bug#43195: [PATCH] Remove definitions of UP, BC and PC which should be provided by terminfo

[Fangrui Song]

On 2020-09-04, Eli Zaretskii wrote:
> > Cc: Fangrui Song <maskray@google.com>
> > Date: Thu,  3 Sep 2020 17:57:48 -0700
> > From: Fangrui Song via "Bug reports for GNU Emacs,
> >  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> >
> > Otherwise if terminfo.c is compiled with -fno-common (GCC 10 and clang
> > 11 default) and the archive version of the terminfo library is linked,
> > there will be a multiple definition linker error.
> >
> > * src/terminfo.c (UP, BC, PC): Delete.
>
> Given the comment there, I think this should be conditioned on
> actually using terminfo.  Does the following patch work for you?
>
> diff --git a/src/terminfo.c b/src/terminfo.c
> index 51fd32e..0765996 100644
> --- a/src/terminfo.c
> +++ b/src/terminfo.c
> @@ -23,9 +23,12 @@
>
> /* Define these variables that serve as global parameters to termcap,
>    so that we do not need to conditionalize the places in Emacs
> -   that set them.  */
> +   that set them.  But don't do that for terminfo, as that could
> +   cause link errors when using -fno-common.  */
>
> +#if !TERMINFO
> char *UP, *BC, PC;
> +#endif
>
> /* Interface to curses/terminfo library.
>    Turns out that all of the terminfo-level routines look

Looks great! Thanks!

One nit, 

  #if !TERMINFO

probably should be 

  #ifndef TERMINFO


I don't know whether it is worth mentioning that -fcommon/-fno-common does not
cause a linker error when libtinfo.so is linked (a common/regular definition
preempts a shared definition).

-fno-common + libtinfo.a => multiple definition error