Re: RFC: Two small remote protocol extensions

Daniel Jacobowitz
2002-08-16T14:30:12Z

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.

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.

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.

--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer

2002-08-16 Daniel Jacobowitz <drow@mvista.com>

* remote.c (remote_resume): Also send inferior_ptid.

2002-08-16 Daniel Jacobowitz <drow@mvista.com>

* target.c (set_desired_inferior): Respect general_thread
if cont_thread is 0 or -1.

Index: remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.91
diff -u -p -r1.91 remote.c
--- remote.c 9 Aug 2002 16:41:24 -0000 1.91
+++ remote.c 16 Aug 2002 14:26:51 -0000
@@ -2616,8 +2616,13 @@ remote_resume (ptid_t ptid, int step, en
{
struct remote_state *rs = get_remote_state ();
char *buf = alloca (rs->remote_packet_size);
- int pid = PIDGET (ptid);
+ int pid = PIDGET (ptid), inf_pid = PIDGET (inferior_ptid);
char *p;
+
+ if (inf_pid == -1)
+ set_thread (0, 1);
+ else
+ set_thread (inf_pid, 1);

if (pid == -1)
set_thread (0, 0); /* run any thread */
Index: gdbserver/target.c
===================================================================
RCS file: /cvs/src/src/gdb/gdbserver/target.c,v
retrieving revision 1.3
diff -u -p -r1.3 target.c
--- gdbserver/target.c 11 Jun 2002 17:32:40 -0000 1.3
+++ gdbserver/target.c 16 Aug 2002 14:26:51 -0000
@@ -46,6 +46,10 @@ set_desired_inferior (int use_general)
found = (struct thread_info *) find_inferior_id (&all_threads,
step_thread);

+ if (general_thread > 0 && (cont_thread == 0 || cont_thread == -1))
+ found = (struct thread_info *) find_inferior_id (&all_threads,
+ general_thread);
+
if (found == NULL)
found = (struct thread_info *) find_inferior_id (&all_threads,
cont_thread);