Re: [PATCH] [gdb/tui] Make tui_setup_io more robust

[Andrew Burgess <aburgess@redhat.com>]

Tom de Vries <tdevries@suse.de> writes:

> The following sequence of events may happen when enabling TUI:
> - tui_enable () is called,
> - a SIGFPE happens, before tui_setup_io (1) is called,
> - the SIGFPE triggers handle_fatal_signal, which calls tui_disable (),
> - during tui_disable (), tui_setup_io (0) is called, and
> - tui_setup_io (0) tries to restore things that were saved during a previous
>   tui_setup_io (1) call, but tui_setup_io (1) was never called so the saving
>   never happened.
>
> This can cause current_ui.m_ui_stderr to be nullptr, which then can cause a
> crash in sig_write (PR33918).

If this bug number is worth mentioning, then we should add a 'Bug:...'
tag to the commit message.  I like them if for nothing else they are
clickable in my terminal :)

>
> Fix this by:
> - adding a variable tui_io_mode, and
> - using the variable to bail out of tui_setup_io in case the current mode
>   doesn't change.

What's one more global, the tui already has so many!

This seems a reasonable change to me.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew


>
> Tested on x86_64-linux.
> ---
>  gdb/tui/tui-io.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/gdb/tui/tui-io.c b/gdb/tui/tui-io.c
> index f673fbf36f6..5a3bc604592 100644
> --- a/gdb/tui/tui-io.c
> +++ b/gdb/tui/tui-io.c
> @@ -824,6 +824,10 @@ tui_rl_display_match_list (char **matches, int len, int max)
>    gdb_display_match_list (matches, len, max, &displayer);
>  }
>  
> +/* Whether the IO is setup for curses (1) or non-curses (0).  */
> +
> +static int tui_io_mode;
> +
>  /* Setup the IO for curses or non-curses mode.
>     - In non-curses mode, readline and gdb use the standard input and
>     standard output/error directly.
> @@ -837,6 +841,14 @@ tui_setup_io (int mode)
>  {
>    extern int _rl_echoing_p;
>  
> +  if (tui_io_mode == mode)
> +    {
> +      /* Nothing to do.  Also, this makes sure that we don't try to restore
> +	 things before having saved them. */
> +      return;
> +    }
> +  tui_io_mode = mode;
> +
>    if (mode)
>      {
>        /* Ensure that readline has been initialized before saving any
>
> base-commit: 646982f4295bf0a1e64867606d496c34c9a15a0c
> -- 
> 2.51.0