Re: [PATCH] tui-out: don't "inherit" redirect from CLI

[Pedro Alves <pedro@codesourcery.com>]

On Monday 30 August 2010 10:29:10, Paul Bolle wrote:
> Since revision 1.17 tui_ui_out_impl "inherits" from cli_ui_out_impl (ie,
> it starts as a copy of that struct). tui_ui_out_impl.redirect is never
> redefined after that so it points to cli_redirect(). (Before revision
> 1.17 it was NULL.)

That was the main reason that tui_ui_out_impl was made to inherit
cli_ui_out_impl in the first place.
See <http://sourceware.org/ml/gdb-patches/2010-04/msg00540.html>.

> As a consequence, uo_redirect() will actually try to redirect if passed
> a tui_ui_out_impl. That will probably crash gdb (as
> tui_ui_out_impl->data->stream and tui_ui_out_impl->data->original_stream
> don't exist).

Yes they do exist, because tui_ui_out_data "inherits" cli_ui_out_data.
See:

struct tui_ui_out_data
  {
    struct cli_ui_out_data base;
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^

    int line;
    int start_of_line;
  };
typedef struct tui_ui_out_data tui_out_data;

"base" is the first field of tui_ui_out_data, so you can
pass a pointer to a tui_ui_out_data to a function that expects
a cli_ui_out_data pointer.  This is legal, and a common idiom on C,
as means to implementing "is-a" inheritance.

> 
> So set tui_ui_out_impl.redirect to NULL after "inheriting".

Nope, sorry, this isn't correct.

> (Just something I noticed while trying to understand the ui code.)

-- 
Pedro Alves