RFA: fix PR breakpoints/13776

[Tom Tromey <tromey at redhat dot com>]

I'd appreciate comments on this patch.
I have no idea whether it is the best way to fix the problem.

Bug 13776 concerns 'next'ing over an exit.  For the trivial:

    #include <stdlib.h> 
    int
    main (void)
    {
      exit (0);
    }

We get this behavior:

    (gdb) start
    Temporary breakpoint 1, main () at exit0.c:5
    5      exit (0);
    (gdb) next
    [Inferior 1 (process 2428) exited normally]
    warning: Error removing breakpoint 0
    warning: Error removing breakpoint 0
    warning: Error removing breakpoint 0

The bug is that exit_inferior ends up calling delete_longjmp_breakpoint,
which tries to delete the longjmp breakpoints -- but as the inferior is
dead, this fails.

This patch fixes this problem by moving the breakpoint_init_inferior
call earlier in generic_mourn_inferior.  This causes the breakpoints to
be marked as uninserted before they are deleted.

While doing this I noticed that after the inferior exits, we are left
with a step-resume breakpoint:

(gdb) maint info b
Num     Type           Disp Enb Address            What
[...]
0       step resume    dstp y   0x00000000004004d2  inf 1 thread 1
	stop only in thread 1

The breakpoint.c patch causes this to be removed as well.

Built and regtested on x86-64 Fedora 16.

Tom

2012-02-28  Tom Tromey  <tromey@redhat.com>

	PR breakpoints/13776:
	* target.c (generic_mourn_inferior): Call breakpoint_init_inferior
	earlier.
	* breakpoint.c (breakpoint_init_inferior): Delete step-resume
	breakpoints.

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index db05b97..048cc63 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -3341,6 +3341,10 @@ breakpoint_init_inferior (enum inf_context context)
 	   (gdb) tar rem :9999     # remote Windows gdbserver.
 	*/
 
+      case bp_step_resume:
+
+	/* Also remove step-resume breakpoints.  */
+
 	delete_breakpoint (b);
 	break;
 
diff --git a/gdb/target.c b/gdb/target.c
index 1f408f6..65a6c23 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -3583,13 +3583,14 @@ generic_mourn_inferior (void)
   ptid = inferior_ptid;
   inferior_ptid = null_ptid;
 
+  breakpoint_init_inferior (inf_exited);
+
   if (!ptid_equal (ptid, null_ptid))
     {
       int pid = ptid_get_pid (ptid);
       exit_inferior (pid);
     }
 
-  breakpoint_init_inferior (inf_exited);
   registers_changed ();
 
   reopen_exec_file ();