RFC: Two small remote protocol extensions

[Daniel Jacobowitz <drow@mvista.com>]

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.

  - A new 'Hs' packet, paralleling Hc and Hg.  This sets the "step" thread.

Basically, despite a comment that it didn't work earlier on this list, I
discovered that lin-lwp does correctly honor `set scheduler-locking'.  It
works by controlling which threads are resumed by resume_ptid.  However,
for stepping, inferior_ptid is also consulted.  That way all threads can
be resumed but a particular thread stepped.  The `thread <N>' command
changes the thread to be stepped.

resume_ptid is communicated to the remote host.  inferior_ptid is not
necessarily the same as general_ptid, however - after information requests
like `thread apply all bt', for instance.

Reading over the above, I suppose I could use general_ptid for this instead,
with a slightly smaller patch to remote_resume to guarantee that it is set.
That makes a little more sense than my current approach.  Still needs a
documentation patch to clarify it; I intend to fix up most of the protocol
specification (which is woefully out of date, and hideous in texinfo) as
soon as I get a chance.

Any thoughts on the two above changes?

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer