/src/gdb/async-event.c:335
#8  0x0000000000df5cb7 in gdb_do_one_event ()
    at /home/vries/gdb_versions/devel/src/gdbsupport/event-loop.cc:216
#9  0x00000000007fa045 in start_event_loop ()
    at /home/vries/gdb_versions/devel/src/gdb/main.c:348
#10 0x00000000007fa165 in captured_command_loop ()
    at /home/vries/gdb_versions/devel/src/gdb/main.c:408
#11 0x00000000007fb846 in captured_main (data=0x7ffe5cb2a9d0)
    at /home/vries/gdb_versions/devel/src/gdb/main.c:1242
#12 0x00000000007fb8ac in gdb_main (args=0x7ffe5cb2a9d0)
    at /home/vries/gdb_versions/devel/src/gdb/main.c:1257
#13 0x00000000004187ee in main (argc=15, argv=0x7ffe5cb2aad8)
    at /home/vries/gdb_versions/devel/src/gdb/gdb.c:32
...

So, we hit the assert:
...
  gdb_assert (target_is_non_stop_p ());
...

The function is defined as:
...
bool
target_is_non_stop_p ()
{
  return ((non_stop
           || target_non_stop_enabled == AUTO_BOOLEAN_TRUE
           || (target_non_stop_enabled == AUTO_BOOLEAN_AUTO
               && target_always_non_stop_p ()))
          && target_can_async_p ());
}
...
and:
...
(gdb) p non_stop
$1 = true
...
so presumably the assert fails because target_can_async_p () == false.

We have:
...
bool
target_can_async_p ()
{
  return current_inferior ()->top_target ()->can_async_p ();
}
...

AFAIU, current_inferior ()->top_target () translates to:
...
(gdb) p
current_inferior_.m_obj.m_target_stack.m_stack[current_inferior_.m_obj.m_target_stack.m_top]
$16 = (target_ops *) 0x16c6cd0 <exec_ops>
...

Exec_ops has type exec_target, which subclasses target_ops without implementing
a can_async_p override, so we have the default:
...
    virtual bool can_async_p ()
      TARGET_DEFAULT_RETURN (false);
...

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