[PATCH] remote: Fix a crash on longjmp breakpoint removal

["Maciej W. Rozycki" <macro@codesourcery.com>]

Hi,

 I have observed a crash, where GDB attempts to send a packet to gdbserver 
after the remote target has already exited (and the gdbserver process 
terminated) -- here's the tail of an example remote session transcript:

Sending packet: $vCont;c#a8...Packet received: W00
[Inferior 1 (Remote target) exited normally]
Sending packet: $Hg0#df...

This happens on the MIPS/Linux target while GDB is single-stepping with 
the "step" command.

 I have tracked it down to remote_close calling discard_all_inferiors, 
which in turn eventually calls delete_thread_of_inferior, which calls 
clear_thread_inferior_resources, which calls delete_longjmp_breakpoint, 
which calls remote_remove_breakpoint, which needs to send some packets to 
the remote target to get the breakpoint removed.  But at this point the 
remote file descriptor has already been closed; after a W00 stop reply 
gdbserver does not expect any further input anyway.

 I have looked through ChangeLogs and I believe this is a regression 
caused by:

2010-12-09  Tom Tromey  <tromey@redhat.com>

	PR c++/9593:
	* thread.c (clear_thread_inferior_resources): Call
	delete_longjmp_breakpoint.
	[...]

 I have been able to get rid of the crash with the change below, no test 
suite regressions on mips-linux-gnu (remote target).  OK to apply?

2011-12-13  Maciej W. Rozycki  <macro@codesourcery.com>

	gdb/
	* thread.c (clear_thread_inferior_resources): Don't call 
	delete_longjmp_breakpoint if there's no inferior.

  Maciej

gdb-inferior-resources-crash.diff
Index: gdb-fsf-trunk-quilt/gdb/thread.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/thread.c	2011-11-02 21:28:38.000000000 +0000
+++ gdb-fsf-trunk-quilt/gdb/thread.c	2011-12-13 19:42:25.805620748 +0000
@@ -119,7 +119,8 @@ clear_thread_inferior_resources (struct 
   do_all_intermediate_continuations_thread (tp, 1);
   do_all_continuations_thread (tp, 1);
 
-  delete_longjmp_breakpoint (tp->num);
+  if (!ptid_equal (inferior_ptid, null_ptid))
+    delete_longjmp_breakpoint (tp->num);
 }
 
 static void