[patch] Fix remote.c incorrectly using pop_target (wrt btrace)

[Jan Kratochvil <jan.kratochvil@redhat.com>]

Hi,

with the btrace patchset checked in one may get stuck when using btrace and
gdbserver:

./gdbserver :1234 true
./gdb true -ex 'target remote localhost:1234' -ex 'set debug remote 1' -ex 'record btrace'
(gdb) stepi
Sending packet: $qTStatus#49...qTStatus: Remote connection closed
Sending packet: $Z0,7ffff7debd10,1#09...Sending packet: $QPassSignals:e;10;14;17;1a;1b;1c;21;24;25;2c;4c;#5f...0x00007ffff7ddd420 in _start () from /lib64/ld-linux-x86-64.so.2
putpkt: write failed: Broken pipe.
(gdb) q
A debugging session is active.
        Inferior 1 [process 26817] will be killed.
Quit anyway? (y or n) y
Sending packet: $qTStatus#49...putpkt: write failed: Broken pipe.
(gdb) _

as discussed in:
	RE: Crash of GDB with gdbserver btrace enabled [Re: [patch v9 00/23] branch tracing support for Atom]
	http://sourceware.org/ml/gdb-patches/2013-03/msg00296.html
	Message-ID: <A78C989F6D9628469189715575E55B2307B9C2F6@IRSMSX102.ger.corp.intel.com>
	From: "Metzger, Markus T" <markus.t.metzger@intel.com>

with the fix below:

(gdb) stepi
Sending packet: $qTStatus#49...qTStatus: You can't do that when your target is `record-btrace'
PC register is not available
(gdb) stepi
The program is not being run.
(gdb) q
$ _

Those two removed pop_target calls around
	target_preopen (from_tty);
	unpush_target (target);

were redundant as they were added by:
	commit ef378e83937c25e9da9c4e545bb1a8bb5fd767f1
	Author: Daniel Jacobowitz <dan@debian.org>
	Date:   Wed Jan 30 00:51:50 2008 +0000

but later target_preopen started removing all the targets in target_preopen by:
	commit 3db54b199473ba136a4821c420f85096ff17e98e
	Author: Pedro Alves <pedro@codesourcery.com>
	Date:   Mon Aug 18 23:12:39 2008 +0000

No regressions on {x86_64,x86_64-m32,i686}-fedora19pre-linux-gnu and with
gdbserver.

I would like to get it checked in for 7.6 is it is some sort of regression
from btrace.


Thanks,
Jan


gdb/
2013-03-11  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* remote.c (remote_unpush_target): New function.
	(remote_open_1): Remove two pop_target calls, update one comment, add
	comment to target_preopen call.  Replace pop_target call by
	remote_unpush_target call.
	(interrupt_query, readchar, getpkt_or_notif_sane_1): Replace
	pop_target calls by remote_unpush_target calls.

diff --git a/gdb/remote.c b/gdb/remote.c
index 8fc6b85..6e6c0d6 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -4188,6 +4188,14 @@ remote_query_supported (void)
       }
 }
 
+/* Remove any of the remote.c targets from target stack.  */
+
+static void
+remote_unpush_target (void)
+{
+  unpush_target (&remote_ops);
+  unpush_target (&extended_remote_ops);
+}
 
 static void
 remote_open_1 (char *name, int from_tty,
@@ -4205,30 +4213,18 @@ remote_open_1 (char *name, int from_tty,
     wait_forever_enabled_p = 1;
 
   /* If we're connected to a running target, target_preopen will kill it.
-     But if we're connected to a target system with no running process,
-     then we will still be connected when it returns.  Ask this question
-     first, before target_preopen has a chance to kill anything.  */
+     Ask this question first, before target_preopen has a chance to kill
+     anything.  */
   if (remote_desc != NULL && !have_inferiors ())
     {
-      if (!from_tty
-	  || query (_("Already connected to a remote target.  Disconnect? ")))
-	pop_target ();
-      else
+      if (from_tty
+	  && !query (_("Already connected to a remote target.  Disconnect? ")))
 	error (_("Still connected."));
     }
 
+  /* Here the possibly existing remote target gets unpushed.  */
   target_preopen (from_tty);
 
-  unpush_target (target);
-
-  /* This time without a query.  If we were connected to an
-     extended-remote target and target_preopen killed the running
-     process, we may still be connected.  If we are starting "target
-     remote" now, the extended-remote target will not have been
-     removed by unpush_target.  */
-  if (remote_desc != NULL && !have_inferiors ())
-    pop_target ();
-
   /* Make sure we send the passed signals list the next time we resume.  */
   xfree (last_pass_packet);
   last_pass_packet = NULL;
@@ -4348,7 +4344,7 @@ remote_open_1 (char *name, int from_tty,
 	/* Pop the partially set up target - unless something else did
 	   already before throwing the exception.  */
 	if (remote_desc != NULL)
-	  pop_target ();
+	  remote_unpush_target ();
 	if (target_async_permitted)
 	  wait_forever_enabled_p = 1;
 	throw_exception (ex);
@@ -5096,7 +5092,7 @@ interrupt_query (void)
       if (query (_("Interrupted while waiting for the program.\n\
 Give up (and stop debugging it)? ")))
 	{
-	  pop_target ();
+	  remote_unpush_target ();
 	  deprecated_throw_reason (RETURN_QUIT);
 	}
     }
@@ -7051,11 +7047,11 @@ readchar (int timeout)
   switch ((enum serial_rc) ch)
     {
     case SERIAL_EOF:
-      pop_target ();
+      remote_unpush_target ();
       error (_("Remote connection closed"));
       /* no return */
     case SERIAL_ERROR:
-      pop_target ();
+      remote_unpush_target ();
       perror_with_name (_("Remote communication error.  "
 			  "Target disconnected."));
       /* no return */
@@ -7579,7 +7575,7 @@ getpkt_or_notif_sane_1 (char **buf, long *sizeof_buf, int forever,
 	      if (forever)	/* Watchdog went off?  Kill the target.  */
 		{
 		  QUIT;
-		  pop_target ();
+		  remote_unpush_target ();
 		  error (_("Watchdog timeout has expired.  Target detached."));
 		}
 	      if (remote_debug)