Re: [PATCH] tui: replace deprecated_register_changed_hook with observer

[Pedro Alves <palves at redhat dot com>]

On 07/06/2015 02:17 AM, Patrick Palka wrote:
> This is a straightforward replacement of the TUI's use of the
> aforementioned hook with the register_changed observer.  Since this was
> the only user of the hook, this patch also removes the hook.
> 
> [ I am not sure if the changes to the function tui_register_changed are
>   correct.  In particular, the inputted frame argument is now passed down
>   to tui_check_data_values instead of the frame returned by
>   get_selected_frame.  The frame argument passed to each register_changed
>   observer corresponds to the VALUE_FRAME_ID of the register being
>   modified within a register assignment, e.g. the $rax in "print $rax =
>   FOO".  When would the frame corresponding to the VALUE_FRAME_ID of a
>   register not be the currently selected frame?  ]
> 

Grepping for value_assign callers finds e.g., varobjs:

  varobj.c:      val = value_assign (var->value, value);

Adding an assertion like this:

@@ -1169,6 +1169,7 @@ value_assign (struct value *toval, struct value *fromval)
              }
          }

+       gdb_assert (frame == get_selected_frame (NULL));
        observer_notify_register_changed (frame, value_reg);
        if (deprecated_register_changed_hook)
          deprecated_register_changed_hook (-1);

and playing with varobjs shows the assertion failing:

 (gdb) interpreter-exec mi "-var-create - * $rax"
 ^done,name="var1",numchild="0",value="6295640",type="int64_t",has_more="0"
 (gdb) up
 #1  0x000000000040082a in thread_function0 (arg=0x0) at threads.c:69
 69              usleep (1);  /* Loop increment.  */
 (gdb) up
 #2  0x0000003616a07ee5 in start_thread (arg=0x7ffff7fc1700) at pthread_create.c:309
 309           THREAD_SETMEM (pd, result, CALL_THREAD_FCT (pd));
 (gdb) interpreter-exec mi "-var-assign var1 1"
 ~"/home/pedro/gdb/mygit/build/../src/gdb/valops.c:1172: internal-error: value_assign: Assertion `frame == get_selected_frame (NULL)' failed.\nA problem internal to GDB has been detected,\nfurther debugging may prove unreliable.\nQuit this debugging session? (y or n) "

The TUI doesn't use MI, but there are probably other similar cases
in the tree.  E.g., I'd assume you can create a register Value with Python,
and then assign to it when the selected frame is not
the register's frame.

Thanks,
Pedro Alves