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Re: RFC: Two small remote protocol extensions


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



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