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

[Jan Vrany <jan.vrany@labware.com>]

On Mon, 2022-03-21 at 16:35 -0400, Simon Marchi wrote:
> 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://urldefense.proofpoint.com/v2/url?u=https-3A__sourceware.org_pipermail_gdb-2Dpatches_2022-2DFebruary_185989.html&d=DwICaQ&c=sPZ6DeHLiehUHQWKIrsNwWp3t7snrE-az24ztT0w7Jc&r=WpFFGgYa98Yp-c29WHTCwU1wAGFBvszA6a4RzgpMSqc&m=qn1ryn0GnzccCli0TKe7kc6WpMiz1opcXfyT-fLWkIk&s=XoLasKCD9agRgS73PoGDnzPlKbo4_lL616HCUvldty0&e= 
> > 
> > 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://urldefense.proofpoint.com/v2/url?u=https-3A__sourceware.org_bugzilla_show-5Fbug.cgi-3Fid-3D20631&d=DwICaQ&c=sPZ6DeHLiehUHQWKIrsNwWp3t7snrE-az24ztT0w7Jc&r=WpFFGgYa98Yp-c29WHTCwU1wAGFBvszA6a4RzgpMSqc&m=qn1ryn0GnzccCli0TKe7kc6WpMiz1opcXfyT-fLWkIk&s=_9JOeNLk-p5CQtAtasdJbRyV5KK5tq1qLb_IxeKdmMw&e= 
> 
> Hi,
> 
> I see this on Ubuntu 20.04, am I the only one?

Weird. I just compiled GDB commit f55649cc and see no such failures:

> make check RUNTESTFLAGS='TRANSCRIPT=y  gdb.mi/user-select*.exp'
...
Running /home/jv/Projects/gdb/origin_master/gdb/testsuite/gdb.mi/user-selected-context-sync.exp ...

		=== gdb Summary ===

# of expected passes		419

I'll try on Ubuntu 20.04 tomorrow. 

Jan

> 
> 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