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Re: [PATCH] tui: replace deprecated_register_changed_hook with observer
- From: Pedro Alves <palves at redhat dot com>
- To: Patrick Palka <patrick at parcs dot ath dot cx>
- Cc: "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>
- Date: Wed, 08 Jul 2015 13:48:24 +0100
- Subject: Re: [PATCH] tui: replace deprecated_register_changed_hook with observer
- Authentication-results: sourceware.org; auth=none
- References: <1436145432-6502-1-git-send-email-patrick at parcs dot ath dot cx> <559D0C63 dot 3000200 at redhat dot com> <CA+C-WL8xaUs2=e21O_Q1v6q4r2K092yGavXgg6AFBsw6kXeQTg at mail dot gmail dot com>
On 07/08/2015 01:30 PM, Patrick Palka wrote:
> On Wed, Jul 8, 2015 at 7:41 AM, Pedro Alves <palves@redhat.com> wrote:
>> 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.
>
> Ah okay.. So it seems to me that if the frame argument !=
> get_selected_frame, then we should not update the register window at
> all since the register window is supposed to show the register values
> of the currently selected frame.
Yes, I think so.
> Or instead, just ignore the frame argument and always pass
> get_selected_frame to tui_check_data_values, even if frame !=
> get_selected_frame. Seems to me that this is the safest option.
That'd be a 1-1 with the current code. Though, I believe
that results in spuriously clearing the highlight of
previously changed registers (of the selected frame), because
nothing will have changed. So seems like the other option
actually fixes a bug.
Thanks,
Pedro Alves