Re: [pushed] gdb/mi: consistently notify user when GDB/MI client uses -thread-select

Simon Marchi
2022-03-21T20:36:05Z

On 2022-03-16 11:09, Jan Vrany via Gdb-patches wrote:
> GDB notifies users about user selected thread changes somewhat
> inconsistently as mentioned on gdb-patches mailing list here:
>
> https://sourceware.org/pipermail/gdb-patches/2022-February/185989.html
>
> Consider GDB debugging a multi-threaded inferior with both CLI and GDB/MI
> interfaces connected to separate terminals.
>
> Assuming inferior is stopped and thread 1 is selected, when a thread
> 2 is selected using '-thread-select 2' command on GDB/MI terminal:
>
> -thread-select 2
> ^done,new-thread-id="2",frame={level="0",addr="0x00005555555551cd",func="child_sub_function",args=[],file="/home/jv/Projects/gdb/users_jv_patches/gdb/testsuite/gdb.mi/user-selected-context-sync.c",fullname="/home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="30",arch="i386:x86-64"}
> (gdb)
>
> and on CLI terminal we get the notification (as expected):
>
> [Switching to thread 2 (Thread 0x7ffff7daa640 (LWP 389659))]
> #0 child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30
> 30 volatile int dummy = 0;
>
> However, now that thread 2 is selected, if thread 1 is selected
> using 'thread-select --thread 1 1' command on GDB/MI terminal
> terminal:
>
> -thread-select --thread 1 1
> ^done,new-thread-id="1",frame={level="0",addr="0x0000555555555294",func="main",args=[],file="/home/jv/Projects/gdb/users_jv_patches/gdb/testsuite/gdb.mi/user-selected-context-sync.c",fullname="/home/jv/Projects/gdb/users_jv_patches/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="66",arch="i386:x86-64"}
> (gdb)
>
> but no notification is printed on CLI terminal, despite the fact
> that user selected thread has changed.
>
> The problem is that when `-thread-select --thread 1 1` is executed
> then thread is switched to thread 1 before mi_cmd_thread_select () is
> called, therefore the condition "inferior_ptid != previous_ptid"
> there does not hold.
>
> To address this problem, we have to move notification logic up to
> mi_cmd_execute () where --thread option is processed and notify
> user selected contents observers there if context changes.
>
> However, this in itself breaks GDB/MI because it would cause context
> notification to be sent on MI channel. This is because by the time
> we notify, MI notification suppression is already restored (done in
> mi_command::invoke(). Therefore we had to lift notification suppression
> logic also up to mi_cmd_execute (). This change in made distinction
> between mi_command::invoke() and mi_command::do_invoke() unnecessary
> as all mi_command::invoke() did (after the change) was to call
> do_invoke(). So this patches removes do_invoke() and moves the command
> execution logic directly to invoke().
>
> With this change, all gdb.mi tests pass, tested on x86_64-linux.
>
> Co-authored-by: Andrew Burgess <aburgess@redhat.com>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=20631

Hi,

I see this on Ubuntu 20.04, am I the only one?

FAIL: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again, event on CLI, ensure no output CLI
FAIL: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.3: -thread-select again, event on CLI, ensure no output CLI
FAIL: gdb.mi/user-selected-context-sync.exp: mode=non-stop: test_mi_thread_select: thread 1.2: -thread-select again, event on CLI, ensure no output CLI

Just the first one here:

-thread-select 2
^done,new-thread-id="2",frame={level="0",addr="0x00005555555551b8",func="child_sub_function",args=[],file="/home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-
sync.c",fullname="/home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c",line="33",arch="i386:x86-64"}
(gdb)
PASS: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again
[Switching to thread 1.2 (Thread 0x7ffff7d99700 (LWP 1763981))]
#0 child_sub_function () at /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:33
33 dummy = !dummy; /* thread loop line */
print 666
$9 = 666
(gdb) FAIL: gdb.mi/user-selected-context-sync.exp: mode=all-stop: test_mi_thread_select: thread 1.2: -thread-select again, event on CLI, ensure no output CLI

Simon