Re: Q: %Stop && gdb crash

[Oleg Nesterov <oleg at redhat dot com>]

On 08/03, Jan Kratochvil wrote:
>
> On Tue, 03 Aug 2010 14:24:34 +0200, Oleg Nesterov wrote:
> > >
> > > So I assumed it is always safe to resend the notification unless gdb already
> > > sent vStopped. Since it is not clear to me when it makes sense to resend it,
> > > currently gdbstub does re-send every time /proc/ugdb reports the new event
> > > (T00 in this case). I agree this is not optimal, but this looks correct to me.
> >
> > I'll change gdbstub to never resend the notification to avoid the problem.
>
> Yes, I has been now just writing you such reply.

Sure, will do.

> > But probably gdb should be fixed anyway.
>
> There are so many serious bugs in GDB affecting regular GDB usage...

OK, so I assume that the current behaviour of gdbstub is correct, even
if stupid.

> > To avoid the unnecessary details, consider the oversimplified example,
> >
> > 	$ sleep 10000&
> > 	[1] 2923
> >
> > 	$ cat > SLEEP
> > 	set target-async on
> > 	set non-stop
> > 	target extended-remote :2000
> > 	file /bin/sleep
> > 	attach 2923
> > 	info registers
> > 	detach
> > 	^D
> >
> > 	$ gdb <SLEEP
> > 	GNU gdb (GDB) 7.1
> > 	Copyright (C) 2010 Free Software Foundation, Inc.
> > 	License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> > 	This is free software: you are free to change and redistribute it.
> > 	There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> > 	and "show warranty" for details.
> > 	This GDB was configured as "x86_64-unknown-linux-gnu".
> > 	For bug reporting instructions, please see:
> > 	<http://www.gnu.org/software/gdb/bugs/>.
> > 	(gdb) (gdb) (gdb) Remote debugging using :2000
> > 	(gdb) Reading symbols from /bin/sleep...(no debugging symbols found)...done.
> > 	(gdb) Attached to process 2923
> > 	[New Thread 2923.2923]
> > 	Target is executing.
> > 	(gdb) Detached from remote process 2923.
> > 	(gdb) quit
> >
> > And yes, gdb ignores %Stop and just detaches. But this is because
> > of another issue (which looks like a minor gdb bug to me), note the
> >
> > 	"Target is executing."
> >
> > above. This is the reply to "info registers". Why? OK, yes, it is
> > executing.
>
> Yes.
>
>
> > Then send vCont:t ? "attach PID" means attach and stop it, no?
>
> But it is not yet stopped that time.

Well. And how can I stop it?

Once again, this all works in CLI mode. And this looks very natural

	(gdb) attach PID
	(gdb) info registers

As a newbie user of gdb, I expected it is gdb who should take care
and stop the tracee after "attach". And please remember, "interrupt"
doesn't help.

OK, please ignore. Now that I know I can't trust 'gdb < BATCH' I do
not use this.

> > Can't resist, I spent a lot of time trying to understand what is wrong.
>
> Nothing, you should wait till GDB reports the inferior has stopped.

Yes, yes, now I understand this. Once again, I was greatly confused
because I didn't know that CLI mode makes the difference. Even if I
enter the commands via copy-and-paste, gdb always "completes" this
attach before it reacts to "info registers".

And there were other issues which I didn't understand when I tried
to solve this problem...

> It is
> easy/normal in the GDB testsuite

Hmm. How? probably the tests in testsuite wait for something which
looks like "[Thread 5683.5683] #1 stopped." from gdb?

> > I tried to achieve the same results with /proc/ugdb doing
> > "$ gdb < BATCH_FILE" with the same commands.
>
> Maybe you can write a new *.exp testcase for such testing.

I guess you want me to learn /usr/bin/expect ;)

Oleg.