Re: Fix crash on "quit" + TUI + remote + async

[Pedro Alves <pedro at codesourcery dot com>]

Ahem, EWRONGPATCH.

Here is the correct one.  OK?

On Monday 28 July 2008 16:33:40, Pedro Alves wrote:
> I was debugging against a remote stub in async mode, using the TUI, and I
> issued "quit" while still connected, in the hopes of bailing out of GDB
> without much fuss, but, I ran into this SEGV:
>
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7fcf597fb6e0 (LWP 13869)]
> 0x0000000000552f5e in serial_can_async_p (scb=0x0) at
> ../../src/gdb/serial.c:504 504       return (scb->ops->async != NULL);
> (top-gdb) bt
> #0  0x0000000000552f5e in serial_can_async_p (scb=0x0) at
> ../../src/gdb/serial.c:504 During symbol reading, unsupported tag:
> 'DW_TAG_const_type'.
> #1  0x000000000042ffa3 in remote_can_async_p () at
> ../../src/gdb/remote.c:8207 During symbol reading, DW_AT_type missing from
> DW_TAG_subrange_type. #2  0x000000000040d740 in execute_command
> (p=0x7fff618212a0 "set width 118", from_tty=0) at ../../src/gdb/top.c:382
> #3  0x0000000000457d1c in tui_update_gdb_sizes () at
> ../../src/gdb/tui/tui-win.c:468 #4  0x0000000000452002 in tui_disable () at
> ../../src/gdb/tui/tui.c:455 #5  0x0000000000452581 in tui_exit () at
> ../../src/gdb/tui/tui-interp.c:45 #6  0x00007fcf589e0110 in exit () from
> /lib/libc.so.6
> #7  0x000000000040edeb in quit_force (args=0x0, from_tty=1) at
> ../../src/gdb/top.c:1292 #8  0x0000000000443f20 in quit_command (args=0x0,
> from_tty=1) at ../../src/gdb/cli/cli-cmds.c:315 #9  0x000000000043e660 in
> do_cfunc (c=0xa344b0, args=0x0, from_tty=1) at
> ../../src/gdb/cli/cli-decode.c:60 #10 0x00000000004412a3 in cmd_func
> (cmd=0xa344b0, args=0x0, from_tty=1) at ../../src/gdb/cli/cli-decode.c:1680
> #11 0x000000000040d9df in execute_command (p=0x9e81c1 "", from_tty=1) at
> ../../src/gdb/top.c:465 #12 0x00000000004c19ea in command_handler
> (command=0x9e81c0 "q") at ../../src/gdb/event-top.c:514
>
> As you can see from from #2, disabling the tui ends up
> executing a command.  At this point, the remote target was still
> pushed on the stack, but it had already been closed, hence the remote
> connection was closed, and remote_desc was == NULL.
>
> There are target_can_async_p call around every command invocation,
> and since the remote target was still on the stack, remote_can_async_p
> was called, but it isn't expecting to be reached with remote_desc == NULL,
> as most of remote's code:
>
>  static int
>  remote_can_async_p (void)
>  {
>    if (!remote_async_permitted)
>      /* We only enable async when the user specifically asks for it.  */
>      return 0;
>
>    /* We're async whenever the serial device is.  */
>    return remote_async_mask_value && serial_can_async_p (remote_desc);
>  }
>
> The issue is that quit_target closes the current target, but doesn't
> pop it:
>
>  static int
>  quit_target (void *arg)
>  {
>    struct qt_args *qt = (struct qt_args *)arg;
>
>    if (! ptid_equal (inferior_ptid, null_ptid) && target_has_execution)
>      {
>        if (attach_flag)
>          target_detach (qt->args, qt->from_tty);
>        else
>          target_kill ();
>      }
>
>    /* UDI wants this, to kill the TIP.  */
>    target_close (&current_target, 1);
>
>    /* Save the history information if it is appropriate to do so.  */
>    if (write_history_p && history_filename)
>      write_history (history_filename);
>
>    do_final_cleanups (ALL_CLEANUPS);	/* Do any final cleanups before
> exiting */
>
>    return 0;
>  }
>
>
> The UDI target seems to be gone from the sources, but, even if it's still
> here and I missed it, this is broken.  It should at best be a pop_target. 
> But, while I'm at it, if the current target is of stratum >
> process_stratum, this will still leave the process_stratum target open,
> which is much
> more likelly to need closing.  So, I've come up with a new
> pop_all_targets method and used it instead.
>
> Tested against x86_64-unknown-linux-gnu native and gdbserver.
>
> OK?

-- 
Pedro Alves

2008-07-28  Pedro Alves  <pedro@codesourcery.com>

	* target.h (pop_all_targets): Declare.
	* target.c (pop_all_targets): New.
	* top.c (quit_target): Pop all targets instead of just closing the
	current.

---
 gdb/target.c |   18 ++++++++++++++++++
 gdb/target.h |    7 +++++++
 gdb/top.c    |    5 +++--
 3 files changed, 28 insertions(+), 2 deletions(-)

Index: src/gdb/target.c
===================================================================
--- src.orig/gdb/target.c	2008-07-28 16:36:34.000000000 +0100
+++ src/gdb/target.c	2008-07-28 16:41:53.000000000 +0100
@@ -820,6 +820,24 @@ pop_target (void)
   internal_error (__FILE__, __LINE__, _("failed internal consistency check"));
 }
 
+void
+pop_all_targets (int quitting)
+{
+  while ((int) (current_target.to_stratum) > (int) dummy_stratum)
+    {
+      target_close (&current_target, quitting);
+      if (!unpush_target (target_stack))
+	{
+	  fprintf_unfiltered (gdb_stderr,
+			      "pop_all_targets couldn't find target %s\n",
+			      current_target.to_shortname);
+	  internal_error (__FILE__, __LINE__,
+			  _("failed internal consistency check"));
+	  break;
+	}
+    }
+}
+
 /* Using the objfile specified in OBJFILE, find the address for the
    current thread's thread-local storage with offset OFFSET.  */
 CORE_ADDR
Index: src/gdb/target.h
===================================================================
--- src.orig/gdb/target.h	2008-07-28 16:36:34.000000000 +0100
+++ src/gdb/target.h	2008-07-28 16:39:25.000000000 +0100
@@ -1172,6 +1172,13 @@ extern void target_preopen (int);
 
 extern void pop_target (void);
 
+/* Does whatever cleanup is required to get rid of all pushed targets.
+   QUITTING is propagated to target_close; it indicates that GDB is
+   exiting and should not get hung on an error (otherwise it is
+   important to perform clean termination, even if it takes a
+   while).  */
+extern void pop_all_targets (int quitting);
+
 extern CORE_ADDR target_translate_tls_address (struct objfile *objfile,
 					       CORE_ADDR offset);
 
Index: src/gdb/top.c
===================================================================
--- src.orig/gdb/top.c	2008-07-28 16:36:34.000000000 +0100
+++ src/gdb/top.c	2008-07-28 16:39:25.000000000 +0100
@@ -1229,8 +1229,9 @@ quit_target (void *arg)
         target_kill ();
     }
 
-  /* UDI wants this, to kill the TIP.  */
-  target_close (&current_target, 1);
+  /* Give all pushed targets a chance to do minimal cleanup, and pop
+     them all out.  */
+  pop_all_targets (1);
 
   /* Save the history information if it is appropriate to do so.  */
   if (write_history_p && history_filename)