Re: RFC: Two small remote protocol extensions

Andrew Cagney
2002-08-16T14:42:50Z

> On Wed, May 01, 2002 at 10:25:43PM -0400, Daniel Jacobowitz wrote:
>
>> In making remote thread debugging work on GNU/Linux, I needed two additions
>> to the remote protocol. Neither is strictly necessary, but both are useful,
>> IMHO.
>>
>> They are:
>>
>> - two new replies to the continue/step packets, 'n' and 'x'. They
>> indicate thread creation and death respectively, and are asynchronous;
>> the target is not stopped when they are sent.
>
>
> This one got shouted down, I'm not going to bring it up again.
>
>
>> - A new 'Hs' packet, paralleling Hc and Hg. This sets the "step" thread.

How is ``Hs'' different to:

Hc<PID>
s

> This one, however, needs feedback. A user just reported a bogus
> SIGTRAP bug to me which is fixed by the above.
>
> To elaborate on the problem: right now we have two ways of specifying a
> thread to the remote agent. Hg specifies the "general" thread, and Hc
> specifies the "continue" thread. These correspond to inferior_ptid and
> resume_ptid, roughly.
>
> When we single-step, if we are not using some form of
> scheduler-locking, resume_ptid is 0. We don't tell the agent at that
> point what inferior_ptid is; it has to step _some_ thread, and it picks
> one, and if it doesn't pick the one GDB expected we get problems.

Shouldn't it pick the current-thread.

> We need to either:
> - Communicate inferior_ptid via Hg at this time
> - Communicate inferior_ptid via a new Hs explicitly
>
> I think the former makes sense. Here's a patch; what do you think of
> it? Also included is the patch for gdbserver; I'd send a separate
> patch along afterwards to remove the vestiges of Hs from my testing,
> which escaped in the original threads patch.

No. general thread is really ``selected thread'' the thread for which
the [gG][pP] packets apply. It is not involved in thread scheduling.

Separate to this is the user interface issue of, if you select a
different thread, and then do a step, things get real confused (I think
GDB tries to step the current (or stop) thread).

Andrew